Emerging Views of SedimentBuried
Ocean Basement Biosphere
James P. Cowen
Department of Oceanography
University of Hawaii
jcowen@soest.hawaii.edu
Emerging Views of the Biosphere w/in Aging
Ocean Basement
• Ocean basement provinces
• Biosphere of aging basement
– Access—tough
– General physical (e.g., fluid flow; temperature)
and chemical characteristics
– Evidence of extant biosphere
– Speculated metabolic pathways
– Challenges and future research directions
Why do we care?
• Ocean basement is a huge volume
• Potential for extensive biomass
– Basalt to gabbro rocks
• Prone to alteration disequilibria
– Fluids circulate even in old basement
– Thermal, chemical gradients
• Potential for exotic metabolisms/strategies
• Analogue for extraterrestrial fluid covered, rocky
bodies
Detrick 2004
crust
ocean
basement
Ocean crust
Karson et al. 2002
Zone I: Ridge axis
— active exchange
— high/low temperature venting;
— sharp thermal / redox / chemical gradients
Zone II: Unsedimented ridge flank
— active (advective) exchange, low (to high ?) temperature venting
— poorly explored
~165 m
Diffuse
upwelling
Impenetrable
Zone III: Sedimented ridge flanks (a) and basin (b)
—increasing sediment cover;
—hydrologic seal at ~165 m thickness
—conductive heat / diffusive chemical exchange
Zone IV: Exposed rocky outcrops (Seamounts)
— Local advective recharge or discharge;
— Natural access to fluids
Access to crustal fluids
ODP/IODP Boreholes
- Sediment and basement cores
- Observatories: CORKs (Circulation Obviation retrofit Kits)
* Engineered access to basement rock and fluids
CORK-I Observatory
Biological
Diversity
Biomass
Metabolism
Activity/survival
Consortia
Heat (temp)
Geochemical
Redox potential
Essential elements
Water/rock
Rock mineralogy
Basement age
Spreading rate
Sedimentation
Fluid Flow
Permeability
Porosity
Driving energy
Global Ocean Basement
JdF Ridge
flank
Lau Basin
Reykajanes
MAR
west flank
Costa Rica Rift
South flank
Basement temperatures
(east flank JFR)
0.8 My
0
20
3.5 My
40
60
80
100
120
Distance from ridge axis (km)
from Davis et al. 1999
JFR, CRR
0
10
20
30
40
50
60
Crustal Age (Ma)
Wheat et al. 2003
Ocean Lithospheric Heat Flux
Total: ~32 TW
Hydrothermal circulation to 65 Ma:
~11 TW
Off-axis (1-65 Ma) heat flux:
~9.25 TW Low Temp
Associated Water Flux
Near ridge (0-1 Ma): ~3.7 x 1016 g/yr
Flanks (1-65 Ma): ~0.2-2 x 1019 g/yr
Flank fluid flow = 50-500 X Axial flow
Schultz and Elderfield 1997
Cycle entire ocean through flank basement in
70,000 to 700,000 yrs
Mottl 2004
Bulk Permeability of Upper Basement
 Crustal Age
Suggests a decrease
In bulk flow w/in aging
basement
Consistent with seismic velocity
(faster in denser, less porous media),
but inconsistent with heat flow obs
(signif. advective heat loss to 65 My)
Fisher (2004)
Channelized flow
Fluid flows:
Diffusive flux
Tortuous advective
Rapid channelized
Borehole 395A:
MAR flanks
• Zones of deflection in
SP log (10-100 m thick)
Suggest:
Channelized flow
modified from Matthews et al. (1984),
Becker et al. (1998)
measures pressure
differences
Basement rock/fluid chemistry
– Temperature of rocks (e.g., <2 to >100oC)
– How much fluid previously passed
• History of fluids
– Composition of host rock (primary/secondary
mineralogy)
• age
• water : rock ratios
• flow rates (i.e., general and local permeability)
• microbial activity
Basement mineral alteration
(bulk basement rock)
JdFR flanks
Fe2+
(Fe2++Fe3+)
Age of basement
Distance from ridge axis
Marescotti et al 2000
Johnson and Semyan 1994, reploted by Bach and Edwards 2003
JdFR
Increasing (upper) Basement Age
Marescotti et al. 2000
Alt and Mata 2000
Bach and Edwards 2003
Olivines
FeOOH
Celadonite/
saponite
Pyrite
Alteration Halo within Fracture (fluid conduit)
Microbial role ?
O2 reduction
NO3- reduction
+ H2 oxidation
Fe3+ reduction
SO42- reduction
-
O2,NO3 +
Fe+2 oxidation
S oxidation
H2
Fe2+
Olivines
Furnes and Staudigal1999
estimate 75% of upper
basement is microbially
altered !?
