Current Placement: Assistant Professor, University of Tennessee, 2014-
Award Dates: April 1, 2016 — March 31, 2017
Microbial life persists in deep marine sediments, despite the spectacularly low quantity of energy available in those environments. Molecular results reveal that many of these organisms are heterotrophs, despite the fact that the organic matter in such environments is old and seemingly highly recalcitrant. It has conclusively been shown that the radiolysis of water by natural radionuclides in sediment produces a flux of molecular hydrogen which can support a fraction of microbial metabolisms. Radiolysis of water also produces reactive oxygen species (ROS), even in anoxic water, including hydroxyl radical and hydrogen peroxide. In surface seawater, ROS are well known to react with dissolved organic matter to produce a suite of bioavailable, low-molecular weight organic compounds including acetate, acetaldehyde and formaldehyde, as well as carbon monoxide. Here we propose to test the hypothesis that hydroxyl radicals and H2O2 can stimulate heterotrophic activity in deep sediments from the Baltic Sea Basin, collected on IODP Expedition 347, by oxidizing sedimentary organic matter and releasing small, bioavailable molecules. If it indeed occurs, this process would represent a previously unknown source of energy to fuel microbial metabolisms in any subsurface environment containing organic matter and radionuclides.