PRIMARY PROPOSED SITES

Site EQP-2A (ODP Site 851)
Owing to the ship's track, our first site will be the open-ocean proposed Site EQP-2A (Fig. 1). The extremely low sedimentary organic carbon concentrations (¾0.1%) (Fig. 2) and relatively high burial depths (>300 mbsf) expected for this site render it ideal for testing whether the microbial communities, activities, and survival strategies necessary to survive in very deeply buried organic poor marine sediments are similar to or different from those in open-ocean sediments with an order of magnitude more organic matter (e.g., proposed Site EQP-1A) or distant locations with shallower burial depths, lower mean rates of subsurface catabolic activity, and perhaps different principal electron donors (MnO2) (e.g., proposed Sites PRB-1A and PRB-2A). Because Site EQP-2A contains a deeply buried interval of subsurface (basement) hydrologic flow, coring this site will also enable Leg 201 scientists to test how subsurface hydrologic flow affects community structure and sediment chemistry in organic-poor sediments with sulfate-rich pore waters. Our drilling target is to penetrate a few meters into basement.

Site EQP-1A (ODP Site 846)
Coring at proposed Site EQP-1A will allow Leg 201 scientists to document the environmental and microbial circumstances under which the standard microbial paradigm (of catabolic control by standard free energy) is violated by methanogenesis occurring in sulfate-rich open-ocean sediments (CH₄exceeds 120 µL/L at depth here). Because Site EQP-1A contains a deeply buried interval of subsurface (basement) hydrologic flow, drilling this site will also enable Leg 201 scientists to test how subsurface hydrologic flow affects community structure and sediment chemistry in relatively organic-poor sediments with sulfate-rich pore waters.

Site PRU-3A (ODP Site 684)
Coring at proposed Site PRU-3A will provide a critical standard of comparison for the other shallow-water Peru Margin sites (proposed Sites PRU-1A and PRU-2A) (Fig. 3) because Site PRU-3A contains the same near-surface sulfate/methane transition as Site PRU-1A, but may lack the subsurface brine flow of Sites PRU-1A and PRU-2A. In short, Site PRU-3A is the only "normal" upwelling zone methanogenic sedimentary sequence proposed for coring during Leg 201. Coring this site will also provide an opportunity for identifying the methanotrophic communities of deeply buried marine sediments.

Site PRU-2A (ODP Site 680)
Coring at proposed Site PRU-2A will provide a critical standard of comparison for Site PRU-1A because the same subsurface brine flow as at Site PRU-1A introduces sulfate into sulfate-rich sediments at Site PRU-2A. Consequently, we expect that the effect of that flow on microbial communities and activity is likely to be very different at the two sites.

Site PRU-1A (ODP Site 681)
Coring at proposed Site PRU-1A will enable Leg 201 scientists to test how introduction of an electron acceptor by subsurface hydrologic flow affects community structure and sediment chemistry in organic-rich (methanogenic) sediments. Coring this site will also provide multiple opportunities for identifying the methanotrophic communities of deeply buried marine sediments.

Site PRU-4A (ODP Site 685)
Coring at proposed Site PRU-4A will allow Leg 201 scientists to determine if and how hydrate bearing sequences differ in microbial activity and community structure from nearby methane-rich sequences that lack hydrates (Sites PRU-1A and PRU-3A) and nearby sulfate-rich sequences with low methane concentrations. It will also provide a Peru-Margin microbial and biogeochemical counterpoint to the hydrate-rich sites targeted for coring during Leg 204 (Hydrate Ridge).

Site PRB-2A (DSDP Site 321)
Because Mn concentrations are expected to peak unusually deep in this sequence (at 50 mbsf or deeper, based on DSDP Site 321) (Fig. 4), coring at proposed Site PRB-2A will provide an excellent opportunity to sample Mn-reducing microbial communities in very organic-poor relatively deeply buried marine sediments. Because of its extremely low electron donor (organic matter) concentrations, Site PRB-2A will provide a challenging opportunity for (1) determining conditions under which subsurface microbes may be active, inactive, or dead and (2) assessing metabolic strategies that are necessary for survival in deeply buried marine sediments.