FeOOH
Celadonite/
saponite
Pyrite
O2
Making a Living
in Subseafloor Basement Environments
Photoautotroph
Chemotroph
(reduced) organic carbon
In situ abiogenic
organic carbon
Chemoorganotroph (heterotroph)
Chemolithoautotroph
organic carbon
Chemolithoautotrophy:
Energy: Oxidation/reduction reactions using
inorganic e- donor & e- acceptor pairs
C-source: inorganic (CO2)
Relevant, microbially meaningful reactions
(chemolithoautotrophic)
4FeO + O2 + 6H2O = 4Fe(OH)3,s
Aerobic Fe2+ oxidation
[5FeO + NO3- + H+ + 7H20 = 5Fe(OH)3,s + 0.5N2] Anaerobic Fe2+ oxidation
FeS + 2O2 = Fe2+ + SO42-
2 FeO + 4 H2O = 2 Fe(OH)3 + H2
2 FeO + 2 H2O = 2 FeOOH + H2
2 FeO + H2O = Fe2O3 + H2
H2 oxid by O2, NO3-, Fe3+, SO42-,
Sulfide oxidation
Low-To, abiogenic
anaerobic hydrolysis
H2 oxidation
Potential metabolic processes active in
subseafloor basement
e- donor
e- acceptor
By-product
Subsurface habitat
zonesa
H2
NO3-, NO2-, N20, NO, N2
NH3, N2, NO2-, NO, N2O
I, II, IVa,b
H2
SO42-, SO32-, S2O32-, S4O62-, S
H2S, S2O32
I, II, IIIa,b, IVb
H2
CO2
Acetic acid
I, II, IIIa,b, IVb
NH3
NO2-, MnIV
N2, MnII
I, II, IIIa, IVa
S2-
NO3-
NH3, SO42-
I, II, IIIa, IVa
S2-
NO3-
NH3, S0
I, II, IIIa, IVa
Organic-C
SO42-, SO32-, S2O32-, S
CO2, CH4, CO, reduced S
I, II, IIIa,b, IVb
Organic-C
O2
CO2
I, II, IVa
Organic-C
NO3-
NO2-, N2, NH3, CO2
I, II, IV
H2, CH4, NH3, O2
S-2, FeII, MnII
H2O, CO2, NO2-, NO3-, FeIII,
MnIV
I, II, IIIa, IVa
Organic-C
Organic-C
(fermentation)
I, II, III, IV
Organic-C,
FeIII, other minerals
Gr = Gr0 + RT ln(Q)
I, II, IIIa,b, IVb
Q = activity product?
Edwards 2004
Bottom
seawater
Basement
Fluids
(1.2 Ma; 40.5oC)
Basement
Fluids
(3.5 Ma; 64oC)
pH
7.9
7.2
7.4
Alkalinity (meq/l)
2.5
1.4
0.6
SO42-
(mmol/kg)
26.1
26.5
17.5
Mg2+
(mmol/kg)
52.5
27.5
4
Ca2+
(mmol/kg)
10.3
34.2
56.2
2.4
1.4
0.5
<0.002
0.4
1.8
~0.0002
0.4
0.6
Fluid Composition
TCO2 (mmol/kg)
CH4
H2
(mol/kg)
(mol/kg)
NH3
(mol/kg)
0.9
60
90
Mn
(mmol/kg)
0.0
48
4
Fe
(mmol/kg)
0.0
62
1.1
190
590
750
Si
(mmol/kg)
Enriched
Cowen et al. 2003; Wheat et al. in review; M. Lilley, unpubl. data
Depleted
Basement fluid chemistry
Depleted Mg2+/ enriched Si, Ca2+, Sr2+, H2
– Reaction with basaltic rocks
Enriched H2
– Hydrolysis of ferrous Fe in basalt rocks
Depleted sulfate
– Sulfate reduction (H2, Org-C)
– Diffusion to sediments
– Sulfate mineral precipitation (e.g., Jarosite, anhydrite)
Elevated ammonia
– Nitrate reduction (e.g., e- donor: Org-C, Fe2+, or H2)
– N2 fixation
– Diffusion from sediments
Depleted TCO2, alkalinity
– Carbonate precipitation
Enriched Si, Fe
– Seawater-basalt reactions
– Contamination (e.g., drilling ops, borehole casings)
Sediment-Basement Exchange:
Borehole 1027 (3.5 Mya)
Sediments
basement
Mather and Parkes 2000
Borehole 1027: sediment profiles
Mather and Parkes 2000
Inferred Microbial-Produced Alteration Textures
BSE-SEM
images
MAR
7 mbs
<2 Ma
Lau
3 mbs
4-7 Ma
Reykj R
51 mbs
2.3 Ma
MAR
45 mbs
10 Ma
Reykj R
124 mbs
38 Ma
MAR
157 mbs
10 Ma
Furnes et al. 2001
mbs: meters below sediments
Costa Rica Rift
~50 mbs
Phase contrast
DNA (DAPI)
~120 mbs
Phase contrast
DNA (DAPI)
Arch344
Bac388
Bac388
Arch344
Fluorescent in situ
hybridization—
probes specific for
Bacteria or Archaea
Torsvik et al. 1998
Elemental X-ray maps
C
N
(K)
resin in fracture
Costa Rica Rift
~100 mbs
5.9 Ma
Costa Rica Rift
~100 mbs
Other maps:
5.9 Ma
Si, Mg, Ca, Na depleted
Ti, Al, Fe, Mn, enriched
P
(S)
Torsvik et al. 1998
