Contrasting paleoceanographic conditions off Morocco during Heinrich events (1 and 2) and the Last Glacial Maximum

Abstract

Past hydrological and primary productivity regimes, on the basis of dinocyst and foraminiferal fossil assemblages as well as on stable isotopes (O, C) and alkenones, were investigated over the last 30 ka at upwelling site MD04-2805 CQ off Morocco. The results show highest upwelling intensity during Heinrich event (HE) 1, time-coeval with a distinct plateau of heavy planktonic δ 13C values, high concentrations of Pinus pollen and heterotrophic dinocysts, caused by an increased northern wind regime. In addition, we also present regional reconstructions of paleo-sea-surface temperatures (SSTs) using three different proxy tools: dinocyst and foraminiferal transfer functions as well as alkenones (U k′ 37 – SST). The reconstructed SSTs depict coherent scenarios as modulated by the typical Northern Hemisphere climatic fluctuations. Furthermore, specific occurrences of the dinocyst Spiniferites lazus and of the foraminifer Turborotalita quinqueloba are noted for HE 2, HE 1, and the Younger Dryas, whereas in the Alboran Sea and in peri-Iberian waters these cold events were accompanied by the dinocyst Bitectatodinium tepikiense and the subpolar foraminifer Neogloboquadrina pachyderma s., both implying a marked southward shift in the planktonic population in response to the migration of polar water masses. This very pronounced demarcation between the planktonic communities better seems to attest the presence of a distinct hydrological structure in proximity of the strait of Gibraltar which separated at that time African (north of Morocco) from European (southern Iberia) water masses.