Dissolved Inorganic Carbon and Its Isotopic Composition
in the Waters of Anoxic Marine Basins

I. I. Volkov

Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia

Received May 25, 1999

Abstract—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 (res-
idence time of anoxic waters). The isotopic composition of the total inorganic carbon (C_T) is enriched in ¹²C
due to the increase in CO₂(C) resulting from the anaerobic mineralization of organic matter. In anoxic waters,
a linear dependence between ¹³C and C/C_T is observed. Isotopic composition of the CO₂ formed during min-
eralization of OM is not the same as the composition of carbon in the source plankton or organic detritus, but
it is enriched in ¹³C by ¹³C = 47‰. 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.

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