Scientific Ocean Drilling: Accomplishments and Challenges (2011)

C

Workshop White Papers

SCIENTIFIC OCEAN DRILLING:
PAST, PRESENT AND FUTURE

Ted Moore
University of Michigan

U.S. oceanographic institutions banded together in 1968 to take the first steps toward exploring the sedimentary record and the crustal rocks of the deep ocean basins. It was auspicious timing. The new paradigms of seafloor spreading and plate tectonics had only recently been accepted by the broad scientific community. Based on the early results and technological developments of the Moho Project and on a careful consideration of all the potential scientific questions that might be addressed by drilling in the deep sea, a new effort was proposed that led to the development of the Deep Sea Drilling Project (DSDP). Unlike the Moho Project, DSDP would not involve large-scale technological development. Rather it would use “off the shelf” technology developed by the offshore oil drilling industry and placed on a single deep-water, dynamically positioned drillship. This did, of course, limit the scope of the problems addressed by the project. There would be no deep drilling down to the Mohorovičić discontinuity; drilling in ice-covered regions could not be undertaken; and drilling in very shallow water was not appropriate for the deep-water drill ship. But this still left a vast, unexplored region of the deep oceans open to investigation. In addition to limits on the range of operations, the technology of that day did not allow drilling with a riser in deep water. Seawater rather than drilling “mud” was usually used as the drilling fluid to clear debris from the hole and expel it onto the seafloor. This approach to deep-sea drilling has effectively limited the depth of section drilled and recovered to about 2 km.

The most important difference in how this “cutting edge” (for 1968) technology was used by DSDP scientists as opposed to how it was being used by the oil industry lay in the overall purpose of the drilling. The purpose of drilling for oil is to create a hole through which to extract hydrocarbons. The purpose of the scientific drilling is to recover the sedimentary and rock section in the deep sea and avoid encountering oil and gas at all costs. From the start, a safety advisory panel of oil company experts was set up to review required surveys and seismic data from every site drilled to assure there was no likelihood that reservoirs of oil and gas would be encountered in the drilling.

The desire by scientists to recover a complete, undisturbed section of the uppermost crustal material has required some technological development by the scientific community. The greatest advance in this regard for the recovery of sediments was the development of a hydraulic piston core that can be triggered to shoot out ahead of the drill bit and recover a virtually undisturbed 9 m section of sediment. When the sediment becomes too stiff to core in this way, an extended core barrel with a thin cutting face can be pushed ahead of the massive roller-cone drill bit and recover relatively undisturbed sections, until finally when the section becomes totally lithified, the standard roller-cone drill bit with an open center can core and recover the section.

In addition to the technical enhancements that were achieved during DSDP and the subsequent Ocean Drilling Program (ODP), there was a continued improvement in how these devices were used to achieve the recovery of a complete section and how the recovered section was described and documented. Initially in DSDP on-board core description was rather rudimentary: physical core/rock description, biostratigraphic age, smear slide description, core photographs, physical properties, and carbonate content. This could all be done on board with about 10 scientists and 6 technicians. By

the end of the ODP program the greatly improved quality of the cores permitted the useful employment of core scanning devices that measure density, magnetic susceptibility, P-wave velocity, natural gamma radiation, color, and magnetic polarity. These digital measurements are in addition to pore water chemistry, physical properties, microbiological samples, biostratigraphy, and other measurements that were standard in the days of DSDP. In ODP the shipboard scientific party grew to as many as 30 scientists who operated the machines, did the descriptions, made the measurements, and carried out the scientific studies. Their efforts over 12-hour shifts, 7 days/week, on a 56-day expedition constitute an aggregate 9 to 10 man-years of work achieved during the at-sea time. These expeditions are very productive efforts.

The substantial improvements made in the recovery and documentation of the recovered section came in parallel to improvements in how we used the holes that were drilled. Logging of the holes has come very close to keeping pace with developments in the industry. Other measurements such as heat flow and vertical velocity profiles have also been commonly made. Perhaps one of the most elegant innovations in down-hole instrumentation has been the circulation obviation retrofit kit (CORK), a device that seals off one or more sections of the drill hole and allows measurements of the chemical and physical nature of the waters in that section to be made over time. Thus, the holes themselves can become deep-sea observatories or laboratories for chemistry, microbiology, and seismology.

As our knowledge of the deep-sea environment and the scientific questions we address expands, our technical capabilities continue to improve. Now with the Integrated Ocean Drilling Program (IODP) we have also been able to go beyond the limitations first accepted as necessary in the early days of DSDP. We have drilled in the ice-covered region of the high Arctic and brought back a startling record of climate change associated with the CO₂ rich atmosphere of the Eocene. We have drilled on the very shallow shelf off New Jersey and the reefs of Tahiti to delve into the history of sea level changes and its impact on the sedimentary architecture of shallow water environments. And we are beginning an ambitious program of exploring the tectonic, depositional, and hydrologic environment of convergent margins. We no longer have to drill lacking the well control provided by a riser and will hopefully extend the water depth in which we can operate in the riser (or “well control”) mode beyond the present 2,500 m.

The envisioned scope of the great exploration that awaited us in the beginning days of scientific ocean drilling has been exceeded. Not only have we applied crucial tests to the plate tectonic theory but also we have created a whole new scientific field—paleoceanography. Through the exploration of the deep-sea environment we have also expanded the science we address far beyond that envisioned in the early days of DSDP. The chemistry and hydrology of water in the sediments and the crust are now thought to play a key role in the chemistry of the oceans and the weathering of the basalt both near the ridge axes and far off the axes into the older crust. The structure of the oceanic crust itself is gradually being revealed as we penetrate deeper into the basaltic sections. And we are just beginning to realize the great importance of microbes in the ocean environment. These are just some of the aspects of scientific ocean drilling that continue to intrigue the scientific mind and expand both the science and the scientific community that use scientific ocean drilling to increase the scope of our knowledge.

Supporting References

Coffin, M.F. and J.A. McKenzie. 2001. Earth, Oceans and Life: Scientific Investigation of the Earth System Using Multiple Drilling Platforms and New Technologies, Initial Science Plan, 2003-2013. Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas.

Gornitz, V. 2009. Encyclopedia of Paleoclimatology and Ancient Environments. Springer, The Netherlands.

THE RECORD OF HYDROTHERMAL
PROCESSES IN THE OCEANIC CRUST

Susan E. Humphris
Woods Hole Oceanographic Institution

Hydrothermal chemical exchange between the crust and oceans is a fundamental component of global geochemical cycles, affecting the composition of the lithosphere, the oceans and, through subduction, the mantle and arc magmas. In addition, this process provides the energy and nutrients for chemosynthetic organisms. Understanding the processes that control chemical fluxes resulting from water-rock reactions requires direct sampling of in situ crust, and has been an overarching goal of the lithosphere community for more than 40 years. Scientific ocean drilling has played a critical role in (i) advancing our understanding of subsurface water-rock reactions and the mechanisms of formation of seafloor massive sulfide deposits in active hydrothermal systems at mid-ocean ridges, and (ii) the development of a conceptual model for the alteration reactions that occur in off-axis convection systems driven by lithospheric cooling.

ACTIVE HYDROTHERMAL SYSTEMS AT
OCEANIC SPREADING CENTERS

Scientific drilling at three active hydrothermal sites in different geotectonic settings has revolutionized our understanding of the formation and subsurface structure of seafloor massive sulfide deposits. Drilling at the basalt-hosted active TAG hydrothermal mound (~26°N, Mid-Atlantic Ridge) revealed abundant anhydrite (CaSO₄)—a mineral that is very uncommon in ancient deposits due to its retrograde solubility—attesting to considerable entrainment and heating of seawater into the subsurface. Although its formation provides a framework for construction of the deposit, the ultimate dissolution of anhydrite was recognized as an important mechanism for the formation of sulfide breccia—a lithology that had been previously interpreted in ancient ophiolite massive sulfide deposits to result from post-depositional weathering.

Drilling at the sediment-hosted Middle Valley hydrothermal sites (~48°N, Juan de Fuca Ridge) resulted in the first successful recovery of feeder zone mineralization underlying a seafloor massive sulfide deposit. Feeder zones in ancient deposits commonly account for a significant portion of the economic reserves of a deposit. An unexpected finding was the presence of a stratified zone of high-grade Cu-rich replacement mineralization (~16 wt.% Cu) at the base of the feeder zone formed by lateral flow of hydrothermal fluids beneath an impermeable silicified mudstone horizon. This type of mineralization had not been previously recognized below seafloor mineral deposits, and hence has implications for land-based mineral exploration.

The felsic-hosted PACMANUS hydrothermal system (~3°S, Manus Basin) provided the opportunity to investigate the characteristics of hydrothermalism in a back-arc basin. Drilling beneath active hydrothermal systems revealed a cap of unaltered dacites and rhyolites, below which the volcanics are pervasively and intensely altered rather than alteration being confined to a narrow upflow zone, with clay minerals dominating the alteration assemblage. In addition, fluid inclusion data provided clear evidence for a magmatic component to the hydrothermal fluid that played a fundamental role in the nature of alteration—a clear distinction from the TAG and Middle Valley hydrothermal sites.

Although drilling seafloor sulfide deposits has been technologically challenging, often with poor recovery, it has nevertheless revealed previously unrecognized shallow subseafloor processes—entrainment of seawater, mixing of hydrothermal fluids with seawater and magmatic components, deposition of secondary phases that play key roles in deposit construction but are not preserved in ancient deposits—that are now demonstrated to be critical in the formation of massive sulfide deposits.

THE RECORD OF OFF-AXIS CONVECTION SYSTEMS

As the crust spreads, hydrothermal alteration continues in off-axis convection systems driven by lithospheric cooling. This process is believed to continue to an age of ~65 myr when the crust effectively becomes “sealed.” Hence, the ocean crust provides a time-integrated record of water-rock reactions that occurred both on- and off-axis.

Scientific ocean drilling has provided many sections of the uppermost few hundred meters of ocean crust. These have predominantly been focused in young (< 20 Ma) and ancient (> 110 Ma) crust. Of particular note are two long sections of upper ocean crust formed at intermediate (Hole 504B on 6 Ma crust) and superfast spreading rates (Hole 1256D on 15 Ma crust) in the eastern Pacific. No holes penetrate greater than 50 m in 45-80 Ma basement, the interval in which the crust becomes sealed. Although details vary, the mineralogical and geochemical characteristics of all the upper crustal sections support a model whereby greenschist alteration of dikes at low water/rock ratios is overprinted by fracture-controlled alteration and mineralization by upwelling hydrothermal fluids, a conductive boundary layer above gabbroic intrusions, leaching of metals from dikes and gabbros in the deep “root zone,” and stepped thermal and alteration gradients in the basement. The prediction that conductive boundary layers separate hydrothermal systems from the heat source that drives them has been confirmed by the identification of recrystallized sheeted dikes at the dike—gabbro transition at all locations. Incipient alteration of the uppermost gabbros occurs at high temperatures, with fluid flow along fracture networks occurring over very short timescales.

Drilling at oceanic core complexes on the more litho-logically heterogeneous slow spreading ridges (e.g., the Atlantis Massif [30°N, Mid-Atlantic Ridge] and Atlantis Bank [Southwest Indian Ridge]) has provided access to lower ocean crust that has been tectonically exhumed at the seafloor. The combination of regional-scale geophysical and geological surveys with deep drill holes at these locations indicate that detachment zones act to focus fluids at high and low temperatures. Gabbroic rocks are variably altered at these two sites, and preserve complex, but different, records of metamorphism, brittle failure, and hydrothermal alteration. At the Atlantis Massif, greenschist facies alteration occurred at depths at least 1 km below seafloor, with variable degrees of interaction with seawater at temperatures generally >250 °C. In contrast, at Atlantis Bank, patchy high temperature alteration (up to 600 °C) by hydrothermal fluids over a wide range of temperatures likely occurred at or very near the spreading axis, while later, low temperature alteration is likely related to cooling during uplift.

In summary, drilling to date has highlighted the critical, but highly variable, interplay between fluid flow, lithology, and magmatism from the seafloor down to the axial magma chamber. Investigations of this interplay, and of the hydrological-geochemical-microbiological feedbacks in aging oceanic lithosphere—the largest fractured aquifer on Earth—require access to in situ oceanic crust and subsurface experimentation that can be provided only by drilling.

Supporting References

Alt, J. 2004. Alteration of the upper oceanic crust: Mineralogy, chemistry, and processes. In Hydrogeology of the Oceanic Lithosphere, Elderfield, H. and E. Davis (Eds.). Cambridge University Press, New York. Humphris, S.E., P.M. Herzig, D.J. Miller, J.C. Alt, K. Becker, D. Brown, G. Brügmann, H Chiba, Y. Fouquet, J.B. Gemmell, G. Guerin, M.D. Hannington, N.G. Holm, J.J. Honnorez, G.J. Iturrino, R. Knott, R. Ludwig, K. Nakamura, S. Petersen, A.L. Reysenbach, P.A. Rona, S. Smith, A.A. Sturz, M.K. Tivey, and X. Zhao. 1995. The internal structure of an active sea-floor massive sulphide deposit. Nature 377:713-716.

Zierenberg, R.A., Y. Fouquet, D.J. Miller, J.M. Bahr, P.A. Baker, T. Bjerkgard, C.A. Brunner, R.C. Duckworth, R. Gable, J. Gieskes, W.D. Goodfellow, H.M. Groschel-Becker, G. Guerin, J. Ishibashi, G.J. Iturrino, R.H. James, K.S. Lackschewitz, L.L. Marquez, P. Nehlig, J.M. Peter, C.A. Rigsby, P.J. Schultheiss, W.C. Shanks, B.R.T. Simoneit, M. Summit, D.A.H. Teagle, M. Urbat, and G.G. Zuffa. 1998. The deep structure of a sea-floor hydrothermal deposit. Nature 392:485-488.

HEAT AND FLUID FLOW

Keir Becker
University of Miami

From the time of Project Mohole, researchers have recognized the opportunities that scientific ocean drilling presents to investigate heat and fluid flow processes in oceanic sediments and crust (e.g., Von Herzen and Maxwell, 1964). The early Deep Dea Drilling Project (DSDP) measurements were made primarily in sediments (see review by Erickson et al., 1975), before the discovery of hydrothermal circulation in the mid-1970s and the subsequent realization that fluid flow in subseafloor formations is a key process in nearly all subsea geological type settings from spreading centers to continental margins. Hence, the COSOD I (Conference on Scientific Ocean Drilling) report recognized the importance of subseafloor fluid flow, and understanding it fully became a focal point/major theme of DSDP/ODP (Ocean Drilling Program)/IODP (Integrated Ocean Drilling Program) scientific drilling starting with the 1987 COSOD II report. Since subseafloor fluid circulation occurs in most seafloor geological type settings, this summary overlaps several others from the workshop (e.g., S. Humphris on hydrothermal circulation, K. Edwards on deep biosphere, C. Ruppel on gas hydrates, and J.C. Moore on convergent margins). The table below summarizes in a historical context the main technical and scientific contributions of scientific ocean drilling in understanding subseafloor heat and fluid flow. This written summary touches on some of the themes covered by other speakers, but mainly features the off-axis, low-temperature, ridge-flank setting that for technical reasons has been the main setting to date for scientific ocean drilling into oceanic crust.

The early- to mid-1970s deduction of the likelihood of hydrothermal circulation in young oceanic crust was roughly coincident with the internationalization of DSDP (the IPOD or International Phase of Ocean Drilling) and a special IPOD focus on penetrating significantly into ocean basement. The last started with several important young Atlantic crustal holes, and borehole temperature measurements in some of them revealed a new phenomenon: that ocean bottom water was being drawn down the holes into the upper levels of basement beneath the sediment cover required to spud the holes (e.g., Hyndman et al., 1976). It was deduced that the upper oceanic basement in young crust is much more permeable than the overlying sediments. The first direct measurements of the upper basement permeability—the key parameter that controls fluid flow through the formation—were made in 1979 with a drillstring packer experiment in the famous crustal reference Hole 504B, located in thickly sedimented young crust on the south flank of the Costa Rica Rift (Anderson and Zoback, 1982). Thermal measurements in Hole 504B also indicated that ocean bottom water was flowing down the cased section into upper basement, and it was shown that these data could be interpreted to estimate both downhole flow rate and permeability of the formation into which the flow was directed (Becker et al., 1983). This method has been applied to numerous holes since then, including some less common examples that were drilled in sediment-covered basement highs and actually produced formation fluids up the hole (e.g., Fisher et al., 1997). Since 1979, drillstring packer experiments have been conducted deeper in Hole 504B and in the upper basement sections of several crustal holes. The combined datasets have documented a reduction over several orders of magnitude of permeability with depth in young oceanic crust and a reduction of permeability of uppermost crust with crustal age (e.g., Fisher, 1998; Fisher and Becker, 2000; Becker and Fisher, 2000, 2008) that are often used in current numerical models of hydrothermal circulation in oceanic crust. It is probably an oversimplification, but there seems to be a rough identity among the most permeable and porous upper few hundred m of young oceanic basement, seismic Layer 2A, and the zone of oxidative alteration.

While the down- or uphole flow in many crustal reentry holes can be interpreted to estimate permeability, it also represents a significant perturbation to the in situ subseafloor hydrological systems that we are trying to understand with scientific ocean drilling. This led to the development in 1989-1990 of a new experimental approach to seal these reentry holes, simultaneously emplacing long-term instrumentation to record in situ temperatures and pressures and to sample formation fluids. This concept was named the CORK (Circulation Obviation Retrofit Kit) hydrogeological observatory (Davis et al., 1992). CORKs have allowed for determination of in situ temperature and pore pressure state after the perturbation due to drilling has decayed (e.g., Davis and Becker, 2002). The subseafloor pressure data show an attenuated and phase-lagged seafloor tidal loading signal that can be interpreted to constrain hydraulic diffusivity and derived permeability at formation scales (Davis et al., 2000). In addition, once the tidal signals are filtered out, the subseafloor pressures also show formation responses to tectonic events, acting essentially as crustal strain meters (e.g., Davis et al., 2001). The combination of CORK and packer observations in ridge-flank sites indicates high lateral fluids fluxes and short residence times in very permeable upper basement under relatively small pressure differentials (e.g., Davis and Becker, 2002). This conclusion is supported by geochemical analyses of pore waters and long-term “OsmoSamplers” recovered from the CORKs (e.g., Elderfield et al., 1999; Wheat et al., 2000, 2003).

During the late 1990s, newer CORK concepts were developed to separately seal multiple zones in a single hole; these models include the “Advanced CORK,” “CORK-II,” and a “wireline CORK” that can be installed from oceanographic vessels. More than 20 CORKs of various models have been installed to date, primarily in ridge-flank settings

and in subduction zones. In the latter setting, a prime goal has been to document fluid pressures in plate boundary faults and the relationship between fluid processes and subduction earthquakes. To date, overpressures as high as 1 MPa have been documented in the monitored plate boundary faults, but this is significantly less than lithostatic pressure and thus not enough to enable slip along the faults. In the Hydrate Ridge subduction setting offshore Oregon, a CORK through a thrust fault apparently recorded the transient thermal signal of an up-fault fluid flow event. Even more ambitious observatories are planned for the IODP NanTroSEIZE program, combining seismic and strain instruments with the CORK hydrological concept.

In the process of installing wireline CORKs in Hole 504B and a companion Hole 896A ~1km away in 2001, it was determined that Hole 896A was producing crustal fluids and the first (only?) true video from within oceanic basement was collected (Becker et al., 2004). That video seems to show copious microbiota within the hole and images individual formations that are producing fluids into the hole and probably represent most of the bulk permeability of the formation. That serves to emphasize the fact that the permeability of oceanic crust—and probably most other subseafloor formations—is fracture-dominated and multi-scalar, so it cannot be accurately represented as a single-valued parameter (e.g., Fisher, 1998; Becker and Davis, 2003; Fisher et al., 2008). In summer 2010, IODP Expedition 327 to the Juan de Fuca Ridge flank featured the first attempt to resolve directional variation of crustal permeability and natural fluid flow via the first planned hole-to-hole pumping tests in an array of CORKs penetrating upper basement. (An unplanned hole-to-hole experiment in the same array is described by Fisher et al., 2008.) That array of CORKs has also involved the first in situ microbiological cultivation experiments in oceanic basement, and so represents an important new future direction for CORKs and scientific ocean drilling discussed in more detail by K. Edwards.

Supporting References

Anderson, R.N. and M.D. Zoback. 1982. Permeability, underpressures, and convection in the oceanic crust near the Costa Rica Rift, eastern equatorial Pacific. Journal of Geophysical Research 87(B4):2860-2868.

Becker, K. and E.E. Davis. 2003. New evidence for age variation and scale effects of permeabilities of young oceanic crust from borehole thermal and pressure measurements. Earth and Planetary Science Letters 210(3-4):499-508.

Becker, K. and A.T. Fisher. 2000. Permeability of upper oceanic basement on the eastern flank of the Juan de Fuca Ridge determined with drill-string packer experiments. Journal of Geophysical Research 105(B1):897-912.

Becker, K. and A.T. Fisher. 2008. Borehole packer tests at multiple depths resolve distinct hydrologic intervals in 3.5-Ma upper oceanic crust on the eastern flank of the Juan de Fuca Ridge. Journal of Geophysical Letters 113(B07105):1-12.

Becker, K., M.G. Langseth, R.P. Von Herzen, and R.N. Anderson. 1983. Deep crustal geothermal measurements, Hole 504B, Costa Rica Rift. Journal of Geophysical Research 88(B4):3447-3457.

Becker, K., E.E. Davis, F.N. Spiess, and C.P. deMoustier. 2004. Temperature and video logs from the upper oceanic curst, Holes 504B and 896A, Costa Rica Rift flank: Implications for the permeability of upper oceanic crust. Earth and Planetary Science Letters 222(3-4):881-896.

Davis, E.E. and K. Becker. 2002. Observations of natural-state fluid pressures and temperatures in young oceanic crust and inferences regarding hydrothermal circulation. Earth and Planetary Science Letters 204(1-2):231-248.

Davis, E.E., K. Becker, T. Pettigrew, B. Carson, and R. MacDonald. 1992. CORK: A hydrologic seal and downhole observatory for deep-ocean boreholes. In Proceedings of the Ocean Drilling Program, Initial Reports, Volume 139, Davis E.E., M.J. Mottl, A.T. Fisher, et al. (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Davis, E.E., K. Wang, K. Becker, and R.E. Thomson. 2000. Formation-scale hydraulic and mechanical properties of oceanic crust inferred from pore pressure response to periodic seafloor loading. Journal of Geophysical Research 105(B6):13423-13435.

Davis, E.E., K. Wang, R.E. Thomson, K. Becker, and J. Cassidy. 2001. An episode of seafloor spreading and associated plate deformation inferred from crustal fluid pressure transients. Journal of Geophysical Research 106(B10):21953-21963.

Elderfield, H., C.G. Wheat, M.J. Mottl, C. Monnin, and B. Spiro. 1999. Fluid and geochemical transport through oceanic crust: A transect across the eastern flank of the Juan de Fuca Ridge. Earth and Planetary Science Letters 172(1-2):151-165.

Erickson, A.J., R.P. Von Herzen, J.G. Sclater, R.W. Girdler, B.V. Marshall, and R. Hyndman. 1975. Geothermal measurements in deep-sea drill holes. Journal of Geophysical Research 80(17):2515-2528.

Fisher, A.T. 1998. Permeability within basaltic oceanic crust. Reviews of Geophysics 36(2):143-182.

