ON THE ECOLOGY OF CALCAREOUS DINOFLAGELLATES - THE QUATERNARY EASTERNEQUATORIAL ATLANTIC

Sediments of the Equatorial Atlantic (core GeoB 1105-4) have been inve stigated for both calcareous dinoflagellates and organic-walled dinofl agellate cysts. In order to determine the ecological affinity of calca reous dinoflagellates the statistical methods of Detrended Corresponde nce Analysis (DCA) and Redundancy Analysis (RDA) were used. Utilising DCA, distribution patterns of calcareous dinoflagellates have been com pared with those of the ecologically much better known organic-walled dinoflagellate cysts. This method was also used to determine which env ironmental gradients have a major influence on the species composition . By using existing environmental information based on benthic and pla nktic foraminifera, such as Sea Surface Temperature (SST) and stable o xygen and carbon isotopes, as well as information on the amount of Cal cium Carbonate and Total Organic Carbon (TOC) in bottom sediments, the se gradients could be interpreted in terms of productivity and glacial -interglacial trends. Using RDA, the direct relationships between the distribution patterns of calcareous dinoflagellates with the above men tioned external variables could be determined. For the studied region and time interval (141-6.7 ka) the calcareous dinoflagellates show enh anced abundances in periods with reduced productivity most probably re lated to decreased divergence and relatively stratified, oligotrophic oceanic conditions. (C) 1998 Elsevier Science B.V. All rights reserved .