Hydrological processes affecting the subtropical NE Atlantic (34-38° N) over the last 30 ka: Evidence from phyto- and zooplankton assemblages

Abstract

International audienceNew dinocyst analyses were conducted on core MD99-2339 retrieved from the central Gulf of Cadiz. Dinocyst and foraminiferal assemblages from this core are combined with existing data off SW Portugal and NW Morocco to investigate past hydrological and primary productivity regimes in the subtropical NE Atlantic Ocean over the last 30 ka. Our results have revealed highest upwelling intensity during Heinrich Stadial 1 (HS 1) and the Younger Dryas and weaker upwelling cells during the Last Glacial Maximum and HS 2, off the SW Iberian and NW Moroccan margins. Similar assemblages between Cadiz and Morocco and distinct species off Portugal were observed during the cold climatic extremes that punctuated the last 30 ka. This pattern has been linked to the occurrence of a hydrological structure between SW Iberia and Cadiz during the last glacial period, probably similar to the modern Azores Front. This front was probably responsible locally for heterotrophic dinocysts found in the Gulf of Cadiz during the last glacial period, even if this sector is not conductive to upwelling phenomena by Ekman transport. Regional reconstructions of paleo-sea-surface temperatures using dinocyst and foraminiferal transfer functions, as well as alkenones, are also discussed and depict coherent scenarios over the last 30 ka. However, some mismatches are observed between the different quantitative reconstructions such as during HS 1 in the Gulf of Cadiz and during the LGM at the three core locations. © 2011 Author(s)