INCREASED UPWELLING OFF PORTUGAL DURING THE LAST GLACIATION - DIATOM EVIDENCE

Quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest Quarternary (congruent-to 100 ka to P.D.) cores from the continental slope of Portugal. The sites are located in an area of modern summer coastal upwelling created by northerly trade winds. The spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments. The diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late Holocene, interglacial Stage 3 and late Stage 5; higher during Stage 2; and lower in the early Holocene. Paleoproductivity estimates are consistent with the diatom accumulation rates from Stage 3 to the Recent. This indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone.