The Deep Biosphere and the Subseafloor Ocean

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The Deep Biosphere and the Subseafloor Ocean

• Deep Biosphere
• everywhere weve looked

• Subseafloor Ocean
• subduction zones
• ridges, ridge flanks
• passive margins
• carbonate platforms
• ocean basins

• Gas Hydrates
• most continental margins

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Commonality Measurement Objectives

• Driving forces
• Fluxes/Rates/Budgets
• Temperature
• Chemistry of fluids and solids
• Biological Activity
• Formation properties State
• Heterogeneity Architecture
• Many scales of interest

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Subseafloor Ocean Overview

• Heat Redistribution
• Chemical Cycling
• Faulting Mechanics
• Rock Alteration and Diagenesis
• Volcanism
• Mineral Deposits
• Control on (and impacted by) Biosphere

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Fluids Influence and Feedbacks on Geologic
Processes
Energy Transport
Thermal State
Mechanical State
Solute Transport
Permeability Fluid Flow
Mass Transport
Hydrologic State (Pore Pressure)
Chemical Biological State
Crustal Mechanics
After Fisher, 1998
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Subseafloor Ocean

• Most constraints are indirect, knowledge via
  inference
• Dynamic System (non steady-state)
• Time variability
• Feedbacks between flow, mechanical behavior,
  chemistry, formation properties
• Drilling used in combination with models and
  other data (lab, shallow subseafloor, water
  column, regional geophysical measurements)

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Subduction Zones Margin-Scale Fluid Flow
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TIME
Flow conduit geometry is spatially limited and
shifts with time Changes related to pressure
cycles and/or fault slip Leads to transient
signal at individual boreholes Can explain common
observation of transient signal
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Ridge Ridge Flank Circulation
From IODP Initial Science Plan
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Flow focusing along Permeable Strata Impacts on
transport, slope stability
From Flemings et al., 2000
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Subseafloor Ocean DHT Needs

• Fluid Pressure (z, t)
• Temperature (z, t)
• Fluid Chemistry (z, t)
• Permeability (z, t)
• Stress (z, t)
• Rock composition
• Undisturbed Samples!

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Deep Biosphere Overview

• Evolution Distribution of Life
• Chemical Cycling, Ocean Composition
• Carbon Cycle Climate Change
• Biotechnical Applications
• Tied to Subsea Ocean Hydrates

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Deep Biosphere

• Also a Dynamic System w/ Many Feedbacks
• Occlusion of flow paths
• Fluid and solid chemistry feedbacks
• Interaction of multiple organisms
• Tied to a possibly non-steady subseafloor ocean
• Role in Hydrate Systems may be Significant
• Probably Varies with Geologic (and Hydrologic)
  Setting

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Bacterial Population vs. Depth
From IODP Initial Science Plan
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Microbially Mediated Alteration
From IODP Initial Science Plan
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PCS System Sampling for Microbiology
ODP Leg 201
cutting shoes
PCS system
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Deep Biosphere Measurement Objectives DHT
Needs

• Fluid and Solid Chemistry (z, t)
• Fluxes/Rates/Budgets (z, t)
• Temperature (z, t)
• Biomarkers (z, t)
• Level of Drilling Contamination
• In situ experiments
• Uncontaminated Samples!

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Gas Hydrates Overview

• Carbon Cycle Climate Change
• Seafloor Stability
• Tied to Subsea Ocean Deep Biosphere
• Energy Source

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Hydrate Ridge (From IODP Initial Science Plan)
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Gas Hydrates

• Many Unknowns
• Distribution
• Physical Properties
• Rates of Generation, Fluxes
• Concentrations
• A Key Player in Environmental Change
• Highly Sensitive to Pressure Temperature
• Dynamic System

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Gas Hydrate Links to Subseafloor Ocean and
Biosphere
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Gas Hydrates Response to S.L. change (or to
bottom water warming)
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Gas Hydrates DHT Needs

• Fluid Pressure (z, t)
• Stress (z, t)
• Temperature (z, t)
• Chemistry of fluids (z, t) and solids
• Biological Numbers and Activity (z, t)
• Formation properties (z, t)
• Hydrologic
• Acoustic