AFRICA AS SOURCE AND SINK FOR ATMOSPHERIC CARBON-DIOXIDE

Comparison of a set of paleogeographic maps of Africa for the Last Gla cial Maximum (LGM) and the Holocene Climatic Optimum (HCO) allows us t o discuss the contribution of paleocontinental proxy-data in paleobiom ass calculations and their accuracy. Maps show considerable shifts in the area covered by the main ecosystems. In this study we have quantif ied these areal changes, from the LGM to the HCO, in terms of variatio ns in carbon storage. Each biome has been assigned a carbon density in living and soil organic matter. From desert to tropical forest the me an carbon densities vary from 0 to 20 kg m-2 for phytomass and from 0 to 13 kg m-2 for soil (peat excluded). During the world deglaciation A frica was a sink for 154 Gt (standard deviation 42 Gt) of atmospheric carbon. Since the HCO Africa has been a source of carbon. More recentl y human deforestation is responsible for a carbon flux towards the atm osphere which is ten times the mean annual flux due to vegetation chan ge in response to climate change. Extended to a global scale this regi onal test shows that the paleoenvironmental approach is more appropria te for paleobiomass estimates than calculations based only on oceanic data.