ABSTRACTDuring Ocean Drilling Program Leg 201, we will core and recover deep-sea sediments at a series of sites in the eastern equatorial Pacific, the Peru Basin, and the Peru Margin. The purpose of Leg 201 is to explore the distribution, activities, community structure, phylogenetic affinities, and global biogeochemical consequences of microbial communities buried in deep-sea sediments. Subsurface sedimentary environments to be explored during Leg 201 include (1) sulfate reducing, sulfate depleted methanogenic, and sulfate-reducing methanotrophic zones of the Peru coastal margin; (2) open-ocean sulfate-rich sediments where sulfate reduction, methanogenesis, and methanotrophy apparently co-occur (equatorial Pacific); and (3) open-ocean sulfate-rich sediments where manganese reduction occurs (Peru Basin). The coastal-margin sites will include both shallow-water sites where all of the methane is present as free gas and a deep-water site where methane hydrates occur. This cruise will address several fundamental questions about the deeply buried biosphere. These include: (1) Are different sedimentary geochemical regimes characterized by very different microbial communitiesor merely by shifts in the dominating organisms and the level of community activity? (2) How does hydrologic flow through deeply buried sediments and possibly through basement rock affect subsurface microbial communities and their activities? (3) To what extent do past oceanographic conditions affect microbial communities now buried in deep-sea sediments?
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