Fisher, A.T. and K. Becker. 2000. Channelized fluid flow in oceanic crust reconciles heat-flow and permeability data. Nature 403:71-74.

Fisher, A.T., K. Becker, and E.E. Davis. 1997. The permeability of young oceanic crust east of Juan de Fuca Ridge determined using borehole thermal measurements. Geophysical Research Letters 24(11):1311-1314.

Fisher, A.T., E.E. Davis, and K. Becker. 2008. Borehole-to-borehole hydrologic response across 2.4 km in the upper oceanic crust: Implication for crustal-scale properties. Journal of Geophysical Research 113(B7):B07106.

Hyndman, R.D., R.P. Von Herzen, A.J. Erickson, and J. Jolivet. 1976. Heat flow measurements in deep crustal holes on the Mid-Atlantic Ridge. Journal of Geophysical Research 81(23):4053-4060.

Von Herzen, R.P. and A.E. Maxwell. 1964. Measurements of heat flow at the preliminary Mohole site off Mexico. Journal of Geophysical Research 69(4):741-748.

Wheat, C.G., H. Elderfield, M.J. Mottl, and C. Monnin. 2000. Chemical composition of basement fluids within an oceanic ridge flank: Implications for along-strike and across-strike hydrothermal circulation. Journal of Geophysical Research 105(B6):13437-13447.

Wheat, C.G., H.W. Jannasch, M. Kastner, J.N. Plant, and E.H. DeCarlo. 2003. Seawater transport and reaction in upper oceanic basaltic basement: Chemical data from continuous monitoring of sealed borehole in a ridge flank environment. Earth and Planetary Science Letters 216(4):549-564.

SUBSURFACE MICROBIAL OBSERVATORIES
TO INVESTIGATE THE DEEP OCEAN CRUST
BIOSPHERE: DEVELOPMENT, TESTING, AND FUTURE

Katrina J. Edwards
University of Southern California

Scientific ocean drilling has historically yielded some of the most transformative advances in the Earth sciences, cross-cutting many of its disciplines, and providing fundamental advances to our knowledge of how the Earth works. Today, ocean drilling is poised to offer these same transformative advances to disciplines within the life sciences, and provide insight into how life operates and interacts with Earth processes at and below the seafloor. To date, many exciting discoveries have been made about the nature of the deep microbial biosphere in marine sediments. In comparison, there is relatively little information about the nature, extent, and activity of microorganisms living in the volcanic oceanic crust. Because of the size and hydrodynamics of this potential biome, crustal life may have profound influence on global chemical cycles and, as a consequence, the physical and chemical evolution of the crust and ocean. Hence, it is imperative that the scientific community develops a more complete understanding of life in ocean crust. To do this, researchers must develop the appropriate tools for studying this unique habitat, and recent engineering and methodological advancements make now a particularly opportunistic time to do so. Subseafloor borehole observatories (Circulation Obviation Retrofit Kits or CORKs) can help to provide representative samples of crustal fluids and microbiological samples, reducing the extent of contamination associated with drilling, coring, and other operations.

SUBSURFACE MICROBIAL OBSERVATORY TECHNOLOGY

Tools available for CORK-associated microbial observatory experiments can be broken down into two categories: those that are deployed down hole (“subsurface”) within the CORK casing, and those that are deployed at the seafloor and connected to the horizon of interest via pumping of fluids through umbilicals. Redundancy between seafloor and subsurface sampling and experimental units allows for a higher confidence of capturing representative samples for targeted questions.

First-generation downhole observatory technology consisted of subsurface temperature and pressure loggers and osmotically driven fluid samplers (“OsmoSamplers”), which collect a continuous record of temperature, pressure, and composition of the fluid within CORKed boreholes. Second-generation downhole devices couple these to microbial colonization experiments. All downhole technology is limited by the lateral dimension of the experimental environment (i.e., all instruments must fit within the innermost borehole casing, which is typically on the order of 9 cm diameter). Downhole instruments also must provide necessary power for the duration of the deployment (4-5 years).

The continuing adaptation of technologies from other disciplines will advance capabilities to observe and sample the subseafloor crustal biosphere. Technologies that are suitable for long-term deployment, with ultra-low power consumptions and minimal impact by biofouling, are ideal for crustal biosphere observatories. Instrumentation for making remote measurements of downhole conditions is also required. This includes designing downhole electrochemical and mass spectrometer analyzers, for measuring changes in fluid and gas compositions, and also developing new ways to measure rates of chemical reactions in situ. For example, a protoype downhole sampler for manipulative experiments is nearly ready for field trials. Another promising adaptation would be instrumentation for measuring deep ultraviolet fluorescence downhole, permitting the detection of the native fluorescence of microbial cells without the use of stains or dyes or interference from auto-fluorescent mineral particles.

Future observatory experiments will also benefit from the utilization of components that are compatible with objectives in multiple disciplines (microbiology, hydrogeology, chemistry, etc.).

Supporting References

Becker, K. and E.E. Davis. 2005. A review of CORK designs and operations during the Ocean Drilling Program. In Proceedings of the Integrated Ocean Drilling Program, Volume 301, Fisher, A.T., T. Urabe, A. Klaus, and the Expedition 301 Scientists (Eds.). Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas.

Bhartia, R., W.F. Hug, E.C. Salas, R.D. Reid, K. Sijapat, A. Tsapin, K.H. Nealson, A.L. Lane, and P.G. Conrad. 2008. Native fluorescence spectroscopy: Classification of organics with deep UV to UV excitation. Applied Spectroscopy 62(10):1070-1077.

Cowen, J.P., S.J. Giovannoni, F. Kenig, H.P. Johnson, D. Butterfield, M.S. Rappé, M. Hutnak, and P. Lam. 2003. Fluids from aging ocean crust that support microbial life. Science 299(5603):120-123.

D’Hondt, S., B.B. Jørgensen, D.J. Miller, A. Batzke, R. Blake, B.A. Cragg, H. Cypionka, G.R. Dickens, T. Ferdelman, K.U. Hinrichs, N.G. Holm, R. Mitterer, A. Spivack, G. Wang, B. Bekins, B. Engelen, K. Ford, G. Gettemy, S.D. Rutherford, H. Sass, C.G. Skillbeck, I.W. Aiello, G. Guèrin, C.H. House, F. Inagaki, P. Meister, T. Naehr, S. Niitsuma, R.J. Parkes, A. Schippers, D.C. Smith, A. Teske, J. Wiegel, C.N. Padilla, and J.L.S. Acosta. 2004. Distributions of microbial activities in deep subseafloor sediments. Science 306(5705):2216-2221.

Davis, E.E., K. Becker, T. Pettigrew, B. Carson, and R. MacDonald. 1992. CORK: A hydrological seal and downhole observatory for deep-ocean boreholes. In Proceedings of the Ocean Drilling Program, Initial Reports, Volume 139, Davis, E.E., M.J. Mottl, A.T. Fisher, and the ODP Leg 130 Scientists (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Fisher, A.T., C.G. Wheat, K. Becker, E.E. Davis, H. Jannasch, D. Schroeder, R. Dixon, T.L. Pettigrew, R. Meldrum, R. MacDonald, M. Nielsen, M. Fisk, J. Cowen, W. Bach, and K.J. Edwards. 2005. Scientific and technical design and deployment of long-term subseafloor observatories for hydrogeologic and related experiments, IDOP Expedition 301, eastern flank of Juan de Fuca Ridge. In Proceedings of the Integrated Ocean Drilling Program, Volume 301, Fisher, A.T., T. Urabe, A. Klaus, and the Expedition 301 Scientists (Eds.). Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas.

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SCIENTIFIC OCEAN DRILLING AND GAS
HYDRATES STUDIES

Carolyn Ruppel
U.S. Geological Survey

Gas hydrates and the huge quantities of methane that they sequester in marine sediments are typically linked to three broad scientific themes: carbon cycling and global climate change (e.g., Dickens et al., 1995, 1997a; Dickens, 2003; Kennett et al., 2003), submarine slope stability (e.g., Kvenvolden, 1999; Grozic, 2010; Maslin et al., 2010), and energy resources (e.g., Collett, 2002). The last element— the energy resource potential of gas hydrates—renders gas hydrates unique within the scientific ocean drilling (SOD) community: There has always been the expectation that routine gas hydrates drilling for resource issues would someday reach such maturity that SOD would no longer be appropriate. We are largely operating in this era now, with no gas hydrates drilling having been conducted by the Integrated Ocean Drilling Program (IODP) since 2005 (Expedition 311; Riedel et al., 2006). Over the past decade, government/private-sector operators in Japan, the United States, South Korea, India, China, and Malaysia (e.g., Collett et al., 2008a, b, 2009; Hadley et al., 2008; Jones et al., 2008; Park et al., 2008; Ruppel et al., 2008; Wu et al., 2008; Yang et al., 2008; Tsuji et al., 2009; National Energy Technology Laboratory, 2010) completed and/or have begun planning deepwater drilling operations to investigate the resource potential of gas hydrates and, in some cases, to assess geohazards related to drilling and eventual production. None of this government/ private-sector activity would have been possible without the fundamental knowledge and technological developments provided by SOD activities during the Ocean Drilling Program (ODP) and IODP. In this brief, I review the contributions of ODP/IODP to gas hydrates science, highlight special technology developed by SOD for studying hydrates-bearing sediments (known as HBS), and make recommendations about the appropriate niche for SOD in future gas hydrates investigations.

Gas hydrates research has had a long history in the SOD community, even before its elevation to a focus area within the theme of “Subseafloor Ocean and Deep Biosphere” during IODP’s formulation. Before the early 1990s, most of the direct knowledge about subseafloor gas hydrates had been acquired when gas hydrates were encountered, sometimes accidentally, during DSDP and ODP expeditions focused on other scientific goals. Leg 146 in 1992 (Westbrook et al., 1994) was an exception, having been designed to conduct limited gas hydrates investigations within the context of broader-scale fluids research on the Oregon and Vancouver parts of the Cascadian margin.

In 1995, ODP Leg 164 (Dillon et al., 1996) was the first expedition committed exclusively to gas hydrates objectives, focusing on the extensive gas hydrates province in the fine-grained sediments of the Blake Ridge. For the first time, ODP purposely cored and logged the entire hydrates stability zone and the underlying free gas zone, countering critics concerned about the safety of such activities. Many accomplishments of ODP Leg 164 have stood the test of time, with similar phenomena being rediscovered in other marine hydrates provinces even today. ODP Leg 164 proved that gas hydrates occurred even in the absence of the bottom simulating reflector (BSR) that sometimes marks the base of gas hydrates stability (Dillon et al., 1996) and provided strong evidence that small-scale permeability variations (e.g., slightly coarser-grained sediments or dual-porosity/diatomaceous layers) locally control preferential accumulation of gas hydrates in seemingly homogeneous sediments (Ginsburg et al., 2000; Kraemer et al., 2000). The expedition yielded a rich dataset for calibration of logging, vertical seismic profiles (VSP), and geochemical constraints on in situ hydrates concentrations (e.g., Holbrook et al., 1996; Collett and Ladd, 2000; Lorenson et al., 2000); demonstrated that gas hydrates filled only a small percentage of available pore space despite the widespread occurrence of a BSR; and marked a first attempt at shipboard microbiology within SOD (Wellsbury et al., 2000).

By the late 1990s, it was clear that ODP Leg 164, despite far exceeding initial expectations, had yielded a largely static picture of gas hydrates systems that are more properly considered dynamic and hydrologically driven. With the publication of studies that linked the evolution of gas hydrates provinces to fluxes of fluids, gas, and energy (Rempel and Buffett, 1998; Xu and Ruppel, 1999; Ruppel and Kinoshita, 2000) and with the increasing emphasis on gas hydrates “plumbing systems,” the Gas Hydrates PPG, the Hydrogeology PPG (Ge et al., 2002), and subsequently the IODP science plan all alluded to a strategy of drilling in gas hydrates provinces characterized by different flux regimes. ODP Leg 204 (Tréhu et al., 2003) was the second SOD expedition fully committed to the exploration of gas hydrates, this time in the highly dynamic setting of Hydrate Ridge, an accretionary ridge offshore Oregon. Leg 204 yielded important constraints on processes and gas hydrates distributions in three dimensions (Tréhu et al., 2004a), sometimes with the additional fourth dimension of time. Leg 204 had unusually rich ancillary data-sets (e.g., 3D seismic [Tréhu et al., 2002] and CSEM [Weitemeyer et al., 2006]), included sophisticated microbiology (e.g., Colwell et al., 2008; Nunoura et al., 2008), and provided detailed insights into the nature of flux regimes and gas/hydrates dynamics at hydrates-bearing seeps (e.g., Torres et al., 2004; Tréhu et al., 2004b; Liu and Flemings, 2006). A few years later, Expedition 311 (Riedel et al., 2006) became the only IODP activity exclusively focused on gas hydrates, completing a drilling transect from the subducting plate onto the overriding plate on the northern Cascadia margin. The project highlighted lateral heterogeneity in gas hydrates distributions and discovered concentrations of gas

hydrates in coarse-grained sediments well above the base of the gas hydrates stability zone, a finding that challenges simple models (e.g., Hyndman and Davis, 1992; Rempel and Buffett, 1998; Xu and Ruppel, 1999) for gas hydrates system dynamics (e.g., Malinverno, 2010). In September 2010, Site 889, which was drilled on Leg 146 and which lies close to IODP Expedition 311 Sites U1327/U1328, will be re-instrumented and prepared for eventual linkage of the borehole instrumentation to Canada’s NEPTUNE cabled observatory (Davis et al., 2010). While the primary focus of this effort is not gas hydrates, it is noteworthy that SOD boreholes drilled originally for gas hydrates objectives will be the first on the North American Margin to be part of a cabled observatory.

Gas hydrates are unique among geologic materials studied by SOD: They are highly accessible to the drill (within the uppermost 10s to 100s of meters subseafloor), are stable over a specific pressure and temperature range, and rapidly dissociate to water and large volumes of gas. The dissociation process is strongly endothermic, which has led to reliance on routine thermal infrared imaging (e.g., Ford et al., 2003; Weinberger et al., 2005) to locate gas hydrates nodules in recovered conventional cores. Because the removal of hydrates-bearing cores from the gas hydrates stability field leads to rapid degassing, the destruction of sediment textures, and irreversible changes in bulk sediment properties (e.g., Francisca et al., 2005), pressure coring—coring that maintains in situ hydrostatic pressure—has long been viewed as a necessity for gas hydrates studies. Even in the mid-1980s, SOD was experimenting with pressure coring, but true success with the Pressure Core Sampler (PCS; Pettigrew, 1992) was not attained until ODP Leg 164 (Dickens et al., 1997b, 2000). The success of the PCS set the stage for larger, more sophisticated pressure corers (e.g., Hydrate Autoclave Coring Equipment (HYACE)/deployment of HYACE tools in new tests on hydrates (HYACINTH); Fugro corer) that are now routinely deployed to obtain high-quality, hydrates-bearing samples, particularly in relatively fine-grained sediments. Subsequent technical innovations made for sampling and testing of HBS at in situ hydrostatic pressure (e.g., Park et al., 2009) also owe a great deal to the initial work done within SOD. These outside-SOD developments include: (a) the pressure-temperature core sampler (PTCS), a chilled 3-m-long pressure corer developed for Nankai Trough drilling (Takahashi and Tsuji, 2005); (b) a chilled vessel to transfer pressure cores into imaging/measurement devices (PCATS) and an instrument to provide pressure core sub-samples for microbiological and other studies (Schultheiss et al., 2006, 2010; Parkes et al., 2009); and (c) devices to measure the physical properties of pressure cores both at hydrostatic pressure (IPTC; Yun et al., 2006) and with effective stress restored (Ruppel et al., 2008). Other key technical contributions of SOD to the numerous international non-SOD gas hydrates drilling projects are the development of reliable borehole pressure-temperature tools (e.g., the Davis- Villinger Temperature Tool (DVTP) and DVTP-P; Graber et al., 2002), SOD’s model of rapid, post-drilling publication of archival initial reports, and the shipboard deployment of imaging equipment capable of determining the distribution and character of gas hydrates in recovered cores (e.g., Abegg et al., 2006).

The international focus on developing deepwater hydrates as an energy resource means that SOD will not play a leading role in most future gas hydrates drilling. SOD’s drilling platforms may on occasion be suitable for use for non-SOD projects that involve straightforward gas hydrates investigations, little advanced mud handling, and few special logging requirements.

SOD does have an important role to play in non-resource aspects of gas hydrates in a future program. First, marine gas hydrates at the upper feather edge of stability on the continental slopes (e.g., Westbrook et al., 2009) and those associated with subsea permafrost in shallow circum-Arctic areas (e.g., Rachold et al., 2007; Ruppel, 2009; Shakhova et al., 2010) are probably actively deteriorating now in response to climate change on relatively short timescales (contemporary to 20 ka). The dynamics of these gas hydrates systems represents a compelling, multidisciplinary problem that is well-suited for the future of SOD under the auspices of the “Earth in Motion” theme. Second, despite decades’ worth of anecdotal studies exploring possible links between submarine slope stability and gas hydrates (e.g., Carpenter, 1981; Kayen and Lee, 1991; Paull et al., 1991), there remains no proof that gas hydrates and/or free gas play a causal role in triggering failures or exacerbate major failures once they are initiated (e.g., Bryn et al., 2005; Tappin, 2010). In light of (a) the tsunamogenic potential of major slope failures that occur in or near gas hydrates areas (e.g., Long et al., 1990; Hornbach et al., 2007), (b) advances in understanding the geomechanics of hydrate-bearing and gas-charged slope sediments (e.g., Sultan et al., 2004; Nixon and Grozic, 2007; Kwon et al., 2008; Liu and Flemings, 2009); and (c) inferred climate-induced dissociation of marine gas hydrates (e.g., Westbrook et al., 2009) under way now in areas near previously documented slope failures, the time is ripe for a fresh focus on the links between gas hydrates and slope stability issues within SOD.

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THE DYNAMICS OF GREENHOUSE FORCING
AND CLIMATE EXTREMES: PROGRESS AND
PROMISE FROM OCEAN DRILLING

James C. Zachos
University of California, Santa Cruz

One of the more prominent accomplishments of earth sciences is the detailed depiction of the extreme, sometimes rapid, changes in climate that have occurred over the past 100 million years. This accomplishment, which is based largely on evidence gleaned from marine sediment cores recovered by the Deep Sea Drilling Project and Ocean Drilling Program (ODP), includes (1) the reconstruction of ocean temperatures, circulation, and pCO₂ during the well-known greenhouse periods (e.g., early Pliocene, early Eocene, and late Cretaceous), (2) the recent discovery and characterization of relatively rapid, but short-lived climatic excursions, or thermal maxima, and (3) the onset and scale of both Antarctic and Northern Hemisphere continental glaciation. These accomplishments were aided partly by innovations in drilling technologies and coring strategies that allowed for the recovery of high-quality marine sediment cores in older, more deeply buried sediments, and by a deliberate effort to focus on climatically sensitive regions, such as the Arctic, southern oceans, tropics, and on depth transects. Additional innovations such as the development of program planning groups (PPG) during ODP improved the organization of drilling strategies, identification of targets, and coordination of expeditions. Some of the key findings on greenhouse climates, particularly those involving extreme climatic events, have played a central role in the testing of greenhouse climate theory, and foretelling the potential long-term impacts of anthropogenic activity such as ocean acidification. To be sure, deep-sea based proxy records of the thermal maxima were included in the most recent IPCC report (Jansen et al., 2007).

The key contributions in characterizing the long-term greenhouse climates of the Pliocene, Eocene, and Cretaceous have come in two specific areas: (1) improving the spatial and temporal resolution and quality of the paleoclimate signals (i.e., temperature and circulation; Zachos et al., 2001; Wara et al., 2005; Cramer et al., 2009), and (2) in constraining past atmospheric pCO₂ (Pagani et al., 2005, 2010). ODP coring in the Southern Ocean (e.g., Legs 113, 119, 120), for example, provided the sediment archives that were essential for establishing the evolution of Atlantic and Indian Ocean sub-polar marine temperatures through the late Cretaceous and Cenozoic, and linking these changes to the appearance and evolution of the Antarctic ice-sheet (Ehrmann and Mackensen, 1992; Zachos et al., 1992). Similarly, successful expeditions in the Northern Hemisphere, particularly the Arctic (ACEX), provided the first constraints on marine polar climates of several intervals of the Eocene greenhouse (Sluijs et al., 2006; Stickley et al., 2009). With advanced piston coring and offset multi-hole strategies, most of the new paleoclimate records have been constructed at high-resolution with astronomically tuned age models, thereby aiding the correlation and development of high-fidelity climate reconstructions. Although the progress in building the Cenozoic atmospheric pCO₂ record has lagged that of the climate records, the recent development and integration of multiple marine organic- and inorganic-based proxies (i.e., alkenone e_p, B isotopes & B/Ca) has already produced more precise and detailed estimates of the pCO₂ for key intervals (Pagani et al., 2005; Pearson et al., 2009; Seki et al., 2010). Collectively, these records demonstrate that as pCO₂ levels have declined (by >1,000 ppm) since the early Eocene, surface temperatures have dropped accordingly and that the present-day levels of pCO₂ (~400 ppm) were last experienced during the early Pliocene and forecasted levels (~1,600 ppm) were last experienced in the Eocene.

The startling discovery of transient thermal maxima in ODP cores, coupled with massive carbon cycle perturbations, clearly represents one of the more transformative scientific achievements in the Geosciences Directorate in the past two decades. The most prominent, the Paleocene-Eocene thermal maximum (PETM; 56 Mya), first discovered in ODP Site 690 (Kennett and Stott, 1991), involved a global warming of 5 to 6 °C, with polar temperatures peaking at over 20 °C (Sluijs et al., 2006). A coeval negative carbon isotope excursion was viewed as evidence that the thermal maximum was driven by a relatively fast and massive release of carbon (Dickens et al., 1997). This hypothesis was tested with detailed reconstructions of depth-dependent changes in ocean carbonate saturation state (e.g., primarily with depth transects drilled during ODP Legs 198, 199, 207, 208; Zachos et al., 2005). With these observational constraints (C-isotopes and carbonate compensation depth [CCD]), it was possible to demonstrate that greater than 4500 Gt C were released in just a few thousands of years, while also computing the change in pCO₂ (800-1000 ppm ΔpCO₂) and extent of ocean acidification (Panchuk et al., 2008; Zeebe et al., 2009). Although the exact source(s) of this carbon remains uncertain, given the input rates (>0.1 GtC/y) it is likely that a significant portion was supplied by exogenic (surface) reservoirs, of which only a few (i.e., soil peats, hydrates) would be of sufficient size to supply so much carbon so quickly. Regardless, the very existence of the hyperthermals has validated aspects of greenhouse climate theory, for example by revealing relatively uniform short-term warming from pole to pole (with the absence of an ice-albedo feedback). More importantly, along with the detailed records of the long-lived warm periods, hyperthermals serve as an additional means of assessing climate sensitivity (°C per doubling of CO₂) and testing numerical models. For example, the extreme polar temperatures of the Cretaceous, early Eocene, and PETM have proved difficult to replicate with general circulation models (GCMs), even under extreme greenhouse levels, thus motivating climatolo-

gists to reevaluate the processes that might amplify polar warming, for example ocean/atmosphere heat transport and clouds. Recent findings have implicated convective cloud activity as potentially significant amplifier of Arctic warmth (Abbot and Tziperman, 2008), a finding, if confirmed, that will have potentially serious implications for forecasts of future warming (Abbot and Tziperman, 2009).

