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 (CGM) atmosphere CO2 content w as 80-90 ppm lower than the mid-Holocene. This represents a transfer o f over 160 GtC into the atmosphere since the LGM. Palaeovegetation stu dies suggest that up to 1350 GtC was transferred from the oceans to th e terrestrial biosphere at the end of the last glacial. Evidence from carbon isotopes in deep sea sediments, however, indicates a smaller sh ift of between 400 and 700 GtC. To understand the functioning of the c arbon cycle this apparent discrepancy needs to be resolved. Thus, olde r data have been reassessed, new data provided and the potential error s of both methods estimated. New estimates of the expansion of terrest rial biomass between the LGM and mid-Holocene are 700 GtC +/-> 300 GtC , using the ocean carbon isotope-based method, compared with of 1100 G tC +/-> 500 GtC using the palaeovegetation estimate. If these estimate s of the carbon shift to the terrestrial biosphere are equilibrated wi th the dissolved carbon in the oceans, and the CaCO3 compensation of t he ocean is taken into account, then the glacial atmospheric CO2 would have been between 50 (+/-30) ppm and 95 (+/-50) ppm higher. The glaci al atmosphere therefore should have had a CO2 partial pressure of betw een 330 and 375 mu atm. Hence, a rise of between 130 and 175 mu atm in atmospheric CO2, rather than 80 mu atm, at the end of the last glacia l must be accounted for.