A 95-myr continuous record of sea-surface temperatures and polar amplification from planktonic foraminiferal 18O

Polar amplification is observed in the geologic record as a decrease in the latitudinal temperature gradient (LTG, here defined as the difference in sea-surface temperatures between high and low latitudes) during warmer climate states. However, there remain large disagreements (up to 10 C) in LTGs predicted by proxies vs. models, due in large part to differing reconstructions of high-latitude sea-surface temperatures (SSTs) in warm climate states. We develop methods leveraging an extensive compilation of planktonic foraminifera 18O to reconstruct a continuous record of LTGs over the last 95 Myr, accounting for diagenetic and hydrologic concerns. We show that LTGs exhibit a consistent negative relationship with mean global SST, with the highest gradients during the coldest intervals of time. From this relationship, we calculate an equilibrium polar amplification factor (PAF, the ratio of change in high latitude SST to change in global mean SST) of 1.390.15. Our results are closer to model predictions than estimates based on organic biomarkers, primarily due to our high-latitude SST estimates closely tracking benthic temperatures rather than showing the large surface-to-deep temperature gradient implied by organic records. The consistent covariance of 18O values in low- and high-latitude planktonic and benthic foraminifera, across numerous climate states, suggests an important underlying predictability of high-latitude climate forcings across large changes in atmospheric CO2, continental configuration, oceanic gateways, and the extent of continental ice sheets.