Late Pleistocene sedimentation in the Western Mediterranean Sea: implications for productivity changes and climatic conditions in the catchment areas

摘要

Sediment cores from the Western Mediterranean Sea (WMS) have been analyzed for their bulk element composition, δ~(18)O values of planktic foraminiferal tests, and ~(87)Sr/~(86)Sr and ~(143)Nd/~(144)Nd ratios of their bulk lithogenic components. The investigated time interval comprises the last 215 kyr. Si/Al and Ti/Al ratios as well as radiogenic isotope compositions indicate changes in the provenance of the lithogenic components between glacial intervals and interglacial phases. Comparison with modern data indicates that detrital input from the northwestern and northeastern Sahara may have dominated during interglacial phases. In contrast, during glacial periods the accumulation rate of terrigenous sediment is high and changes in the sediment source areas are evident that may be related to changes in the prevailing atmospheric circulation over the basin and its source areas. A productivity reconstruction based on bio-mediated barium accumulation rates reveals increased surface productivity during glacial phases. Intervals time-equivalent to sapropel formation in the Easter Mediterranean Sea (EMS) show no changes in surface productivity compared to the intervening intervals. Comparison of the productivity patterns patterns between the WMS and EMS suggests a decoupling during Late Pleistocene sapropel formation and highlights the importance of more localized factors such as the freshwater drainage basin.