Inter-basin comparison of deep ocean temperature change at the Eocene-Oligocene Transition

The abrupt onset of large-scale Antarctic glaciation approximately 34 million years ago, at the Eocene-Oligocene Transition (EOT), was the pivot point in Cenozoic climate history between greenhouse and icehouse climate states. Our understanding of this event relies heavily on benthic foraminiferal oxygen isotope (18Ob) records but the paucity of independent temperature reconstructions prevents an assessment of the contributions of temperature and ice volume to the rapid 18Ob increase which is interpreted to mark the onset of large-scale Antarctic glaciation. Here we present records of deep-sea temperature change for the EOT using clumped isotope thermometry which permits explicit temperature reconstructions independent of seawater chemistry and ice volume. Recently published benthic foraminiferal clumped isotope records from the eastern equatorial Pacific (Taylor et al. 2023) and a low-resolution long-term record from the northwest Atlantic Ocean (Meckler et al. 2022) hint at a possible thermal decoupling of these two major deep ocean basins at the EOT. To investigate this further, we present new temperature records from the Newfoundland margin in the northwest North Atlantic Ocean (IODP Exp. 342 Sites U1406 and U1411). In addition, we supplement the previously published records from the eastern equatorial Pacific (Taylor et al. 2023) with additional data (ODP Leg 199 Site 1218 and IODP Exp. 320 Sites U1334 and U1333) to better constrain the timing of the onset of deep ocean cooling relative to the onset of large-scale Antarctic glaciation. These new detailed records from both ocean basins enable an assessment of potential divergences in the evolution of deep ocean temperatures in the North Atlantic and Pacific at the EOT, and thus changes in ocean circulation prior to and/or in response to the onset of Antarctic glaciation. Meckler, A. N. et al., (2022). Cenozoic evolution of deep ocean temperature from clumped isotope thermometry. Science,377 (6601), 86-90. Taylor, V. E., Wilson, P. A., Bohaty, S. M., Meckler, A. N., (2023). Transient deep ocean cooling in the eastern equatorial Pacific Ocean at the Eocene-Oligocene Transition. Paleoceanography and Paleoclimatology, 38, e2023PA004650. https://doi. org/10.1029/2023PA00465