Timing and magnitude of equatorial Atlantic surface warming during the last glacial bipolar oscillation
Abstract. The timing and magnitude of millennial-scale thermal oscillation in the equatorial Atlantic during the last glacial and marine isotope stage 3 have been perceived as merely a response to meltwater-induced perturbations of the northern high latitude climate. The relatively asymmetric distribution of available temperature records has so far impeded testing whether this view is valid across the equatorial Atlantic. This study presents a centennially resolved record of Mg/Ca-derived sea surface temperature (SST) estimates from the eastern equatorial Atlantic (EEA) and a core top-based proxy validation. Multivariate analysis of the EEA core top data indicates that the Mg/Ca ratio varies by 8 ± 2% per unit SST (°C) and 1 ± 0.9% per unit salinity (psu) change, indicating that temperature is the most dominant factor controlling planktonic foraminiferal Mg/Ca variation. The EEA SST time series exhibits a close correlation between episodes of rapid equatorial surface water warming, the onset of massive meltwater inputs into the North Atlantic (Heinrich events H3–H6), and Antarctic climate changes, indicating that the EEA was very sensitive to millennial-scale bipolar oscillations. 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 warming in response to meltwater-induced perturbation of Atlantic meridional ocean circulation (AMOC). At variance with model results that suggest a basin-wide SST rise during and rapid surface cooling concomitant with the termination of Heinrich events, this study indicates persistently elevated EEA SST during and up to 2300 yr after the abrupt termination of Heinrich events. This study emphasizes that changes in wind-induced low-latitude zonal surface currents were crucial in shaping the spatial heterogeneity and duration of equatorial Atlantic surface water warmth.