The relatively rapid release of several thousand Gt C during the thermal maxima has also provided insight into the processes of acidification and carbon sequestration, as well as the impacts of such perturbations on ocean biogeochemistry. Similar to the modern, the rapid absorption of CO₂ lowered the ocean pH and carbonate saturation state. As a buffering response, the acidified waters were advected to the deep sea where dissolution of carbonate sediments resupplied carbonate. Because the latter scaled with the degree of acidification, by reconstructing the changes in carbonate sediment accumulation (~CCD), it was possible to estimate the total flux of carbon independent of other proxies, and estimate the change in pCO₂. The eventual sequestration of this carbon occurred via silicate weathering. In the case of the PETM, the rate of carbon release was slow relative to the mixing time of the ocean, so that severe lowering of surface ocean pH was avoided. Still, the rate was rapid enough relative to the residence time of carbon (~100 k.y.), so that the PETM serves as the best analog for assessing rates of carbon sequestration by natural processes (e.g., organic carbon burial, rock weathering/deposition). Indeed, the PETM has validated theory on the long-term fate of anthropogenic carbon emissions and potential biological impacts (Archer, 2005; Kump et al., 2009; Zeebe et al., 2009; Ridgwell and Schmidt, 2010).

The final key contribution to be highlighted by this paper is the role of ocean drilling in identifying the timing and hence the conditions under which the major ice-sheets originated. The high-latitude marine sediment archives have provided both the direct and indirect evidence required for assessing the evolution of the cryosphere (ice-sheets and sea ice). The direct evidence including glaciomarine sediments and ice-rafted debris point to a latest Eocene to earliest Oligocene onset to Antarctic continental ice-sheets and sea ice formation, with the mid-late Eocene initial appearance of sea-ice in the Arctic and mountain glaciers, pre-dating the appearance of full-scale Northern Hemisphere ice-sheets by a significant margin (Stickley et al., 2009). Indirect evidence, such as high-resolution oxygen isotope records, combined with independent proxies of temperature (e.g., Mg/Ca) have proved essential for establishing both the timing relative to forcing (i.e., pCO₂ and orbital), as well as the scale (volume) of continental ice-sheets on short and long time scales (Pälike et al., 2006; Lear at al., 2008).

It is evident that an opportunity now exists to test the sensitivity of climate models to the extreme range of greenhouse gas levels experienced in the Cenozoic. The observational dataset that is required includes, but is not limited to, reconstructions of pole to equator thermal gradients and pCO₂ during the transitions into extreme states. The drilling needs and challenges that remain for extreme climates are thus quite clear. First and foremost is simply the need to close critical gaps in the climatic reconstructions of the extreme warm intervals, particularly the polar regions and tropics. This includes the Arctic, where only a single, poorly recovered section is available to constrain the Cenozoic climatic evolution of this entire region. Coring in other parts of the basin are required at the very least to close the stratigraphic gaps, and to also verify the inferred extreme warmth in those intervals representing the thermal maxima, as well as the history of the arctic cryosphere. Another critical region is the sub-tropics to tropics, where sediment archives are required to establish zonal thermal gradients and circulation (Fedorov et al., 2006). Records from continental margins are needed to establish maximum sea surface temperatures, and to assess whether temperature exceeded key thresholds (e.g., for life) during the warmest intervals (Sherwood and Huber, 2010). The second critical data gap is the lack of suitable depth transects of multiple holes to constrain the changes in deep-sea carbonate chemistry and circulation, particularly during the abrupt events, in several regions (e.g., North Atlantic, South Pacific, Indian Oceans). The rapid changes in ocean carbonate chemistry have proved to be essential in constraining the carbon cycle fluxes and pCO₂ during the thermal maxima, as well as over the long-term. In this regard, the Pacific is key because of its contribution to the total carbon budget (Zeebe et al., 2009). New strategies devised to develop details reconstructions of the CCD, for example, appear to be successful for the middle Eocene and younger (IODP Expeditions 320/321) and should be extended further back in time to span the extreme greenhouse intervals/thermal maxima. Such observational constraints on ocean carbon chemistry combined with numerical models and proxies of pCO₂ offer the best hope of establishing both the long- and short-term variations in carbon dioxide levels that accompanied periods of ice-sheet formation/decay and extreme warmth, and impacts on sea level and the biosphere (see white papers by K. Miller, D. Norris).

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OCEAN DRILLING TO EXPLORE PAST
OCEAN CIRCULATION AND CLIMATE CHANGE

Jerry F. McManus
Lamont-Doherty Earth Observatory of Columbia University

Ocean drilling has provided opportunities and enabled important discoveries in a number of Earth science disciplines. Although they were not primary motivations for initial deep-sea drilling, the research disciplines of paleocean-ography and paleoclimate are two of the outstanding successes of each of the international drilling programs, and they remain likely areas of future advances. This white paper will touch on some examples and highlights in these fields, as the number of significant contributions enabled by ocean drilling makes it impossible to be comprehensive in a short paper. The scientific progress associated with ocean drilling is made possible by logistical and technical advantages that can be broadly considered in two categories. One category is the active development and recovery of targeted sediment sequences from particular locations designed to address specific scientific questions. The other is the ready existence and expansion of high-quality sedimentary archives from globally distributed locations that may be utilized by any scientist seeking appropriate material to address newly arising questions about Earth’s past. Uncovering changes in ocean circulation and regional and global climate requires accurate reconstruction of past oceanographic and environmental conditions using so-called sedimentary proxies as stand-ins for modern physical, chemical, or biological observations. These reconstructions typically demand relatively high spatial and/or temporal resolution, and are most often successful when utilizing long, continuous, high-quality sedimentary sequences such as best or even uniquely recovered through ocean drilling. The resolution of higher frequency variability and rapid changes requires, in addition, elevated rates of sediment accumulation resulting in thicker sequences representing shorter intervals of time. At a certain level, only ocean drilling provides the technology and logistical support to acquire such sequences successfully. Two examples of the unique opportunities presented by ocean drilling are the influence of tectonic gateways and the long-term evolution of the ocean-climate system. The global system of abyssal currents connects the ocean basins of the world and has a profound climatic influence because of the heat transport associated with the thermocline and shallow flows required to balance the deep transport. Particularly in the Atlantic, this system of currents has mean transports that are largely meridional, enhancing the climate impact at high latitudes. It was established in its present form only after the closure of Panama removed the low-latitude connection between the Atlantic and Pacific Oceans, thus potentially setting the stage for the dramatic warm-cold cycles of the Plio-Pleistocene ice ages (Raymo et al., 1992). The production of North Atlantic Deep Water (NADW), an important element of this global circulation, was enabled by the tectonic establishment of shallow sills defined by a series of ridges connecting Greenland, Iceland, and Scotland. Subsequently, salty northward surface flows could attain enhanced density at the high latitudes of the Nordic Seas before spilling over the ridges to form the core of the NADW (Wright and Miller, 1996). Investigation of the Cenozoic decline over tens of millions of years into the Plio-Pleistocene ice ages, as discussed in greater detail in a separate paper, has almost entirely been made possible by ocean drilling. Similarly, the discovery of an acceleration of Northern Hemisphere glaciation approximately 2.5 million years ago came directly from the pairing of evidence of iceberg debris and the oxygen isotope indicator of colder temperatures and more ice derived in a single long sequence drilled in the North Atlantic (Shackleton and Hall, 1984). On a similarly long time scale, it was discovered that the deep ocean stratification had changed markedly at high latitudes, an aspect strongly tied to ventilation of the deep ocean by the global ocean circulation (Haug et al., 1999). Far afield from these high-latitude processes, but no less important for the global climate, is the variable longitudinal asymmetry of sea surface temperatures (SSTs) produced by the interconnected dynamics of the atmosphere and shallow ocean in the tropical Pacific. This oscillating system, now known as El Niño-Southern Oscillation (ENSO), plays a fundamental role in the global climate, yet was only established as we know it since the Pliocene, evolving from a more persistent and symmetric pattern known as “El Padre” that could only have been uncovered and explored through a distributed array of long sediment sequences taken from sites across the equatorial Pacific recovered by multiple ocean drilling campaigns (Wara et al., 2005). The tropical Pacific was the focus of another breakthrough study, which applied a trace element geochemical proxy to microfossils preserved in long sediment sequences from the eastern and western equatorial Pacific to discover the pattern and magnitude of SST variations through the last several global ice age climate cycles (Lea et al., 2000). Although this study also utilized sediments that were recovered without ocean drilling, it was enabled by the existence of high-quality drilled sequences from Ontong Java, and could clearly only be extended further back in time through the use of cores from multiple ocean drilling sites. The discovery of ice-age cycles on so-called orbital or Milankovitch time scales constitutes a major contribution to our understanding of Earth’s climate system. These cycles are associated with changes in the seasonal distribution of sunlight resulting from the varying tilt and orientation of Earth’s axis of rotation, and changes in the ellipticity, or eccentricity, of its orbit. Although the cycles were first uncovered from continental and relatively thin marine sequences, they have best been established and explored through ocean drilling. Stacked microfossil oxygen isotope records from

multiple drilling sites were used to establish the influence of Earth’s varying tilt on the pacing of ice ages in a statistically robust way (Huybers and Wunsch, 2004). An even broader and far longer array of similar records from ocean drilling now stands as the gold standard of the entire sequence of Plio-Pleistocene glacial cycles, and a target to which any new paleoclimate record for this interval may be compared and matched (Lisiecki and Raymo, 2005). The recovery of long, continuous sequences allowed the exploration of the evolution of periodic behavior in the global glacial cycles. Drilling in moderate- to high-accumulation sites in the North Atlantic and elsewhere established that early Pleistocene ice ages were repeated every 40,000 years, whereas within the past million years these cycles slowed in pacing to approximately 100,000-year intervals and increased in magnitude to include some of the most extreme glaciations interspersed with enhanced warm interglacial intervals (Ruddiman et al., 1986; Shackleton, 2000). The shift from the “40K world” that shared timing with changes in the tilt of Earth’s axis to the “100K world” pacing of changes in the eccentricity of Earth’s orbit is a fundamental discovery, yet one that remains poorly understood in terms of climate physics. The large-scale ocean circulation has also varied, along with the global climate, and the two are inextricably coupled, although not in any simple, linear fashion. One valuable tool, perhaps the best, for reconstructing this circulation is the stable carbon isotopes of dissolved inorganic carbon in seawater, which is also recorded in microfossil shells. One now classic approach is the identification of approximately global geochemical end-members, because deep waters are formed at a limited number of locations, typically at the high latitudes in each hemisphere. Locations at the mid and low latitudes can then be examined to see which proportion of end-member signatures characterizes a given site through time. Such an approach, enabled by ocean drilling, was utilized to show that northern-sourced meridional overturning circulation (MOC), including the volumetric influence of NADW, was generally diminished during each Pleistocene glaciation (Raymo et al., 1990). The recovery of sediment sequences from depth transects has allowed the discovery of distinctly different patterns of variability in the intermediate and deep water masses and also in the deep waters influencing the various ocean basins (Hodell et al., 2003; Raymo et al., 2004). More recent discoveries of variability and the connection to climate have come from study of long records in the frequency domain as well as in the time domain (Lisiecki et al., 2008).

At higher frequencies, the MOC has varied persistently through successive glacial cycles, coupled strongly to millennial climate cycles (McManus et al., 1999), although the question of whether ocean or climate is the primary driver of the coupled changes remains an open one.

Combining the long continuous records of glacial cycles provided by ocean drilling with detailed analysis to explore abrupt changes reveals an apparent ice volume threshold in the ocean and climate response, such that an amount of ice equivalent to approximately 30 meters of sea level is enough to amplify rapid climate changes (McManus et al., 1999).

Following the discovery of dramatic oscillations in Greenland ice cores, an explosion of information has been uncovered about rapid changes in the regional and global climate, much of it made possible by ocean drilling. In a series of studies, it was found that the millennial climate cycles in ice cores had equivalents in deep-sea sediments, and that massive iceberg discharges had also left their episodic imprint (Broecker et al., 1992; Bond et al., 1992, 1993; McManus et al., 1994). These studies relied on the ready existence of high-quality ocean drilling sediments, and they have been followed by hundreds of globally distributed studies demonstrating the transformative power of discoveries resulting from ocean drilling. Some of these subsequent studies utilized ocean drilling material from unusual environments such as near-shore basins with limited ventilation and bioturbation (Hendy and Kennett, 1999; Peterson et al., 2000). Studies building upon these discoveries may now utilize ocean drilling sediments extending back in time (Oppo et al., 1998; Martrat et al., 2004), but also in the most recent climate cycle of the last ice age and even the Holocene (deMenocal et al., 2000; Haug et al., 2001; Oppo et al., 2003; Praetorius et al., 2008). The high quality of the sediments recovered, the ready availability of ancillary chemical and physical data, and the existence of a previous benchmark study only add to the value of existing ocean drilling sediments. In some cases the coverage is incomplete, so the choice of existing locations is a necessary compromise, and some of the oldest non-duplicated sediments are becoming depleted, or do not have the full suite of related data to optimize their use. There are also large, if not vast, stretches of the ocean floor that have not been explored and recovered by ocean drilling. So there are good reasons to expect that there are abundant opportunities for additional fundamental discoveries about the ocean-climate system based on continuing ocean drilling, even if it remains impossible to predict any one of them beforehand.

Supporting References

Bond, G.C., H. Heinrich, W. Broecker, L. Labeyrie, J. McManus, J. Andrews, S. Huon, R. Jantschik, S. Clasen, C. Simet, K. Tedesco, M. Klas, G. Bonani, and S. Ivy. 1992. Evidence for massive discharges of icebergs into the northern Atlantic Ocean during the last glacial period. Nature 360:245-249.

Bond, G.C., W. Broecker S. Johnsen, J. McManus, L. Labeyrie, J. Jouzel, and G. Bonani. 1993. Correlations between climate records from North Atlantic sediments and Greenland ice. Nature 365:143-147. Broecker, W.S., G.C. Bond, M. Klas, E. Clark, and J. McManus. 1992. Origin of the northern Atlantic’s Heinrich events. Climate Dynamics 6(3-4):265-273.

deMenocal, P., J. Ortiz, T. Guilderson, and M. Sarnthein. 2000. Coherent high- and low-latitude climate variability during the Holocene warm period. Science 288(5471):2198-2202.

Haug, G.H., D.M. Sigman, R. Tiedemann, T.F. Pedersen, and M. Sarnthein. 1999. Onset of permanent stratification in the subarctic Pacific Ocean. Nature 40:779-782.

Haug, G.H., K.A. Hughen, D.M. Sigman, L.C. Peterseon, and U. Röhl. 2001. Southward migration of the Intertropical convergence zone through the Holocene. Science 293(5533):1304-1308.

Hodell, D.A., K.A. Venz, C.D. Charles, and U.S. Ninnemann. 2003. Pleistocene vertical carbon isotope and carbonate gradients in the South Atlantic sector of the Southern Ocean. Geochmistry, Geophysics, and Geosystems 4(1004):1-19.

Hendy, I. and J.P. Kennett. 1999. Latest Quaternary North Pacific surface-water responses imply atmosphere-driven climate instability. Geology 27(4):291-294.

Huybers, P. and C. Wunsch. 2004. A depth-derived Pleistocene age-model: Uncertainty estimates, sedimentation variability, and nonlinear climate change. Paleoceanography 19(PA1028):1-24.

Lea, D.W., D.K. Pak, and H.J. Spero. 2000. Climate impact of Late Quaternary equatorial Pacific sea surface temperature variations. Science 289(5485):1719-1724.

Lisiecki, L.E. and M.E. Raymo. 2005. A Pliocene-Pleistocene stack of 57 globally distributed benthic d18O records. Paleoceanography 20:PA1003.

Lisiecki, L.E., M.E. Raymo, and W.B. Curry. 2008. Atlantic overturning responses to Late Pleistocene climate forcings. Nature 456:85-88.

Martrat, B., J.O. Grimalt, C. Lopez-Martinez, I. Cacho, F.J. Sierro, J.A. Flores, R. Zahn, M. Canals, J.H. Curtis, and D.A. Hodell. 2004. Abrupt temperature changes in the western Mediterranean over the past 250,000 years. Science 306(5702):1762-1765.

McManus, J.F., G.C. Bond, W.S. Broecker, S. Johnsen, L. Labeyrie, and S. Higgins. 1994. High-resolution climate records from the North Atlantic during the last interglacial. Nature 371:326-329.

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Praetorius, S.K., J.F. McManus, D.W. Oppo, and W.B. Curry. 2008. Episodic reductions in bottom-water currents since the last ice age. Nature Geoscience 1:449-452.

Raymo, M.E., W.F. Ruddiman, N.J. Shackleton, and D.W. Oppo. 1990. Evolution of Atlantic-Pacific 13C gradients over the last 2.5 m.y. Earth and Planetary Science Letters 97(3-4):353-368.

Raymo, M.E., D. Hodell, and E. Jansen. 1992. Response of deep ocean circulation to initiation of northern hemisphere glaciation (3-2 MA). Paleoceanography 7(5):645-672.

Raymo, M.E., D.W. Oppo, B.P. Flower, D.A. Hodell, J.F. McManus, K.A. Venz, K.F. Keliven, and K. McIntyre. 2004. Stability of North Atlantic water masses in the face of pronounced natural climate variability. Paleoceanography 19:PA2008.

Ruddiman, W.F., M. Raymo, and A. McIntyre. 1986. Matuyama 41,000-year cycles: North Atlantic Ocean and Northern Hemisphere ice sheets. Earth and Planetary Science Letters 80(1-2):117-129.

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Shackleton, N.J. and M.A. Hall. 1984. Oxygen and carbon isotope stratigraphy of Deep Sea Drilling Project Hole 552A: Plio-Pleistocene glacial history. In Initial Reports of the Deep Sea Drilling Project, Roberts, D.G. and D. Schnitker (Eds.). U.S. Government Printing Office, Washington, DC.

Wara, M.W., A.C. Ravelo, and M.L. Delaney. 2005. Permanent El Niño-like conditions during the Pliocene warm period. Science 309(5735):758-761.

Wright, J.D. and K.G. Miller. 1996. Control of North Atlantic deep water circulation by the Greenland-Scotland Ridge. Paleoceanography 11(2):157-170.

ROLE OF OCEAN DRILLING IN
UNDERSTANDING CAUSES AND EFFECTS
OF GLOBAL SEA-LEVEL CHANGE

Kenneth G. Miller
Rutgers University

Although the Intergovernmental Panel on Climate Change (IPCC) projected a 40 cm global sea-level rise in the 21st century (Intergovernmental Panel on Climate Change, 2007), we are tracking a minimal 80 cm rise and semi-empirical calibrations predict >1 m rise (Vemeer and Rahmstorf, 2009; Jevrejeva et al., 2010). Holocene reconstructions are needed to isolate anthropogenic influences on sea level determined from instruments (tide gauge, satellite, and temperature measurements) (Cazenave and Llovell, 2010). Evaluation of pre-Holocene records is required to understand the rates, amplitudes, and mechanisms controlling sea level, both global (eustatic) and relative (i.e., including subsidence and uplift). Calibration of sea level to temperature and CO₂ provides a sensitivity experiment that requires pre-Holocene records.

Sea level can be reconstructed by studying continental margin sequences, the δ¹⁸O proxy of ice volume, and drilling coral reefs (“fossil sunshine”). Ocean drilling on passive continental margins has provided a detailed (±10m resolution) 100 myr history of sea-level change that yields insight into global climates and tectonics (Miller et al., 2005). A global array of ocean coreholes provides δ¹⁸O proxy for glacioeustasy (Miller et al., 1991, 1996; Zachos et al., 2001; Cramer et al., 2009), although separating ice volume from temperature is progressively more uncertain prior to the Pleistocene. Coral drilling in Barbados (Fairbanks, 1988; Peltier and Fairbanks, 2006) and Tahiti (Bard et al., 2010) has shown a rise in excess of 40 mm/yr during the last deglaciation (MWP1a; ca. 14 ka) (Deschamps et al., 2009).

Extracting sea level from continental margin records is complicated by tectonism (subsidence and uplift), sediment compaction, and changes in sediment supply. Exxon Production Research (EPR) scientists (Vail et al., 1977) made a revolutionary breakthrough in using seismic reflection profiles to identify sequences (an assumption tested by Eberli et al., [2002]) by Legs 150, 166, 174, 313, and 317 and to estimate the magnitude and ages of past sea-level changes. The Deep Sea Drilling Project (DSDP) drilled the passive continental margins of Ireland (Leg 80) and New Jersey (Legs 93 and 95), but these deep-water (>1 km) sites provided little constraint on amplitudes. The Ocean Drilling Program (ODP) early on (COSODII [Conference on Scientific Ocean Drilling], 1987; JOI/USSAC [Joint Oceanographic Institutions’ U.S. Scientific Advisory Committee] Workshop, 1990; JOIDES [Joint Oceanographic Insitutions for Deep Earth Sampling] Sea-level Working Group, 1992) suggested drilling a global array of passive continental margin transects, deep-sea δ¹⁸O records, and coral reefs to determine sea-level changes and identified four goals: (1) test the synchrony of events; (2) estimate amplitudes; (3) evaluate various models for the stratigraphic response to sea-level change; and (4) determine the controlling mechanism.

Recognizing the importance of margin transects, ODP endorsed drilling onshore and offshore New Jersey as an integrated study. ODP Legs 150 (slope), 174A (outer shelf), and Leg 150X/174AX (onshore) dated seismic sequence boundaries and tied them to δ¹⁸O increases indicative of glacioeustatic falls (Miller et al., 1998; Eberli et al., 2002). ODP drilling on the margins of Australia (Legs 133, 182, and 194) and the Bahamas (Leg 166) provided sea-level records from carbonate settings, although atoll drilling suffered from core recovery problems (Legs 143 and 144). Drilling documented that similar Miocene unconformities, progradation, and stacking patterns occur in both carbonate and siliciclastic (New Jersey) basins. Drilling by Marion Plateau Leg 194 provided a eustatic estimate of 57±12 m for a major middle Miocene (ca. 13.9-13.8 Ma) lowering.

ODP accomplished the following: (1) validated the transect approach; (2) confirmed that the primary cause of impedance contrasts are unconformities; (3) demonstrated interregional correlation of unconformities, suggesting that they are global; (4) determined the ages of sequence boundaries better than ±0.5 Myr and provided a chronology of eustatic lowering for the past 100 Myr; (5) linked sequence boundaries directly to global δ¹⁸O increases, demonstrating a causal relationship between sea level and ice volume; (6) provided evidence of small ice sheets during the Late Cretaceous-Eocene; and (7) showed that siliciclastic and carbonate margins yield comparable records of sea level (Miller, 2002).

Drilling onshore in New Jersey by ODP Legs 150X and 174AX resulted in the first testable Late Cretaceous to Cenozoic eustatic curve, derived with an inverse modeling technique termed backstripping that progressively removes the effects of sediment compaction, loading, and thermal subsidence. Backstripping showed that long-term sea-level changes were smaller than previously inferred, with a Cretaceous peak of 150±50 m, implying lower changes in ocean crust production rates than previously assumed. The New Jersey record has been criticized for its relatively low long-term peak due to epierogeny, but interregional correlations and ties to the δ¹⁸O record demonstrate that is it untainted by tectonic overprints at higher frequencies. Comparison of eustatic estimates from New Jersey drilling mirrors δ¹⁸O variations developed from global deep-sea cores, validating the link with ice-volume on the 104-106 yr scale. Finally, eustatic and δ¹⁸O-based temperature estimates allow calibration of sea level, global temperature, and atmospheric CO₂ estimates.

