Estimating the carbon transfer between the ocean, atmosphere and the terrestrial biosphere since the last glacial maximum

Carbon dioxide records from polar ice cores and marine ocean sediments indicate that the last glacial maximum (LGM) atmosphere C02 content was 80-90 pprn lower than the mid-Holocene. This represents a transfer of over 160 GtC into the atmosphere since the LGM. Palaeovegetation studies suggest that up to 1350 GtC was transferred from the oceans to the terrestrial biosphere at the end of the last glacial. Evidence from carbon isotopes in deep sea sediments, however, indicates a smaller shift of between 400 and 700 GtC. To understand the functioning of the carbon cycle this apparent discrepancy needs to be resolved. Thus, older data have been reassessed, new data provided and the potential errors of both methods estimated. New estimates of the expansion of terrestrial biomass between the LGM and mid-Holocene are 700 GtC f> 300 GtC, using the ocean carbon isotope-based method, compared with of 1100 GtC *> 500 GtC using the palaeovegetation estimate. If these estimates of the carbon shift to the terrestrial biosphere are equilibrated with the dissolved carbon in the oceans, and the CaC03 compensation of the ocean is taken into account, then the glacial atmospheric COz would have been between 50 ( f 30) pprn and 95 ( f 50) pprn higher. The glacial atmosphere therefore should have had a CO2 partial pressure of between 330 and 375 patm. Hence, a rise of between 130 and 175 patm in atmospheric COz, rather than 80 patm, at the end of the last glacial must be accounted for. Terra Nova, 7, 358-366, 1995.