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6 Assessment of Illuminating Earth’s Past, Present, and Future: The International Ocean Discovery Program Science Plan for 2013-2023 rocks with radiometric methods); (3) observations obtained One of the fundamental premises of I lluminating in a frontier area (e.g., massive sulﬁde deposits beneath Earth’s Past, Present, and Future: The International Ocean hydrothermal vents); and (4) novel integration of different Discovery Program Science Plan for 2013-2023 (referred data types or cross-disciplinary interchange (e.g., additional to hereafter as the “science plan”; IODP-MI, 2011) is that linkages between regional marine and on-land investigations scientiﬁc ocean drilling has the potential to enable essential of similar environments). advances in multiple ﬁelds of scientiﬁc inquiry, as it has done The ﬁrst case of transformative discovery (new interpre- so signiﬁcantly in the past (see Chapters 2-4 of this report for tations of existing data) is very difﬁcult, if not impossible, to discussion of accomplishments in previous scientiﬁc ocean predict. Technological development will most directly lead to drilling programs). In this chapter, the committee assesses transformative discoveries through drilling to depths greater the potential for the scientiﬁc challenges described in the than have been reached previously or by coupling drilling science plan to lead to transformative scientiﬁc discovery. with long-term time series measurements on scales not previ- Because the committee’s intent was to provide guidance on ously seen. Conventional drilling may lead to transformative how the plan could be most effectively implemented, recom- science in regions that have not been previously drilled or mendations are also offered on relevant areas of scientiﬁc sampled, while drilling transects of spatially related holes ocean drilling inquiry that have the greatest potential for could lead to pathways for novel integration of data. There- success. fore, the committee focused on assessing the science plan The committee examined the potential for transforma- through all of the pathways detailed above, except the ﬁrst. tive discoveries that might result from research conducted This chapter begins with a discussion of overarching within the framework of the science plan. The National comments regarding the science plan, including conclusions Science Foundation (NSF) deﬁnes transformative research and recommendations. Following sections address each as research that “involves ideas, discoveries, or tools that of the four research themes identiﬁed in the science plan. radically change our understanding of an important existing General comments on the theme are followed by a detailed scientiﬁc or engineering concept or educational practice or analysis of each of the science plan challenges listed within leads to the creation of a new paradigm or ﬁeld of science, the theme, assessment of other challenges or opportunities engineering, or education. Such research challenges cur- rent understanding or provides pathways to new frontiers.”1 for transformative science beyond that in the science plan, synergies between the themes, and linkages between scien- Under this deﬁnition, the committee has considered those tiﬁc ocean drilling, other NSF-supported science programs discoveries that might result from several different path- and facilities, and non-NSF programs. The wording of the ways, including: (1) new ways to interpret existing data, themes and challenges after the overarching comments are which lead to testable new theories or paradigms that can taken directly from the science plan in order to easily map be assessed through the collection of new data (e.g., plate the science plan challenges to the committee’s assessment. tectonics); (2) technological developments that enable previously impossible measurements (e.g., ability to date 1 See http://www.nsf.gov/about/transformative_research/deﬁnition.jsp. 59
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60 SCIENTIFIC OCEAN DRILLING OVERARCHING COMMENTS to prioritize, but given the ﬁnancial constraints that the next phase of scientiﬁc ocean drilling is likely to face, it may now The science plan is divided into four research themes: be appropriate for the scientiﬁc ocean drilling community climate and ocean change, biosphere frontiers, Earth con- to provide additional guidance on prioritization of potential nections (deep Earth processes), and Earth in motion (direct drilling objectives. Such a prioritization could include guid- time series observations on human scales). Fourteen spe- ance on which drilling objectives might be dependent on ciﬁc challenges, posed as questions, are included in these platform capabilities and availability, innovations in technol- themes. In addition, chapters on education and outreach and ogy, challenges in obtaining supporting data (such as in high on implementation are included. Although the document latitudes), or global political or safety concerns. has no explicit vision statement, the science plan’s focus is clearly on new discoveries and better understanding of RECOMMENDATION: The scientific ocean drilling Earth science topics to meet emerging societal challenges community should establish a mechanism to prioritize and enhance decision making. This overarching focus is the challenges outlined in the science plan in a manner considerably different from the Integrated Ocean Drilling that complements the existing peer-review process. Program (IODP) Initial Science Plan (IODP, 2001), which was based on further exploration of the ocean and new sci- The scientiﬁc ocean drilling programs have a history of entiﬁc understanding of Earth systems, with the assumption making excellent use of legacy samples and data that have that recognition of how to apply that knowledge to relevant helped to quickly advance new areas of research (see in par- societal issues would be automatic. The committee sup- ticular the discussion of accomplishments in the section on ports linking scientiﬁc ocean drilling to issues of societal Abrupt Climate Change in Chapter 4). On the other hand, the relevance and commends the writers of the science plan for science plan is justiﬁably focused on the importance of future taking this approach. The climate and ocean change (e.g., drilling challenges and thus spends little time discussing the climate change, sea level rise, ocean acidiﬁcation) and Earth use of legacy information and samples. in motion (e.g., earthquakes and other geohazards) themes identify challenges with the most direct societal relevance, Using legacy data and samples to their maximum but relevant topics also exist in the biosphere and Earth con- capabilities will continue to increase the scien- nections themes. tiﬁc value of the scientiﬁc ocean drilling programs. Overall, the science plan presents a strong case for the Expanded use of legacy materials could help, for continuation of scientiﬁc ocean drilling, with its possible example, with prioritization of drilling objectives in beneﬁts for science and society. The committee was particu- the next phase of scientiﬁc ocean drilling. larly positive about the potential for transformative science resulting from studies of the subseaﬂoor biosphere and about A more thorough future examination of the areas of the importance of continuing paleoclimate studies that will natural integration among scientiﬁc ocean drilling objec- provide analogs and likely constraints on global and regional tives would also be valuable. Although several natural points changes predicted with future climate. It also agreed that the of synergy between the challenges and themes are well emphasis on sampling deeper into the crystalline basement described in the science plan, a more detailed examination of will lead to better understanding of deep earth processes, the areas where natural integration could occur between and especially if high percentages of intact core are recovered among the science challenges would have further strength- and if active tectonic processes are monitored in situ. ened the science plan (see following sections for further discussion). An increase in efﬁciency and integration of Each of the four themes within the science plan multiple science objectives is one means by which resources identiﬁes compelling challenges with potential for can be most effectively used. For example, integrating mul- transformative science that can only be addressed tiple drilling objectives in the early planning stages of single by scientiﬁc ocean drilling. Some challenges within expeditions would maximize scientiﬁc output in relation to these themes appear to have greater potential for costs. This approach is successfully used by the International transformative science than others. Continental Scientiﬁc Drilling Program (ICDP)2 and polar expeditions. Integrating multiple objectives into a single The committee’s assessments of each theme and spe- expedition requires compromises, but certain practices, ciﬁc challenge identiﬁed in the science plan are discussed such as bringing expedition leaders together beforehand in greater detail in the following sections. The themes and to ensure agreement on expedition goals and providing challenges are pertinent and well-justiﬁed, although the adequate planning to create a viable work plan, will make committee was concerned that the science plan reads like a success more likely. Other potential approaches to increasing wish list with little guidance as to which of the 14 challenges efﬁciency include evolving efforts to optimize ship tracks, were considered most important. The committee is aware that the writers of the science plan may not have been asked 2 See http://www.icdp-online.org.