Initial coral sea-level studies were done outside of ODP (e.g., Barbados and Tahiti), but IODP has successfully drilled reefs and shallow water siliciclastic sequences with mission-specific platforms in Tahiti (Exp. 310), the New Jeresy shal-

low shelf (Exp. 313), and the Great Barrier Reef (Exp. 325), and with the JOIDES Resolution in New Zealand (Exp. 317). IODP Expedition 313 cored nearshore New Jersey lower to middle Miocene (24-14 Ma) sequences that are poorly represented onshore but seismically well-imaged nearshore; good recovery was obtained using jack-up platform at three strategically placed nearshore (35 m water depth) sites recording half a dozen early Miocene sea-level cycles. Expedition 317 cored upper Miocene to recent sequences in a transect of one slope and three shelf sites in the Canterbury Basin, New Zealand, providing a stratigraphic record of relative sea-level cycles that is complementary to New Jersey. Expedition 325 drilled 34 holes along four transects of the Great Barrier Reef with good recovery from key water depths (90-120 m) spanning the last glacial cycle. Tahiti (Exp. 310) recovered excellent records of the “stage” 5e interglacial and meltwater pulse (MWP) 1a, with critical constraints on maximum rates and fingerprinting meltwater sources.

Extracting a eustatic signal requires integrated onshore/ offshore drilling transects involving global retrieval of cores representing multiple timeframes and depositional settings, including siliciclastic, carbonate and mixed systems (Fulthorpe et al., 2008). Opportunities exist for ocean drilling to build on cooperation with ICDP, which contributed funds to the New Jersey Expedition and a recent IODP-ICDP-DOSECC (Drilling, Observation and Sampling of the Earth’s Continental Crust) sea-level workshop. Continuous coring is needed, although most sea-level drilling takes place in challenging environments with loose sands or coral debris. Although IODP mission-specific platforms have addressed recovery issues (e.g., Exp. 310 and 313 had >80 percent recovery), logging-while-drilling technology must be used to fill in the gaps despite its high costs.

Sea-level change captures the imagination of the public and scientists alike, with linkages to many fields, including climate change, geochemistry, biogeochemical cycles, sedimentology, stratigraphy, biologic evolution, tectonophysics, basin evolution, and resources (oil, gas, water, carbon sequestration [CCS]). The links to climate change are fundamental: sea-level studies have challenged conventional views of much of Earth history as an ice-free greenhouse. The evolution of eukaryotic phytoplankton appears directly related to long-term sea level (Katz et al., 2005). Facies models developed for sea-level cycles yield predictions about sand versus mud distribution directly applicable to reservoir/aquifer and cap rock/confining beds for hydrocarbon, groundwater, and CCS applications (Posamentier et al., 1988; Sugarman et al., 2006). Constraining eustatic history has important feedbacks into tectonophysics. Backstripping was developed to evaluate basin evolution, assuming sea level was known (e.g., the EPR record). ODP/IODP studies have demonstrated the inadequacy of the EPR curves and provided new eustatic estimates that can then be used to solve for tectonism. With recent and anticipated future accomplishments, sea-level studies are riding a high tide.

Supporting References

Bard, E., B. Hamelin, and D. Delanghe-Sabatier. 2010. Deglacial meltwater pulse 1B and Younger Dryas sea levels revisited with boreholes at Tahiti. Science 327(5970):1235-1237.

Cazenave, A. and W. Llovell. 2010. Contemporary sea level rise. Annual Review of Marine Science 2:1451-1473.

Cramer, B.S., J.R. Toggweiler, J.D. Wright, M.E. Katz, and K.G. Miller. 2009. Ocean overturning since the Late Cretaceous: Inferences from a new benthic foraminiferal isotope compilation. Paleoceanography 24(PA4216):1-14.

Deschamps P., N. Durand, E. Bard, B. Hamelin, G. Camoin, A.L. Thomas, G.M. Henderson, and Y. Yokoyama. 2009. Synchroneity of Meltwater Pulse 1A and the Bolling onset: New evidence from the IODP “Tahiti Sea-Level” Expedition. Geophysical Research Abstracts 11:EGU2009-10233.

Eberli, G.E., F.S. Anselmetti, D. Kroon, T. Sato, and J.D. Wright. 2002. The chronostratigraphic significance of seismic reflections along the Bahamas Transect. Marine Geology Volume 185(1-2):1-17.

Fairbanks, R.G. 1988. Barbados Offshore Drilling Program. Lamont-Doherty Earth Observatory, Palisades, New York.

Fulthorpe, C.S., K.G. Miller, A. Droxler, S.P. Hesselbo, G.F. Camoin, and M.A. Kominz. 2008. Drilling to decipher long-term sea-level changes and effects: A joint ocean leadership, ICP, IODP, DOSECC, and Chevron workshop. Scientific Drilling 6:19-28.

Intergovernmental Panel on Climate Change. 2007. IPCC Fourth Assessment Report: Climate Change 2007. [Online]. Available: http://www.ipcc.ch/publications_and_data/ar4/syr/en/spm.html [2010, September 28].

Jevrejeva, S., J.C. Moore, and A. Grinsted. 2010. How will sea level respond to changes in natural and anthropogenic forcings by 2100? Geophysical Research Letters 37(L07703):1-5.

Katz, M.E., J.D. Wright, K.G. Miller, B.S. Cramer, K. Fennel, and P.G. Falkowski. 2005. Biological overprint of the geological carbon cycle. Marine Geology 217:323-338.

Miller, K.G. 2002. The role of ODP in understanding the causes and effects of global sea-level change. JOIDES Journal 28(1):23-28.

Miller, K.G., J.D. Wright, and R.G. Fairbanks. 1991. Unlocking the ice house: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion. Journal of Geophysical Research 96(B4):6829-6848.

Miller, K.G., G.S. Mountain, the Leg 150 Shipboard Party, and Members of the New Jersey Coastal Plain Drilling Project. 1996. Drilling and dating New Jersey Oligocene-Miocene sequences: Ice volume, global sea level, and Exxon records. Science 271(5252):1092-1094.

Miller, K.G., G.S. Mountain, J.V. Browning, M. Kominz, P.J. Sugarman, N. Christie-Blick, M.E. Katz, and J.D. Wright. 1998. Cenozoic global sea-level, sequences, and the New Jersey transect: Results from coastal plain and slope drilling. Reviews of Geophysics 36(4):569-601.

Miller, K.G., M.A. Kominz, J.V. Browning, J.D. Wright, G.S. Mountain, M.E. Katz, P.J. Sugarman, B.S. Cramer, N. Christie-Blick, and S.F. Pekar. 2005. The Phanerozoic record of global sea-level change. Science 310(5752):1293-1298.

Peltier, W.R. and R.G. Fairbanks. 2006. Global glacial ice volume and last glacial maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25(23-24):3322-3337.

Posamentier, H.W., M.T. Jervey, and P.R. Vail. 1988. Eustatic controls on clastic deposition I—Conceptual framework. Society of Economic Paleontologists and Mineralogists Special Publication 42:109-124.

Sugarman, P.J., K.G. Miller, J.V. Browning, A.A. Kulpecz, P.P. McLaughlin, and D.H. Monteverde. 2006. Hydrostratigraphy of the New Jersey coastal plain: Sequences and facies predict continuity of aquifers and confining units. Stratigraphy 2(3):259-275.

Vail, P.R., R.M. Mitchum, Jr., R.G. Todd, J.M. Widmier, S. Thompson, III, J.B. Sangree, J.N. Bubb, and W.G. Hatlelid. 1977. Seismic stratigraphy and global changes of sea level. In Seismic Stratigraphy: Applications to Hydrocarbon Exploration, Payton, C.E. (Eds.), American Association of Petroleum Geologists Memoir 26:49-212.

Vemeer, M. and S. Rahmstorf. 2009. Global sea level linked to global temperature. Proceedings of the National Academy of Sciences of the United States of America 106:21527-21532.

Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292(5517):686-693.

CO-EVOLUTION OF LIFE AND THE PLANET,
MASS EXTINCTIONS, AND BOLIDE IMPACTS

Richard D. Norris
Scripps Institution of Oceanography

What would our understanding of Earth’s past and future look like if there had been no deep ocean drilling? The deep marine fossil record gives us three vital tools—time, dynamics, and linkages—that become richly textured in the chronicle of oceanic fossils. Ocean drilling provides a highly resolved, near global, narrative of the rate and pacing of events in biological evolution that simply is unresolvable, with few exceptions, in erosion-prone strata preserved on land. Our knowledge of the dynamics of biotic evolution is brightly illuminated by the global correlation and incredibly detailed record of both marine and terrestrial fossils preserved in open ocean sediments. Finally, linkages can be resolved between the environment and the evolution of life far better than we ever could deduce from scattered exposures on land.

One of the most important legacies of ocean drilling has been the development of a highly resolved timescale for Earth processes and biotic evolution. The time scale is capable of identifying events at century to millennial resolution back into the Pliocene (~5 Ma). The network of orbitally tuned deep-sea cores also allows us to trace the timing of evolutionary events throughout the oceans. We can now demonstrate that some oceanic species can spread throughout the oceans in less than a few thousand years—an unexpected feat when faced with tectonic barriers like the Panama Isthmus. Much of modern evolutionary theory is based upon observations of living species, in which historical processes like speciation, extinction, and ecological assembly can only be inferred from modern patterns. The rich oceanic fossil record makes it possible, almost uniquely, to actually see history unfold, to trace the creation and destruction of communities, and to do so through many repeated “natural experiments” made possible by Milankovitch cycles and extreme climate change (deMenocal, 2004).

Drill cores also provide very high-quality time scales to examine evolutionary events in pre-Quaternary time such as major Antarctic glaciation (33 Ma), the Paleocene Eocene Thermal Maximum (PETM; 55 ma), a major impact event (65.5 Ma), and ocean stagnation events (~90-100 Ma). In many of these cases, marine coring has provided particularly highly resolved time scales of ecosystem change that can then be transferred to terrestrial exposures. Orbital chronologies for the marine record of the PETM, for instance, were used to show that global warming not only occurred with pacing broadly similar to anthropogenic warming, but also rapidly and profoundly disrupted marine ecosystems and precipitated a major extinction in the deep sea (Kump et al., 2009). The orbitally resolved time scale for the PETM was then used to date evolutionary events on land. These land-sea correlations allowed us to establish the rate of mammalian interchange between the continents during the PETM (Bains et al., 2003).

Such chronologies reveal an unexpected vulnerability of open ocean plankton to climate change. For example, plankton commonly display both rapid and massive changes in abundance tuned to orbital climate cycles. The dramatic changes in abundance (from near absence to 30 percent or more of a fauna) on century to millennial time scales demonstrate that marine ecosystems are much more dynamic than once thought (Norris, 2000). Studies of radiolarians and foraminifera show that both are subject to much higher rates of extinction (similar to that of large mammals) than was thought possible for the huge and widespread populations of most open ocean species. Indeed, the ocean fossil record shows parallels to the discovery of climate swings in ice cores in which the closer we look, the more rapid and frequent ecosystem change is seen.

The emerging picture is one of surprising sensitivity of oceanic and terrestrial ecosystems to small changes in climate forcing. The marine record of terrestrial pollen, wind-blown dust, and charcoal demonstrates the susceptibility of the land surface to small changes in precipitation or temperature (deMenocal, 2004). These same indicators of ecological change are also instrumental in demonstrating the vulnerability of human societies to drought and other ecological disruptions. Oceanic records are widely used to provide both a time scale to human evolution as well as to test theories of the collapse of highly structured human cultures (deMenocal, 2001).

A notable legacy of ocean drilling has been the ability to evaluate how impacts, large volcanic events, and abrupt climate events affect life on Earth. Most terrestrial records do not provide sufficient temporal resolution, or a sufficiently detailed fossil record, to produce the extremely detailed records of biotic change needed to test cause-and-effect models. For example, in the continuing debate over the causes of the Cretaceous-Paleogene mass extinction, the terrestrial vertebrate fossil record is simply too incomplete to do more than suggest that most species die out some time before the Chicxulub impact debris layer fell to Earth (Schulte et al., 2010). However, the impact precisely correlates with major turnover in many microfossil groups in the oceans as well as a host of geochemical and sedimentological indicators of marine and terrestrial ecosystem collapse. Ocean drilling has also shown that the extinction and impact were not presaged in the oceanic record as might be expected if the Deccan traps eruptions were an important source of ecological change. Remarkably, the deep-sea fossil record reveals that unusual “disaster” ecosystems last for nearly a million years after the impact in agreement with models of species evolution in disrupted ecosystems.

The deep-sea fossil record provides insight for how our world might react to major ecosystem changes today or in

the future. Past extreme events represent analogs that show us how complex ecological systems respond to major shocks to our planet. Ecosystem changes are hard to model, so the fossil record has particular value in illustrating how Earth’s biota has reacted to and recovered from hits to the biosphere. Drill cores show, for example, that ocean acidification during the PETM did not result in a major extinction of marine calcareous plankton even though current models suggest the total greenhouse gas release was on a similar scale to that expected from human fossil fuel consumption (Kump et al., 2009; Ridgwell and Schmidt, 2010).

What should ocean drilling do in the future to test evolutionary models? To date, the marine fossil record has mostly been used to explore long-term changes in marine and terrestrial ecosystems but there is much potential for incisive testing of current evolutionary theory. We have particular need to obtain astronomically tuned records of transects within the major oceanic ecosystems to be able to compare, at century to millennial time scales, changes in population size and distribution. Such comparisons are needed to test models of ecosystem stability developed for terrestrial environments. Most modern ecology and evolutionary biology does not deeply consider history, so ocean drilling can, almost uniquely, provide the long, temporally and spatially resolved records needed to test models of speciation that have been with us, unresolved, since Darwin. Finally, ocean drilling can examine questions that have not even occurred to ecologists such as whether the productivity and biodiversity of the Earth oscillates over time thanks to long-period orbital or tectonic cycles. Does Earth’s biosphere have a “heartbeat” (Pälike et al., 2006)?

Supporting References

Bains, S., R.D. Norris, R.M. Corfield, G.J. Bowen, P.D.Gingerich, and P.L. Koch. 2003. Marine-terrestrial linkages at the Paleocene-Eocene boundary. Special Paper Geological Society of America 369:1-9.

deMenocal, P.B. 2001. Cultural responses to climate change during the Late Holocene. Science 292(5517):667-673.

deMenocal, P.B. 2004. African climate change and faunal evolution during the Pliocene-Pleistocene. Earth and Planetary Science Letters 220(1-2):3-24.

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94-107.

Norris, R.D. 2000. Pelagic species diversity, biogeography, and evolution. Paleobiology 26(4):236-258.

Pälike, H., R.D. Norris, J.O. Herrle, P.A. Wilson, H.K. Coxall, C.H. Lear, N.J. Shackleton, A.K. Tripati, and B.S. Wade. 2006. The heartbeat of the oligocene climate system. Science 314(5807):1894-1898.

Ridgwell, A. and D.N. Schmidt. 2010. Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release. Nature Geoscience 3(3):196-200.

Schulte, P., L. Alegret, I. Arenillas, J.A. Arz, P.J. Barton, P.R. Bown, T.J. Bralower, G.L. Christeson, P.C., C.S. Cockell, G.S. Collins, A. Deutsch, T.J. Goldin, K. Goto, J.M. Grajales-Nishimura, R.A.F. Grieve, S.P.S. Gulick, K.R. Johnson, W. Kiessling, C. Koeberl, D.A. Kring, K.G. MacLeod, T. Matsui, J. Melosh, A. Montanari, J.V. Morgan, C.R. Neal, D.J. Nichols, R.D. Norris, E. Pierazzo, G. Ravizza, M. Rebolledo-Vieyra, W.U. Reimold, E. Robin, T. Salge, R.P. Speijer, A.R. Sweet, J. Urrutia-Fucugauchi, V. Vajda, M.T. Whalen, and P.S. Willumsen. 2010. The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science 327(5970):1214-1218.

HOW HAS THE AVAILABILITY OF DEEP-
OCEAN DRILLING CAPABILITIES ENABLED
NEW FIELDS OF INQUIRY?

Dennis Kent
Rutgers University & Lamont-Doherty Earth Observatory

Earth is largely covered by water: two-thirds of the surface area with an average water depth of 3,700 m. The United States is essentially surrounded by oceans—Atlantic, Gulf of Mexico, Pacific, and Arctic. Deep-ocean research and drilling capabilities are important for a U.S. leadership role in global geosciences as well as for strategic, economic, and environmental reasons. This white paper attempts to outline some of the contributions of this technology.

Project Mohole (1958-1966) inaugurated deep-ocean drilling capability with a converted Navy barge fitted with experimental deep-water drilling equipment and a dynamic positioning system invented for the occasion. Phase 1 drilling was done off Guadalupe, Mexico, in March and April 1961 in 11,700 feet of water and penetrated more than 600 feet beneath seafloor to find that oceanic crust consisted of basalt. The project was discontinued before Phase II could be implemented.

Drillship Glomar Challenger operating under the National Science Foundation (NSF)-funded Deep Sea Drilling Project (DSDP; 1968-1985) almost immediately hit a grand slam by determining on Leg 3 (December 1968-Janu-ary 1969) that the ages of sediment overlying oceanic crust at 8 sites in the South Atlantic increased systematically with distance from the ridge axis (Maxwell et al., 1970), as predicted by the new geomagnetic polarity time scale (Heirtzler et al., 1968). This landmark verification of seafloor spreading was decisive and only possible by deep-ocean drilling. Moreover, the discovery directly led to the paradigm of plate tectonics and heralded the development of integrated geologic time scales.

The recovery of undisturbed sediment with the hydraulic piston corer (HPC) starting on DSDP Leg 64 and especially Leg 68 (Prell et al., 1980), and subsequently the advanced piston corer (APC) beginning with Leg 94 (Ruddiman et al., 1986), revolutionized the study of Earth history and major events in deep time by providing long continuous sediment columns for high-resolution biostratigraphic, magnetostratigraphic, and isotopic studies. These records are the backbone of our understanding of Milankovitch cyclicity (e.g., Lisiecki and Raymo, 2005; Herbert et al., 2010) and the ongoing construction of high-precision astrochronologies further and further back in time (e.g., Pälike et al., 2006).

Examples of results from HPC coring include an oxygen isotope calibration of the onset of ice-rafting in the North Atlantic (Leg 81, Site 552A; Shackleton et al., 1984a) and broadly of environmental changes over the Cenozoic (Leg 74, Site 525-529; Shackleton et al., 1984b), as well as the construction of a composite isotope record (Miller et al., 1987) linked by more accurate geologic and geomagnetic polarity time scales (e.g., Berggren et al., 1985) for global sea-level and other studies including the overarching greenhouse-icehouse transition (Miller et al., 1991) in the Cenozoic.

Results from APC coring are ongoing (e.g., Channell et al., 2009), and examples include the discovery of episodes of extreme and rapid climate change, notably the Paleocene/ Eocene thermal maximum and carbon isotope excursion at ODP Site 690 (Kennett and Stott, 1991), an event that has attracted huge research attention and has been widely verified and elaborated upon (e.g., Thomas et al., 2002; Zachos et al., 2005). The Paleocene Ecocene Thermal Maximum/ Carbon Isotope Excursion (PETM/CIE) is often regarded as a geologic analog to anthropogenic production of CO₂ and global warming (e.g., Dickens, 2004). A net result of these studies is the development of a global picture of Cenozoic ocean circulation and climate change, including growth of Antarctic and Greenland ice sheets, and possible links to atmospheric CO₂ (Zachos et al., 2008; Cramer et al., 2009).

The Integrated Ocean Drilling Program (IODP) Arctic Coring Expedition in August 2004 produced a long continuous sedimentary record from this logistically difficult area that shows the transition from an exceptionally warm world during the late Paleocene and early Eocene to a progressively colder world increasingly influenced by ice (Moran et al., 2006).

Leg 130 drilling on Ontong Java Plateau (OJP) confirmed earlier drilling results that it formed by rapid volcanism during the Aptian (Tarduno et al., 1991). Emplacement of the OJP, which is likely to be the most voluminous oceanic large igneous province (LIP) known (Coffin and Eldholm, 1994), seems to be closely (causally?) associated with the beginning of the Cretaceous long normal superchron and may have contributed to generally warm mid-Cretaceous climates, a eustatic rise, and the formation of oceanic anoxia due to increased crust production and higher mantle outgassing (Larson, 1991; Tejada et al., 2009). However, there are still conflicting estimates of the precise relationship and age(s) of the OTP, Chron CM0 and OAE1 (oceanic anoxic event) (or Selli Event) (Larson and Erba, 1999; Gradstein et al., 2004) with major consequences for global systems such as seafloor production rates (Cogné and Humler, 2006) and associated geochemical cycles.

A volcanic origin for seaward dipping seismic reflectors that may be related to the North Atlantic igneous province was determined by drilling on Rockall Plateau on Leg 81 (Roberts et al., 1984; the same expedition that produced the seminal record of Northern Hemisphere glaciations; paragraph above). Seaward dipping reflectors elsewhere may also be associated with LIP magmatism, for example, in the southeastern margin of North America and Central Atlantic magmatic province (Austin et al., 1990).

With the exception of the highly speculative idea of the Ontong Java Plateau being due to a massive impact (Ingle and Coffin, 2004), impact structures on oceanic crust have yet to be found but must exist. Deep ocean drilling capability will be the only way to sample, verify, and better understand the dynamics of an oceanic impact crater when one is eventually identified, much like the strategy of the International Continental Scientific Drilling Program (ICDP) (and forth-coming Integrated Ocean Drilling Program/Mission Specific Platforms [IODP/MSP]) drilling on the Chicxulub impact crater in the Yucatan (Joanna Morgan, personal communication, 2010).

Direct estimates of paleolatitude by deep-ocean drilling of submerged edifices formed along the Hawaiian-Emperor hotspot track have challenged the fixed hotspot model (Tarduno et al., 2003) and provide dramatic support for predicted motion of mantle plumes wafting in the mantle wind (Tarduno et al., 2009). Results from scheduled drilling on the Louisville track will be essential toward resolving this issue.

Drilling that started on DSDP Leg 69 at Site 504B on the Nazca plate and continued on a half dozen subsequent expeditions penetrated through about 500 m of pillow lavas and about a 1,000 m section of dike rocks (Pariso et al., 1995; see compilation of magnetic data and discussion by Gee and Kent, 2007). The results provide the first in situ reference section for Seismic Layer 2 of the oceanic crust and documented the importance of the sheeted dike complex as a viable source of lineated magnetic anomalies.

Multi-leg drilling at ODP Site 1256 on the Cocos plate penetrated more than 1,250 m section of lavas, sheeted dikes and into gabbros of Seismic Layer 3, extending direct sampling of in situ ocean crust (Wilson et al., 2006). A 1,500 m section of tectonically exposed gabbros drilled at ODP Site 735B on the slow-spreading Southwest Indian Ridge provides evidence for a strongly heterogeneous lower ocean crust (Dick et al., 2003). It may be time to revisit a mission to the Moho.

Supporting References

Austin, J.A., P.L. Stoffa, J.D. Phillips, J. Oh, D.S. Sawyer, G.M. Purdy, E. Reiter, and J. Makris. 1990. Crustal structure of the Southeast Georgia embayment-Carolina trough: Preliminary results of a composite seismic image of a continental suture(?) and a volcanic passive margin. Geology 18(10):1023-1027.

