Dissolved inorganic carbon and its isotopic composition in the waters of anoxic marine basins

Accumulation of total inorganic carbon (as well of hydrogen sulfide) in the waters of anoxic basins is determined by the scales of the mineralization processes of organic matter (OM) and depends on the rate of bacterial sulfate reduction in the water and on the time of exchange between the surface and deep waters (residence time of anoxic waters). The isotopic composition of the total inorganic carbon (C(T)) is enriched in (12)C due to the increase in CO(2)(Delta C) resulting from the anaerobic mineralization of organic matter. In anoxic waters, a linear dependence between delta(13)C and Delta C/C(T) is observed. Isotopic composition of the CO(2) formed during mineralization of OM is not the same as the composition of carbon in the source plankton or organic detritus, but it is enriched in (13)C by Delta(13)C = 4-7%. This correlates with the "lightening" of the OM carbon in the water basins in the succession: source plankton-organic detritus of particulate matter-bottom sediments.