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61 ASSESSMENT OF ILLUMINATING EARTH’S PAST, PRESENT, AND FUTURE ocean drilling. The climate theme has a strong focus which also has possible implications for prioritization of on achievements, speciﬁcally those within the past science objectives. 10 years, and suggests that more related work is RECOMMENDATION: From the earliest stages of needed, especially on certain targeted topics (e.g., proposal development and evaluation, possibilities for polar regions, permanent El Niño states, monsoon increasing program efﬁciency through integration of patterns). multiple objectives into single expeditions should be considered by proponents and panels. The science plan emphasizes the critical need to inte- grate proxy observations from paleoclimate data with numer- Chapters 2-4 extensively discuss the vital role played by ical modeling of past climates to better understand climate technology in achieving many scientiﬁc advances in previ- system responses and feedbacks. In addition, there will be ous scientiﬁc ocean drilling programs (Deep Sea Drilling a need to develop new paleoclimate proxies and improve Project [DSDP], Ocean Drilling Program [ODP], and IODP). existing proxies. Both of these objectives will require strong Although the committee’s charge for this section was to linkages among the scientiﬁc ocean drilling, modeling, and assess the potential for transformative science in the science climate proxy communities. The theme highlights the need plan, it determined that transformative science is critically for innovative thought and for collaboration with other dependent on technological breakthroughs and could not be drilling programs (e.g., Antarctic Geological Drilling pro- fully assessed without considering the need for continued gram [ANDRILL], ICDP) to accomplish transects from the technological development. Any future scientific ocean continental margin to the deep ocean, as well as the need for drilling program must continue to push the technological mission-speciﬁc platforms that have the ﬂexibility to drill in envelope. Previous scientiﬁc ocean drilling programs have difﬁcult areas (e.g., shallow and ice covered regions) with shown great strength in this area, and the committee believes increased core recovery. In many of these cases, the JOIDES that the promise of continued innovation is high. Approaches Resolution may not be the optimum platform for future such as dedicated engineering legs or establishment of sites climate science needs. The next phase of scientiﬁc ocean with different lithologies to test and reﬁne instruments could drilling may need to consider new technology development increase the potential for achievement of groundbreaking or alignment with other programs that have common goals science. and appropriate technology. The science plan also articulates well the case for the RECOMMENDATION: Pathways for innovations in importance and societal relevance of these topics to decision technology should be encouraged. In addition, setting makers. It acknowledges a number of international efforts aside some resources speciﬁcally to promote technologi- (IPCC, International Geosphere-Biosphere Programme 3 cal research and development could increase the potential and the Past Global Changes project,4 European Project for for transformative science. Ice Coring in Antarctica, Scientiﬁc Committee on Antarctic Research5) that have developed strategies to address these challenges. One especially well-justiﬁed point is that of all THEME 1—CLIMATE AND OCEAN CHANGE: paleoclimate drilling initiatives, only the next phase of scien- READING THE PAST, INFORMING THE tiﬁc ocean drilling can consistently recover time-continuous, FUTURE high-resolution records of warmer, high-CO2 climates in the This theme identiﬁes four key challenges related to deep past. Earth responses to changes in atmospheric carbon dioxide (CO2) concentration, sea level rise and diminishing ice sheets Challenge 1: How Does Earth’s Climate System Respond due to warming climate trends, regional precipitation pattern to Elevated Levels of Atmospheric CO2? changes and potential impacts, and the ocean’s sensitivity to changes in chemistry. All of these challenges are relevant to Sediment cores document the strong relationship between future Intergovernmental Panel on Climate Change (IPCC) mean global atmospheric temperature and CO2 over millions projections and can help provide constraints on the range of to tens of millions of years, and demonstrate the potential for possible future impacts. They map well to the IPCC Fifth using warmer-than-present pre-Quaternary climates as a rich Assessment Report, which is currently in preparation, and venue for exploring the behavior of Earth system models that also represent issues of signiﬁcant uncertainty and high are used for future projections (provided that relevant proxies importance that will remain relevant for the follow-up Sixth can be convincingly shown to be reliable). Quantifying this Assessment Report. relationship has been assisted by dramatic improvements in The science described in these challenges has poten- 3 See http://igbp.sv.internetborder.se. tial to be transformative and, in most cases, can 4 See http://www.pages-igbp.org. only be achieved through a continuation of scientiﬁc 5 See http://www.scar.org/.
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62 SCIENTIFIC OCEAN DRILLING Challenge 3: What Controls Regional Patterns of the quality of proxy temperature and pCO2 reconstructions Precipitation, Such as Those Associated with Monsoons from scientiﬁc ocean drilling records. This challenge has or El Niño? great potential for societally relevant outcomes, especially in quantifying and understanding the processes involved in This challenge focuses on better understanding of ampliﬁed temperature changes at the poles. Polar ampliﬁca- regional climate variability, with speciﬁc focus on changes tion is strongly linked with responses of ice sheets and sea to the Paciﬁc El Niño-Southern Oscillation (ENSO) due to level, which are addressed in the discussion of Challenge warming and associated dramatic impacts on precipitation, 2. The continued focus on this topic places scientiﬁc ocean drought, cyclonic activity, and the Asian monsoon. The aim drilling at the forefront of transformative science. of this topic is to quantify decadal and longer-term variabil- This challenge also identiﬁes climate system sensitivity ity in regional climates and hydrological cycles, to support and the performance of IPCC climate models under different development of regional climate models on intermediate CO2 concentrations as areas where pre-Quaternary proxy (10 yr-1 kyr) time scales, and to consider potential extreme temperature data are needed to increase understanding. events, such as ﬂoods and droughts. The challenge requires Differences in climate sensitivity between data and models zonal and meridional transects of temperature gradients at low CO2 levels (<400 ppm) raises the question of other and their seasonal and longer-term variations, coupled with underappreciated but important feedbacks. records of past intermediate and deepwater overturning. Sedimentary records from continental margins would need to Challenge 2: How Do Ice Sheets and Sea Level Respond be supported by synchronous continental records from lake to a Warming Climate? sediments, ice cores, and speleothems. Scientiﬁc ocean drilling in the equatorial Paciﬁc identi- This challenge encompasses three areas of critical and ﬁed weakening of the Paciﬁc zonal temperature gradient transformative emphasis. The ﬁrst area involves the need and permanent El Niño-like conditions during the Pliocene. for more globally distributed atolls and coral reef records The reasons for these changes are unclear. The Pliocene is to constrain the rate, amplitude, and melt water source for one of the best geological analogs for future warming, and, sea level rise since the last glacial period, which is key to because El Niño has a major impact on global weather and understanding the rate and pattern of future sea level rise. moisture patterns, the study of this and similar past warmer The second area pertains to spatially distributed sea level climates has a high potential to improve understanding of records for pre-Quaternary warm climate analogs such as the the coupled ocean-atmosphere system. However, more data Pliocene (5-3 myr), which allow ice sheet-climate and proxy from scientiﬁc ocean drilling needs to be integrated with ice volume