(Table 1) Composition of pore water from ODP Site 997 holes A and B

Pore water extracted from sediments penetrated on Leg 164 of the Ocean Drilling Program at the Blake Ridge West. Atlantic were analyzed for acetate, total dissolved organic carbon, bromide and iodide, to help explain the occurrence of subsurface maxima in bacteria biomass and activity reported previously from a nearby site. The high concentrations of these organic matter decomposition by-products in the pore waters from sediments with moderate concentrations of sedimentary organic matter can convincingly be modelled as resulting from upward migration of pore water. The amount of acetate and unidentified DOC transported by the pore water contribute significantly to the pool of metabolizable carbon, and may be the most important substances in energetic terms.