NOAA/WDS Paleoclimatology - Brazil Margin Benthic Stable Isotope Data over the last 100ka

The rise in atmospheric CO2 during Heinrich Stadial 1 (HS1; 14.5-17.5 kyr B.P.) may have been driven by the release of carbon from the abyssal ocean. Model simulations suggest that wind-driven upwelling in the Southern Ocean can liberate 13C-depleted carbon from the abyss, causing atmospheric CO2 to increase and the d13C of CO2 to decrease. One prediction of the Southern Ocean hypothesis is that water mass tracers in the deep South Atlantic should register a circulation response early in the deglaciation. Here we test this idea using a depth transect of 12 cores from the Brazil Margin. We show that records below 2300 m remained 13C-depleted until 15 kyr B.P. or later, indicating that the abyssal South Atlantic was an unlikely source of light carbon to the atmosphere during HS1. Benthic d18O results are consistent with abyssal South Atlantic isolation until 15 kyr B.P., in contrast to shallower sites. The depth dependent timing of the d18O signal suggests that correcting d18O for ice volume is problematic on glacial terminations. New data from 2700 to 3000 m show that the deep SW Atlantic was isotopically distinct from the abyss during HS1. As a result, we find that mid-depth d13C minima were most likely driven by an abrupt drop in d13C of northern component water. Low d13C at the Brazil Margin also coincided with an ~80 per mil decrease in D14C. Our results are consistent with a weakening of the Atlantic meridional overturning circulation and point toward a northern hemisphere trigger for the initial rise in atmospheric CO2 during HS1.