Relationships between primary productivity and bottom-water oxygenation off northwest Africa during the last deglaciation

The upwelling region off northwest Africa is one of the most productive regions in the world ocean. This study details the response of surface-and deep-water environments off Mauritania, northwest Africa, to the rapid climate events of the last deglaciation, especially the Bolling-Allerod (15.5-13.5 ka BP) and Younger Dryas (13.5-11.5 ka BP). A high accumulation rate gravity core GeoB7926-2, recovered at similar to 20 degrees N, 18 degrees W, was analysed for the grain size distribution of the terrigenous sediment fraction, the organic carbon content, diatom and benthic foraminifera communities. Humid conditions were observed during the Bolling-Allerod with a high contribution of fluvial sediment input. During the Younger Dryas intensified trade winds caused a larger sediment input of aeolian dust from the Sahara and more intense upwelling with higher primary productivity, as indicated by high diatom concentrations. The abrupt and large increase of organic matter caused low oxygen conditions at the sea floor, reflected by the poor benthic foraminiferal fauna and the dominance of the low-oxygen-tolerant foraminiferal species Bulimina exilis. This is surprising since low-oxygen conditions have not been recorded during modern times at the sea floor in this region, despite present-day intensive upwelling and high primary productivity. After the Younger Dryas, more humid conditions returned, diatom abundance decreased and B. exilis was replaced by typical deep-sea species as found in the region today, indicating the return of more oxygenated conditions at the sea floor. Copyright (C) 2011 John Wiley & Sons, Ltd