Benthic foraminiferal response to the Middle Eocene Climatic Optimum (MECO) in the South-Eastern Atlantic (ODP Site 1263)

The response of marine biota to the Middle Eocene Climatic Optimum (MECO) is still poorly constrained. Specifically, changes in deep-sea benthic foraminiferal faunas have been documented at few locations only. We carried out a quantitative study of benthic foraminiferal assemblages at lower-bathyal ODP Site 1263 (Walvis Ridge, SE Atlantic), providing documentation of the response of benthic foraminiferal assemblage to the MECO in an open ocean setting. There was no major temporary or persistent assemblage turnover in benthic foraminiferal faunas in the SE Atlantic Ocean. The benthic foraminiferal accumulation rates (BFAR) and assemblage composition indicate that the delivery of food to the seafloor increased during the early stages of surface and deep-sea warming. During this period, the absolute and relative abundance of phytodetritus exploiters increased pronouncedly, indicating that the increase in the flux of organic matter to the sea floor was largely seasonal or otherwise pulsed. During later stages and peak warming of MECO, in contrast, the flux of organic matter to the seafloor declined markedly, as shown by a decrease in both infaunal and epifaunal benthic foraminiferal accumulation rates. The low flux of organic matter during the more extreme parts of the MECO thus did not favor one of these broad groups, but affected all common taxa. Paleoceanographic reconstructions combined with data on benthic foraminifera suggest that the MECO warming was the main cause of the reduction in the flux of organic matter to the sea floor, by increasing the metabolic rates of pelagic consumers, which thus used more food, preventing it from reaching the sea floor, as well as increasing remineralization of organic matter in the water column.