Deep water temperature, carbonate ion, and ice volume changes across the Eocene-Oligocene climate transition

Paired benthic foraminiferal stable isotope and Mg/Ca data are used to estimate bottom water temperature (BWT) and ice volume changes associated with the Eocene-Oligocene Transition (EOT), the largest global climate event of the past 50 Myr. We utilized ODP Sites 1090 and 1265 in the South Atlantic to assess seawater delta O-18 (delta(w)), Antarctic ice volume, and sea level changes across the EOT (similar to 33.8-33.54 Ma). We also use benthic delta C-13 data to reconstruct the sources of the deep water masses in this region during the EOT. Our data, together with previously published records, indicate that a pulse of Northern Component Water influenced the South Atlantic immediately prior to and following the EOT. Benthic delta O-18 records show a 0.5% increase at similar to 33.8 Ma (EOT-1) that represents a similar to 2 degrees C cooling and a small (similar to 10 m) eustatic fall that is followed by a 1.0% increase associated with Oi-1. The expected cooling of deep waters at Oi-1 (similar to 33.54 Ma) is not apparent in our Mg/Ca records. We suggest the cooling is masked by coeval changes in the carbonate saturation state (Delta[CO32-]) which affect the Mg/Ca data. To account for this, the BWT, ice volume, and delta(w) estimates are corrected for a change in the Delta[CO32-] of deep waters on the basis of recently published work. Corrected BWT at Sites 1090 and 1265 show a similar to 1.5 degrees C cooling coincident with Oi-1 and an average delta(w) increase of similar to 0.75%. The increase in ice volume during Oi-1 resulted in a similar to 70 m drop in global sea level and the development of an Antarctic ice sheet that was near modern size or slightly larger.