Thursday, 17 December 2015: 08:00
2012 (Moscone West)
Steven D'Hondt, University of Rhode Island, Narragansett, RI, United States, Robert A Pockalny, Univ Rhode Island, Narragansett, RI, United States, Arthur J Spivack, University of Rhode Island - GSO, Oceanography, Narragansett, RI, United States, Fumio Inagaki, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kochi Institute for Core Sample Research, Kanagawa, Japan, Richard W Murray, Boston University, Boston, MA, United States, Rishi Ram Adhikari, University of Bremen, Bremen, Germany, Britta Gribsholt, Viden Djurs, Grenå, Denmark, Jens Kallmeyer, Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, Claire Cecelia McKinley, Texas A & M University College Station, College Station, TX, United States, Yuki Morono, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, Hans Røy, Center for Geomicrobiology, Aarhus University, Dept. of Biosciences, Aarhus, Denmark, Justine Sauvage, University of Rhode Island - GSO, West Warwick, RI, United States and Wiebke Ziebis, University of Southern California, Biological Sciences, Los Angeles, CA, United States
Dissolved oxygen content defines two broad categories of subseafloor sediment. In areas with high rates of microbial respiration, most of the sediment column is anoxic and active anaerobic microbial communities are present for hundreds of meters or more below the seafloor. In these regions, O2 and aerobic communities penetrate only millimeters to centimeters into the sediment from the sediment-water interface. In some areas of active fluid flow through the underlying basalt, O2 may also penetrate meters upward into the sediment from the basalt. In areas with low sedimentary respiration, O2 and aerobic communities penetrate tens of meters downward from the seafloor and may persist throughout the entire sediment column. IODP Expedition 329 showed that microbial cells and aerobic respiration persist through the entire sediment sequence (to depths of at least 75 meters below seafloor) in the South Pacific Gyre. Extrapolating from these results and a global relationship of O2 penetration depth to sedimentation rate and sediment thickness, we suggest that oxygen and aerobic communities occur throughout the entire sediment sequence in 15–44% of the Pacific and 9–37% of the global seafloor. Subduction of sediment from largely anoxic regions and subduction of sediment and basalt from fully oxic regions are respectively sources of reduced and oxidized material to the mantle. The balance between oxic and anoxic regions has presumably changed considerably throughout Earth history. Regions with largely anoxic sediment and regions with fully oxic sediment present fundamentally different opportunities for understanding of (i) paleoceanographic history and (ii) the nature of microbial life under extreme energy limitations.