Early to Late Pliocene climate change at mid-latitudinal North Atlantic Site U1313

The early Pliocene, with atmospheric CO₂ concentrations at levels similar to today, is seen as a case study for Earth’s future climate evolution. During this period the progressive closing of the Central American Seaway led to increased poleward heat and salt transport within the Atlantic with North Atlantic Deep Water (NADW) becoming warmer and saltier and resulting in an enhanced Atlantic Meridional Overturning Circulation (AMOC). To evaluate the stability of the Pliocene AMOC, we are producing centennial-scale surface and deep-water records for IODP Site U1313 (41°N, 33°W, 3412m) for the interval from 3.3 to 4.4 Ma. This site is ideally located to monitor past AMOC changes with North Atlantic Drift waters at the surface and NADW, exported by the deep western boundary current, in the deep. Surface water variations are reconstructed based on the stable isotope data of the planktonic foraminifer genus Globigerinoides sp. and on Mg/Ca derived temperatures during the late Pliocene, whereas deep-water changes are revealed by the stable isotope records of the benthic foraminifer genus Cibicidoides. Besides the interglacial/glacial cycles, higher frequency oscillations are recorded in the foraminiferal records. Varying surface water conditions, especially during Late Pliocene interglacial periods, are observed and we will use the pending Mg/Ca temperature data to assess if they are linked to salinity changes. The high-frequency oscillations are related to precession forcing, especially its harmonics in the 5.5 kyr and 11 kyr ranges. The benthic δ¹³C values indicate nearly continuous NADW presence and confirm a strong AMOC throughout the studied interval, also during most of the glacial periods. During the early Pliocene, glacial stage Gi 6 had a stronger impact on the AMOC than Gi 2 and Gi 4. Overall, the AMOC was strong throughout, but experienced high frequency oscillations at a level similar to the middle Pleistocene interglacial periods.