models to be veriﬁed. This issue is important, but coupled ocean-atmospheric climate modeling. Although difﬁculties exist with reconstructing sea level amplitudes by some progress can be made through the application of new applying backstripping6 methods to continental margin drill temperature proxies to legacy cores, the large geographic core records. Getting these types of spatially distributed scale of the problem requires that many new, strategically cores requires mission-speciﬁc expeditions and the ability located drill cores be obtained to achieve the necessary high to drill transects in difﬁcult drilling environments, which spatial and temporal resolutions. Because current numerical can be costly and often need long lead times to develop models cannot simulate permanent El Niño-like conditions successful research strategies and the necessary pre-cruise without prescribing initial sea-surface temperatures, meeting site survey information. Finally, the ability to locate drill this challenge requires close collaboration among groups cores proximally to ice sheets, which is the subject of the working on model and proxy development. Developing third area, is critical to the success of this challenge, because hemispheric and regional temperature gradients for past cli- these sites provide direct physical evidence of variability in mate states through targeted drilling is needed to achieve this sea ice behavior and past ice sheet extent. This challenge is and other theme challenges. The record of abrupt millennial- very important in terms of societal relevance, has potential scale changes in ENSO above inter-annual variability, which for transformative discovery, and can only be achieved by has been identiﬁed in speleothems and corals, could also be continued scientiﬁc ocean drilling. Drilling near ice sheets explored through targeted high-resolution sediment cores. and improved sediment recovery in high-latitude regions are However, achieving the necessary resolution is generally dif- important technical challenges that need to be addressed by ﬁcult in oxygenated deep ocean regions, where bioturbation the next phase of the program. smoothes the records. The prospect of achieving regional climate models on decadal time scales has lately been given considerable atten- 6 “Backstripping” refers to a technique in which sediments are progres- tion. Several European Union member states (e.g., France, sively removed from a basin in order to determine its subsidence and sedi- the Netherlands, and Sweden) have invested in research mentary history. In addition to sediment loading, corrections for changes in funding and infrastructure and have launched a joint research sea level, sediment compaction, and paleobathymetry are needed to separate program to look at modeling on this time scale. The U.S. sci- out the sedimentary signal from thermal, crustal, and tectonic changes (Miall, 1997 and references therein).
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63 ASSESSMENT OF ILLUMINATING EARTH’S PAST, PRESENT, AND FUTURE entiﬁc community is aware of these climate modeling needs high-resolution ocean sediment cores and of the relationship (e.g., Cane, 2010), and NSF supports the research through to environmental change at a range of time scales has clear targeted calls within the context of climate, energy, and synergy with time series of climate proxies (e.g., tempera- sustainability (e.g., decadal and regional climate prediction ture, pCO2) that document major environmental perturba- using Earth system models, water sustainability and climate tions. Another area of connection is with Challenge 13 in change). A number of related programs exist within NSF’s Earth in Motion, which focuses on carbon ﬂow and storage Directorate for Geosciences; better integration between in the seaﬂoor. Understanding carbon cycle perturbations in those programs and scientiﬁc ocean drilling could support general and the Cenozoic evolution of atmospheric carbon advances in this area. dioxide in particular, especially their relationship to Earth’s Finally, this challenge focuses on improved understand- surface temperature during past warmer times, clearly links ing of the role of tectonics and uplift on atmospheric circu- the climate objectives discussed in this theme with borehole lation and precipitation patterns, as well as the inﬂuence of observatory science discussed in the Earth in Motion theme. mountains and high terrain on erosion, precipitation, weath- ering, and CO2 drawdown through the silicate weathering Linkages with NSF and Other Programs cycle. Although having less immediate societal relevance, this much longer term process is important for understanding The science plan attempts to acknowledge linkages the Cenozoic evolution of atmospheric greenhouse gas con- with continental margin drilling programs such as ICDP, centrations, ocean nutrient production, and the carbon cycle. ANDRILL, and SHALDRIL (Shallow Drilling on the Ant- arctic Continental Margin). These programs are signiﬁcant in the context of achieving transects from shallow marine Challenge 4: How Resilient Is the Ocean to Chemical to deep ocean settings, as well as in expeditions in season- Perturbation? ally ice-covered environments. However, the science plan This challenge focuses on the carbon and nitrogen provides little discussion of how these collaborative models cycles, has the potential for transformative science, and is could be advanced and implemented and how they could be among the most societally relevant challenges in the cli- balanced with mission-speciﬁc platforms. The science plan mate theme. This challenge involves developing a better also identiﬁes linkages that need to be developed between understanding of ocean resilience to large perturbations in climate modeling programs and climate proxy development atmospheric CO2 and ocean acidiﬁcation, building on one of programs funded by NSF, including those at the National the major successes of IODP (see Box 4.2 on the Paleocene- Center for Atmospheric Research, and other international Eocene Thermal Maximum [PETM]). The challenge identi- partners and funding agencies. Finally, achievement of these ﬁes ocean eutrophication and oxygen depletion as key issues challenges, especially Challenge 3, will require close integra- that can be addressed by scientiﬁc ocean drilling. In addition, tion with on-land climate and tectonics research communities the challenge poses a question about the length of time it that work on continental margins and mountain systems. takes for the ocean to neutralize carbonic acid following an abrupt increase in atmospheric CO2. Continued development THEME 2 —BIOSPHERE FRONTIERS: and application of CO2 and carbonate system proxies (e.g., DEEP LIFE, BIODIVERSITY, AND boron isotopes, boron/calcium ratios in carbonate fossils, ENVIRONMENTAL FORCING OF carbon isotopic variations in alkenones, and other molecular ECOSYSTEMS organic compounds) will be required to address these issues. Although this challenge is of high importance, it is the most This theme outlines three main challenges: the origins weakly justiﬁed within this theme. The science plan does not and importance of subseaﬂoor microbial communities; limits present a clear strategy for how future scientiﬁc ocean drill- to life in the deep biosphere; and the relationship between ing will provide further insights on what is already known. marine ecosystems and changes in the environment. Of Previous successful drilling of the PETM and the Eocene- all of the challenges in this theme, some are quite novel, Oligocene boundary (Coxall et al., 2005; DeConto et al., while others represent the continuation of present scientiﬁc 2008), however, has demonstrated that the current scientiﬁc ocean drilling work. This area of research is new, exciting, ocean drilling program has a strategy for and is capable of and cutting-edge, particularly with respect to microbiology successfully addressing this challenge. within igneous rocks and linkages between marine organism evolution and environmental changes. The possibility of an extensive population of microbes Synergies Between This and Other Science Plan Themes living beneath the seaﬂoor raises many important and intrigu- There are linkages between the challenges in this theme ing questions about the limits of microbial life, the role of and Challenge 7 in Biosphere Frontiers regarding the sen- marine microbes in essential biogeochemical cycles, and sitivity of ecosystems to environmental change. Increased the origin and evolution of life on Earth and other planets. understanding of evolutionary events that are recorded in Scientists are presently very much in the exploratory phase