Berggren, W.A., D.V. Kent, J.J. Flynn, and J.A. Van Couvering. 1985. Cenozoic geochronology. Geological Society of America Bulletin 96(11):1407-1418.

Channell, J.E.T., C. Xuan, and D.A. Hodell. 2009. Stacking paleointensity and oxygen isotope data for the last 1.5 Myr (PISO-1500). Earth and Planetary Science Letters 283(1-4):14-23.

Coffin, M.F. and O. Eldholm. 1994. Large igneous provinces, crustal structure, dimensions, and external consequences. Reviews of Geophysics 32(1):1-36.

Cogné, J.P. and E. Humler. 2006. Trends and rhythms in global sea-floor generation rate. Geochemistry, Geophysics, and Geosystems 7(Q03011):1-17.

Cramer, B.S., J.R. Toggweiler, J.D. Wright, M.E. Katz, and K.G. Miller. 2009. Ocean overturning since the Late Cretaceous: Inferences from a new benthic foraminiferal isotope compilation. Paleoceanography 24(PA4216):1-14.

Dick, H.J.B., J. Lin, and H. Schouten. 2003. An ultraslow-spreading class of ocean ridge. Nature 426:405-412.

Dickens, G.R. 2004. Hydrocarbon-driven warming. Nature 429:513-515.

Gee, J.S. and D.V. Kent. 2007. Source of oceanic magnetic anomalies and the geomagnetic polarity time scale. In Treatise on Geophysics, Volume 5. Geomagnetism, Elsevier, Amsterdam, The Netherlands.

Gradstein, F.M., J.G. Ogg, and A.G. Smith. (Eds.). 2004. A Geologic Time Scale 2004. Cambridge University Press, Cambridge, England, United Kingdom.

Herbert, T.D., L.C. Peterson, K.T. Lawrence, and Z. Liu. 2010. Tropical ocean temperatures over the past 3.5 million years. Science 328(5985):1530-1534.

Heirtzler, J.R., G.O. Dickson, E.M. Herron, W.C. Pitman, and X.L. Pichon. 1968. Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents. Journal of Geophysical Research 73(6):2119-2136.

Ingle, S. and M.F. Coffin. 2004. Impact origin for the greater Ontong Java Plateau? Earth and Planetary Science Letters 218(1-2):123-134.

Kennett, J.P. and L.D. Stott. 1991. Abrupt deep-sea warming, palaeoceano-graphic changes and benthic extinctions at the end of the Palaeocene. Nature 353:225-229.

Larson, R.L. 1991. Geological consequences of superplumes. Geology 19(10):963-966.

Larson, R.L. and E. Erba. 1999. Onset of the mid-Cretaceous greenhouse in the Barremian-Aptian: Igneous events and the biological, sedimentary, and geochemical responses. Paleoceanography 14(6):663-668.

Lisiecki, L.E. and M.E. Raymo. 2005. A Pliocene-Pleistocene stack of 57 globally distributed benthic d¹⁸O records. Paleoceanography 20(PA1003)1-17.

Maxwell, A.E., R.P. von Herzen, J.E. Andrews, R.E. Boyce, E.D. Milow, K.J. Hsu, S.F. Percival, and T. Saito (Eds.). 1970. Summary and conclusions. In Initial Reports of the Deep Sea Drilling Project, Volume 3. Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Miller, K.G., R.G. Fairbanks, and G.S. Mountain. 1987. Tertiary oxygen isotope synthesis, sea level history, and continental margin erosion. Paleoceanography 2(1):1-19.

Miller, K.G., J.D. Wright, and R.G. Fairbanks. 1991. Unlocking the ice house: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion. Journal of Geophysical Research 96(B4):6829-6848.

Moran, K., J. Backman, H. Brinkhuis, S.C. Clemens, T. Cronin, G.R. Dickens, F. Eynaud, J. Gattacceca, M. Jakobsson, R.W. Jordan, M. Kaminski, J. King, N. Koc, A. Krylov, N. Martinez, J. Matthiessen, D. McInroy, T.C. Moore, J. Onodera, M. O’Regan, H. Pälike, B. Rea, D. Rio, T. Sakamoto, D.C. Smith, R. Stein, K. St John, I. Suto, N. Suzuki, K. Takahashi, M. Watanabe, M. Yamamoto, J. Farrell, M. Frank, P. Kubik, W. Jokat, and Y. Kristoffersen. 2006. The Cenozoic palaeoenvironment of the Arctic Ocean. Nature 441:601-605.

Pariso, J.E., L.B. Stokking, and S. Allerton. 1995. Rock magnetism and magnetic mineralogy of a 1-km section of sheeted dikes, Hole 504B. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 137/140, Erzinger, J., K Becker, H.J.B. Dick, and L.B. Stokking (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Pälike, H., R.D. Norris, J.O. Herrle, P.A. Wilson, H.K. Coxall, C.H. Lear, N.J. Shackleton, A.K. Tripati, and B.S. Wade. 2006. The heartbeat of the Oligocene climate system. Science 314(5807):1894-1898.

Prell, W.L., J.V. Gardner, C. Adelseck, G. Blechschmidt, A.J. Fleet, Keigwin, L.D., D.V. Kent, M.T. Ledbetter, U. Mann, L. Mayer, W.R. Reidel, C. Sancetta, D. Spariosu, and H.B. Zimmerman. 1980. Hydraulic piston coring of late Neogene and Quaternary sections in the Caribbean and equatorial Pacific: Preliminary results of Deep Sea Drilling Project Leg 68. Geological Society of America Bulletin 91(7):433-444.

Roberts, D.G., J. Backman, A.C. Morton, J.W. Murray, and J.B. Keene. 1984. Evolution of volcanic rifted margins: Synthesis of Leg 81 results on the west margin of Rockall Plateau. In Initial Reports of the Deep Sea Drilling Project, Volume 81, Roberts, D.G., D. Schnitker, et al. (Eds.). Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Ruddiman, W.F., R.B. Kidd, and E. Thomas, J.G. Baldauf, B.M. Clement, J.F. Dolan, M.R. Eggers, P.R. Hill, L.D. Keigwin, Jr., M. Mitchell, I. Phillips, F. Robinson, S.A. Salehipour, T. Takayama, G. Unsold, and P.P.E. Weaver. (Eds.). 1986. In Initial Reports of the Deep Sea Drilling Project, Volume 94. U.S. Government Printing Office, Washington, DC.

Shackleton, N.J., J. Backman, H. Zimmerman, D.V. Kent, M.A. Hall, D.G. Roberts, D. Schnitker, J.G. Baldauf, A. Despraries, R. Homrighausen, P. Huddlestun, J.B. Keene, A.J. Kaltenback, A.O. Drumsiek, A.C. Morton, J.W. Murray, and J. Westberg-Smith. 1984a. Oxygen isotope calibration of the onset of ice-rafting and history of glaciation in the North Atlantic region. Nature 307:620-623.

Shackleton, N.J., M.A. Hall, and A. Boersma. 1984b. Oxygen and carbon isotope data from Leg 74 foraminifers. In Initial Reports of the Deep Sea Drilling Project, Volume 74, Moore, Jr., T.C., P.D. Rabinowitz, et al. (Eds.). Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Tarduno, J.A., W.V. Sliter, L. Korenke, M. Leckie, H. Mayer, J.J. Mahoney, R. Musgrave, M. Storey, and E.L. Winterer. 1991. Rapid formation of Ontong Java Plateau by Aptian mantle plume volcanism. Science 254(5030):399-403.

Tarduno, J.A., R.A. Duncan, D.W. Scholl, R.D. Cottrell, B. Steinberger, T. Thordarson, B.C. Kerr, C.R. Neal, F.A. Frey, M. Torii, and C. Carvallo. 2003. The Emperor Seamounts: Southward motion of the Hawaiian hotspot plume in Earth’s mantle. Science 301(5636):1064-1069.

Tarduno, J.A., H.P. Bunge, N. Sleep, and U. Hansen. 2009. The bent Hawaiian-Emperor hotspot track: Inheriting the mantle wind. Science 324(5923):50-53.

Tejada, M.L.G., K. Suzuki, J. Kuroda, R. Coccioni, J.J. Mahoney, N. Ohkouchi, T. Sakamoto, and Y. Tatsumi. 2009. Ontong Java Plateau eruption as a trigger for the early Aptian oceanic anoxic event. Geology 37(9):855-858.

Thomas, D.J., J.C. Zachos, T.J. Bralower, E. Thomas, and S. Bohaty. 2002. Warming the fuel for the fire: Evidence for the thermal dissociation of methane hydrate during the Paleocene-Eocene thermal maximum. Geology 30(12):1067-1070.

Wilson, D.S., D.A.H. Teagle, J.C. Alt, N.R. Banerjee, S. Umino, S. Miyashita, G.D. Acton, R. Anma, S.R. Barr, A. Belghoul, J. Carlut, D.M. Christie, R.M. Coggon, K.M. Cooper, C. Cordier, L. Crispini, S.R. Durand, F. Einaudi, L. Galli, Y. Gao, J. Geldmacher, L.A. Gilbert, N.W. Hayman, E. Herrero-Bervera, N. Hirano, S. Holter, S. Ingle, S. Jiang, U. Kalberkamp, M. Kerneklian, J. Koepke, C. Laverne, H.L.L. Vasquez, J. Maclennan, S. Morgan, N. Neo, H.J. Nichols, S.-H. Park, M.K. Reichow, T. Sakuyama, T. Sano, R. Sandwell, B. Scheibner, C.E. Smith-Duque, S.A. Swift, P. Tartarotti, A.A. Tikku, M. Tominaga, E.A. Veloso, T. Yamasaki, S. Yamazaki, and C. Ziegler. 2006. Drilling to gabbro in intact ocean crust. Science 312(5776):1016-1020.

Zachos, J.C., U. Rohl, S.A. Schellenberg, A. Sluijs, D.A. Hodell, D.C. Kelly, E. Thomas, M. Nicolo, I. Raffi, L.J. Lourens, H. McCarren, and D. Kroon. 2005. Rapid acidification of the ocean during the Paleocene-Eocene thermal maximum. Science 308(5728):1611-1614.

Zachos, J.C., G.R. Dickens, and R.E. Zeebe. 2008. An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics. Nature 451:279-283.

CONFIRMATION OF SEA FLOOR SPREADING

Douglas S. Wilson
University of California, Santa Barbara

The first big success of scientific ocean drilling was the confirmation of the sea floor spreading theory with the results of the Deep Sea Drilling Project (DSDP) Leg 3. The sea floor spreading theory started to gain wide acceptance in 1966, with the publication of the Eltanin-19 profile from the southeast Pacific (Pitman and Heirtzler, 1966) showing highly symmetric magnetic anomalies and bathymetry, and the demonstration by both Pitman and Heirtzler (1966) and Vine (1966) that magnetic anomalies over multiple mid-ocean ridges could be explained by the Vine-Matthews mechanisms at different, nearly constant spreading rates according to the magnetic reversal time scale of Cox et al. (1964) and Doell and Dalyrmple (1966). These time scales were based on K-Ar dating and magnetic polarity stratigraphy of mostly basaltic lavas with ages 0-4 Ma. Heirtzler et al. (1968) took the bold step of calibrating a magnetic polarity time scale to ~80 Ma by assuming that magnetic anomalies mapped in the South Atlantic by Dickson et al. (1968) all formed at the same spreading rate of 19 mm/yr half rate, as deduced for 0-4 Ma.

DSDP Leg 3 drilled a transect across the South Atlantic in the 1968-1969 Austral summer with goals of testing both the general sea floor spreading theory and the specifics of the Heirtzler et al. age model. As reported by Maxwell et al. (1970a, b), the leg was a spectacular success. Basement age, as judged from overlying microfossils, was a nearly linear function of distance from the spreading ridge, with limited scatter, and agreed with a half spreading rate of about 20 mm/yr. The young ages near the ridge axis and the close agreement of the spreading rate determined from microfossil ages and the spreading rate determined from young magnetic anomalies both conferred the strongest possible confirmation of the revolutionary sea floor spreading theory.

Numerous later studies have continued to confirm the close correspondence of sea floor age inferred from magnetic anomalies and the age of overlying sediments sampled by scientific ocean drilling. This correspondence is so broadly accepted that it is rarely tabulated or reviewed, an exception being the time scale work of Berggren et al. (1995), which draws heavily on microfossil stratigraphy from DSDP and ODP (Ocean Drilling Program).

One interesting case involves the sea floor age of the tropical eastern Pacific, where the stratigraphic basement ages from DSDP Leg 9 (Hays et al., 1972) preceded confident magnetic anomaly identifications by many years. The wide spacing of Miocene Sites 79-82 on the Pacific plate led Hayes et al. to interpret a half spreading rate of 130 mm/yr, assuming the spreading history was simple, although they acknowledged that complex tectonic histories could mean that the full spreading rate was much less than twice the apparent half spreading rate. Subsequent work has overcome the challenges of low-latitude magnetic anomaly interpretation (Wilson, 1996; Barckhausen et al., 2001, 2008; Horner-Johnson and Gordon, 2003). The corridor of the first East Pacific Rise drilling transect of Leg 9 turns out to have been tectonically relatively simple, and the long-forgotten high spreading rate interpreted by Hays et al. (1972) has been confirmed.

An additional way scientific ocean drilling has confirmed sea floor spreading is by demonstrating that the same magnetic polarity record is recorded in both marine magnetic anomalies measured at the sea surface and in paleomagnetic records in drilled cores. Advances in dating the geologic record by recognizing the signature of predictable variations in Earth’s orbit have revolutionized stratigraphic geochronology over the past 20 years. Although often the most useful records for such dating are from sections in outcrops (e.g., Hilgen, 1991), ocean drilling cores have also played a key role. Probably the best example of calibrating the ages of magnetic reversal from drilled cores is the calibration of Pälike et al. (2006), which provides a precise record of most of the Oligocene from the equatorial Pacific record of Site 1218 (ODP Leg 199). Spreading on the relatively steady Australia-Antarctica plate pair is very constant at about 70 mm/yr full rate (maximum rate) according to this calibration. According to the calibration, the Oligocene South Atlantic full spreading rate of about 50 mm/yr is slightly above the long-term average that figured so prominently in the Leg 3 results.

More recent research has focused much more on understanding processes of sea floor spreading rather than the long-acknowledged confirmation of the basic theory. As one example, Purdy et al. (1992) noted that the depth below active midocean ridges of seismic reflectors interpreted as melt bodies varies inversely with spreading rate at intermediate and fast spreading rates. Deep drilling at Hole 1256D in the Miocene equatorial Pacific allows this relationship to be tested at a superfast rate well outside the modern range of spreading rates. Drilling during IODP Exp. 312 encountered a gabbro body at 1,160-1,210 m below basement that would have originally had properties of the modern seismic reflectors. The depth fits perfectly within the range extrapolated from the results of Purdy et al. and subsequent workers. The fractionated composition of the gabbro allows us to begin to understand the magma-chamber processes that segregate the fractionated upper crust from the residual lower crust.

Supporting References

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Barckhausen, U., C.R. Ranero, S.C. Cande, M. Engels, and W. Weinrebe. 2008. Birth of an intraoceanic spreading center. Geology 36(10):767-770.

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Hilgen, F. 1991. Extension of the astronomically calibrated (polarity) time scale to the Miocene/Pliocene boundary. Earth and Planetary Science Letters 107(2):349-368.

Horner-Johnson, B. and R.G. Gordon. 2003. Equatorial Pacific magnetic anomalies identified from vector aeromagnetic data. Geophysical Journal International 155(2):547-556.

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Maxwell, A.E., R.P. Von Herzen, J.E. Andrews, R.E. Boyce, E.D. Milow, K.J. Hsü, S.F. Percival, and T. Saito. 1970b. Summary and conclusions. In Initial Reports of the Deep Sea Drilling Project, Volume 3, Maxwell, A.E., et al. (Eds.). Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Pälike, H., R.D. Norris, J.O. Herrle, P.A. Wilson, H.K. Coxall, C.H. Lear, N.J. Shackleton, A.K. Tripati, and B.S. Wade. 2006. The heartbeat of the Oligocene climate system. Science 314(5807):1894-1898.

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Vine, F.J. 1966. Spreading of the ocean floor: New evidence. Science 154:1405-1415.

Wilson, D.S. 1996. Fastest known spreading on the Miocene Cocos-Pacific plate boundary. Geophysical Research Letters 23(21):3003-3006.

CHRONOSTRATIGRAPHY AND
GEOMAGNETISM

James E.T. Channell
University of Florida

Early DSDP (Deep Sea Drilling Project) drilling contributed substantially to the revolution in the Earth sciences that took place in the late 1960s. Apart from documenting the age and nature of oceanic basement, DSDP opened up the deep-sea sediment archive of Earth history to lithological, micropaleontological, geochemical, and magnetostratigraphic studies. Prior to that time, conventional piston cores limited investigations to the top ~20 m of the sediment sequence. The development of the hydraulic piston corer (HPC), first used in 1979 during DSDP Leg 64, improved sediment core quality and allowed recovery of long (~300 m) sequences of undisturbed sediments. The field of paleoceanography was born, and research in micropaleontology, and isotope and magnetic stratigraphy, blossomed.

Traditional magnetic polarity stratigraphy has become the backbone of geologic timescales because polarity reversal is attributable to the main dipole field, and therefore provides global timelines for precise correlation at the time of reversal. In modern Cenozoic and Mesozoic timescales, the GPTS (geomagnetic polarity timescale) is the central thread to which the other facets of geologic time (bio- and chemostratigraphic and radiometric) are correlated. The Late Cretaceous-Cenozoic GPTS of Cande and Kent (1992, 1995) was temporally calibrated by interpolation among available radiometric ages using a uniformly varying spreading-rate assumption, with astrochronological calibration for the last ~4 Myr (Cande and Kent, 1995). Astrochronological calibration of the GPTS has now been extended further back into the Cenozoic.

The correlation of the Cenozoic polarity record to biostratigraphies and chemostratigraphies, and to the cyclostratigraphies that provide the astrochronologies, has been largely achieved through DSDP, ODP (Ocean Drilling Program), and IODP (Integrated Ocean Drilling Program). The timescales with which we calibrate Earth history, and the paleontological and isotopic data that are the building blocks of paleoceanography, would not have progressed to anything like the same level in the absence of DSDP/ODP/ IODP. We would have relied on sequences exposed on land and on conventional piston cores. The task of GPTS calibration has yet to be satisfactorily accomplished, even for the late Cenozoic; however, cyclostratigraphies tuned to orbital solutions (astrochronologies) provide the way forward, and these calibrations are likely to be accomplished largely through IODP and its successor program.

For obvious societal reasons, the study of rapid climate change is of paramount importance. The marine sediment archive has become increasingly important for understanding the climate system because historical direct measurements are woefully inadequate in detail, distribution, and duration (~100 yrs), and ice cores, although providing wonderful detail, are also restricted in distribution and duration. Marine “drift” sequences, characterized by elevated mean sedimentation rates, have become targets for documenting the record of climate change on millennial timescales.

The study of rapid change requires stratigraphic correlation at an appropriate resolution. In spite of the considerable progress made in the past 40 years, the quest for improved stratigraphic correlation remains one of the great challenges in paleoceanography. Benthic δ¹⁸O is the hallmark of Quaternary marine stratigraphy; however, δ¹⁸O changes in seawater are not globally synchronous on millennial timescales (see Skinner and Shackleton, 2005), and the rate of change of global ice volume (the basis for δ¹⁸O stratigraphy) is gradual other than at Terminations, limiting the correlation potential of the records.

There would be great advantage in coupling oxygen isotopes with an independent stratigraphic tool that is global in nature and devoid of environmental influences. The accumulation of relative paleointensity (RPI) data in the past 10 years holds the promise of stratigraphic correlation within polarity chrons, possibly at millennial scale. A first step in the utilization of RPI records in stratigraphy has been the development of RPI stacks (e.g., Valet et al., 2005) and an RPI stack based on the tandem correlation of RPI and δ¹⁸O data (Channell et al., 2009).

An objective in the next phase of IODP should be the coring of sediment drifts, not only to exploit the high-resolution environmental/climate records associated with them, but also to utilize stratigraphic tools (δ¹⁸O and RPI) to place these records in a stratigraphic framework appropriate for the study of rapid climate change. When these tandem correlations (δ¹⁸O and RPI) have been satisfactorily established, RPI can be used with confidence in locations where δ¹⁸O is unavailable due to lack of foraminifera, such as the Antarctic Margins where sediment drifts document the history of Antarctic ice sheets and related sea-level change.

Magnetic excursions are brief directional excursions that usually, when adequately recorded, constitute paired polarity reversals. Knowledge of magnetic excursions has been greatly enhanced by ODP and IODP expeditions in the past 15 years. The best-recorded excursions have durations of ~1 kyr, and apparently not exceeding a few kyr. The brief duration of excursions is such that they are rarely recorded except in sediments with accumulation rates exceeding 10 cm/kyr. Excursions occupy minima in RPI records, and RPI minima are more readily recorded than excursions because troughs in RPI records are longer lasting than directional excursions. There are ~6 excursions that are adequately recorded in the Brunhes Chron, and ~8 in the Matuyama Chron (see review by Laj and Channell, 2007). Excursions are believed to be manifest globally and are therefore important for

stratigraphy, although they are too brief to be recorded at typical pelagic sedimentation rates.

RPI and magnetic excursions are geomagnetic phenomena that could not have been studied in the absence of HPC technology, developed by DSDP, for recovering long sediment sequences. Additionally, the shipboard procedure for real-time control of drilling strategy, developed by ODP and first utilized in 1991, for construction of complete composite sections from multiple holes drilled at a single site, has been critical to modern high-resolution stratigraphy, not just to magnetic stratigraphy but also to bio- and chemostratigraphy, and hence to paleoceanography.

Finally, the new magnetic stratigraphies described above are an important means of testing numerical simulations of the geodynamo. Such simulations can now mimic a wide range of geomagnetic field behavior depending on input parameters. Records (from sediment drifts) are needed to compare with numerical simulations, and in so doing refine the simulations and obtain important mechanistic information for the geodynamo.

Supporting References

Cande, S.C. and D.V. Kent. 1992. A new geomagnetic polarity timescale for the late Cretaceous and Cenozoic. Journal of Geophysical Research 97(B10):13917-13951.

Cande, S.C. and D.V. Kent. 1995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. Journal of Geophysical Research 100(B4):6093-6095.

Channell, J.E.T., C. Xuan, and D.A. Hodell. 2009. Stacking paleointensity and oxygen isotope data for the last 1.5 Myr (PISO-1500). Earth and Planetary Science Letters 283(1-4):14-23.

Laj, C. and J.E.T. Channell. 2007. Geomagnetic excursions. In Treatise on Geophysics: Volume 5, Kono, M. (Ed.). Geomagnetism, Elsevier, Amsterdam, The Netherlands.

Skinner, L.C. and N.J. Shackleton. 2005. An Atlantic lead over Pacific deep-water change across Termination I: Implications for the application of the marine isotope stage stratigraphy. Quaternary Science Reviews 24(5-6):571-580.

Valet, J.P, L. Meynadier, and Y. Guyodo. 2005. Geomagnetic dipole strength and reversal rate over the past two million years. Nature 435:802-805.

