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 δ 18 O ( δ w ), Antarctic ice volume, and sea level changes across the EOT (∼33.8–33.54 Ma). We also use benthic δ 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 δ 18 O records show a 0.5‰ increase at ∼33.8 Ma (EOT‐1) that represents a ∼2°C cooling and a small (∼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 (∼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 (Δ[CO 3 2− ]) which affect the Mg/Ca data. To account for this, the BWT, ice volume, and δ w estimates are corrected for a change in the Δ[CO 3 2− ] of deep waters on the basis of recently published work. Corrected BWT at Sites 1090 and 1265 show a ∼1.5°C cooling coincident with Oi‐1 and an average δ w increase of ∼0.75‰. The increase in ice volume during Oi‐1 resulted in a ∼70 m drop in global sea level and the development of an Antarctic ice sheet that was near modern size or slightly larger.

Chief Scientists: Miller, Sugarman Staff Scientist: Browning Operations: Cobbs, Miller, Sugarman Lithostratigraphy: Browning, Kulpecz, McLaughlin, Miller, Mizintseva, Monteverde, Pusz, Rankin, Sugarman, Tomlinson, Uptegrove, Velez Biostratigraphy: Planktonic foraminifers: Olsson Calcareous nannofossils: Aubry (Cenozoic), Bukry (Mesozoic), Mizintseva (Mesozoic) Spores and pollen: Brenner, McLaughlin Logging: McLaughlin Sr isotopic stratigraphy: Browning, Feigenson

We evaluated the age of two Upper Eocene impact ejecta layers (North American microtektites linked to the Chesapeake Bay impact structure and clinopyroxene [cpx] spherules from the Popigai crater) and the global effects of the associated impact events. The reported occurrence of cpx spherules from the Popigai impact structure at South Atlantic ODP Site 1090 within the middle of magnetochron C16n.1n yields a magnetochronologic age of 35.4 Ma. We generated high-resolution stable isotope records at Sites 1090, 612 (New Jersey slope), and Caribbean core RC9-58 that show: (1) a 0.5% delta C-13 decrease in bulk-carbonate at Site 1090 coincident with the Popigai cpx spherule layer, and (2) a 0.4%-0.5% decrease in deep-water benthic for aminiferal delta C-13 values across the Popigai impact ejecta layer at Site 612 and core RC9-58. We conclude that the delta C-13 excursion associated with Popigai was a global event throughout the marine realm that can be correlated to magnetochron C16n.1n. The amplitude of this excursion (similar to 0.5%) is within the limits of natural variability, suggesting it was caused by a decrease in carbon export productivity, potentially triggered by the impact event(s). North American microtektites associated with the Chesapeake Bay impact occur stratigraphically above the Popigai cpx spherules at Site 612 and core RC9-58. We found no definite evidence of a delta C-13 anomaly associated with the North American microtektite layer, though further studies are warranted. High-resolution bulk-carbonate and benthic foraminiferal delta O-18 records show no global temperature change associated with the cpx spherule or North American microtektite layers.