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64 SCIENTIFIC OCEAN DRILLING of some of these research areas, especially with regard nities has been accomplished compared to the sedimentary to the application of next-generation “-omic” approaches microbial community. First-order questions concerning the (e.g., DNA and RNA metagenomic sequencing, proteomic origin and composition of igneous rock-hosted communi- analyses) that allow for detailed examination of the diver- ties still need to be addressed, and the interactions between sity, activity, and evolution of microbes in the subseaﬂoor. sediment and rock communities explored. As new observa- However, exactly how to couple small-scale studies of tory tools (CORKs; Circulation Obviation Retroﬁt Kits), subseaﬂoor microbiology with large-scale biogeochemistry instrumentation (in situ biosensors, tracer experiments), and remains challenging. Because microbial biomass in marine hard-rock drilling techniques combine with microbiological rocks and sediments may have planetary-scale consequences, and molecular techniques, exploration of the subseaﬂoor execution of these challenges is critical for success of the habitat in oceanic rocks will advance considerably in the next phase of scientiﬁc ocean drilling. next phase of scientiﬁc ocean drilling. Understanding the microbiology of the deep seaﬂoor can only be accomplished through scientiﬁc ocean drilling. Challenge 6: What Are the Limits of Life in the Given the large amount of data on sediment-hosted microbial Subseaﬂoor? communities that has already been collected by scientiﬁc ocean drilling, and the ability of microbiologists to now Marine microbes thrive in diverse and extreme environ- access “clean” crystalline rock, there is great potential for ments that push the known limits of life. Challenge 6 would transformative science in this compelling area of research. extend understanding of the limits of microbial life on earth This potential includes the interaction of microbial commu- in a transformative way, and its aspects (e.g., collection of nities at the interface between sediments and crust, and the extremely deep microbes) can only be accomplished through use of drill-hole observatories to advance understanding of scientiﬁc ocean drilling. The committee believed that this subseaﬂoor microbial communities. challenge would integrate well with Challenge 5, given that the study of microbial life in rocks and sediments will nec- Although not speciﬁcally identiﬁed in the science essarily include determining where in temperature-energy- plan, identifying the synergies in understanding pressure space these organisms are surviving. Although ecosystem dynamics in the deep sea— from microbes cataloging the diversity of life in these different extremes to viruses to eukaryotes, both living and fossil—is a is important, in situ technologies such as biosensors or fertile way to advance the science. downhole activity enrichments, for example, could also be used to examine the limits of life. Laboratory experiments will also assist in deﬁning the limits of life and are critical Challenge 5: What Are the Origin, Composition, and for strengthening ﬁeld collections and experiments. Finally, Global Signiﬁcance of Subseaﬂoor Communities? although the connections between life in the subseaﬂoor The study of sediment microbiology has been an impor- and the origins of life on Earth are intriguing, the commit- tant aspect of both ODP and IODP, with scientists on numer- tee believed that stronger experimental linkages could be ous expeditions obtaining representative cores throughout made between currently measurable limits to life, laboratory the global ocean. Progress continues in the quantiﬁcation simulations of abiotic carbon and energy generation in the and description of sediment-hosted microbial communities subseaﬂoor, and the origins of life. through a variety of microscopic and genetic tools, and the microbial community is poised to make signiﬁcant strides in Challenge 7: How Sensitive Are Ecosystems and addressing some of the overarching questions related to the Biodiversity to Environmental Change? impact of microbial communities on geochemical transfor- mations by moving beyond “who is there and how many” to Understanding of abrupt environmental change and the “what is the activity, function, and contribution of sediment role of CO2 on marine ecosystems has important implica- communities to carbon, sulfur, and iron cycling?” Speciﬁc tions for current anthropogenic change and great potential missions and experiments to push our understanding of sedi- for transformative science with strong societal relevance. ment communities to this next level have great potential for In particular, past environmental perturbations potentially transformative science. driven by CO2 may have occurred at time scales similar In contrast to sediment microbiology, the study of to anthropogenically driven change, providing an opportu- microbial life in igneous rocks is a relatively new facet of nity to study biological consequences of rapid changes in scientiﬁc ocean drilling, and there is yet to be a drilling expe- atmospheric composition. Understanding the patterns and dition dedicated to igneous rock-hosted subseaﬂoor micro- mechanisms of how marine ecosystems adapt to abrupt biology. Although studies from the 1990s employed various environmental change and longer-term orbitally forced envi- DNA stains to drilling-recovered rocks and suggested the ronmental change also has great potential for transformative presence of microbes in basalt alteration zones, much less understanding of biological systems on Earth and is on the global sampling and detailed analyses of indigenous commu- cutting edge of new science. This challenge provides justiﬁ-
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65 ASSESSMENT OF ILLUMINATING EARTH’S PAST, PRESENT, AND FUTURE cation for the need to study marine ecosystem response and implications in the United States and beyond. The second is organismal evolution at large scales, which requires samples the unique technological challenge presented by microbiol- obtained through scientiﬁc ocean drilling. Such studies ogy during drilling operations in terms of sampling, process- would complement studies of ecosystem and biodiversity ing, and instrument construction. sensitivity in non-marine samples (e.g., outcrops, etc), which are at smaller spatial scales than those possible in the oceans Synergies Between This and Other Science Plan Themes for Jurassic and younger age strata. This challenge has strong links to the climate chal- There are natural synergies between Challenges 5 and 6 lenges in the previous theme. For example, Understanding in this theme and Challenges 10 (Earth Connections; chemi- Climate’s Influence on Human Evolution (NRC, 2010) cal exchanges between the ocean and the crust) and 14 (Earth highlights continent-ocean and climate-evolution linkages in Motion; ﬂuid ﬂow in the crust), but they could have been by proposing to drill not only lake strata spanning the time better developed in the science plan. For example, the use of human origin in the relevant geography, but also marine of borehole CORK observatories to link hydrogeological, strata adjacent to Africa that received inputs from rivers with chemical, and microbiological observations is essential drainage areas covering the areas critical for human evolu- for integrating and understanding life within basaltic crust. tion. The goal is to link hominin evolutionary and ecological Borehole observatories and the time series measurements history with the high-resolution lacustrine record of environ- they entail are discussed in great depth in Challenge 14, but mental, particularly climatic, change within Africa and with they could have been more formally linked to the challenges the already developed global marine chronology. in this theme. There are also obvious synergies between Challenge 7 and the climate theme regarding the sensitiv- ity of ecosystems to environmental change, especially in Other Challenges and Opportunities understanding major climate perturbations that can impact The science plan misses the potential opportunity to the evolution of life. study (living) eukaryotes (such as fungi and protists) and viruses in the subseaﬂoor biosphere, information on which Linkages with NSF and Other Programs is