GEOCHRONOLOGY OF THE OCEAN FLOOR

Robert A. Duncan
Oregon State University

The principal goal of the initial phase (1968) of scientific ocean drilling was to test the plate tectonics model. Namely, the ocean floor is generated by a process of seafloor spreading, and so is progressively older with distance away from spreading ridges. The ocean basins, as a consequence, are relatively young features developed as a result of divergence and convergence of more permanent continental lithosphere. Hence, the ability to accurately and precisely estimate the ages of the ocean floor has been an ongoing critical need in scientific ocean drilling. In the first decade, ages of the ocean floor were provided predominantly by biostratigraphic data (microfossils) obtained from the lowermost (oldest) sediments deposited on the volcanic crust because of the lack of a reliable radiometric method. Such indirect dating provides a minimum age.

Potassium-argon (K-Ar) dating is the most readily applicable radiometric method because (1) the decay constant for ⁴⁰K⁴⁰Ar is appropriate for dating volcanic rocks and minerals over a wide age range (~10⁴ to 10⁹ years), and (2) K is a minor but ubiquitous element in ocean crustal rocks. Several issues make K-Ar dating of ocean floor rocks problematic, however. The most serious of these are (1) seafloor weathering with post-crystallization addition of K (from seawater) and loss of Ar (during breakdown of primary igneous minerals to clays)—both of which violate the closed chemical system assumption of the K-Ar method and lead to measured ages younger than the crystallization age, and (2) quenching of magmas in seawater under high hydrostatic pressures, that causes glassy, poorly crystallized material to retain a mantle-derived Ar isotopic composition different from the atmospheric composition of Ar, leading to an erroneously old calculated age. The ⁴⁰Ar-³⁹Ar incremental heating variation of the K-Ar method has been successful in providing reliable crystallization ages for ocean floor rocks. In this technique, developed from the mid-1960s to 1970s, whole rocks or minerals are heated under vacuum in progressive temperature increments, to separate Ar released from low-temperature (alteration, e.g., clay) minerals from high-temperature (primary igneous) minerals, or altered margins from fresh cores of minerals. The isotopic composition of Ar released from the range of temperature steps can also be used to calculate an isochron and an initial composition of Ar in the sample at the time of crystallization. Recently, improvements in instrument sensitivity and sample preparation methods have meant that more precise ages can be measured on smaller masses of less altered phases (e.g., plagioclase feldspar, biotite, groundmass).

The following significant achievements have followed the success in reliable dating of crystallization ages for ocean floor rocks obtained by scientific ocean drilling:

(1) Confirmation of the age-distance relationship for ocean floor predicted by plate tectonics. Initially substantiat ed by biostratigraphic dating of lowermost marine sediments overlying the volcanic ocean crust, basement rocks at many drilling sites have now been dated by the ⁴⁰Ar-³⁹Ar method.

Because the ocean floor also records a continuous record of the alternating polarity of the geomagnetic field, these radiometric ages have led to calibration of the Geomagnetic Polarity Time Scale.

(2) Age-progressive trends of “primary” hotspot tracks. Linear arrays of ocean islands and seamounts that occur within plates and crossing plate boundaries have been related to deep-seated, upwelling plumes of warmer than ambient mantle. Because of thermal subsidence of aging ocean plates, volcanoes initially constructed as islands eventually sink below sea level and are covered with marine sediments (including coral and carbonate banks in tropical latitudes). In many important cases, volcanic samples of these older parts of hotspot tracks can be obtained only through drilling through the sedimentary cover. Radiometric dating has provided ages that confirm the motion of plates over quasistationary hotspots (e.g., Hawaiian-Emperor chain and Hawaii; Walvis Ridge and Tristan da Cunha; Mascarene-Maldive chain and Reunion). This has resulted in a reference frame for plate motions that is tied to the pattern of deep convection—independent of the relative motion reference frame provided by seafloor spreading magnetic anomalies and fracture zones, and the geomagnetic field reference frame. Recently, comparison of hotspot and geomagnetic reference frames derived from drilling in the Emperor seamounts (ODP Leg 197) has shown trans-latitude (N to S) motion of the Hawaii hotspot of 4-5cm/yr in the period 80-50 Ma.

(3) Hotspots begin with catastrophic volcanic events. Prominent hotspots are now linked, through age-progressions and chemical tracers, to vast outpourings of basaltic lavas constructed in geologically brief periods, called large igneous provinces (LIPs). Examples are Iceland-North Atlantic Igneous Province (East Greenland Margin and Faeroes-British Tertiary); Tristan da Cunha-Parana/Etendeka basalts; Reunion-Deccan basalts; and Kerguelen-Rajmahal basalts/Kerguelen plateau. This has led to a geodynamic model for mantle plume behavior (large impact “head” and continuous but smaller volume “tail”) and a recognition that the enormous eruption rates during LIP formation should have important environmental impacts, such as mass extinctions and ocean anoxic events. Ocean plateaus (e.g., Ontong Java, Manihiki, Caribbean) are now recognized as LIPs erupted in ocean basins, equivalent to the more accessible subaerial versions. These developments would not have been possible without precise dating of hotspot tracks and submarine portions of LIPs sampled by ocean drilling.

(4) Time scale of seafloor hydrothermal systems. The dramatic “black smokers” discovered at many seafloor spreading systems are driven by the intense thermal gradient at ocean ridges, a highly permeable ocean crust, and ubiquitous seawater. How long do these systems last, and how far off-ridge is hydrothermal circulation an important process in chemical exchange and removing heat from the seafloor? With cooling to fluid temperatures of 50-60 °C, zeolites, clays, and micas (celadonite) with relatively high %K contents precipitate in voids and fractures in the ocean crustal rocks. This is the end stage of sealing the permeability of the crust, and dating celadonite provides an age estimate for the end of fluid circulation. 3D sampling and K-Ar dating of celadonite at the Troodos ocean crust section (Cyprus) reveal a pattern of progressive filling of small to large fractures over ~30 m.y. A similar large age range has been found for celadonites from ocean crust drillsites, and confirms evidence from seismic imaging and heat flow measurements that off-ridge hydrothermal circulation ends about this time.

Supporting References

Duncan, R.A. 2002. A time frame for construction of the Kerguelen Plateau and Broken Ridge. Journal of Petrology 43(7):1109-1119.

Duncan, R.A. and M.A. Richards. 1991. Hotspots, mantle plumes, flood basalts, and true polar wander. Reviews of Geophysics 29(1):31-50.

Gallahan, W.E. and R.A. Duncan. 1994. Spatial and temporal variability in crystallization of celadonites within the Troodos ophiolite, Cyprus: Implications for low-temperature alteration of the oceanic crust. Journal of Geophysical Research 99(B2):3147-3161.

Koppers, A.A.P., H. Staudigel, and R.A. Duncan. 2003. High resolution ⁴⁰Ar/³⁹Ar dating of the oldest oceanic basement in the western Pacific basin. Geochemistry, Geophysics, and Geosystems 4(11):8914.

Sinton, C.W., R.A. Duncan, M. Storey, J. Lewis, J.J. Estrada, and G. Klaver. 1998. An oceanic flood basalt province within the Caribbean plate. Earth and Planetary Science Letters 155(3-4):221-235.

Tarduno, J.A., R.A. Duncan, D.W. Scholl, R.D. Cottrell, B. Steinberger, T. Thordarson, B.C. Kerr, C.R. Neal, F.A. Frey, M. Torii, and C. Carvallo. 2003. The Emperor seamounts: Southward motion of the Hawaiian hotspot plume in Earth’s mantle. Science 301(5636):1064-1069.

THE SEISMOGENIC ZONE OF SUBDUCTION THRUSTS

J. Casey Moore
University of California, Santa Cruz

The current seismogenic zone drilling program is based on the National Science Foundation (NSF) MARGINS Seismogenic Zone Experiment concept (SEIZE). This program examines the movement of sediments, rocks, and fluids from the surface to the seismogenic zone and intends to understand how these materials produce the world’s largest earthquakes. The program’s goals are to (1) determine the nature of the material incoming to the subduction zone, (2) predict its changes at depth through experiments, (3) image the seismogenic zone through active and passive source seismology, (4) drill into the upper extent of the seismogenic zone, and (5) monitor the behavior of the seismogenic zone with seafloor and borehole instrumentation. Focus areas are currently southwest Japan and Costa Rica. Under the renewed MARGINS program the focus will move to Cascadia and perhaps other convergent margins.

Scientific ocean drilling has concentrated on the seismogenic zone of subduction thrusts off southwest Japan recently. This program has completed an extensive transect across a subduction zone that produced an 8.1 magnitude earthquake in 1944 (Ando, 1975; Park et al., 2002). This effort has involved drilling 12 sites to depths of 1,600 m, extending from the incoming oceanic crust landward to the center of the forearc basin (Saffer et al., 2009; Tobin and Kinoshita, 2009; Underwood et al., 2009). Penetrations include one riser hole and the emplacement of a pressure-monitoring device in a tsunamigenic thrust fault. The 2010 program involves installing the initial casing string for the deep riser hole, installing a riserless observatory near the accretionary prism-forearc basin boundary, and completing the subduction input drilling. In 2011 and beyond the program intends to extend a deep riser hole into one of the thrust faults responsible for the 1944 earthquake. During 2011, in the broader SEIZE context, a 3D seismic survey and riserless drilling will occur off Costa Rica.

Currently, the transect off southwest Japan has virtually completed goal 1 of SEIZE, made excellent progress on goal 2, is continuing to complete goal 3, plans to initiate goal 4 this summer, and has begun to work on goal 5. Deep riser drilling has been slowed by high current problems; however, the Chikyu engineering group has added fairings to the riser, tested their performance, and are ready to drill in the high current environment.

SOME KEY SCIENTIFIC RESULTS OF
SEISMOGENIC ZONE DRILLING

Drilling on the main transect off southwest Japan began in September 2007 (Tobin and Kinoshita, 2009), and imaging somewhat before. The capstone achievements are yet to come; nevertheless, what are some of the exciting results?

(1) The seismogenic zone is not so far away: Seismic activity, tremor, and very low frequency earthquakes occur at very shallow depths (1-2 km) along thrust faults in the accretionary prism (Ito and Obara, 2006; Obana and Kodaira, 2009). The shallow seismic activity means that some current holes may have drilled into the zone of conditional stability of earthquakes; instruments placed into this zone can provide meaningful understanding of earthquake cycles in the near term. The full 7 km borehole depth may not be required to achieve the SEIZE goals.

(2) Earthquake slip propagates through the accretionary prism to the surface: People have questioned whether the soft sediments of accretionary prisms absorb high-velocity slip through distributed deformation or not. Major candidates for transfer of seismic slip to the surface are the frontal thrust and megasplay faults (Plafker, 1972; Moore et al., 2007; Strasser et al., 2009). Inversions of tsunami waves (Cummins et al., 2001; Baba and Cummins, 2006) suggest displacement of the splay fault during the 1944 great earthquake, as does extension of the thrust interface directly to the surface (Moore et al., 2007). Finally the drilling recovered the splay fault interface, within which a mm-thick gouge zone at 400 mbsf shows anomalously high vitrinite reflectance and other geochemical anomalies, suggesting high temperatures and high-velocity slip (Sakaguchi et al., 2009, 2011; Yamaguchi et al., 2009). These authors have also found a similar result on the frontal thrust at the base of the slope. Apparently, high-velocity slip has propagated to the surface or near surface during the recent earthquakes, explaining the devastating tsunamis that characterize this margin. This result is consistent with the extension of the conditional stability zone of earthquakes to very shallow depths (see 1 above).

(3) Stress magnitudes and strain responses vary during the earthquake cycle: Apparently the interseismic stress regime, now observed, contrasts to the coseismic stress and strain regime of the great earthquakes. Complete borehole imaging and caliper data across the margin indicate maximum horizontal stresses nearly perpendicular to the margin across the trench slope with a 90-degree rotation at the transition into the forearc basin (Tobin and Kinoshita, 2009). Farther landward in the forearc basin the maximum horizontal stress again becomes nearly perpendicular to the margin (Lin et al., 2010). The outer forearc basin is characterized by normal faulting (Martin et al., 2010). Stress magnitude estimates and core observations suggest the accretionary prism has currently active strike-slip and normal faulting at the depths drilled (Byrne et al., 2009; Chang et al., 2010).

This suggests that the major thrust faulting both drilled and observed on the seismic data must be coseismic, as inferred from temperature anomalies along slip surfaces (Sakaguchi et al., 2011) and the earthquake focal mechanisms (Ando, 1975). The variable types of strains observed at shallow depths, in the 100 year plus interseismic interval, are probably caused by small differences in magnitude of principal stresses; these minor variations in stress can “flip” the strain response (Tobin et al., 2009). Conversely the few minutes of coseismic activity every 100 plus years imprint the margin with its dominantly thrust faulted architecture.

LEGACY OF DSDP/ODP CONVERGENT
MARGIN DRILLING

Although the seismogenic zone is the focus of the current convergent margin drilling, it stands on a foundation developed during the preceding three decades. For example, the community has become very skilled at using 3D seismic imaging to extend core-log observations away from the 1D borehole realm (Bangs et al., 1999). In the absence of pressure measurements, both thermal and geochemical anomalies have been developed as tools to recognize fluid migration along faults (Moore et al., 1987; Kastner et al., 1991). The techniques for long-term pressure and geochemical monitoring were developed during ODP (e.g., Solomon et al., 2009). The earliest efforts of convergent margin drilling in the 1970s and early 1980s were focused on unraveling the margin tectonics including documentation of accretionary versus ero-sional subduction zones (von Huene and Scholl, 1991). This concept has been used to frame the contrast between the two main focus sites of the SEIZE experiment—southwest Japan (accretionary margin) and Costa Rica (erosional margin).

PROGNOSIS

The current seismogenic zone drilling activity has produced the best convergent margin transect ever. Numerous ground-breaking results stem from this recent activity. But, fully transformative achievements await the completion of the deep riser boreholes and associated instrumentation. Lessons from this focused effort will be clearly applicable to ongoing programs at U.S. convergent margins in Cascadia and Alaska.

Supporting References

Ando, M. 1975. Source mechanisms and tectonic significance of historical earthquakes along the Nankai Trough, Japan. Tectonophysics 27(2):119-140.

Baba, T. and P.R. Cummins. 2006. Contiguous rupture areas of the two Nankai Trough earthquake revealed by high-resolution tsunami waveform inversion. Geophysical Research Letters 32(L08305):1-4.

Bangs, N.L., T.H. Shipley, J.C. Moore, and G. Moore. 1999. Fluid accumulations and channeling along the Northern Barbados Ridge decollement thrust. Journal of Geophysical Research 104(B9):20399-20414.

Byrne, T.B., W. Lin, A. Tsutsumi, Y. Yamamoto, J.C. Lewis, K. Kanagawa, Y. Kitamura, A. Yamaguchi, and G. Kimura. 2009. Anelastic strain recovery reveals extension across SW Japan subduction zone. Geophysical Research Letters 36(L23310):1-6.

Chang, C.D., L. McNeill, J.C. Moore, W. Lin, M. Conin, and Y. Yamada. 2010. In situ stress state in the Nankai accretionary wedge estimated from borehole wall failures. Geochemistry, Geophysics, and Geosystems 11(Q0AD04):1-17.

Cummins, P.R., T. Hori, and Y. Kaneda. 2001. Splay fault and megathrust earthquake slip in the Nankai Trough. Earth Planets Space 53(4):243-248.

Ito, Y. and K. Obara. 2006. Very low frequency earthquakes within accretionary prisms are very low stress-drop earthquakes. Geophysical Research Letters 33(L09302):1-4.

Kastner, M., H. Elderfield, and J.B. Martin. 1991. Fluids in convergent margins: What do we know about their composition, origin, role in diagenesis and importance for oceanic chemical fluxes. Philosophical Transactions of the Royal Society of London Service A 335(1638):243-259.

Lin, W., M.L. Doan, J.C. Moore, L. McNeill, T.B. Byrne, T. Ito, D. Saffer, M. Conin, M. Kinoshita, Y. Sanada, K.T. Moe, E. Araki, H. Tobin, D. Boutt, Y. Kano, N.W. Hayman, P. Flemings, G.J. Huftile, D. Cukur, C. Buret, A.M. Schleicher, N. Efimenko, K. Kawabata, D.M. Buchs, S. Jiang, K. Kameo, K. Horiguchi, T. Wiersberg, A. Kopf, K. Kitada, N. Eguchi, S. Toczko, K. Takahashi, and Y. Kido. 2010. Present day principal horizontal stress orientations in the Kumano forearc basin of the southwest Japan subduction zone determined from IODP NanTroSEIZE drilling Site C0009. Geophysical Research Letters 37(L13303):1-6.

Martin, K., S. Gulick, N. Bangs, G. Moore, J. Ashi, J.O. Park, S. Kuramoto, and A. Taira. 2010. Possible strain partitioning structure between the Kumano fore-arc basin and the slope of the Nankai Trough accretionary prism. Geochemistry, Geophysics, and Geosystems 11(Q0AD02):1-15.

Moore, J.C., A. Mascle, E. Taylor, P. Andreieff, F. Alvarez, R. Barnes, C. Beck, J. Behrmann, F. Blanc, K. Brown, M. Clark, J. Dolan, A. Fisher, J. Gieskes, M. Hounslow, P. McClellan, K. Moran, Y. Ogawa, T. Sakai, J. Schoonmaker, P. Vrolijk, R. Wilkens, and C. Williams. 1987. Expulsion of fluids from depth along a subduction-zone décollement horizon. Nature 326:785-788.

Moore, G.F., N.L. Bangs, A. Taira, S. Kuramoto, E. Pangborn, and H.T. Tobin. 2007. Three-dimensional splay fault geometry and implications for tsunami generation. Science 318(5853):1128-1131.

Obana, K. and S. Kodaira. 2009. Low-frequency tremors associated with reverse faults in a shallow accretionary prism. Earth and Planetary Science Letters 287(1-2):168-174.

Park, J.O., T. Tsuru, S. Kodaira, P.R. Cummins, and Y. Kaneda. 2002. Splay fault branching along the Nankai subduction zone. Science 297(5584):1157-1160.

Plafker, G. 1972. Alaskan earthquake of 1964 and Chilean earthquake of 1960: Implications for arc tectonics. Journal of Geophysical Research 77(5):901-925.

Saffer, D., L. McNeill, E. Araki, T. Byrne, N. Eguchi, S. Toczko, K. Takahashi, and Expedition 319 Scientists. 2009. NanTroSEIZE Stage 2: NanTroSEIZE riser/riserless observatory. In Integrated Ocean Drilling Program, Volume 319. Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas.

Sakaguchi, A., F.M. Chester, D. Curewitz, O. Fabbri, D.L. Goldsby, G. Kimura, L. Chung-Feng, Y. Masaki, E. Screaton, A. Tsutsumi, K. Ujiie, and A. Yamaguchi. 2011. Seismic slip extends to up-dip end in the plate subduction faults. Geology 39(4):395-398.

Sakaguchi, A., F.M. Chester, O. Fabbri, D.L. Goldsby, C. Li, G. Kimura, A. Tsutsumi, K. Ujie, A. Yamaguchi, and D. Curewitz. 2009. Paleo-thermal condition of the shallow mega-splay fault based on vitrinite reflectance: Core analysis of IODP NanTroSEIZE stage 1. American Geophysical Union 90:52.

Solomon, E.A., M. Kastner, G. Wheat, H. Jannasch, G. Robertson, E. Davis, and J. Morris. 2009. long-term hydrogeochemical records in the oceanic basement and forearc prism at the Costa Rica subduction zone. Earth and Planetary Science Letters 282(1-4):240-251.

Strasser, M., G.F. Moore, G. Kimura, Y. Kitamura, A.J. Kopf, S. Lallemant, J.O. Park, E.J. Screaton, X. Su, M.B. Underwood, and X. Zhao. 2009. Origin and evolution of a splay fault in the Nankai accretionary wedge. Nature Geoscience 2:648-652.

Tobin, H. and M. Kinoshita. 2009. NanTroSEIZE Stage 1 summary. In Proceedings of Integrated Ocean Drilling Program, Volume 314/315/316, Kinoshita, M., H. Tobin, J. Ashi, G. Kimura, S. Lallemant, E.J. Screaton, D. Curewitz, H. Masago, K.T. Moe, and the Expedition 314/315/316 Scientists (Eds.). Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas.

Underwood, M.B., S. Saito, Y. Kubo, and the Expedition 322 Scientists. 2009. NanTroSEIZE Stage 2: Subduction inputs. In Integrated Ocean Drilling Program, Preliminary Reports, Expedition 322. Integreated Ocean Drilling Program, Texas A&M University, College Station, Texas.

von Huene, R.and D.W. Scholl. 1991. Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust. Reviews in Geophysics 29(3):279-316.

Yamaguchi, A., A. Sakaguchi, T. Sakamoto, K. Iijima, G. Kimura, K. Ujiie, F.M. Chester, O. Fabbri, D.L. Goldsby, A. Tsutsumi, C. Li, and D. Curewitz. 2009. Geochemical features of shallow subduction thrusts: Non-destructive XRF core-imaging scanner analyses of NanTroSEIZE C0004 and C0007 fault zone slabs. American Geophysical Union 90:52.

WHAT MAJOR TECHNOLOGICAL ADVANCES
AND INNOVATIONS HAVE DEVELOPED
FROM THE DRILLING PROGRAM?

Hans Christian Larsen
IODP Management International, Inc.

This white paper summarizes some major technological advances and innovations made over the 40+ years since the inception of scientific ocean drilling by the Deep Sea Drilling Project (DSDP) in 1966. The focus is on the more recent developments from the later part of the Ocean Drilling Program (ODP) and from the Integrated Ocean Drilling Program (IODP). Limits on report length only allow highlights to be included. Funding of many of the technical developments is from outside the program, which traditionally deploy most of its funds for operations. According to AGI (American Geosciences Institute), scientific publications underpinned by these technologies now exceed 26,000 (>1,500 in Science or Nature).

Scientific ocean drilling (SOD) deployed the first ever deepwater drill-ship, the CUSS 1 for project Mohole in 1961 in a water depth of 3,500 m. The thruster-supported positioning system laid the groundwork for modern dynamic positioning (DP) systems. The offshore hydrocarbon industry that subsequently developed is now a top global industry with development budgets many orders of magnitude higher than within SOD. SOD therefore piggy-backs on industry developments, such as coring, sampling from boreholes, core description, core-log integration, borehole observatories, and development of new research tools and environmental proxies. SOD set the benchmark in these fields using a truly unique set of tools and expertise, and is at the forefront of coring within extreme environments. Four key topics of technology developments and spin-offs are reviewed.

PLATFORMS, DRILLING, AND CORING TECHNOLOGY

The DSDP R/V Glomar Challenger was a purpose-built, first-generation deepwater drillship, globally breaking new ground drilling in water as deep as 7,044 m (open hole, non-riser). ODP was served by the R/V JOIDES Resolution (JR), an oil exploration platform converted to a non-riser scientific drilling vessel. Superior to Glomar Challenger in all aspects (e.g., tonnage, drill string capabilities, DP performance, heave compensation), JR drilled deeper, in shallower waters, in higher latitudes, and with improved core recovery. JR underwent major refurbishment during IODP years 2006-2008, extending vessel lifetime, improving accommodations and laboratory space, further improving heave compensation, and adding newly developed, state-of-the-art coring analytical facilities.

