The Deep Biosphere

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The Deep Biosphere
Tom Kieft New Mexico Tech
DOSECC Conference on The Future of Continental
Scientific Drilling A U.S. Perspective
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Why study subsurface microbes?

• The majority of prokaryotic biomass appears to be
  in the subsurface (Whitman et al., 1998)
• Reveal unknown metabolic capabilities and
  ecosystems
• Applications of novel microbes
• Bioremediation of contaminated aquifers
• Understanding waste repositories
• Analogs for life on other planets?
• C sequestration

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Whos there?
microorganisms
macroorganisms
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How do they make a living?
Microbes couple oxidation of fuels (electron
donors) with reduction of oxidants (electron
acceptors). Subsurface Fuels Microbes near the
surface depend on photosynthetically generated
organic carbon. The deep biosphere may depend on
geochemically derived energy sources H2, CH4,
etc.
or lt 20 kJ/mole
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What are the rates of activity?
Life in the slow lane!
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The Deep Terrestrial Biosphere 25 years of
research

• Funding DOE, NSF, NASA Astrobiology, others
• Major Accomplishments
• Drilling and tracer technologies
• Extended known biosphere to gt4 km
• Revealed high biomass biodiversity
• Isolates in culture collections
• Linked microbial activity with geological
  interfaces
• Slow rates of subsurface microbial activity
• Discovery of subsurface lithoautotrophic
  microbial ecosystems (SLiMEs)

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EarthLab
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Shallow aquifers
tens of km
Terminal electron-accepting processes along a
flow-path. From Smith and Harris, 2007
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The Witwatersrand Deep Microbiology
Project Witwatersrand Basin, South Africa
Evander
3.0 Ga basement 2.0 Ga meteorite impact Uplift 2
km at 90 myr
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2.0 Ga
2.0 Ga
300 Ma
121oC
2.9 Ga
2.3 Ga
2.7 Ga
Basement 3.4 Ga
Thermal gradients
25oC/km
9-15oC/km
20oC/km
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Desulforudis audaxviator Ubiquitous in 3-km deep
groundwater Sulfate-reducer Novel
taxon Uncultured Genome has now been sequenced
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H2O
FeS2
Radiolysis
Geochemical Reactions
4H2 H SO42- -----gt HS- 4H2O
O2, H2O2
H2
SRB
Desulforudis audaxviator
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Flowing borehole sampling March 2006 Henderson
Mine, CO
Packer inserted in borehole
Filtering cells
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Henderson Mine, Colorado -- new bacterial
division dominates
Sahl et al., 2008
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Deep drilling into the Chesapeake Bay Impact
Structure
from Charles Cockell
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NELSAM (Natural Earthquake Laboratory in a South
African Mine)
DAFBIO instrumented borehole
Seismic events release H2
from T.C. Onstott, Princeton Univ.
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Microbial diversity declines with depth
Chinese Continental Scientific Drilling (CCSD)
project
No. of Taxa
5 km!
Depth (m)
from Hailiang Dong, Miami Univ.
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Opportunities to probe the deep biosphere via
continental drilling

• Select sites that can address one or more of the
  big scientific questions, e.g.,
• Mineralogy with potential for H2 generation
• Sites with high geothermal gradients to allow
  penetration of the 121C isotherm
• Drilling/coring in deep mines, e.g.,
  DUSEL-Homestake
• Plan up front for geobiological studies in
  drilling projects

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Deep Biosphere Major Research Questions (from
NSF Deep Science)

• How deeply does life extend into the Earth?
• What fuels the deep biosphere?
• How does the interplay between biology and
  geology shape the subsurface?
• What are subsurface genomes telling us?
• Did life on the earth's surface come from
  underground?
• Is there life as we don't know it?

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1. How deeply does life extend into the Earth?

• What are the factors that control distribution of
  life in the deep subsurface?
• Temperature?
• 121C current known upper limit.
• Geothermal gradient 10-60C/km, average
  20C/km.
• Temperature-limited biosphere may extend 2-12 km
  below land surface
• Pressure?
• Energy and nutrient availability?
• Pore space?
• A combination of these factors?

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2. What fuels the deep subsurface?

• Buried organic C
• Transported organic C
• Abiogenic chemical energy sources H2, CH4,
  ethane, propane, etc.

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Rock-Water Interactions that Generate Geogas
(H2), etc.

• Basalt-water interactions, e.g., in Snake River
  Plain basalt aquifers (Stevens and McKinley,
  1995 Chapelle et al., 2002)
• Serpentinization, e.g., at the Lost City vent
  (Kelley et al., 2005)
• Granite-water interactions, Aspo Hard Rock Lab,
  Sweden (Pedersen, 1997)
• Radiolysis of water, e.g., in the Witwatersrand
  Basin, South Africa (Lin et al., 2005, 2006).

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IODP as a model for integrating geobiology into
scientific drilling

• First cores for microbiology (mid-1980s)
• Deep Biosphere designated as one of three major
  themes (2003)
• Acquisition of bio sample handling and tracer
  technologies
• so far one cruise with Deep Biosphere as the
  major theme
• 3 more in the queue
• other cruises have included microbiology
• papers in high-profile journals Science and
  Nature
• increased funding, buy-in from multiple NSF
  programs

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Examples of NSF programs with potential to fund
subsurface geobiology

• Geosciences (GEO) - EAR
• Geobiology and Low-temperature Geochemistry
• Emerging Topics in Biogeochemical Cycles
• Biological Sciences (BIO)
• Life in Transition
• Microbial Systems in the Biosphere
• Possible new GEO-BIO node
• Other agencies, too e.g., DOE, NASA

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Technical requirements for geomicrobiological
sampling

• tracers
• Solute Br-, fluorochromes (e.g., rhodamine),
  perfluorinated hydrocarbons
• Particulate fluorescent carboxylated 1-µm
  microbeads
• core diameters gt2 inches preferred
• drilling methods are highly site specific.
• anaerobic glove bag
• core barrels should be steam cleaned, core barrel
  liners
• freezer onsite

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Drilling plans at DUSEL - Homestake
Integrated geohydrology, geophysics,
geomicrobiology
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0 m 7.5C
Geothermal gradient 22.3 C/km
2440 m 62C
4880 m 116C 16,000
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Drilling to great depth is cheaper if you start
in a deep mine
Drilling in Henderson Mine, CO
Drilling costs
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Recommendations

• Include the deep biosphere as a major scientific
  theme for deep continental drilling.
• Look for opportunities to integrate geomicro
  studies into each drilling project
• Add tracers and geomicrobiological handling as
  part of deep drilling tool kit.
• Use interdisciplinar deep geomicrobiological
  research as means of broadening the funding base
  for continental scientific drilling.