Stable isotopes, calcareous nannoplankton and benthic foraminiferal records of ODP Sites 208-1262 and 208-1263 on Walvis Ridge

We combine stable isotope, calcareous nannoplankton and benthic foraminiferal records for Ocean Drilling Program Sites 1262 (paleodepth ~ 3500 m) and 1263 (paleodepth ~ 1500 m) on Walvis Ridge (SE Atlantic), to document the marine biotic response to Eocene Thermal Maximum 3, in the early part of the Early Eocene Climate Optimum, ~3.1 myr after the Paleocene/Eocene Thermal Maximum (PETM). Bottom water warming may have decreased the vertical thermal gradient at both sites, but more at Site 1263 than at 1262. Floral and faunal changes were more muted at Site 1262 than at shallower Site 1263, indicating that carbonate dissolution was not the most important cause of biotic effects. Assemblage changes were more pronounced in benthos than in plankton.Calcareous nannofossils underwent minor ecological changes, possibly related to the presence of warmer waters, especially at Site 1263, and dissolution-resistant taxa increased in abundance. Benthic foraminiferal diversity decreased at both sites, but benthic foraminiferal accumulation rates (BFAR) declined dramatically at Site 1263, remaining stable at Site 1262.Ocean circulation may have changed during ETM3, resulting in the presence of a warmer (intermediate) water mass at Site 1263. More pronounced warming may have caused enhanced remineralization of organic matter, so less food reached the benthos. The biotic response to the X-event was less pronounced than that to earlier and more severe hyperthermal events, the PETM and Eocene Thermal Maximum 2. The extent of the biotic response reflects the severity of the environmental disturbance, but varies by location (e.g., paleodepth on Walvis Ridge).