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Modern Upwelling Systems and Palaeo-Upwelling Criteria |
GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1–3, Bldg. no. 4, D-2300 Kiel 14, Germany
Sediments under coastal upwelling regimes contain pelagic fossil assemblages that differ from those of non-upwelling coastal areas and of the open ocean. In this paper we describe the composition and biogeographical distribution of skeletal material of living planktic and benthic organisms in two of the most important coastal upwelling regions. Particular attention is paid to planktic foraminifers and pelagic gastropods off NW Africa and off NW South America. In both regions, near-surface water masses covering coastal waters of the upwelling region per se, of the coastal regions to the North and South of the upwelling centres as well as of the adjacent open ocean, were sampled during 1971 and 1977. The upwelled water masses were characterized by very high concentrations of radiolarians, planktic foraminifers, pteropods and small fish bones (the latter off NW South America only).
The biogeographical distribution of planktic foraminifers and pelagic gastropods can be related particularly well to upwelling. Off NW South America, Globigerinoides ruber, Globigerina bulloides and Globoquadrina dutertrei are found in high abundances near the coast. A region of high concentrations of these species extends from the areas of maximum occurrence towards the west and south into the open Pacific Ocean. Analogous biogeographical patterns can be observed off NW Africa. Concentrations of pelagic gastropods also are high in both coastal upwelling regions. Typical upwelling species are Limacina inflata, L. trochiformis and Creseis acicula a.. The biogeography of pelagic fossil groups is therefore particularly well suited to delimit the spatial extent of coastal upwelling regions.
