The continental carbon cycle during the last glacial maximum

Abstract

During the last glacial maximum at 18 k.y. B.P. (18,000 years before present) atmospheric CO 2 and CH 4 concentrations varied in a parallel direction to surface temperature over East Antartica. This variation implicates that paleoclimate induced a change of the carbon cycle at the Earth's surface. Here the corresponding change of terrestrial carbon storage is estimated. The decrease of the surface temperature over land and the extent of the ice sheet on land of the Northern Hemisphere led to a reduction of terrestrial carbon storage of 363–544 GtC (1 GtC=10 15 g carbon), about 2 or 3 fold that of CO 2C in the atmosphere. The extension of vegetation on new land formed by the drop of sea level appears to have been small. Therefore the decrease carbon storage in the atmosphere an on land corresponds to a net carbon transfer to the oceans of about 533–714 GtC. At the same time, the decrease of 46% in atmospheric CH 4 concentration can be attributed to a reduction in the emissions of continental sources. A latitudinal distribution of these emissions has been calculated. It is shown that one of the main reductions in the CH 4 emissions took place at boreal latitudes parallel with the extent of ice sheet over land, and amounts to about 37 Tg CH 4C yr −1 (1 Tg CH 4 C yr −1=10 12 g CH 4 C per year). The second reduction, in South America, with the lowering of surface temperature and possibly rainfall, accounts for an other 17 Tg CH 4C yr −1. The decrease in atmospheric CH 4 level can also be partly attributed to an increase of the OH level in atmospheric air, about 20% at a maximum.