‘BioColumn’
basement fluid sampler
Cowen et al. 2003
Cell products from basement fluids
(1026b, JFR)
Propidium iodine-stained
Giovannoni
0.5 um
Low
G+C
Borehole 1026b
basement fluids:
Phylogenetic tree
(ssu rRNA):
bacterial groups
-Proteobacteria
1026B clones’ closest known
relations:
Cowen et al. 2003
Sulfate reducers
Fermentative heterotrophs
Nitrate reducers
(NH3 production)
N2 fixers? (NH3 production)
Thermophilic members
Borehole 1026b fluids:
Phylogenetic tree
(ssu rRNA):
Archaea
1026B clones’ closest known
relations to:
Sulfate reducers
Genes from Yellowstone
hot springs
Thermophiles
Cowen et al. 2003
Basement fluid ages
(east flank JFR)
recharge
Fluid
14C ages:
4.5ky
1ky 9.9ky
0.8 My
0
20
3.5 My
40
60
80
100
120
Distance from ridge axis (km)
from Davis et al. 1999
(partially) Reset time clock
and redox conditions
Older,
reduced
Cowen 2004, as modified from Wheat et al. 2002
Fisher et al. 2003
Wheat et al. 2002
Speculated characteristics of buried
ocean basement biosphere
• Low cell abundance
• Slow growing
• Highly heterogeneous distributions (& activities)
– Localized populations consistent w/ channelized flow
– Punctuated by recharge zones
• Diverse chemoautolithotrophic and heterotrophic
(& unusual) metabolisms
• Microbial consortia likely important and
associated with biofilm formation
Summary
• Ocean Basement environments are dynamic and
complex
• Biosphere within aging basement is predicted:
–
–
–
–
Favorable temperature ranges,
Active fluid flow (is it enough?)
Reactive basaltic rocks
Existing (preliminary) phylogentic data consistent w/ chemical
data
• Challenges
– Accessibility
– Contamination
– Life perhaps ubiquitous, but low biomass/activity?
Future borehole observatory
opportunities
• Cores from drilling operations
• Short and long-term observations
– In situ (downhole) instrumentation
– Fluid collections
– In situ incubations
(seafloor and downhole)
– Other experiments (e.g., push-pull)
Contamination issues
Drilling operations
• Drilling muds, bottom seawater, sediments
Observatory materials
• Packing cement
• Borehole casing
• Sample delivery tubing
CORK-II Observatory
Downhole sampling
Cowen and Taylor, in development
In situ Chemical Redox Analyzer
2e-6
free H2S
FeS
dissolved O2, H2S, MnII, FeII,
S2O32-, S4O62-, Sx2-, S0,
aqueous species of FeIII and FeS
i (A)
1e-6
0
*
A
SAVS
-1e-6
-1.5
500
concentration (M)
-1.0
-0.5
Volts (vs AgCl)
400
Free H2S
300
SAVS
FeS
In situ Voltammetric
200
Electrochemical
measurements
100
B
Starring
Brian Glazer!
0
0
30
60
90
120
time (sec)
150
180
Cabled IODP CORK Observatory
(Ocean Observatory Initiative)
– Power:
• In situ filtrations
• Temperature controlled in situ incubations
– Two-way communication: directed sampling
• Fine-scale coordination w/geophysical exp.
• Response to perturbation (e.g., seismic/magmatic
events)
• Chemical/particle tracer transport studies
Colleagues
Co-Investigators
Stephen Giovannoni (OSU)
Michael Rappe (OSU,UH)
Fabien Kenig (UI, Chicago)
Craig Taylor (WHOI)
Brian Glazer (IfA, UH)
David Butterfield (PMEL-NOAA)
Paul Johnson (UW)
Students
Rachel Shackelford (UH)
Phyllis Lam (UH)
Michael Hutnak (UW/UCSC)
Other indispensable colleagues
Andy Fisher (UCSC)
Michael Mottl (UH)
Geoff Wheat (UA, MBARI)
Funding: NSF--Ocean Instrumentation, LExEn, MO, NASA-UHNAI
Propidium iodine-stained sediment-buried basement fluids
(1026b, JFR)
Giovannoni