Coccolithus pelagicus, a productivity proxy related to moderate fronts offWestern Iberia

The traditional interpretation of Coccolithus pelagicus as a cold water pro xy is examined based on its distribution patterns in the water column off t he Portuguese coast (using data from eleven cruises) and in Holocene surfac e sediment samples and Quaternary cores from the same region. Coccolithus pelagicus is common in the Portuguese upwelling system, an area where surface waters are predominantly of subtropical origin. Although rev ealing an affinity for low temperature upwelled waters, the species was fou nd in waters up to 18 degrees C associated with riverine plume and shelf-br eak fronts. C. pelagicus seemed to consistently occupy a particular ecologi cal niche, between other phytoplankton groups, related to moderate turbulen ce conditions combined with nutrient availability. From this behaviour, it is proposed that C. pelagicus can be used as a tracer of the periphery of a reas of enhanced productivity. Coccolithus pelagicus preferences for fronts of moderate temperature and sa linity gradients are tentatively used to explain particular features of its sedimentary record. The repeated increase of C. pelagicus in thanatocoenos es (surface sediment assemblages) close to three river mouths, on the Portu guese shelf are interpreted as a positive response to the development of ri verine plumes. On the other hand, inconsistencies in the correlation betwee n sea surface cooler-glacial and warmer-interglacial isotope stages and the relative abundance pattern of C. pelagicus during the Late Quaternary, as registered in two Galicia Bank piston cores (42 degrees N), are tentatively explained in terms of shifts in the extent of the outer limit of the local palaeoproductivity belt off the Iberian Peninsula. (C) 2000 Elsevier Scien ce B.V. All rights reserved.