GEOPHYSICAL MONOGRAPH SERIES, VOL. 144, PP. 305-323, 2004
Sedimented ridges as a laboratory for exploring the subsurface biosphere
Sediment-buried seafloor spreading centers offer one of the best environments for quantifying the extent and composition of
the subsurface biosphere, particularly chemosynthetic and thermophilic organisms. Critical parameters that control microbial
viability, including temperature, pore fluid composition and fluid advection rates, are routinely measured in sediments, but
these same measurements are difficult or impossible to make in normal oceanic crust. Depth zonation of different metabolic
pathways for organic carbon diagenesis based on availability of electron acceptors has been extensively investigated in the
marine environment and is a fundamental aspect of the subsurface biosphere at sedimented ridges. Additional energy sources
for microbial metabolism, including hydrothermal gases and thermogenic hydrocarbons are present at sedimented ridges. Stable
isotopes provide a useful tool for distinguishing sources of electron donors and acceptors in this environment, but repeated
cycling of compounds across redox boundaries due to burial and diffusion complicates the interpretation of isotope fractionation.
Studies of the microbial ecology of sedimented ridges conducted to date demonstrate that interdisciplinary approaches that
combine microbiology with geophysical and geochemical characterization of the subsurface environment are critical for understanding
the controls on the extent and composition of the subsurface biosphere.
Citation: Zierenberg, R. A., and