Marine sediment records as indicator for the changes in Holocene Saharan landscape: Simulating the dust cycle

Abstract

Marine sediment records reveal an abrupt and strong increase in dust deposition in the North Atlantic at the end of the African Humid Period about 5500 years ago. The change in dust flux has been attributed to varying Saharan land surface cover. Alternatively, variability in climate and ocean conditions, for example changes in sea surface temperature, have been proposed to explain the enhanced dust deposition. Here we demonstrate for the first time the direct link between dust accumulation in marine cores and Saharan land surface. We simulate the mid-Holocene (6 ka BP) and pre-industrial (1850 AD) dust cycle as a function of Saharan land surface cover and atmosphere-ocean conditions using the coupled atmosphere-aerosol model ECHAM6-HAM2.1. Mid-Holocene surface characteristics, including vegetation cover and lake surface area, are derived from proxy data and simulations. In agreement with data from marine sediment cores, our simulations show that mid-Holocene dust deposition fluxes in the North Atlantic were two to three times lower compared with pre-industrial fluxes. We identify Saharan land surface characteristics to be the main control on dust transport from North Africa to the North Atlantic. We conclude that the variation in dust accumulation in marine cores is likely related to a transition of the Saharan landscape during the Holocene and not due to changes in atmospheric or ocean conditions.