Centennial-scale changes in Atlantic Meridional Overturning Circulation (AMOC) strength might disturb global climate by altering interhemispheric heat transport and CO2 partitioning between the ocean and the atmosphere. Due to the short instrumental record and lack of high-resolution paleo records that so far only resolve millennial-scale changes, centennial-scale changes remain elusive. Here we use radiocarbon ventilation ages from a western equatorial Atlantic sediment core with a remarkably high sedimentation rate to reconstruct AMOC variability during the last deglaciation, with a focus on Heinrich Stadial 1 (HS1; 17.8-14.8 ka). Results from model simulations indicate that ventilation ages serve as a sensitive proxy for AMOC variability under weak overturning conditions (i.e., during HS1) at our study location. Notably, within an overall weakened AMOC condition during HS1, our record shows two centennial-scale AMOC intensifications: one from 16.5 to 15.8 ka and another at ~15.4 ka. These centennial-scale episodes of intensified AMOC briefly revitalized Atlantic interhemispheric heat transport during HS1, resulting in decreased precipitation over northeastern Brazil and short-lived but intense changes in climate elsewhere. These episodes of AMOC intensification likely transported substantial volumes of CO2-rich water from the mid-depth Atlantic to the Southern Ocean, where the CO2 was rapidly outgassed to the atmosphere. Using radiocarbon ages from Atlantic sediments, AMOC variability during Heinrich Stadial 1 is reconstructed, revealing brief intensifications that altered heat transport, reduced rainfall over northeastern Brazil, and likely enhanced atmospheric CO2.
Jena et al. (Tue,) studied this question.