Abstract:

Strong middepth warming and weak radiocarbon imprints in the equatorial Atlantic during Heinrich 1 and Younger Dryas

We present a benthic foraminiferal multi-proxy record of eastern equatorial Atlantic (EEA) mid depth water (1295 m) covering the last deglacial. We show that EEA mid depth water temperatures were elevated by 3.9 ± 0.5 °C and 5.2 ± 1.2 °C during Heinrich event 1 (H1) and Younger Dryas (YD), respectively. The radiocarbon content of the EEA mid depth during H1 and YD is relatively low and comparable to the values of the pre-H1 episode and Bølling-Allerød, respectively. A transient earth system model simulation, which mimics the observed deglacial AMOC history, qualitatively reproduces the major features of the EEA proxy records. The simulation results suggest that fresh water-induced weakening of the AMOC leads to a vertical shift of the horizon of Southern Ocean-sourced water and a stronger influence of EEA sea surface temperatures via mixing. Our findings reaffirm the lack of a distinctive signature of radiocarbon depletion and therefore do not support the notion of interhemispheric exchanges of strongly radiocarbon-depleted mid-depth water across the tropical Atlantic during H1 and YD. Our temperature reconstruction presents a critical zonal and water depth extension of existing tropical Atlantic data and documents a large-scale and basin-wide warming across the thermocline and mid-depth of the tropical Atlantic during H1 and YD. Significant difference in the timing and pace of H1 mid-depth warming between tropical Atlantic and North Atlantic likely points to a limited role of the tropical Atlantic mid-depth warming in the rapid heat build up in the North Atlantic mid depth.

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