essential to truly understand subseaﬂoor ecology and the ecosystem that may exist there. Furthermore, understand- The challenges in this theme have many strong link- ing living eukaryotes could perhaps lead to clearer linkages ages to NSF programs and initiatives. Some important links to the fossil eukaryotic community, with stronger overlap include the National Deep Submergence Facility and the between Challenges 5 and 7. The subseaﬂoor may host life UNOLS (University-National Oceanographic Laboratory forms that are completely unknown; new life-detection tools System) ﬂeet. Many subseaﬂoor microbial studies, includ- that do not depend on DNA, for example, could be employed ing those with CORK operations, require deep submergence for studying this potentially novel biosphere (e.g., NRC, assets to sample and service the CORK instrumentation, 2007). The study of life in the subseaﬂoor will also require adding cost and scheduling complexity. In addition, changes changing the way that cores are stored after collection. in marine environments can be expressed in continental Unlike most of the other disciplines involved in scientiﬁc environments and thus links exist with continental dynam- ocean drilling, microbiology core samples need to be frozen ics, sedimentary geology and paleobiology, and other areas and/or preserved with a ﬁxative when collected. Most of within NSF (such as Systematic Biology and Biodiversity the current core repository is not useful for microbiologists Inventories). Opportunities also exist with cross-cutting studying subseaﬂoor life, which needs to be addressed in the programs such as Dimensions of Biodiversity, C-DEBI, and next phase of the program. As suggested by the large number ICDP. Programs of interest outside of NSF include the Sloan of proposals submitted to IODP that focus on subseaﬂoor Foundation’s Deep Carbon Observatory and the Department life and the funding of new programs focused on the deep of Energy’s methane hydrate and bioremediation programs. biosphere (e.g., the Sloan Foundation’s Deep Carbon Obser- vatory, the NSF-funded Center for Dark Energy Biosphere THEME 3—EARTH CONNECTIONS: DEEP Investigations [C-DEBI]7), there is a large and growing PROCESSES AND THEIR IMPACT ON group of scientists interested in studying microbial life in EARTH’S SURFACE ENVIRONMENT the subseaﬂoor. Finally, justiﬁcation for continued research in this area could be strengthened by consideration of two This theme has four key challenges related to the com- issues. The ﬁrst is potential biotechnological applications of position and structure of the upper mantle, architecture of novel organisms and genes recovered from the subseaﬂoor, the ocean crust, chemical cycling between ocean crust and especially under extremes of temperature and pressure. This seawater, and relationships between subduction zones and is a strong point of interest for microbiology, with societal continental crust. These challenges deal with the chemical and energy exchanges between the solid Earth, ocean, and 7 See http://www.darkenergybiosphere.org/.
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66 SCIENTIFIC OCEAN DRILLING atmosphere, as well as their impact on the environment be overcome before such a deep hole could be drilled (Box throughout geologic time. 6.1). Opinions vary about the utility of recovering samples of This theme explores chemical and energy exchanges oceanic crust and mantle at just one location, even if direc- within Earth that lead to a distinctive layered internal struc- tional drilling could be achieved. Mantle heterogeneity may ture, the tectonic activity that shapes the surface environ- preclude broad generalizations about processes, especially ment, and magmatic activity that builds the continents and when based on samples recovered at a single location. ocean basins. The theme also deals with the importance of Nonetheless, first-order petrologic and geochemi- hydrothermal alteration in ocean crust, including how this cal questions could deﬁnitely be addressed by materials process impacts seawater chemistry through time, as well recovered from a hole to the Moho (often referred to as the as mantle rheology and magma generation in subduction “Mohole”). In addition to the signiﬁcant technical challenges zones. Finally, the theme also encompasses the importance involved in drilling to the Moho, recovering Moho samples of convection, both in the mantle where it may play a role might not be the biggest scientiﬁc contribution from the in driving plate tectonics and in the outer core where it is drilling attempt. The presence of exposed, serpentinized responsible for generating Earth’s magnetic ﬁeld. peridotite at slow spreading ridges suggests that in some One of this theme’s main messages is the great need places the Moho is the boundary between maﬁc oceanic to drill more deeply into and through intact ocean crust. crust and ultramaﬁc upper mantle, while in other locations it Although the science plan emphasizes drilling to the is a serpentinization front separating altered from unaltered Mohorovičić discontinuity (Moho), an ocean drilling objec- peridotite. It would be valuable to have good estimates of the tive with a long history (see Box 6.1), another aim could be relative abundance of those two different kinds of Moho. The to obtain good recovery of intact oceanic crust samples along importance of recovering intact samples of oceanic crust and the way. Some of the other objectives related to spatial vari- mantle may lie less in reaching the destination of the Moho, ability in oceanic crustal structure and evolution could be bet- and more in the recovery of materials drilled along the way. ter addressed with multiple, carefully chosen, shorter holes. Having the ability to determine the nature of petrologic and Multiple, shorter holes could be very helpful in understand- geochemical processes in the mantle that lead to the building ing ocean crust hydration (serpentinization), carbonation, of oceanic crust would be a signiﬁcant development, possibly and oxidation, where ultramaﬁcs that are out of equilibrium leading to transformative science. with their environment (usually through uplift processes) are altered through contact with water into serpentinite minerals. Challenge 9: How Are Seaﬂoor Spreading and Mantle Melting Linked to Ocean Crustal Architecture? Drilling intact ocean crust with high recovery rates would allow much to be learned, although a speciﬁc This challenge states that understanding linkages target of drilling to the Moho may not be techni- between seaﬂoor spreading, mantle melting, and ocean crust cally viable and could be cost-prohibitive. Better architecture requires not only recovery of core material from understanding of oceanic mantle serpentinization intact crust from a single Moho location, but also shorter is essential, and could be achieved through shorter holes drilled through tectonically disrupted ocean crust. holes drilled in disrupted ocean crust. Fundamental differences between fast- and slow-spreading mid-ocean ridges and the processes that result in magmatic vs. amagmatic spreading are still poorly understood. These Challenge 8: What Are the Composition, Structure, and are ﬁrst-order plate tectonic phenomena. The prevalence of Dynamics of Earth’s Upper Mantle? detachment faulting at slow-spreading ridges is also a sci- The single longest-running goal of scientiﬁc ocean drill- entiﬁc topic of great signiﬁcance. This challenge states that ing has been recovering samples from the Moho, prompting linking a series of shorter holes with geophysical investiga- the very ﬁrst ocean drilling project (Project Mohole; Box tions and seaﬂoor mapping would add to the understanding 1.3). Despite more than 50 years of scientiﬁc discoveries, of oceanic lithosphere structure that would be gained from there has been little progress toward that goal. Few drill cores drilling to the Moho. Because of the paucity of holes in penetrate deeply into crystalline ocean crust, and none has crystalline basement, better understanding would almost remotely approached the Moho. The science plan states that certainly result. However, signiﬁcant difﬁculties have been the scientiﬁc ocean drilling community is working concert- encountered when attempting to drill directly into crystal- edly toward this goal, and that doing so is scientiﬁcally sig- line ocean crust that lacks sediment cover, especially young niﬁcant. Several community workshop reports on this topic volcanic crust, which could prevent progress on this front discuss the scientiﬁc merits in greater detail than that found unless new technologies are developed. in the science plan. Clearly, it seems that a substantial part of The magnetic ﬁeld is a shield that allows planets to the scientiﬁc ocean drilling community is ready to embrace maintain an atmosphere and is therefore a prerequisite for life this project. The committee discussed this topic at length on Earth. In addition, any major change in Earth’s magnetic and recognized technological challenges that would have to ﬁeld will impact important infrastructure such as telecom-