Innovations and improvement of drilling and coring systems on JR over time include: unique bare-rock, spud-in guide-base allowing use of rotary coring bit (RCB); extended core barrel (XCB) for improved recovery in formations too hard for piston coring; motor-driven core barrel for environments of highly alternating formation strength; and advanced piston coring (APC) system (developed from the previous hydraulic piston coring [HPC]) for ultra-high recovery (~100 percent) within soft sediments. Recent “drill over” technology has pushed the limit of APC to 458 m below seafloor (HPC: ~100 m). True orientation of cores can also be achieved. Information systems for in-situ monitoring of drill bit conditions are being developed to further enhance recovery.

In addition, IODP saw two major new inventions: the deepwater, riser drilling vessel D/V Chikyu, purpose-built for SOD by Japan; and application of the mission-specific platform (MSP) approach to coring within uniquely challenging environments.

Chikyu is one of the most capable drillships worldwide. Her current riser capability is 2,500 m water depth, amongst the deepest at time of ship design. A 4,000+ m deepwater, benchmark-setting riser is currently being explored through optimization of conventional riser technology (material standards, downsizing of blowout preventors [BOPs]) and a riserless (or dual gravity) mud recovery system (RMR). Chikyu’s double rig design is uniquely well suited for RMR, but RMR could also be applied on JR and may be considered for a new SOD vessel planned by China. Another ongoing riser innovation is a monitoring and vibration mitigation system for operation under strong currents (a condition offshore Japan), pushing the envelope of current industry standards.

The innovative application of the MSP concept to the high Arctic (2004) resulted in a transformative technical achievement of the first ever deep coring within the central Arctic Ocean. This was achieved through sophisticated ice management in conjunction with two powerful ice breakers and a purpose fitted, ice-breaking drilling vessel (a concept now adapted by industry). Application of a piggy-back, narrow kerf coring system to a DP positioned vessel for high-recovery drilling of carbonate reef material is another noteworthy innovation that increased core recovery with one order (+) of magnitude.

Developments by SOD partners (e.g., BGS and MARUM) are pushing the shallow (0-100 m) coring from seabed frames (e.g., MeBo of MARUM), which can provide high-recovery cores from young oceanic crust, otherwise proven impossible to effectively core. SOD is also developing high-temperature core barrels for such environments.

Because of these many incremental innovations in drilling technology, SOD can effectively core in almost any environment, and maintains leadership in deepwater coring, despite being the David compared to the Goliath in the global drilling industry.

SHIPBOARD AND LAB-BASED
TECHNOLOGIES AND MEASUREMENTS

Core splitting and processing tools and protocols still in use by IODP were developed by DSDP and laid the foundation for an unparalleled collection of legacy data from below the oceans. Of course, major advances in both discrete and continuous core measurements have been made over time. In this field, SOD can claim credit per se for innovations within continuous core descriptions and measurements, laying the groundwork for development of different physical/chemical proxies for environmental change and temporal constraints: (1) A core cryogenic magnetometer, which contributed to the commercial product now in use, provides onboard rapid paleomagnetic stratigraphy; (2) Multi-Sensor Track (MST), which is applied pre-core splitting to provide density, magnetic susceptibility, p-wave velocity, and resistivity; (3) rapid measurement color spectrophotometry; (4) spectral natural gamma ray analysis rapidly measuring cores at comparable resolution to downhole logging tools (unique for core-log integration); (5) rapid, high-resolution, high dynamic range linescan split core imager; (6) continuous XRF high-resolution core scanning (split core); (7) ultra-clean sample and curation protocols for microbiological sampling; (8) infrared cameras to identify gas hydrate horizons in core before sublimation; and (9) non-destructive rhizon porewater sampler. Ocean drilling has adapted a number of other advanced facilities for use. Of these, the continuous core computed tomography (CT) scanning stands out and has opened a new world of 3D imaging before core splitting.

The opportunities offered by these advanced core scanning and analytical tools are vastly supplemented by a large number of (non-program) state-of-the-art analytical facilities for mainly discrete samples (e.g., isotopes, magnetic properties including paleo-intensity, microbiology, and DNA sequencing). More than 13,000 scientists are using SOD samples. Approximately 2.2 million ODP samples have been taken; this number is increasing, with a recent record of 53,000 samples provided by a SOD core repository.

DOWNHOLE MEASUREMENTS/LOGGING
AND ADVANCED SAMPLING

Because of its unique expertise in core-log integration, SOD is a respected partner of world-leading geophysical logging companies. Downhole logging has grown in SOD drilling, with logged drill sites increasing from 14 percent during DSDP to 64 percent during IODP. Most technology used in scientific drilling originates from the hydrocarbon industry, from wireline logs to logging-while-drilling measurements. However, SOD likely has the globally best core-log integration data, and specialty tools developed by SOD include magnetic properties, high-resolution natural gamma ray radioactivity, borehole temperature, pressure-measuring penetrometers, and laser imaging for microbiology. Through academic-industry collaboration, IODP supported a logging-while-coring system that measures an electrical image of the borehole while taking a core sample, thereby enhancing core log integration. SOD also developed formation temperatures tools and is the global source of deep temperature data for the subseafloor. Large-diameter drill pipe (6-5/8”) will in the future allow for development of better pore fluid sampling and formation testing, geochemical logging, nuclear magnetic resonance for pore size distribution, and high-coverage electrical imaging.

Gas hydrates and associated logging and sampling tools is an area where SOD has led the initial research and development. Hydrates are unstable at surface conditions. Through core-log integration an estimate of gas hydrate content that is continuous at depth can be made. An SOD-developed pressure core sampler (PCS) paved the way for recovery of gas hydrate to the surface without sublimation of the hydrate. SOD partners (including Geotek Ltd) then developed the PCS into the HYACINTH for in situ pressure and temperature-preserving sampling tool for gas hydrates. This tool is pivotal in the many governmental and commercial investigations of gas hydrates as a possible new hydrocarbon energy source.

In 2009 SOD took borehole-hosted vertical seismic profiling (VSP) to a new level by conducting a wide-angle, semi-3D walk-away experiment over the drill site location offshore Japan that is targeted for ultra-deep (7 km) riser drilling and instrumentation of a seismic plate boundary. In this location SOD activities eventually will enable surface 3D seismic data, advanced VSP data, borehole logging, sampling, and long-term borehole observatory data to be integrated in a unique collage of plate-boundary data.

DEEP EARTH OBSERVATORY SCIENCE

Following successful advances in downhole sampling and logging, the concept of actually installing downhole observatories that could sample time series (e.g., fluids, pressure, and temperature) was introduced during the ODP by the CORK (Circulation Obviation Retrofit Kit) concept. IODP is making big strides toward establishing a permanent presence of subseafloor observatories within critical ocean floor locations, and with a vastly expanded set of observations. These include time-series of pore water geochemistry from osmosamplers (resolution of ~a few days) and geochemical tracer flow-meter allowing estimates of lateral fluid flow rates; microbiological observatory elements into hydrological observatories via use of substrates; vastly improved pressure resolution (order of 1 ppb full scale) as a sensitive proxy for strain, and with sampling frequency <1Hz linking deformation to seismological data; and tilt meter and seismic broadband sensors. Implementation protocols to co-locate multiple sensors for hydrological-geodetic-seismological purposes or hydrological-thermal-microbiological purposes are being developed and planned for upcoming experiments.

Extending these subseafloor observatories to the high-pressure and -temperature regimes at 6-7 km depth (seismogenic zones) is currently under development, and links to land by fiberoptical networks for real-time monitoring are being implemented offshore Japan and Northwest America in two seismically active zones. This SOD development is in cooperation with and co-funded by other entities and programs. These novel technologies, combined with the experience gained to implement them via drillships, submersibles, and remotely operated vehicles (ROVs), underpins a new scientific paradigm of observing processes as they happen (as opposed to simply studying the lasting imprint of processes in the geological record). Naturally, the new science plan (in preparation) for SOD beyond 2013 makes this emerging field of “Earth in Motion” science one of its four grand challenges.

SOD STUDY OF ACTIVE LIFE BELOW THE SEAFLOOR

Rapid and ongoing technology development underpins another emerging field of science: the study of active microbial life, below, in part deeply below (~1,600 m), the seafloor (a second grand challenge of the new science plan). Technology development in this field takes place globally, and with many different entities and constituencies involved. Special contributions by SOD, apart from making sampling possible, are laboratories (on platforms and at core repositories), protocols for clean sampling, curation processes and storage (long-term and legacy), computer-automated cell counts (living cells), and DNA replication from limited amount of material. Initial findings and technology developments by SOD have generated very significant spin-off activities by other groups.

Supporting References

Fisher, A. and K. Becker. 1993. A Guide to ODP Tools for Downhole Measurements: Technical Note 10. [Online]. Available: http://www-odp.tamu.edu/publications/tnotes/tn10/10toc.html [2010, November 29].

Goldberg, D. 1997. The role of downhole measurements in marine geology and geophysics. Reviews of Geophysical 35(3):315-342.

Goldberg, D., G. Myers, G. Iturrino, K. Grigar, T. Pettigrew, and S. Mrozewski. 2006. Logging-while-coring: New technology for the simultaneous recovery of downhole cores and geophysical measurements. Geological Society, London, Special Publications 267:219-228.

Graber, K.K., E. Pollard, B. Jonasson, and E. Schulte. (Eds.). 2002. Overview of Ocean Drilling Program engineering tools and hardware. In Ocean Drilling Program Technical Note 31. Ocean Drilling Program, Texas A&M University, College Station, Texas.

Huey, D.P. and M.A. Storms. 1995. New downhole tools improve recovery. Oil and Gas Journal 23:42-48.

Huey, D.P. and M.A. Storms. 1995. Modified wire line tools improve open hole logging operations. Oil and Gas Journal 30:94-96.

Malinverno, A., M. Kastner, M.E. Torres, and U.G. Wortmann. 2008. Gas hydrate occurrence from pore water chlorinity and downhole logs in a transect across the northern Cascadia margin (Integrated Ocean Drilling Program Expedition 311). Journal of Geophysical Research 113(B13):1-18.

Miller, J.E. and D.P. Huey. 1992. Development of a mud-motor-powered coring tool. In Offshore Technology Conference, Houston, Texas.

Miyazaki, E., M. Ozaki, S. Nishioka, and J. Minamiura. 2008. Application of riser fairings to the D/V “CHIKYU” during drilling in high current area. In Proceedings of Oceans ’08 Mts/Ieee Kobe-Techno-Ocean ’08, Kobe, Japan.

Peter, S., M. Holland, and G. Humphrey. 2009. Wireline coring and analysis under pressure: Recent use and future developments of the HYACINTH system. Scientific Drilling 7:44-50.

Pettigrew, T.L. 1993. Design and operation of a Drill-In-Casing system (DIC). In Ocean Drilling Program Technical Note 21. Ocean Drilling Program, Texas A&M University, College Station, Texas.

Saffer, D., L. McNeill, E. Araki, T. Byrne, N. Eguchi, S. Toczko, K. Takahashi, and the Expedition 319 Scientists. 2009. NanTroSEIZE Stage 2: NanTroSEIZE riser/riserless observatory. In Proceedings of the Integrated Ocean Drilling Program, Volume 319. Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas.

Stahl, M.J. 1994. Automated stress analysis and design of drill strings for riserless offshore coring operations. Oil and Gas Journal 4:43-48.

DRILLING THE OCEAN CRUST

Henry J. B. Dick
Woods Hole Oceanographic Institution

Formation of the ocean lithosphere is the principle magmatic process on the planet, generating some three-fifths of the Earth’s crust by surface area and representing the major transfer of heat, mass, and volatiles between the Earth’s interior, crust oceans, and atmospheres. At the present time we do not have direct knowledge of the composition of the ocean crust or a full understanding of how it forms. What we do know is largely the result of ocean drilling both in intact sections of the ocean crust and in tectonic windows where the lower ocean crust and mantle have been unroofed to the seafloor. The initial stimulus for drilling was to test two competing models for the ocean crust, which at the time was assumed to be a relatively simple layered sequence some 6-7 km thick. Harry Hess, in his landmark paper, History of the Ocean Basins (Hess, 1962), proposed that the ocean crust largely consisted of mantle peridotite hydrothermally altered to serpentine with the Mohorovi?i? discontinuity (Moho) representing the upper temperature limit for the stability of this mineral. The opposing model, which had gained general acceptance from the Earth sciences community, was a layer cake consisting of pillow lavas overlying sheeted dikes and gabbro, with the Moho representing the igneous crust-mantle boundary. In the latter, known as the Penrose ophiolite model (Conference Participants, 1972) the lower ocean crust represented the remains of a large magma chamber in which mantle melts pooled and underwent fractional crystallization, while the dikes represented the conduits through which differentiated magmas erupted to the seafloor to form a layer of pillow lavas. Obvious differences in the morphology of the seafloor between relatively low relief smooth seafloor formed at the fast spreading East Pacific Rise (EPR) and slower spreading ridges were largely ignored in this model.

The ultimate goal of ocean drilling initially was to achieve a full penetration of the crust from pillow lavas to mantle. Given the presumed simplicity of the ocean crust, a single core would answer all questions. A total penetration of “intact” crust has not been achieved, although we now know that it is technically feasible given the will. Thirty-five years of ocean drilling, in combination with seafloor mapping, however, has radically transformed our view of the ocean crust, which is now viewed as highly varied in composition and architecture, with radically different models for fast and slow spread crust. Ironically, both the Hess and the Penrose models have proved to describe the ocean crust as it forms under different tectonic conditions. The mechanisms of accretion of the lower crust now believed to exist are also radically different from the simple closed-system magma chamber that was the widely accepted paradigm at the start of ocean drilling, with direct intrusion of numerous small magma bodies, an absence of large magma chambers, melt-rock reaction, mass transfer by upward percolation of melts through the lower crust, and vertical rafting of intrusions and altered mantle peridotite all having been recognized as major accretionary processes.

Ocean crust drilling began in earnest in 1974 with Leg 37 of DSDP (Deep Sea Drilling Project), which drilled a four hole transect at 37°N on the Mid-Atlantic Ridge (MAR) in shallow ocean crust from 3.5 to 13 myr. The sites included a planned deep hole at Site 332 that penetrated 583 m before abandoned. At Site 334, a tectonically emplaced layer of serpentinized peridotite and gabbro was recovered beneath 50 m of pillow basalts. Ironically, this first in situ section of lower crustal rocks proved to be atypical of what was later drilled on seven legs in the Pacific, Atlantic, and Indian Oceans. In all, about 50 holes were drilled into “intact” sections of oceanic crust up to the start of the Integrated Ocean Drilling Program (IODP) in 2004, when it was believed that layered crust, such as described in the Penrose model, existed in the Atlantic and Pacific Oceans. At Hole 504B south of the Costa Rica Rift, and possibly at Hole 418A in the 108-million-year-old MAR crust, seismic layer 2B was penetrated, with only Hole 504B possibly reaching the very top of seismic layer 3 (Dick et al., 1992; Alt et al., 1993; Detrick et al., 1994). Drilling in young Pacific crust was particularly difficult, with 10 holes in crust less than 30 million years old reaching a maximum penetration of only 178 m—a result attributed to the difficulty of drilling abundant glassy sheet flows. Success was better at slower-spreading ridges, with 11 holes penetrating greater than 200 m, and 7 reaching greater than 500 m. This drilling showed that seismic layer 2A was composed of basalt lavas and rubble, and that at an intermediate spreading ridge, seismic layer 2B at Hole 504B was sheeted dikes as in the Penrose model. Unexpectedly, however, the layer 2B-layer 3 seismic boundary there corresponded to an alteration front in dikes, rather than the dike-gabbro transition. Surprisingly, short sections of often brecciated serpentinized peridotite and gabbro, exhibiting high-temperature alteration and crystal-plastic deformation, were found in six Atlantic holes drilled in supposedly “intact” crust. Drilling at slow spreading ridges demonstrated unexpected tectonic complexity that did not fit the Penrose model and proved a harbinger of things to come.

The early failure to drill deeply into intact oceanic crust was a huge disappointment. Recoveries were low, averaging ~20 percent. Other than sporadic drilling at Hole 504B, no serious attempt to drill ocean crust was made for many years after DSDP Leg 53 in 1977. Drilling difficulties were attributed to highly fractured basalt and diabase and possibly thermal problems deep in Hole 504B, although these were likely due as much to not properly designing holes for deep penetration. Thus, a new strategy was adopted during the Ocean Drilling Program (ODP), using “tectonic windows” to drill lower crust and mantle (Dick, 1989; Dick and Mével, 1996). This drilling strategy targeted peridotite and gabbro

exposed at topographic highs at oceanic core complexes: Atlantis Bank on the Southwest Indian Ridge; the MARK area at 23°N; the MAR Atlantis Massif and tectonic blocks in the rift mountains near the 15°20’ fracture zone; and Hess Deep in the Pacific, where the amagmatic tip of the Cocos-Nazca rift propagates into young (1.5–2 million-year-old) EPR crust.

Drilling at Hess Deep recovered important sections of tectonically disturbed lower crust and mantle that was consistent with the Penrose model. These sections included the important Hole 894G 154-m section of fine-grained gabbros with a few diabase dikes, which are believed to represent a section of lower crust formed in the melt lens beneath the EPR and resembled part of the Oman Ophiolite section. They are believed to be the precursor to a similar thick underlying gabbro section. The gabbros are too evolved, however, to represent crystallization products of the relatively primitive pillow basalts that characterize the East Pacific Rise, in conflict with the generally accepted hypothesis that the melt lens is their primary source. A second result was a series of holes at Site 895 that represent a transect across a melt transport conduit through a mantle section. The host peridotites were highly depleted residues of partial melting, consistent with a fractional melting model, while the dunite conduits contained gabbroic segregations that demonstrated for the first time that the mid-ocean ridge basalt (MORB) is formed within the mantle itself, rather than representing mixing of diverse magmas in a lower crustal magma chamber. The segregations also showed that basaltic melts can crystallize at near constant temperature by reaction with the host mantle—a result whose importance was not fully appreciated until analysis of the Hole 1309D gabbro section in the Atlantic. One of the great successes of IODP has been the penetration of an intact section of EPR crust down to the dike-gabbro transition at Hole 1256 penetrating 1257.1 m of the upper crust, including a 345.7 m sheeted dike complex and 100.5 m into gabbro near the depth predicted by seismologists for the layer 12-3 boundary. Besides affirming the results from Hess Deep, Hole 1256D proved the hypothesis that the shallow ocean crust (dikes and lavas) thins at the fastest spreading rates, confirming the utility of seismology in shallow Pacific crust.

Drilling lower crustal rocks in tectonic windows at slow and ultraslow spreading ridges is one of the dramatic successes of ODP and IODP. Hole 735B penetrated 1,508 m of gabbro at the Atlantis Bank core complex on the southwest Indian Ridge, while Hole 1309D penetrated 1,415 m at the Atlantis Massif on the MAR. Recovery was ~87 percent of both sites. These successes show unequivocally for the first time that thick gabbro sequences do exist at slower spreading ridges, but that they are the remains of numerous small intrusive swarms, not of large magma chambers. Moreover, the sections are riddled with microgabbro dikes and solution channels representing melt transport from depth through preexisting gabbro. Equally startling is a superimposed igneous stratigraphy produced by upward compaction of interstitial melt to produced numerous high-level Fe-Ti rich oxide gabbro layers. In addition, olivine-rich troctolites occur in the mid-section at Hole 1309D. These rocks form by reaction between basalt melt and mantle peridotite at the base of the crust, and are subsequently mechanically rafted up through the section (Drouin et al., 2007a, b, 2009; Suhr et al., 2008). Overall, the large majority of gabbros drilled at these sites and by Leg 153 at MARK are far too evolved to crystallize directly from MORB. Thus, to date, we have not recovered anything like the full lower crustal suite at either slow or fast spreading ridges, which is critical, because until we do we will have only indirect knowledge of the processes that shape MORB—the most abundant magma on earth.

Leg 209 examined what was once thought to be atypical ocean crust. It is drilled 19 holes at eight sites from 14°43?N to 15°39’N on the MAR where dredging found extensive mantle outcrops intruded by small gabbro bodies. This finding led to the hypothesis that the crust was largely serpentinized peridotite with local small magmatic centers cut by small dike swarms and local eruptive sequences (Cannat et al., 1997, 2006). This was what Leg 209 drilled, confirming the existence of crustal sections that form by direct intrusion and hydrothermal alteration of mantle rock along a significant portion of slower spreading ridges. Moreover, the crust consisted of one tectonic block cutting another with alternate fault capture, leading to spreading of blocks in opposite directions from the rift valley (Schroeder et al., 2007)—a new form of seafloor spreading, which morphological analysis of the seafloor suggests makes up a substantial portion (~40 percent) of the crust at slower spreading ridges (e.g., Escartin et al., 2008).

Drilling in lower crust at slower spreading ridges shows that its accretion occurs by mechanisms previously not considered: direct intrusion of small batches of melts at all levels, upward compaction of interstitial melts by permeable flow, and rafting of deeper intrusions and material formed by reaction between melts and mantle at the base of the crust. Moreover, it has also shown that both Penrose- and Hess-type sections exist along slow and ultraslow spreading ridges.

Supporting References

Alt, J.C., H. Kinoshita, and L.B. Stokking, S. Allerton, W. Bach, K. Becker, V.K. Boehm, T.S. Brewer, Y. Dilek, F. Filice, M.R. Fisk, H. Fujisawa, H. Furnes, G. Guerin, G.D. Harper, J. Honnorez, H. Hoskins, H. Ishizuka, C. Laverene, A.W. McNeil, A.J. Magenheim, S. Miyashita, P.A. Pezard, M.H. Salisbury, P. Taratotti, D.A. Teagle, D.A. Vanko, R.H. Wilkens, and H.U. Worm. 1993. Costa Rica Rift. In Proceedings of the Ocean Drilling Program, Initial Reports, Volume 148. Ocean Drilling Program, Texas A&M University, College Station, Texas.

Cannat, M., Y. Lagabrielle, H. Bougault, J. Casey, N. de Coutures, L. Dmitriev, and Y. Fouquet. 1997. Ultramafic and gabbroic exposures at the Mid-Atlantic Ridge: Geologic mapping in the 15°N region. Tecto-nophysics 279(1-4):193-213.

Cannat, M., D. Sauter, V. Mendel, E. Ruellan, K. Okino, J. Escartin, V. Combier, and M. Baala. 2006. Modes of seafloor generation at a melt-poor ultraslow-spreading ridge. Geology 34(7):605-608.

Conference Participants. 1972. Penrose field conference on ophiolites. Geotimes 17:24-26.

Detrick, R., J. Collins, R. Stephen, and S. Swift. 1994. In situ evidence for the nature of the seismic layer 2/3 boundary in oceanic crust. Nature 370:288-290.

Dick, H.J.B. (Ed.). 1989. JOI/USSAC Workshop Report: Drilling the Oceanic Lower Crust and Mantle. Woods Hole Oceanographic Institution, Woods Hole, Massachusetts.

Dick, H.J.B. and C. Mével. (Eds.). 1996. The Ocean Lithosphere and Scientific Drilling into the 21st Century. JOI/U.S. Science Support Program and the InterRidge Office, Washington, DC.

