Magnitude and timing of Equatorial Atlantic surface warming during the last glacial bipolar oscillations

Abstract. We present core top and down core sample analyses of Mg/Ca in tests of planktonic foraminifer Globigerinoides ruber (variety pink) from the eastern Tropical-Equatorial Atlantic. Multivariate analysis of the core top data shows that Mg/Ca varies by 8 ± 2% and 1 ± 0.9% per unit sea surface temperature (SST) (°C) and salinity (psu) changes, respectively, indicating that temperature exerts the most dominant control on planktonic foraminiferal Mg/Ca variation. A centennially resolved record of Mg/Ca-based SST estimates from the Eastern Equatorial Atlantic (EEA) exhibits a close correlation between episodes of equatorial surface water warming, the onset of massive melt-water inputs into the North Atlantic (Heinrich events H3–H6), and rapid drop of air temperature over Greenland, indicating that the Eastern Equatorial Atlantic responded very sensitively to millennial-scale bipolar oscillations of the last glacial and marine isotope stage 3. Rapid EEA SST rise between 0.8 °C and 2 °C synchronous with the onset of Heinrich events is consistent with the concept of Tropical Atlantic warmth in response to meltwater-induced perturbation of Atlantic meridional ocean circulation (AMOC). The persistence of elevated EEA SST after the abrupt termination of Heinrich events and the spatial heterogeneity pertaining the direction, magnitude, and duration of thermal changes in the Equatorial Atlantic, as indicated by our and other proxy records, is at variance with model results that suggest a basin-wide SST rise during and rapid surface cooling after the end of Heinrich events. Our study emphasizes that changes in wind fields and wind-induced low latitude zonal surface currents were crucial in shaping the spatial heterogeneity and duration of Equatorial Atlantic surface water warmth.