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67 ASSESSMENT OF ILLUMINATING EARTH’S PAST, PRESENT, AND FUTURE Box 6.1 Technological Challenges in Drilling to the Moho The first scientific ocean drilling was undertaken as a challenge to drill to the Moho (NRC, 2000). The science plan for the next proposed phase of scientific ocean drilling has renewed this goal. At the beginning of Project Mohole, deepwater technology was in its infancy, with only a few ships capable of drilling in water depths greater than 1,000 m. Although Project Mohole engineers created new methods and technology to achieve scientific ocean drilling goals (see Box 1.3), they were unable to reach the depths needed to drill to the Moho. Since that time, the deepwater drilling and production industry has consistently drilled in water depths greater than 2,500 m, and the JOIDES Resolution reached greater water depths using a riserless drilling system. Advances in materials science, new control systems, and better automation have all contributed to greater abilities in floating production platforms and riser drillships, allowing them to move into very deep water (3,000-4,000 m). This leads to a question: using existing deepwater technology, how can the Moho be drilled with the highest probability of success? Moho drilling involves two major risks: subsea risk arises from drilling very deep water, with issues regarding currents and open water surface conditions, and drilling risk arises from drilling in more than 6,000 m of rock with poorly known properties and composition (e.g., high temperatures). The risk of drilling rock at high temperatures and unknown condi- tions is a topic that would need to be addressed thoroughly before deciding on a target for Moho drilling. A wide range of opinions exist regarding the viability of using existing scientiﬁc ocean drilling platforms to drill the Moho. The committee believes that the technical capabilities of the riser drillship Chikyu are insuf- ﬁcient to ensure success in this endeavor. Even though modern riser-equipped drill ships have achieved outstanding results, drilling on station for long periods of time is still challenging because of risks in handling the riser. Modern deepwater drill ships can drill to 6,000 m while maintaining station, even in severe weather conditions and strong currents. However, the long duration of a Moho project is significantly different than commercial deepwater drilling, and equipment failure over time could lead to operational delays and increased expenses associated with pulling the riser and the blowout preventers. By comparison, a fixed platform only needs to install the riser once, and blowout preventers are at the surface, mitigating subseafloor risk. Fixed platforms also have increased storage, better support facilities, and the ability to drill in extreme weather. Tethered deepwater platforms, for example spars or semi-submersibles, are types of fixed platforms that can be moored in water depths up 2,4501 and 3,000 m, respectively. A fixed or tethered platform may be superior to a mobile drilling platform for the purposes of Moho drilling. If the goal of drilling to the Moho is to be achieved, additional resources for new technologies and perhaps alternate drilling platforms would need to be considered. 1 See http://www.shell.com/home/content/aboutshell/our_strategy/major_projects_2/perdido/overview/. munications and power grids. Geomagnetism, another area excursions from dating continental and marine sediments of scientiﬁc study that will beneﬁt from continued scientiﬁc could provide a new high temporal resolution magnetic time ocean drilling, encompasses three aspects with the poten- scale, in conjunction with currently available geomagnetic tial for transformative change. First, continuous sediment polarity reversal stratigraphy, for dating climatic and envi- records collected from a select number of sites could yield ronmental events. Third, the collection of continuous, intact time series of geomagnetic dipole declination, inclina- cores of fast-spreading ocean crust, when supplemented by tion, and relative paleointensity. These data, best retrieved opportunistic sampling of peridotite and serpentinite from through scientiﬁc ocean drilling, could provide benchmarks tectonically exposed upper mantle, could provide essen- for evaluating numerical models that have been proposed to tial ground-truthing opportunities for proposed sources of describe the ﬂuid core motions thought to be responsible for marine magnetic anomalies. These cores could provide the magnetic dipole and its reversals and excursions. Better valuable information for modeling some anomaly features models and more data would lead to increased understand- that are currently not well understood, including skewness, ing of the ongoing changes in intensity and direction of the amplitude variations, and other parameters that allow for present geomagnetic ﬁeld. Second, validation of true dipole reconstruction of oceanic plate formation and aging.
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68 SCIENTIFIC OCEAN DRILLING Another opportunity for signiﬁcant scientiﬁc break- much could be learned with such a strategy, but has concerns through lies in improved documentation of the emplacement about such an ambitious plan under the current uncertain history of oceanic large igneous provinces (LIPs). Currently, funding climate. If such a strategy is to be employed, it some researchers theorize that LIP emplacement occurred would be best to plan drill holes that could contribute to over short time intervals of no more than 800 kyr, which multiple drilling objectives in addition to studying chemical could explain pulses of CO2 release into the atmosphere and exchanges between seawater and crust. possible relationships to mass extinction events. Very little scientiﬁc ocean drilling and core recovery has been done on Challenge 11: How Do Subduction Zones Initiate, Cycle submarine LIPs, and the paucity of materials has resulted in Volatiles, and Generate Continental Crust? the inability to answer signiﬁcant questions about their tim- ing and origin. Increased activity on this topic, with signiﬁ- Currently, most research focused on the area of subduc- cantly better core recovery, would lead to transformational tion zone initiation, cycling, and generation of continental understanding of oceanic LIPs and the implications of their crust is based on observations and elemental analyses from emplacement. ophiolites, which have mid-ocean ridge geochemical signa- tures overprinted by arc-like elemental distributions from younger magmatism. The proposed studies in the science Challenge 10: What Are the Mechanisms, Magnitude, plan invoke subduction initiation, at least in intra-oceanic and History of Chemical Exchanges Between the Oceanic settings, along fracture zones that are far from ridge systems Crust and Seawater? and occur in signiﬁcantly cooled lithosphere. Although this A broad misconception in the geological research challenge’s concept is indeed important, the science plan community is that the existence of many scientiﬁc ocean does not provide a clear approach on how it could be tack- drilling sites throughout the ocean basins is equivalent to led. Information supporting this challenge is vague, with signiﬁcant sampling of the crystalline crust and underlying no identiﬁcation of potential drill sites and a lack of clarity upper mantle. This challenge underscores the fact that little about whether any exist, which makes it difﬁcult to assess drilling has occurred in crystalline basement and that core whether scientiﬁc ocean drilling could contribute to greater recovery has not been good. Designing drilling objectives understanding in this ﬁeld. Because of this lack of clarity, to increase the volume and spatial distribution of hard rock transformative science is not a likely outcome. cores will result in signiﬁcant advances that are likely to Cycling of volatiles