The response of deep-water benthic foraminiferal assemblages to changes in paleoproductivity during the Pleistocene (last 769.2 kyr), western South Atlantic Ocean

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Benthic foraminiferal assemblages and δ18O records in a core from Santos Basin (western South Atlantic, 2220m water depth) were analyzed to investigate productivity changes during the Pleistocene. The sediment core recorded the last 770kyr, including Marine Isotope Stages (MIS) 19 to 1. The four dominant benthic foraminiferal assemblages were identified using Q-mode Varimax Factor Analysis, and are represented by Globocassidulina crassa, Bolivina spp., Epistominella exigua and Alabaminella weddellensis. From 769.2kyr (MIS 19) to ~300kyr (MIS 8), the highest values of factor 2 (Bolivina spp. assemblage) indicate increased influx of organic matter to the seafloor and a slight decrease in the oxygen concentration at the sediment–water interface. This condition began to change in the stage 8 (~288.9kyr to ~268.3kyr), and it is characterized by high values of factor 1, when the G. crassa assemblage became dominant, indicating an increase in oxygen concentrations and a decrease in the influx of organic matter. Seasonally-pulsed organic matter resulting in a distinct phytodetritus layer accumulated mostly during the glacial MIS 14, 10, 8, 6, and 5.2–5.1, and in the interglacial stage 11 and the end of 9, as indicated by factor 3 (E. exigua assemblage) and factor 4 (A. weddellensis assemblage). The highest peak of the A. weddellensis assemblage during MIS 11 (~401.4kyr) coincides with the Mid-Brunhes Event. The highest benthic foraminiferal accumulation rates occurred during mostly glacial stages, indicating delivery of more organic matter to the seafloor. The changes in benthic foraminifera assemblages in the glacial stages during the Pleistocene indicate changes in primary productivity in surface waters. Increasing the amount of organic matter delivered to the seafloor amplified the benthic foraminiferal response.