Approaches and constraints to the reconstruction of palaeoproductivity from Cape Basin abyssal benthic foraminifera (South Atlantic)

Abstract. The characteristics of benthic foraminiferal assemblages from well-oxygenated deep-sea settings have been used to reconstruct past productivity conditions. None of the different approaches that have been developed is without complications or applies in all settings. In this study we assess the use of benthic foraminifera (accumulation rates and assemblages composition) as proxies for palaeoproductivity changes during the last glacial period (25 – 95 ka) in an abyssal core located in the south of Cape Basin (41.1 °S, 7.8 °E, 4981 m water depth). Assemblage characteristics indicate a generally food-limited environment receiving episodic inputs of labile organic carbon of variable strength. High seasonality in the delivery of organic material to the seafloor in the form of phytodetritus influences the assemblage characteristics because the corresponding response does not involve the whole community. Benefiting from this occasionally high organic input is the opportunistic species Epistominella exigua (Brady) that reproduces rapidly to build up large populations. In general, the rest of the species (i.e. less opportunistic compared to E. exigua) show only subtle variations in their population densities and fauna composition. Under those circumstances benthic foraminiferal accumulation rates seem to be independent of the amount of organic flux arriving at the sediment surface and respond instead to the strength of phytoplankton blooms.