in subduction zones has also been transform understanding of the structure and composition a topic of considerable research since cold seeps and mud of oceanic lithosphere. volcanoes were discovered close to or within accretionary As stated under Challenge 8, quantifying the volume of prisms. Observational data have been collected, leading to altered maﬁc crust and serpentinized ultramaﬁc mantle that some quantiﬁcation of ﬂuxes. Certainly, additional work results from chemical exchanges between the solid Earth could result in new discoveries and further reﬁne ﬂux esti- and seawater are signiﬁcant pursuits likely to provide trans- mates. Scientiﬁc ocean drilling in this area would likely formative understanding of the carbon cycle. For example, contribute to the very signiﬁcant work that has already been studying the distribution of intact vs. tectonically disrupted done. Additionally, the NSF-funded GeoPRISMS (Geody- crust would lead to better understanding of the long-term namic Processes at Rifting and Subducting Margins) and carbon cycle. However, water-rock interaction has been a predecessor MARGINS programs have led to much work on topic of concerted research for at least two decades. It is understanding the “subduction factory.” As with subduction uncertain if truly transformative science can be accomplished initiation, further work in the next phase of scientiﬁc ocean by continued scientiﬁc ocean drilling investigations aimed drilling would be useful but may not be transformative. at such targets. Broad estimates of geochemical and thermal exchanges between various reservoirs can be made with Synergies Between This and Other Science Plan Themes current data; reﬁning those estimates could be a priority within the scientiﬁc ocean drilling community. However, The challenges in this theme have a natural ﬁt with all the ability to place reasonable constraints on the volume of of the challenges in the Earth in Motion theme (discussed serpentinized mantle requires additional drilling and could in the next section). These challenges focus on processes dramatically transform understanding of carbon uptake in controlling geohazard occurrence, the ﬂow and storage of mantle rocks and the long-term carbon cycle. This would be carbon in the ocean crust, and the role of ﬂuids in seaﬂoor one of the more signiﬁcant ocean drilling contributions for processes. Challenge 11, which includes understanding how better understanding of water-rock interaction. subduction zones initiate, has natural synergy with the study The science plan states that the best strategy to address of mechanisms that cause earthquakes (Challenge 12) and this challenge would be a series of drilling transects across implications for cycling of crustal ﬂuids (Challenge 14). ocean basins, from youngest to oldest oceanic crust and in Further study of the architecture of Earth’s crust in Chal- a variety of different regions. The committee believes that
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69 ASSESSMENT OF ILLUMINATING EARTH’S PAST, PRESENT, AND FUTURE lenge 8 has links with Challenge 13, especially in the role tsunami, and landslides; subseaﬂoor carbon sequestration of serpentinization. and cycling; and subseaﬂoor ﬂuid ﬂow processes. Linkages with NSF and Other Programs Challenge 12: What Mechanisms Control the Occurrence of Destructive Earthquakes, Landslides, and Tsunami? There is considerable room for cooperation between activities that would occur under this challenge and the The science plan notes that processes related to land- NSF GeoPRISMS Program, which in its earlier existence slide, earthquake, and tsunami generation comprise “the as MARGINS actively supported research on the topics only large-scale natural hazards for which no short-term covered under Challenge 11. Together, GeoPRISMS and prediction exists.” Any signiﬁcant increase in the short-term the next phase of proposed scientiﬁc ocean drilling could predictive capability for great earthquakes and tsunamis make more concerted progress on signiﬁcant topics if their would be truly transformative. Acquisition of samples from objectives are tightly integrated. In addition, natural linkages the depths at which slip originates and the ability to moni- exist between this theme and those of ICDP, the InterRidge tor physical and chemical changes in the fault zone would Program, and the Deep Carbon Observatory. For example, provide critical new information on how frictional properties further investigation of submarine LIPs will beneﬁt from of faults change with time as a result of diagenesis, changes continued integration with terrestrially based studies. in ﬂuid pressure, or other factors. Many of the largest and most destructive faults are located offshore, so sampling and in situ measurements of these faults can only be achieved THEME 4—EARTH IN MOTION: PROCESSES by scientiﬁc ocean drilling. Because of the great depth and AND HAZARDS ON HUMAN TIME SCALES potentially corrosive conditions in these locations, these are The fourth theme of the science plan concerns scientiﬁc difﬁcult and expensive objectives that can only be achieved objectives that require physical measurements or samples at a small number of sites. from boreholes as a function of time. Because physical and This challenge does a good job of enumerating both the chemical properties of oceanic sediments and rocks change difﬁculties and societal beneﬁts of addressing this challenge. in response to ﬂuid ﬂow and subseaﬂoor biological activity, The likely heterogeneity of fault slip surfaces suggests the the snapshots in time provided by conventional drilling and need to collect a global range of seismological, geodetic, and sampling are not adequate to answer many of the challenges geologic measurements from active faults and incipient land- presented in previous themes or explicitly discussed in the slides. Although scientiﬁc ocean drilling will be required to context of this theme. For example, temporal changes in ﬂuid collect some of these measurements, well-established links composition and ﬂow rates must be measured to understand with other initiatives (e.g., continental drilling) will also be ecological changes beneath the seaﬂoor, as in Challenge required to obtain the complementary information that is 7. Such measurements have been a part of past scientiﬁc needed to fully address the challenge. For example, the NSF/ ocean drilling programs since 1991, with the ﬁrst CORK ICDP/EarthScope SAFOD (San Andreas Fault Observatory installation in Middle Valley on the Juan de Fuca Ridge at Depth) effort to sample and instrument an active strand (Becker and Davis, 2005). However, these measurements of the San Andreas Fault at seismogenic depth provides have been few and far between, mainly because of installa- complementary information on the challenges of maintaining tion expenses and the need for extensive background studies an observatory in a fault zone at several km depth as well as to provide a geologic context for time series measurements. on alteration of fault zone rocks. The relative importance of the information derived from the The past decade’s discovery of episodic tremor and slip limited experiments to date suggests that demand will almost and of very low frequency (slow) earthquakes in subduc- certainly grow in the next decade as new scientiﬁc questions tion zones also provides a potential speciﬁc new target for develop from the information provided by DSDP, ODP, and drilling. The occurrence of this broad spectrum of fault slip IODP cores. behaviors at the down-dip edge of subduction megathrusts is currently being studied primarily by land-based networks Recent developments in ocean observing systems and a recently proposed ocean bottom seismic network in that facilitate data communication to shore-based Cascadia.8 Similar processes may also occur at the up-dip laboratories and in simpler, cheaper, specialized sen- edge of the megathrust, but remain poorly documented sor packages are likely to enable further growth of because of the lack of offshore seismic and geodetic stations borehole observatories. everywhere except offshore Japan. The science plan does not clearly enunciate the contribution of scientiﬁc ocean drilling The research objectives that require time series mea- to understanding these phenomena. Another important aspect surements are grouped into three closely linked challenges: understanding mechanisms related to major earthquakes, 8 See http://www.oceanleadership.org/wp-content/uploads/2010/05/ Casc_Facil_Wkshp_Report.pdf.
