The role of the southern Indian Ocean in the glacial to interglacial atmospheric CO2 change: organic carbon isotope evidences

We use the carbon isotopic composition of sedimentary organic matter from marine cores as a proxy for paleoproductivity and paleo-dissolved carbon dioxide concentrations in surface waters of the Southern Ocean during the last 50,000 years. For the Holocene period, paleo-pCO2 reconstructions between 44° and 55°S reflect the preindustrial values (270 μatm) and are in the variation range of modern ones. During the glaciation and deglaciation periods, pCO2 was 50 to 100 μatm higher in surface water than in the atmosphere as recorded in the Vostok ice core. This suggests that the Southern Indian Ocean could have been a potential source of CO2 for the glacial and deglacial atmosphere. These results, plus those of sedimentary organic carbon content suggest that the biological pump was off and unable to lower atmospheric CO2 concentration. This indicates that a winter ice covered ocean and stratification of summer surface water caused a reduction of gas exchange with the atmosphere during that period.