BIOTIC RESPONSE TO EARLY EOCENE THERMAL MAXIMUM 3 AT WALVIS RIDGE, SE ATLANTIC OCEAN

Late Paleocene - early Eocene climate was punctuated by transient global warming events (thermal maxima) due to release of isotopically light carbon into the ocean-atmosphere, characterized by a global, negative carbon isotope excursion (CIE) coeval with warming and deep-sea carbonate dissolution. The most extreme was the Paleocene-Eocene Thermal Maximum (PETM). The biotic response to the PETM has been widely studied, but less severe hyperthermals have not yet been well documented. Eocene Thermal Maximum 3 (ETM3) was the largest ETM after the PETM and ETM2 (Elmo), occurring ~3.1 myr after the PETM. We combined stable isotope records with calcareous nannoplankton and benthic foraminiferal data for ODP Sites1263 (paleodepth ~ 1500m) and 1262 (paleodepth ~ 3600m) on Walvis Ridge (SE Atlantic). ETM3 (planktic foraminifer Zone P7, calcareous nannofossil Zone CP10) is characterized by a CIE of ~0.9‰, deep-sea warming of ~2.5oC and a rise in the lysocline. Dissolution-resistant calcareous nannoplankton species (species of Discoaster and Sphenolithus) and eutrophic indicators (‘HS’-group) increased in abundances at Site 1263, while mesotrophic Toweius spp., decreased slightly. At Site 1262 changes were more muted. Benthic foraminiferal diversity and relative abundance of cylindrical species decreased at both sites, while the % of opportunistic abyssaminids increased. Benthic Foraminiferal Accumulation Rates (BFAR), indicative of food supply to the benthos, remained stable at Site 1262, but declined severely at 1263, as did ARs of all species. At the deeper Site 1262 assemblage changes in nannofossils and benthic taxa thus were much less pronounced, suggesting that they cannot be due to dissolution alone. Overall, surface primary productivity may have increased, especially at shallower, slightly more coastal Site 1263, where food supply to the benthos declined severely, in contrast to the Site 1262. Increased ocean stratification, warming, and shallowing of the thermocline may have caused increased remineralization of organic matter, resulting in declining food supply to the sea floor, potentially more pronounced at the shallower site because of more pronounced warming due to circulation changes during ETM3.