Dick, H.J.B., J.A. Eringer, L.B. Stokking, P. Agrinier, S. Allerton, J.C. Alt, L.O. Boldreel, M.R. Fisk, P.K.H. Harvey, G.J. Iturrino, K.T.M. Johnson, D.S. Kelley, P.K. Kepezhinskas, C. Laverne, F.C. Marton, A.W. McNeill, H.R. Naslund, J.E. Pariso, N.N. Pertsev, P. Pezard, E.S. Schandi, J.W. Sparks, P. Tartarotti, S. Umino. D.A. Vanko, and E. Zuleger. 1992. 2. Site 504. In Proceedings of the Ocean Drilling Program, Initial Reports, Volume 140, Dick, H.J.B., J.A. Erzinger, and L.B. Stokking (Eds.). Ocean Drilling Program, Texas A&M Univeristy, College Station, Texas.

Drouin, M., M. Godard, and B. Ildefonse. 2007a. Origin of olivine-rich gabbroic rocks from the Atlantis Massif (MAR 30°N, IODP Hole U1309D): Petrostructural and geochemical study. Geophysical Research Abstracts 9(06550).

Drouin, M., M. Godard, and B. Ildefonse. 2007b. Origin of olivine-rich troctolites from IODP Hole U1209D in the Atlantis Massif (Mid-Atlantic Ridge): Petrostructural and geochemical study. Eos, Transactions, American Geophysical Union 88:52.

Drouin, M., M. Godard, B. Ildefonse, O. Bruguier, and C.J. Garrido. 2009. Geochemical and petrographic evidence for magmatic impregnation in the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP Hole U1309D, 30°N). Chemical Geology 264(1-4):71-88.

Escartin, J., D.K. Smith, J.R. Cann, H. Schouten, C.H. Langmuir, and S. Escrig. 2008. Central role of detachment faults in accretion of slow-spreading oceanic lithosphere. Nature 455:790-794.

Hess, H.H. 1962. The history of the ocean basins. In Petrologic Studies: A Volume in Honor of A.F. Buddington, Engel, A.E.J., H.L. James, and B.F. Leonard (Eds.). Geological Society of America, Boudler, Colorado.

Suhr, G., E. Hellebrand, K. Johnson, and D. Brunelli. 2008. Stacked gabbro units and intervening mantle: A detailed look at a section of IODP Leg 305, Hole U1309D. Geochemistry, Geophysics, Geosystems 9(Q10007):1-31.

Schroeder, T., M.J. Cheadle, H.J.B. Dick, U. Faul, J.F. Casey, and P.B. Kelemen. 2007. Nonvolcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15N on the Mid-Atlantic Ridge: A structural synthesis of ODP Leg 209. Geochemistry, Geophysics, Geosystems 8:Q06015.

LARGE IGNEOUS PROVINCES

Millard F. Coffin
University of Tasmania, Australia

Large igneous provinces (LIPs)—oceanic plateaus, volcanic rifted margins, and continental flood basalts—result from fundamental processes in Earth’s interior and have been implicated as a cause of major worldwide environmental changes. Although the plate tectonics paradigm successfully explains volcanic activity on Earth’s surface associated with seafloor spreading and plate subduction, it does not elucidate the massive “hotspot” volcanism that produces LIPs, which dominates the record of volcanism on all other terrestrial planets and satellites in our solar system and the cause of which is debated vigorously. Temporal correlations between LIP emplacements and environmental phenomena such as mass extinctions and oceanic anoxic events (OAEs) are well documented, yet the underlying mechanisms causing these global catastrophes are only beginning to be grasped. Scientific ocean drilling has played a central and critical role in illuminating solid Earth processes causing LIPs and in comprehending the effects of LIP formation on Earth’s environment.

Reconnaissance drilling of oceanic plateaus and volcanic rifted margins began soon after scientific ocean drilling started in 1968, but the first targeted LIP investigations involving drilling, focusing on the ~55 Ma North Atlantic volcanic rifted margins, commenced in the 1980s. Drilling on the UK margin confirmed a hypothesis that submarine “seaward-dipping reflectors” (SDRs) observed on seismic reflection data were stacks of originally subaerial lava flows that subsequently cooled and subsided beneath sea level, where they were buried by sediment—a nearly ubiquitous characteristic of submarine LIPs that precludes their volcanic and plutonic rocks from being sampled by any means other than drilling. Further focused drilling of the North Atlantic LIP, on the Norwegian Margin in the 1980s and the conjugate East Greenland Margin in the 1990s, documented extreme magmatic productivity over a distance of at least 2,000 km during continental rifting and breakup, provided the first age data from an oceanic LIP showing that construction of these margins was geologically “instantaneous” (ca. 1 million years), and yielded geochemical evidence that landward SDRs were contaminated during ascent through continental crust and that oceanward SDRs formed at a seafloor spreading center resembling Iceland. A proposed mechanism for these ~55 Ma magmas triggering the Paleocene-Eocene Thermal Maximum is intrusion of voluminous mantle-derived melts into carbon-rich sedimentary strata in the northeast Atlantic that caused explosive release of methane into the ocean and atmosphere via hydrothermal vent complexes. More than 50 percent of passive margins globally are “volcanic,” but to date scientific ocean drilling has only sampled the North Atlantic LIP at one site.

Focused investigations of oceanic plateaus have targeted the two largest features globally, the ~120 Ma Ontong Java Plateau (Pacific Ocean) and ~120-95 Ma Kerguelen Plateau/Broken Ridge (Indian Ocean), each encompassing an area approximately one-fourth the size of the contiguous United States. Several expeditions have drilled multiple holes penetrating the igneous basement of each. In late 2009, igneous basement of a third oceanic plateau, the ~145-130 Ma Shatsky Rise (Pacific Ocean), was drilled in various locations. These three features constitute the only oceanic plateaus where igneous basement has been drilled at more than one site.

Drilling results from Ontong Java Plateau basement rocks are complemented by studies of obducted plateau rocks exposed in the Solomon Islands. All basement rocks recovered to date are remarkably homogeneous—submarine tholeiitic basalts with minor variations in elemental and iso-topic composition. Partial batch melting (≥30 percent) generated the basalts, with melting and fractional crystallization at depths of <6 km. The lavas and their overlying sediment indicate relatively minor uplift accompanying emplacement and relatively minor subsidence since emplacement. Primarily on the basis of drilling results, multiple models—plume, bolide impact, and upwelling eclogite—have been proposed for the feature’s origin. The Ontong Java Plateau correlates temporally with oceanic anoxic event (OAE-1a), and interpretation of strontium, osmium, and lead isotopic systems during the time of OAE-1a points to a close linkage between the two, with CO₂, Fe, and trace metal emissions from the massive magmatism potentially triggering the event.

Uppermost igneous basement of the Kerguelen Plateau/ Broken Ridge is dominantly subaerial tholeiitic basalt, and it shows two apparent peaks in magmatism at 119-110 Ma and 105-95 Ma. Geochemical differences among these basalts are attributable to varying proportions of components from the primary mantle source (plume?), depleted mid-ocean ridge basalt (MORB)-related asthenosphere, and continental lithosphere. Proterozoic-age zircon and monazite in clasts of garnet-biotite gneiss in a conglomerate intercalated with basalt at one drill site demonstrate the presence of fragments of continental crust in the Kerguelen Plateau, inferred previously from geophysical and geochemical data. For the first time from an intra-oceanic LIP, alkalic lavas, rhyolite, and pyroclastic deposits were sampled. Flora and fauna preserved in sediment overlying igneous basement record long-term plateau subsidence, beginning with terrestrial and shallow marine deposition and continuing to deep water deposition. The first results of 2009 basement drilling on the Shatsky Rise include evidence for initial shallow water or subaerial eruption of predominantly massive lava flows, subsequent deeper water eruption of mainly pillow lava flows, and post-emplacement subsidence resembling that of normal oceanic crust.

Future LIP drilling has the potential to transform our understanding of the Earth system through investigating:

(1) magma (and hence mantle source) variability through time, through drilling deep sections in multiple LIPs; (2) the nature of melting anomalies, i.e., compositional vs. thermal, that produce LIPs; (3) the precise durations of oceanic LIP events; (4) modes of eruption, i.e., constant effusion over one to several million years, or several discrete pulses over the same time interval; and (5) relationships among oceanic LIPs, OAEs, extinction events, and other major environmental changes (e.g., ocean acidification and fertilization). The 2010 Eyjafjallajökull eruption underscores the nascent state of and need for knowledge of the first four pathways of investigation above, and results from the last will contribute to understanding and forecasting regional and global environmental changes during the Anthropocene.

Advancing knowledge of LIPs and the Earth system requires integrated multidisciplinary and cross-disciplinary approaches involving mantle geodynamics, plume modeling, petrology, geochemistry, environmental impacts, pale-oceanography, micropaleontology, physical volcanology, geophysics, and tectonics. Drilling and logging are critical tools for most of these disciplines. Oceanic LIPs must be studied in concert with continental counterparts to better understand emplacement mechanisms and environmental effects of their formation. Needed technology developments include better recovery of syn-sedimentary sections, sidewall coring, oriented cores, and controlled circulation drilling in water depths >2,500 m. The oceanic and continental drilling communities should merge efforts for seamless thematic and onshore/offshore investigations, and LIP-focused IODP-industry collaborations should be enhanced.

Supporting References

Burke, K. and T. Torsvik. 2004. Derivation of large igneous provinces of the past 200 million years from long-term heterogeneities in the deep mantle. Earth and Planetary Science Letters 227(3-4):531-538.

Coffin, M.F. and O. Eldholm. 1994. Large igneous provinces: Crustal structure, dimensions, and external consequences. Reviews of Geophysics 32(1):1-36.

Courtillot, V.E., A. Davaille, J. Besse, and J. Stock. 2003. Three distinct types of hotspots in the Earth’s mantle. Earth and Planetary Science Letters 205(3-4):295-308.

Eldholm, O. and M.F. Coffin. 2000. Large igneous provinces and plate tectonics. In The History and Dynamics of Global Plate Motions, Richards, M.A., R.G. Gordon, and R.D. van der Hilst (Eds.). Geophysical Monograph, American Geophysical Union, Washington, DC.

Ernst, R.E., K.L. Buchan, and I.H. Campbell. 2005. Frontiers in large igneous province research. Lithos 79:271-297.

Kerr, A.C. 2005. Oceanic LIPs: The kiss of death. Elements 1:289-292.

Korenaga, J., P.B. Kelemen, and W.S. Holbrook. 2002. Methods for resolving the origin of large igneous provinces from crustal seismology. Journal of Geophysical Research 107(2178):1-27.

Mahoney, J.J. and M.F. Coffin (Eds.). 1997. Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism. Geophysical Monograph, American Geophysical Union, Washington, DC.

Montelli, R., G. Nolet, F.A. Dahlen, and G. Masters. 2006. A catalogue of deep mantle plumes: New results from finite-frequency tomography. Geochemistry, Geophysics, and Geosystems 7(Q11007):1-69.

Neal, C.R., M.F. Coffin, N. Arndt, R.A. Duncan, O. Eldholm, E. Erba, C. Farnetani, G. Fitton, S. Ingle, N. Ohkouchi, M. Rampino, M.K. Reichow, S. Self, and Y. Tatsumi. 2008. Investigating large igneous province formation and associated paleoenvironmental events: A white paper for scientific drilling. Scientific Drilling 6:4-18.

Ridley, V.A. and M.A. Richards. 2010. Deep crustal structure beneath large igneous provinces and the petrologic evolution of flood basalts. Geochemistry, Geophysics, and Geosystems 11(Q09006):1-21.

Saunders, A.D. 2005. Large igneous provinces: Origin and environmental consequences. Elements 1(5):259-263.

Sleep, N.H. 2006. Mantle plumes from top to bottom. Earth Science Reviews 77(4):231-271.

Svensen, H., S. Planke, A. Malthe-Sorenssen, B. Jamtveit, R. Myklebust, T.R. Eidem, and S.S. Rey. 2004. Release of methane from a volcanic basin as a mechanism for initial Eocene global warming. Nature 429:542-545.

White, R.S. and D. McKenzie. 1995. Mantle plumes and flood basalts. Journal of Geophysical Research 100(17):543-17,585.

Wignall, P. 2005. The link between large igneous province eruptions and mass extinctions. Elements 1(5):293-297.

CONTINENTAL BREAKUP AND
SEDIMENTARY BASIN FORMATION

Dale S. Sawyer
Rice University

In the study of continental breakup (and other large-scale tectonic systems), scientific ocean drilling is not a capstone activity, but rather is part of an iterative process comprising drilling, improved geophysical (primarily controlled source seismology) and geological (including onshore exposures where available) characterization, ongoing geodynamic modeling, and drilling again. Continental breakup and ensuing seafloor spreading inherently separate the “field area” for a study into a pair of conjugate rifted margins. Typically both margins must be studied comprehensively to learn about the whole. Every rifted margin is a blend of end-member types: (1) magma-dominated or magma-poor, (2) actively rifting or no longer rifting, (3) normal spreading, obliquely spreading, and transform, and (4) sediment-dominated or sediment starved. Examination of any single rifting system cannot reveal details of all the important breakup processes. Successful drilling studies will include geodynamic modeling efforts before, during, and after each coordinated drilling activity

In 1991, the Ocean Drilling Program (ODP) Planning Committee formed a North Atlantic Rifted Margins Detailed Planning Group (NARM-DPG) with a charge to explore options and make recommendations for conducting drilling on volcanic and non-volcanic conjugate rifted margins. The NARM-DPG recommended that ODP efforts focus on the Newfoundland-Iberia conjugate pair for studies of magma-poor rifting and the southeast Greenland—northeast Atlantic for studies of magma-dominated rifting.

Drilling on the magma-poor Newfoundland and Iberia rifted margins comprises DSDP (Deep Sea Drilling Project) Leg 47 and ODP Legs 103, 149, 173, and 210. DSDP Leg 47B (Sibuet and Ryan, 1979) drilled a deep sedimentary hole that provided stratigraphic information about the breakup of Newfoundland and Iberia. ODP Leg 103 (Boillot and Winterer, 1988) drilled a transect across the Deep Galicia Basin and demonstrated that (1) a prominent seismic reflector “S,” later to be characterized as a detachment fault, is within or overlain by rotated, fault-bounded blocks of continental crust, (2) peridotite, which ascended from 30 km depth and shows a history of partial melting, stretching, serpentinization, and fracturing, is exposed in a margin parallel ridge at the foot of the margin, and (3) obtained dates for the syn- and post-rift sediments reflect the last stage of breakup. ODP Leg 149 (Whitmarsh and Sawyer, 1996) drilled a transect across the Iberia Abyssal Plain margin segment. Peridotite was again sampled at the top of a ridge, providing additional information about its exhumation history. However, serpentinized peridotite was also sampled 20 km to the east of the peridotite ridge, indicating that there is a wide zone of upper mantle rocks exhumed to the seafloor and presumably separating extended continental crust from oceanic crust. Some of the sampled peridotite contained strong remnant magnetization, explaining the presence of apparent seafloor spreading anomalies over crust that is not oceanic. ODP Leg 173 (Whitmarsh and Wallace, 2001) showed that the continental crust was thinned to nearly zero thickness by low-angle detachment faulting, which in some places brought upper mantle peridotite to within a few hundred meters of the seafloor at the time of breakup. The peridotites are most likely to be subcontinental mantle. Mafic cores were shown to have been emplaced in or just below the thinned lower continental crust. Surprisingly no samples of upper continental crust or synrift melt were obtained, which is attributed to gradual breakup and transition to seafloor spreading. During Leg 173 shipboard scientists noted strong similarities between cores obtained from the Iberia Abyssal Plain and the character and history of rifted margins and transition zones exposed in the modern Alps (Manatschal and Bernoulli, 1998). This line of research has been very fruitful in expanding our understanding of both systems. ODP Leg 210 (Tucholke and Sibuet, 2007) drilled off Newfoundland in a position conjugate to the Legs 149/173 transect. The primary site bottomed in a pair of diabase sills dated at 98 and 105 Ma. The upper sill is intruded at the level of the prominent and widespread “U” reflection, suggesting that sills may be pervasive at this stratigraphic level. No equivalent to these sills was observed on the Iberia Margin. A second site off Newfoundland sampled exhumed peridotite in a shallow basement high that is similar to peridotites sampled off Iberia. As in Iberia, these peridotites showed little evidence of melting even though they were coincident with apparently normal lineated magnetic anomalies.

Extensive reinterpretation of seismic profiles after Legs 173 and 210, synthesis of Alps analogs (Peron-Pinvidic et al., 2007), comparison to drilling results, comparison to slow spreading midocean ridge analogs (Cannat et al., 2009), and geodynamic modeling (Lavier and Manatschal, 2006) has led to a new understanding of the Newfoundland—Iberia breakup (Peron-Pinvidic and Manatschal, 2009). This understanding moves past thinking of continental breakup as mono-phase and laterally uniform rifting followed by an abrupt breakup and formation of a sharp continent-ocean boundary. The new model describes rifting as a process of progressive strain localization, stacking different modes of extension in temporally and spatially varying domains. It defines the end of rifting and onset of seafloor spreading neither as a moment in time, nor a mappable boundary, but as a transition zone in which a series of processes interact and overlap in complex ways. Features that we could not explain are now comprehensible. Furthermore, this new understanding is revolutionizing the way academic and petroleum industry scientists interpret other magma-poor rifted margins around the world (Reston, 2009).

Drilling on the magma-dominated southeast Greenland and northeast Atlantic volcanic margins comprises DSDP Legs 38 and 81 and ODP Legs 104, 152, and 163. DSDP Leg 38 (Talwani and Udintsev, 1976) found that acoustic basement of Vøring Plateau was composed of basaltic volcanics. DSDP Leg 81 (Roberts et al., 1984) drilled Rockall Margin, suggesting that seaward dipping reflectors (SDRs) were subaerial volcanic constructions. ODP Leg 104 (Eldholm et al., 1989) drilled 900 m of subaerial flows of the SDR at the Vøring Margin and was able to characterize events during the initial opening of a volcanic margin. ODP Leg 152 (Larsen and Saunders, 1998) drilled a transect of holes across the southeast Greenland SDR from the middle shelf to deep water. They distinguished continental and oceanic flow sequences and located the seaward extent of rifted continental crust. They showed that the SDR overlies fully oceanic crust and that it formed in the manner of the present-day Iceland rift zone. They were able to infer features of the plume associated with the formation of the margin. ODP Leg 163 (Larsen and Duncan, 1996) was not able to achieve its primary tectonic objectives because of “a drilling accident and damage to the ship sustained during extreme storm conditions” (Initial reports 163). During this period of drilling, 1976 to 1995, and complementary seismic, geological, and modeling studies, the understanding of magma-dominated continental breakup moved forward, as did our conception about the global extent and importance of these margins and large igneous provinces, their counterpart in the oceans.

Future opportunities in the study of continental breakup will depend not just on access to ocean drilling, but also on coordinated high-quality, two- and three-dimensional multichannel seismic reflection profiling and companion long-offset seismic surveys. The INVEST report mentions several times the need for increased collaboration with industry. The study of continental breakup is one of the most obvious and important touch points between academic and industry science.

Supporting References

Boillot, G. and E.L. Winterer. 1988. Drilling across the Galicia Margin: Retrospect and prospect. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 103. Ocean Drilling Program, University of Texas A&M, College Station, Texas.

Cannat, M., G. Manatschal, D. Sauter, and G. Peron-Pinvidic. 2009. Assessing the conditions of continental breakup at magma-poor rifted margins: What can we learn from slow spreading mid-ocean ridges? Comptes Rendus Geoscience 341(5):406-427.

Eldholm, O., J. Thiede, and E. Taylor 1989. Evolution of the Vøring volcanic margin. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 104, Eldholm, O., J. Thiede, E. Taylor, C. Barton, K. Bjørklund, W. Bleil, P. Ciesielski, A. Desprairies, D. Donnally, C. Froget, R. Goll, R. Henrich, E. Jansen, L. Krissek, K. Kvenvolden, A. LeHuray, D. Love, P. Lynse, T. McDonald, P. Mudie, L. Osterman, L. Parson, J.D. Phillips, A. Pittenger, G. Qvale, G. Schönharting, and L. Viereck. (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Larsen, H.C. and R.A. Duncan. 1996. Introduction: Leg 163 background and objectives. In Proceedings of the Ocean Drilling Program, Initial Reports, Volume 163, Duncan, R.A., H.C. Larsen, J.F. Allan, Y. Aita, N.T. Arndt, C.J. Bücker, H. Cambray, K.V. Cashman, B.P. Cemey, P.D. Clift, J.G. Fitton, B. Le Gall, P.R. Hooper, Y. Nakasa, Y. Niu, H. Philipp, S. Planke, J. Rehacek, A.D. Saunders, D.A.H. Teagle, and C. Tenger (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Larsen, H.C. and A.D. Saunders. 1998. Tectonism and volcanism at the Southeast Greenland Rifted Margine: A record of plume impact and later continental rupture. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 152, Saunders, A.D., H.C. Larsen, and S.W. Wise, Jr. (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Lavier, L.L. and G.A. Manatschal. 2006. A mechanism to thin the continental lithosphere at magma-poor margins. Nature 440:324-328.

Manatschal, G. and D. Bernoulli. 1998. Rifting and early evolution of ancient ocean basins: The record of the Mesozoic Tethys and of the Galicia-Newfoundland Margins. Marine Geophysical Research 20(4):371-381.

Peron-Pinvidic, G. and G. Manatschal. 2009. The final rifting evolution at deep magma-poor passive margins from Iberia-Newfoundland: A new point of view. International Journal of Earth Sciences 98(7):1581-1597.

Peron-Pinvidic, G., G. Manatschal, T.A. Minshull, and D.S. Sawyer. 2007. Tectonosedimentary evolution of the deep Iberia-Newfoundland margins: Evidence for a complex breakup history. Tectonics 26(TC2011):1-19.

Reston, T.J. 2009. The extension discrepancy and syn-rift subsidence deficit at rifted margins. Petroleum Geoscience 15(3):217-237.

Roberts, D.G., J. Backman, A.C. Morton, J.W. Murray, and J.B. Keene. 1984. Evolution of volcanic rifted margins: Synthesis of Leg 81 results on the West Margin of Rockall Plateau. In Initial Reports of the Deep Sea Drilling Project, Volume 81, Roberts D.G., D. Schnitker, et al. (Eds.). Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Sibuet, J.C. and W.B.F. Ryan. 1979. Site 398: Evolution of the West Iberian Passive Continental Margin in the framework of the early evolution of the North Atlantic Ocean. In Initial Reports of the Deep Sea Drilling Project, Volume 47, Part II, Sibuet, J.C., W.B.F. Ryan, et al. (Eds.). Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Talwani, M. and G. Udintsev. 1976. Tectonic synthesis. In Initial Reports of the Deep Sea Drilling Project, Volume 38. Deep Sea Drilling Project, U.S. Government Printing Office, Washington, DC.

Tucholke, B.E. and J.C. Sibuet. 2007. Leg 210 synthesis: Tectonic, mag-matic, and sedimentary evolution of the Newfoundland-Iberia rift. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 210, Tucholke, B.E., J.C. Sibuet, and A. Klaus (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Whitmarsh, R.B. and D.S. Sawyer. 1996. The ocean/continent transition beneath the Iberia Abyssal Plain and continental-rifting to seafloor-spreading processes. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 149, Whitmarsh, R.B., D.S. Sawyer, A. Klaus, and D.G. Masson (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

Whitmarsh, R.B. and P.J. Wallace. 2001. The rift-to-drift development of the west Iberia nonvolcanic continental margin: A summary and review of the contribution of Ocean Drilling Program Leg 173. In Proceedings of the Ocean Drilling Program, Scientific Results, Volume 173, Beslier, M.O., R.B. Whitmarsh, P.J. Wallace, and J. Girardeau (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas.

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