IMPACTS OF CLIMATIC-CHANGE ON CARBON STORAGE IN THE SAHARA-GOBI DESERT BELT SINCE THE LAST GLACIAL MAXIMUM

Reconstructions of palaeolandscapes for intervals with different clima tic conditions help define regional trends in palaeobiomass and carbon storage due to global climatic change. The Sahara-Gobi desert belt st retches for about 15,000 km from the Atlantic coast to Northern China. Natural vegetation zones have undergone a number of significant shift s and complex qualitative changes under the contrasting climatic condi tions of the Last Glacial Maximum (LGM) and the Holocene Climatic Opti mum (HCO). The results presented here are based on palynological, pedo logical and sedimentological evidence, which indicate that the amount of carbon stored in vegetation and soils would have been much smaller during the Glacial Maximum than in the interglacial and post glacial t imes. Comparison of a set of palaeogeographic maps of this region for the chosen time-slices (ca. 20-18 ka, 9-8 ka and the present) allows u s to discuss land biomass changes. Dry and cool conditions during the LGM resulted in the spread of arid and semi-arid ecosystems at norther n and southern margins of the desert belt. The southern limit of the S ahara migrated southward at least 400 km relative to its present posit ion, and almost 1000 km south compared to the mid-Holocene. The northe rn margin of the temperate deserts and dry steppes of Central Asia shi fted northward for not less than 200-300 km over Kazakhstan, southern Siberia and Mongolia, In this study we have quantified variations of t he main ecosystems from the LGM to the HCO in terms of changes in carb on storage. Each vegetation zone has been assigned a carbon density fo r living and dead (soil) organic matter. During the last world deglaci ation, the Sahara-Gobi desert belt was a sink for approximately 200 Gt of atmospheric carbon, but since the mid-Holocene, it has been a sour ce of carbon. (C) 1998 Elsevier Science B.V. All rights reserved.