A carbon isotope record of CO2 levels during the late Quaternary

Biochemical and physiological factors associated with photosynthetic carbon fixation in the mixed layer of the ocean should lead to a relationship between concentrations of dissolved CO2 and the carbon isotopic composition of phytoplanktonic organic material, so that increased atmospheric CO2 should enhance the difference in C-13 content between dissolved inorganic carbon and organic products of photosynthesis. It is shown here that a signal related to atmospheric CO2 levels can be seen in the isotope record of a hemipelagic sediment core, and that this record can be correlated with the CO2 record of the Vostok ice core. Calibration of the relationship between isotope fractionation and CO2 levels should permit the extrapolation of CO2 records to times earlier than those for which ice-core records are available.