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 (super 18) O (delta (sub w) ), Antarctic ice volume, and sea level changes across the EOT ( approximately 33.8-33.54 Ma). We also use benthic delta (super 13) C 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 (super 18) O records show a 0.5ppm increase at approximately 33.8 Ma (EOT-1) that represents a approximately 2 degrees C cooling and a small ( approximately 10 m) eustatic fall that is followed by a 1.0 ppm increase associated with Oi-1. The expected cooling of deep waters at Oi-1 ( approximately 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 [CO (sub 3) (super 2-) ]) which affect the Mg/Ca data. To account for this, the BWT, ice volume, and delta (sub w) estimates are corrected for a change in the Delta [CO (sub 3) (super 2-) ] of deep waters on the basis of recently published work. Corrected BWT at Sites 1090 and 1265 show a approximately 1.5 degrees C cooling coincident with Oi-1 and an average delta (sub w) increase of approximately 0.75ppm. The increase in ice volume during Oi-1 resulted in a approximately 70 m drop in global sea level and the development of an Antarctic ice sheet that was near modern size or slightly larger.