Paleoproductivity variations related to climatic conditions in the AlboranSea (western Mediterranean) during the last glacial-interglacial transition: the diatom record

The present study addresses the analysis of changes in marine primary produ ctivity derived from climatic variability over the last 30,000 yr. The stud y area is the Alboran Sea; this is the westernmost basin of the Mediterrane an Sea, and was a very sensitive area to changes in sea levels and atmosphe ric configuration during the last glacial-interglacial transition. We repor t the results from four sediment cores recovered in both the western and ea stern Alboran basins. This allowed us to monitor the W-E evolution of the h ydrological structures. The study is mainly based on the diatom record, alt hough total organic carbon (TOC), isotopes and UK'37-SST were also used to gain further information. Paleoceanographic conditions favoured high paleop roductivity rates during the Last Glacial Maximum, although this occurred a t Termination la and during the Younger Dryas event (YD), increasing toward s the easternmost sites. During these periods, meteorological conditions, w ith increased westerlies, intensified the flow to the east, driving an east ward migration of the Western Anticyclonic Gyre. A possible displacement of the North Alboran upwelling system is also considered. The major component of the diatom assemblage during the YD are the resting spores of Leptocyli ndrus danicus, which suggest the presence of cooler and less saline surface waters. The opposite behaviour between planktonic and benthic proxies in a ddition to the high TOC values allows us to infer a phase of reduced deep w ater renewal between 16.5 and 9 cal ky BP. Fresh-water diatoms and opal phy toliths were used as indicators of aridity and humid land-conditions, respe ctively. During the glacial period and until 14 cal ky BP we observed a gra dual climatic deterioration, accompanied by a loss of grass belts. Climatic conditions were warmer and moister during the B phi lling-Aller phid while the YD was dry. The re-establishment of vegetation belts and replenishment of lakes was observed at 8 cal ky BP, (C) 2001 Elsevier Science B.V. All r ights reserved.