ISOTOPIC CONSTRAINTS ON CARBON EXCHANGE BETWEEN DEEP-OCEAN SEDIMENTS AND SEA-WATER

THE vast reservoirs of organic carbon in marine sediments(1-3) have th e potential to influence the properties of organic matter in the overl ying water column, For example, it has been suggested that marine sedi ments are a possible source of the old, refractory dissolved organic c arbon (DOC) found in deep water(3,4), Natural radiocarbon and stable c arbon isotope ratios (Delta(14)C and delta(13)C) can be used to constr ain the role of sediments in the ocean carbon cycle(5-8). Here we repo rt the distributions of Delta(14)C and delta(13)C associated with diss olved organic and inorganic carbon in sediment pore water, together wi th those of the particulate sedimentary organic carbon, from two geoch emically distinct marine environments, Concentration gradients of diss olved organic and inorganic carbon across the sediment-water interface imply significant diffusive fluxes of these solutes from the sediment to the water column. But the DOC fraction in the sediments is greatly enriched in C-14 compared with that in the overlying sea water (by as much as 370 parts per thousand), indicating that the DOC supplied by sediments to ocean waters must be relatively young, and that its remna nt ages in the water column itself.