TEX86H proxy and BIT index of sediment core GeoB9528-3

Changes in the strength of Atlantic meridional overturning circulation (AMOC) are known to have profound impacts on global climate. Coupled modelling studies have suggested that, on annual to multi-decadal time scales, a slowdown of AMOC causes a deepening of the thermocline in the tropical Atlantic. However, this process has been poorly constrained by sedimentary geochemical records. Here, we reconstruct surface (UK'37 Index) and thermocline (TEXH86) water temperatures from the Guinea Plateau Margin (Eastern tropical Atlantic) over the last two glacial-interglacial cycles (~ 192 kyr). These paleotemperature records show that periods of reduced AMOC, as indicated by the d13 C benthic foraminiferal record from the same core, coincide with a reduction in the near-surface vertical temperature gradient, demonstrating for the first time that AMOC-induced tropical Atlantic thermocline adjustment exists on longer, millennial time scales. Modelling results support the interpretation of the geochemical records and show that thermocline adjustment is particularly pronounced in the eastern tropical Atlantic. Thus, variations in AMOC strength appear to be an important driver of the thermocline structure in the tropical Atlantic from annual to multi-millennial time scales.

Stable isotopes and sea surface temperature on planktic foraminifera of sediment core WIND 28K

We reconstructed the surface hydrography of the South Equatorial Current in the western Indian Ocean for the last 65,000 years using a marine sediment core record. Results show that tropical Indian Ocean temperatures resemble temperatures from Antarctic ice cores with warm and cold fluctuations synchronous with the Antarctic Cold Reversal and the Antarctic warm events A1-A4. The most likely thermal link involves Subantarctic Mode Water (SAMW) which forms north of the subpolar frontal zone and spreads northward into the Indian Ocean. This subsurface water mass is the prime suspect because of a stronger temperature response in the thermocline (recorded by the foraminifer N. dutertrei) than in surface water (G. ruber).