Influence of the Aptian-Albian Boundary Carbon Cycle Perturbation on Benthic Foraminifera from the Atlantic Ocean

The Aptian-Albian boundary is characterized by a carbon cycle perturbation, evidenced by a negative stable carbon isotope excursion (CIE) assigned to Oceanic Anoxic Event (OAE) 1b. During this interval of global warming, planktic foraminiferal assemblages recorded a major faunal turnover, depicted by the extinction of virtually all Aptian species, and the following appearance of weakly calcified Albian taxa. Nevertheless, the impacts of the Aptian-Albian carbon cycle perturbation on benthic foraminiferal assemblages are still poorly understood. Here we present high-resolution benthic foraminiferal faunal records across the Aptian-Albian transition at Deep Sea Drilling Project (DSDP) Site 511, and Ocean Drilling Program (ODP) Site 1049, located in the South and North Atlantic oceans, respectively. Our results indicate that there was no benthic foraminiferal mass extinction at the Aptian-Albian boundary, however, relative abundances of the main benthic foraminiferal groups varied significantly. For instance, benthic foraminiferal diversity and richness dropped across the boundary level. At Site 511, where the record of the Aptian-Albian transition is complete, relative abundances of infaunal benthic foraminifera increased >20% in tandem with the negative CIE, suggesting increased organic carbon burial and/or decreased bottom water oxygenation. The negative CIE interval is also characterized by increased abundances of agglutinated benthic foraminifera, and weakly calcified species assigned to the genera Patellina and Spirillina. In summary, our high-resolution benthic foraminiferal faunal records suggest the onset of poorly oxygenated bottom waters and deep ocean acidification associated with the OAE 1b carbon cycle perturbation in the Atlantic Ocean.