Benthic Foraminifera, Food Supply, and Carbonate Saturation Across the Cretaceous-Palaeogene Boundary: Southern Ocean Site 690

The specific mechanisms causing extinction and faunal turnover after the impact of an asteroid at the Cretaceous-Palaeogene (K-Pg) boundary, and the palaeogeographical variability of the biotic response, are not well understood. In order to evaluate causes of extinction and compare the biotic turnover of deep-sea benthic foraminifera at high southern latitudes with that at globally distributed sites, we analysed benthic foraminiferal assemblages at Southern Ocean ODP Site 690 on Maud Rise, Antarctica. Proxies for export productivity and the species composition of benthic assemblages indicate that the food supply to the seafloor did not change significantly, but diversity and evenness decreased for several hundred thousand years. This transient assemblage change may have been caused by the extinction of pelagic calcifiers, either directly because of the changed nature of the organic flux, or indirectly, because the sharp decline in pelagic carbonate flux to the deep-sea floor caused carbonate oversaturation of deep waters, leading to an increased abundance of large, thick-walled and heavily calcified species.