Mapping of C-4 plant input from North West Africa into North East Atlanticsediments

Mapping the abundance of C-13 in leaf-wax components in surface sediments r ecovered from the seafloor off northwest Africa (0-35 degrees N) reveals a clear pattern of delta(13)C distribution, indicating systematic changes in the proportions of terrestrial C-3 and C-4 plant input. At 20 degrees N lat itude, we fmd that isotopically enriched products characteristic of C-4 pla nts account for more than 50% of the terrigenous inputs. This signal extend s westward beneath the path of the dust-laden Sahara Air Layer (SAL). High C-4 contributions, apparently carried by January trade winds, also extend f ar into the Gulf of Guinea. Similar distributions are obtained if summed po llen counts for the Chenopodiaceae-Amaranthaceae and the Poaceae are used a s an independent C-4 proxy. We conclude that the specificity of the latitud inal distribution of vegetation in North West Africa and the pathways of th e wind systems (trade winds and SAL) are responsible for the observed isoto pic patterns observed in the surface sediments. Molecular-isotopic maps on the marine-sedimentary time horizons (e.g., during the last glacial maximum ) are thus a robust tool for assessing the phytogeographic changes on the t ropical and sub-tropical continents, which have important implications for the changes in climatic and atmospheric conditions. Copyright (C) 2000 Else vier Science Ltd.