Last Glacial Maximum paleoproductivity and water masses off NW-Africa: Evidence from benthic foraminifera and stable isotopes

Abstract

Last Glacial Maximum (LGM) paleoproductivity, organic carbon (C org) fluxes, and seasonality was reconstructed from benthic foraminiferal faunas and the stable carbon and oxygen isotopes of foraminiferal calcite. Sediments of the LGM between 23,000 to 19,000 cal-yr BP of sixteen cores from the upwelling region off Morocco between Cape Ghir (31°N) and Cape Yubi (27.5°N) were investigated. Four regions with distinct paleo-C org fluxes and seasonality were reconstructed based on faunal assemblages and δ 13C values of Hoeglundina elegans: (1) the Cape Yubi Upwelling Region with high paleoproductivity, high paleo-C org fluxes and very low seasonality as indicated by the Bolivina albatrossi/ Uvigerina mediterranea Assemblage and lowest mean δ 13C H.elegans ; (2) the Cape Ghir Upwelling Region with moderate to high paleoproductivity and paleo-C org fluxes and low seasonality as indicated by the Bulimina mexicana/ Gavelinopsis translucens Assemblage, and low mean δ 13C H.elegans ; (3) the Cape Yubi Filament Region with moderate to high paleoproductivity, high paleo-C org fluxes and high seasonality as indicated by the Cassidulina laevigata/ Nonionella iridea Assemblage, and δ 13C H.elegans as low as those from the Cape Ghir Upwelling Region; (4) the Cape Ghir Filament Region with highest paleoproductivity, high paleo-C org fluxes and seasonality as indicated by the Epistominella exigua Assemblage, and highest δ 13C H.elegans . Productivities during the LGM and today were compared based on faunal assemblages and Δ δ 13C values (Δ δ 13C = δ 13C LGM– δ 13C Present) of three infaunal species. Generally, during the LGM, the upwelling region was characterized by higher paleo-C org fluxes, particularly in the area between the capes, similar seasonality along the coast, and higher seasonality further offshore than at present-day. For the reconstruction of LGM water mass stratification we used the δ 13C of Cibicidoides wuellerstorfi and equilibrium adjusted δ 18O of several species. Deep water mass stratification is characterized by glacial North Atlantic Central Water above 800 m, by glacial Mediterranean Outflow Water between 800 and 1900 m and glacial North Atlantic Deep Water below 1900 m and a southern source deep water mass. This means, considering the lowered glacial sea level, water mass stratification during the LGM was similar to present-day conditions.