High resolution Holocene record in the southeastern Bay of Biscay: Global versus regional climate signals

Abstract

Core KS10b (North East Atlantic, 43°50′N, 2°03′W, water depth 550m) was recovered at a location of high sediment deposition, and hence includes a high-resolution palaeoclimatic record for the southeastern Bay of Biscay over the last 9000calyr BP. The effect of global and regional climatic forcing factors (e.g., orbital forcing, North Atlantic Oscillation: NAO) and their subsequent control on water temperature, sea-level, hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas (>150μm), sedimentology, and stable isotopes. Results indicate probable episodic long-term incursions of the warm and salty Iberian Poleward Current (IPC) into the Bay of Biscay during the Holocene by the intermittent presence of subtropical Globigerinoides ruber in the otherwise temperate fauna. These incursions seem to be triggered by negative NAO-like conditions. Our data show five main climatic periods, which are in general agreement with the literature data on the climatic variability in the North Atlantic and the Iberian Peninsula: The early Holocene (~9000–7400calyr BP) is characterized by low sea-level, significant downslope transport, eutrophic benthic settings and high surface water productivity. These environmental characteristics are probably due to the general wet and warm climate under a prevailing negative NAO, increasing precipitation and river runoff and favouring the incursion of the IPC into the Bay of Biscay. The climatic optimum appears between ~7400 and 6000calyr BP under a generally positive NAO index. In the following (~6000–3500calyr BP), surface water cooling is matching a steep decline of the Northern Hemisphere summer insolation. Meanwhile, benthic settings are changing progressively towards present day trophic conditions. The time interval from ~3500 to 1800calyr BP encompasses the Iberian–Roman Humid period characterized by warm and humid conditions, and increasing primary production under a prevailing negative NAO index. The last 1800years were characterized by stable cool conditions, reflecting a change towards a positive NAO state.