Texas A&M University, United States

Integrated Ocean Drilling Program Expedition 329 will core and log deep-sea sediment and basement at a series of sites in the South Pacific Gyre. The sites are characterized by different levels of marine productivity and different basement ages (from 6 to 84-124.6 Ma). The primary purposes of the expedition are to (1) document the nature of microbial communities and test the energetic limit to life in the most food poor deep-sea sediment and (2) test the influence of crust age and sediment thickness on microbial communities, availability of electron donors and acceptors, and the hydrologic evolution of crustal basalt. This project will address fundamental questions about the subseafloor biosphere: Are the communities in mid-gyre subseafloor sediments uniquely structured? Do they contain previously unknown kinds of organisms? Is their primary electron donor organic matter from the surface world or hydrogen from in situ radioactive splitting of water? Do their activities and composition vary with properties of the surface world, such as sea-surface chlorophyll concentrations or organic flux to the seafloor? Is microbial activity sustainable in subseafloor basalt by mineral oxidation (e.g., oxidation of iron in the basaltic minerals) or other processes for tens of millions of years after basalt formation? Are microbial communities recognizably present in subseafloor basalts older than 13 Ma?