Microbial Activities in Deep-Subsurface Sediments Beneath Mid-Ocean Gyres

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The nature of subsurface life is very poorly known. Ocean gyres are the major oceanographic provinces on our planet but the seafloor underlying these oligotrophic open ocean regions is the least explored. Most sub-seafloor investigations have focused on high productivity regions near continental margins. This project proposes to use innovative and experimental stable and radio - isotopiv approaches to address the metabolic activity and the biogeochemical cycling of key compounds (C, N, O) in oligotrophic sub-seafloor sediments underlying the oligotrophic South Pacific Gyre and South Atlantic Gyre.Intellectual Merit: The primary objectives of this proposal are to determine metabolic activities (aerobic respiration, heterotrophy/autotrophy) and to track potential routes of C, N and P fixation and turnover using sensitive stable and radioisotope methods, cell extractions and single cell analyses including nano-scale secondary mass spectrometry (nanoSIMS). The fundamental goals are to document geographic variation in subsurface habitat conditions and microbial metabolic activities and to test the factors controlling those activities. The proposed study will test for and quantify heterotrophic and autotrophic metabolisms in a comparison of (a) ocean regions (gyre center to gyre margin in both the Atlantic and Pacific), b) sediment depth and c) relation to processes in the underlying basalt. This research will addresses key questions in sub-seafloor investigations: What are the principal microbial activities in open ocean sub-seafloor sediments? What are the principal sources of metabolic energy? What are the rates of these activities? The results of the proposed investigations will be transformative to the fields of deep-biosphere microbial ecology and biogeochemistry, as they will significantly advance our understanding of the subsurface biome that may be representative for major areas of the ocean floor. Broader Impacts: One postdoctoral fellow will take part in this project and will receive training in research, mentoring, and career preparation. This project will engage undergraduate students who will participate in the research. The proposed research is directly in support and advances large investments made for IODP expeditions 329 (South Pacific Gyre) and 336 (South Atlantic Gyre), which have a unique focus on subsurface microbiology. This project will strengthen international collaborations between IODP scientists and includes close collaborations with the MPI in Bremen, Germany. The NSF Center for Dark Energy Biosphere Investigations at USC (C-DEBI) provides educational opportunities for teachers, K-12 students, undergraduate and graduate students, as well as post-doctoral researchers to train with the aim to foster the next generation of deep subseafloor biosphere researchers, as well as to translate knowledge in the field of deep biosphere research to the broader public.