Climatic changes in the upwelling region off Cap Blanc, NW Africa, over the last 70 Kyear: a multi-biomarker approach

摘要

Molecular statigraphic records of core SU94-00K (21 deg N, 18 deg W, 1200 m water depth) were reconstructed for organic carbon (OC), carbonates, alkenones, n-alkanols and sterols over the last 70 ky to past changes of production and paleoceanographic conditions in the coastal upwelling of Northwest Africa. U_37~(K')-derived sea surface temperatures (SST) show a 2.5 deg C warming during the last deglaciation. Surprisingly, they also indicate that during the last glacial period, between 24 and 15 kyear, SST rose by 1 deg C, It can be seen from the values of marine and terrigenous biomarker mass accumulation reates (MAR) that this time interval was also the period of lowest marine production and dust supply suggesting a major change in the North East Trade Winds system. This situation would have lasted until the onset of the deglaciation form which upwelling progressively intensified to produce highest marine biomarker MAR at the Holocene. Our data also show a reduced terrigenous supply in late Holocene sediments that may reflect lower emission rates from the vegetation and/or changes in the wind conditions.