Deglacial radiocarbon history of tropical Atlantic thermocline waters: absence of CO 2 reservoir purging signal

Abstract

A current scenario to explain much of the atmospheric CO 2 increase during the Glacial to Holocene climate transition requires the outgassing of a deep, old oceanic CO 2 reservoir thought to be located in the Southern Ocean. In this scenario, CO 2-rich and 14C-depleted subsurface Antarctic-sourced water, ventilates the thermocline where it is purged to the atmosphere in the equatorial regions, a view that has been met with conflicting results. Using a novel approach (paired surface and deep-dwelling planktonic foraminifer radiocarbon analyses), we document that the equatorial Atlantic thermocline did not see old, 14C-depleted water, which would be characteristic of the proposed isolated deep ocean CO 2 reservoir. Data from several studies concur that, during the deglaciation, Antarctic intermediate waters were contributing to Atlantic thermocline waters even more than today, therefore, our observations challenge the current purging hypothesis. Together with other studies, these results suggest that the mechanism responsible for the deglacial CO 2 rise cannot invoke contemporary circulation modes and/or thermocline ventilation pathways.