Grant Institute, United Kingdom

Palaeogene hyperthermals are associated with rapid negative Carbon Isotope Excursions (CIE) and global warming and hence may provide an analogue for future ocean acidification. We present delta (super 11) B (pH), Mg/Ca (temperature), B/Ca (carbonate ion concentration) and wall thickness data from the benthic foraminifer Oridorsalis umbonatus to study the extent of the change in the carbonate system and the calcification response. In addition, we present Electron Backscatter data to assess preservation and diagenetic alteration. Our study examines both the temporal and geographical response of ocean acidification during Palaeogene hyperthermals. For the former we present data from Walvis Ridge (1262, paleodepth 3500 m) for three proposed paleo- ocean acidification events: Early Late Palaeocene Event (ELPE), Paleocene-Eocene Thermal Maximum (PETM) and ELMO (59- 53 Ma). These events differ in the extent of carbonate dissolution and thus allow us to study the relative changes in ocean carbonate chemistry. We also present a detailed study of the PETM across a range of sites on Exmouth Plateau (762), Kerguelen Plateau (1135) and a shallower site on Walvis Ridge (1263, paleodepth 1500 m) to determine the global response.