Spatial distribution of calcareous dinoflagellate cysts in surface sediments of the Atlantic Ocean between 13 degrees N and 36 degrees S.

To enhance the limited information available about the palaeo-ecological si gnificance of calcareous dinoflagellates, we have studied their lateral dis tribution in surface sediments of the equatorial and south Atlantic between 13 degrees N and 36 degrees S. Calcareous dinoflagellate cysts appear to b e widely distributed throughout the studied area. In the surface sediments, concentrations (cyst per gram dry sediment) of the vegetative stage Thorac osphaera heimii are generally higher than that of the (presumably) calcareo us resting cysts. Distribution patterns in surface sediments of Orthopithon ella granifera (Futterer) Keupp and Versteegh, Rhabdothorax spp. Kamptner., Sphaerodinella albatrosiana (Kamptner) Keupp and Versteegh S. albatrosiana praratabulated, Sphaerodinella tuberosa var. 1 (Kamptner) Keupp and Verste egh and S. tuberosa var. 2 and the ratios between these species have been c ompared with temperature, salinity, density and stratification gradients in the upper water column. Rhabdothorax spp. is characteristically present in sediments of more temperate regions characterized by high seasonality. Din oflagellates producing these cysts are able to tolerate high nutrient conce ntrations, and mixing of the water column. S. albatrosiana is abundant in r egions characterized by high sea surface temperatures and oligotrophic surf ace water conditions. In contrast, the distribution of S. tuberosa var. 2 i s negatively related to temperature. The other cyst species did not show a characteristic pattern in relation to the studied environmental gradients. The ratio of Sphaerodinella tuberosa var. 2 to Orthopithonella granifera ca n be used for reconstructing the presence of stratification in the upper 50 m of the water column, whereas the ratios of S. tuberosa var. 2 to Sphaero dinella albatuosiana and of O. granifera to Rhabdothorax spp. might be used for palaeotemperature reconstructions. Calcareous dinoflagellate cysts are abundant in oligotrophic areas and may be useful for the reconstruction of palaeoenvironmental conditions. (C) 2000 Elsevier Science B.V. All rights reserved.