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70 SCIENTIFIC OCEAN DRILLING of subduction zone geohazards that was not included in the tiles through the seaﬂoor are actually much broader and are science plan is the extension of paleoseismic histories further encompassed to some extent within the next challenge. By into the past. Although coring via less expensive platforms quantifying the role of water-rock interactions in the carbon should remain the ﬁrst approach to deﬁning paleoseismic cycle, this challenge would lead to transformative discovery. histories of large submarine faults, scientiﬁc ocean drilling The volume of seawater ﬂowing in the subseaﬂoor aquifer is will be needed to extend these records farther back in time. unusually large, but it is unknown how that impacts carbon For example, short cores (less than 10 m long) have been suc- exchange between water and rock. Similarly, the science plan cessful at deﬁning the earthquake history for the past ~12 kyr discusses the role of serpentinization of exposed peridotite at in Cascadia (Goldﬁnger et al., 2011). Longer time series are slow-spreading ridges. Quantifying the elemental exchange needed to develop robust models for earthquake recurrence associated with that process would lead to more accurate patterns at major subduction megathrusts. modeling and would add signiﬁcantly to understanding of Scientiﬁc ocean drilling has the potential to improve the carbon cycle. forecasting and to provide early warnings of geohazards like earthquakes, tsunamis, and landslides. The science Challenge 14: How Do Fluids Link Subseaﬂoor Tectonic, plan emphasizes installation of observatories at the base of Thermal, and Biogeochemical Processes? landslides and at great depth in the seismogenic zone. How- ever, conventional coring and logging that can be used to This ﬁnal challenge encompasses a wide range of top- groundtruth seismic data, provide shallow holes for installa- ics that have already been partially discussed in the context tion of arrays of buried geodetic and seismic instrumentation, of previous challenges. Recent studies have revealed that and extend paleoseismic histories of major fault zones have the amount of ﬂuid being ﬂuxed through the ocean crust is equal, if not greater, potential for leading to transformative greater than previously thought and that changes in crustal new insights. As the next phase of scientiﬁc ocean drilling ﬂuid pressure and chemistry can change abruptly in response moves forward, it would be helpful to consider a broader to distant earthquakes. The global implications of this appar- range of studies that could be designed in collaboration with ently vigorous exchange between the crustal aquifer and the other national and international geohazard programs (e.g., ocean remain to be explored, and there is little doubt that GeoPRISMS, U.S. Geological Survey). continued exploration will yield new surprises. Calibration and veriﬁcation of subsurface ﬂuid ﬂow requires direct measurement at more than one site so that Challenge 13: What Properties and Processes Govern the more readily acquired proxies for ﬂuid ﬂow and chemical Flow and Storage of Carbon in the Seaﬂoor? exchange in the subseaﬂoor can be exploited, and results This challenge concerns better understanding of the from local studies can be extended globally. Such calibration role of the subseaﬂoor environment in the global carbon and veriﬁcation requires direct sampling of the subseaﬂoor cycle. Three speciﬁc aspects of this problem are highlighted: ﬂuid ﬂow rates and compositional changes, information that distribution and dynamics of gas hydrates in marine sedi- cannot be obtained without scientiﬁc ocean drilling and the ments; the fate of carbon dioxide when it is injected into the installation of long-term monitoring devices. seaﬂoor (carbon sequestration); and the impact of hydration Signiﬁcant potential exists for transformative scientiﬁc (serpentinization), carbonation, and oxidation of ultramaﬁc discovery related to studying subseaﬂoor hydrology. Much rocks by seawater and dissolved CO2. All aspects of this chal- will be gained from installation of monitoring networks lenge potentially have direct societal impacts. Gas hydrates related to seismic, geobiological, and other studies, but have potential importance as an energy source, while their there is also a signiﬁcant need for installations dedicated to destabilization in response to environmental change may long-term hydrological observations. Despite the availability trigger underwater landslides with consequences for coastal of decades of data from terrestrial hydrology monitoring communities. Ocean crust has been proposed as a possible networks, signiﬁcant aspects of the water cycle cannot be repository for excess carbon dioxide, a growing concern due quantified. Developing such broadly based quantitative to global warming, and ﬂuid-rock interactions may provide models of marine hydrogeology will take a signiﬁcant invest- a way to trap excess carbon in deeply buried solids. Serpen- ment of time, but the potential contribution to understanding tinization, meanwhile, may drive or facilitate a number of a wide range of phenomena makes this long-term effort a tectonic processes because of the release of heat, increase high priority. in volume, and lowering of shear strength of serpentine minerals. Measuring rates at which ﬂuids move through Other Challenges and Opportunities the subseaﬂoor and at which rocks and sediments respond requires in situ time series observations, and can beneﬁt Submarine geodesy is an aspect of this theme that is from controlled perturbation experiments. This challenge not discussed in the science plan, but one where long-term emphasizes the ﬂow and storage of CO2, but the implications observatories in the subseaﬂoor could potentially have a for understanding the ﬂux of carbon dioxide and other vola- transformative impact. With the advent of widespread acqui-
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71 ASSESSMENT OF ILLUMINATING EARTH’S PAST, PRESENT, AND FUTURE sition of continuous GPS data on the continents, geodesy has to the Climate and Ocean Change theme, especially with transformed the understanding of the spectrum of fault slip regard to a potential role for geoengineering in mitigating behaviors, revealing a continuum of spatial and temporal climate change. scales. Development of marine geodetic networks on the sea- ﬂoor would require stable baselines for measurement, which Linkages with NSF and Other Programs could perhaps be associated with borehole observatories to measure position and strain as a function of time. A focus on The scientiﬁc objectives of this theme dovetail with this type of interdisciplinary instrumentation could facilitate the objectives of many other national and international transformative understanding of active tectonics in the ocean. initiatives. There is a particularly strong symbiosis with the Ocean Observatories Initiative (OOI), which can enable high-resolution, real-time data ﬂow from instruments that Synergies Between This and Other Science Plan Themes can be deployed in boreholes. It is essential that planning As mentioned previously, Challenge 14 has natural syn- for these two programs be integrated so that boreholes and ergy with topics discussed in all of the previous themes. This observing systems are collocated when appropriate. A com- includes Challenges 1 and 4 (Climate and Ocean Change prehensive assessment of earthquake and tsunami hazards theme) on Earth’s response to higher CO2 concentrations should take into account the full spectrum of observations and resilience to changes in ocean chemistry; Challenges 6 from synergistic programs like EarthScope, GeoPRISMS, and 7 (Biosphere Frontiers theme) on the limits of life and Ocean Bottom Seismography Instrument Pool Cascadia Ini- ecosystem sensitivity in the subseaﬂoor; and Challenges 10 tiative, NEPTUNE Canada, OOI, and the Dense Ocean Floor and 11 (Earth Connection theme) on seawater-crust cycling Network System for Earthquakes and Tsunamis. and initiation of subduction zones. In addition, Challenge 13’s focus on carbon sequestration in the seaﬂoor is related
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