Constraining Millennial‐Scale Changes in Northern Component Water Ventilation in the Western Tropical South Atlantic

Abstract

AbstractNegative excursions in the stable carbon isotopic composition (δ13C) at Atlantic intermediate to mid‐depths are common features of millennial‐scale events named Heinrich Stadials. The mechanisms behind these excursions are not yet fully understood, but most hypotheses agree on the central role played by the weakening of the Atlantic meridional overturning circulation. Marine records registering millennial‐scale negative δ13C excursions in the Atlantic are mostly restricted to the Heinrich Stadials of the last deglacial, while the Heinrich Stadials of the last glacial are poorly studied. Here, we constrain changes in bottom water ventilation in the western tropical South Atlantic mid‐depth during Heinrich Stadials of the last glacial and deglacial by investigating marine core M125‐95‐3. The concurrent decreases in benthic foraminifera δ13C and increases in bulk sediment sulfur indicate an increased Northern Component Water (NCW) residence time in the western tropical South Atlantic mid‐depth during Heinrich Stadials. Furthermore, a coherent meridional pattern emerges from the comparison of our new data to previously published mid‐depth records from the western South Atlantic. While our record shows the largest negative δ13C excursions during almost all Heinrich Stadials, the western equatorialAtlantic showed medium and the subtropical South Atlantic showed the smallest negative excursions. This meridional pattern supports the notion that during Heinrich Stadials, a reduction in the NCW δ13C source signal together with the accumulation of respired carbon at NCW depths drove the negative δ13C excursions. We suggest that the negative δ13C excursions progressively increase along the NCW southwards pathway until the signal dissipates/dilutes by mixing with Southern Component Water.