ODP Leg 201 explores microbial life in deeply buried marine sediments off Peru

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The principal objective of ODP Leg 201 was to document the nature, extent, and biogeochemical consequences of microbial activity and prokaryotic communities in different deeply buried marine sedimentary environments. Seven sites were located in open ocean sediments of the equatorial Pacific and the Peru Basin, ocean margin sediments of the Peru continental shelf, and hydrate-bearing deep water sediment of the Peru continental slope. We drilled up to 420 m into oceanic sediments and the underlying basaltic crust in water depths as great as 5300 m and as shallow as 150 m. Sediment temperatures ranged from 1°C to 25°C and sediment ages from 0 to almost 40 m.y. Three fundamental questions about the deeply buried biosphere were addressed during Leg 201. Are different sedimentary geochemical regimes characterized by completely different prokaryotic activities and communities, or merely by shifts among the dominant species and different levels of community activity? How does the transport of electron acceptors, electron donors, and, potentially, of prokaryotes through deep sediments affect sediment chemistry and community structure? To what extent do past oceanographic conditions affect prokaryotic communities now active in deep-sea sediments? Leg 201 shipboard biogeochemical, geophysical, and sedimentological studies provided new understanding of the effects of interstitial water chemistry, sediment composition and structure, fluid flow, and past oceanographic conditions on metabolic diversity, prokaryotic activities, and the nature of metabolic competition in these subsurface environments (D'Hondt et al., 2003). These studies have improved our understanding of how deep subsurface biogeochemical processes affect both their local environments and the surface world. Other aspects of these questions, such as genetic assays of the prokaryotic communities and isotopic studies of biogeochemical fluxes, require extensive postcruise research.

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JOIDES Journal