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Geological Society, London, Special Publications; 1992; v. 64; p. 499-510;
DOI: 10.1144/GSL.SP.1992.064.01.32
© 1992 Geological Society of London

The Geological Record of Upwelling Evolution

Palaeoproductivity oscillations during the last 130 ka along the Portuguese and NW African margins

Fatima Abrantes

Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA
Serviços Geológicos de Portugal, Rua Academia das Ciências, 19 2°, 1200 Lisboa, Portugal

Diatom abundance and taxonomic changes were quantitatively studied in the latest Quaternary (~ 130 ka to present day) sequences of the upwelling zones associated with the continental margins of Portugal and northwest Africa. Marked oscillations in diatom abundances accompanied by changes in the assemblage composition are evident during the late Quaternary and reflect changes in primary productivity related to upwelling intensity. Upwelling increased during glacial episodes (Isotopic Stages 2 and 6) relative to interglacial intervals (Isotopic Stages 1, 3 and 5). During the late Holocene, primary productivity levels are similar to those for Stage 5, and, lower than today in the early Holocene.

The palaeoproductivity reconstruction based on the diatom record is supported by independent estimates of palaeoproductivity based on the organic carbon content of the sediments.