SCIENTIFIC OBJECTIVES

During ODP Leg 201, we will address several fundamental questions about the deeply buried biosphere:

1) Are different sedimentary geochemical regimes characterized by completely different microbial communities—or merely by shifts among the dominant species and different levels of community activity?

2) How does hydrologic flow of electron acceptors, electron donors, and potentially of microbes through deep sediments affect community structure and sediment chemistry?

3) To what extent do past oceanographic conditions affect microbial communities now active in deep-sea sediments?

4) How do biogeochemical processes of the deep subsurface biosphere affect the surface world?

It is certain that several aspects of these questions will require extensive postcruise research to fully address. This reliance on postcruise research is necessary for at least two reasons. First, some experiments initiated during the cruise will take months (radiotracer experiments) or years (cultivation experiments) to complete. Second, some key studies, such as genetic assays of the microbiological communities and isotopic studies of biogeochemical fluxes, will be undertaken postcruise because they require technical facilities and expenditures of time beyond those available to an ODP shipboard party during a single cruise.

Despite these limitations, other aspects of the above questions should be successfully addressed during Leg 201. In particular, shipboard biogeochemical studies are expected to provide new understanding of the effects of sediment geochemical regimes, hydrologic flow, and past oceanographic conditions on metabolic diversity, microbial activities, and the nature of metabolic competition in these subsurface environments. Shipboard studies are also expected to greatly improve understanding of how deep subsurface biogeochemical processes affect the surface world.