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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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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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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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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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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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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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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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