| Summary: | Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and (14)C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes. J.G. and L.C.S. acknowledge support from the Gates Cambridge Trust, the Royal Society, the Cambridge Newton Trust and NERC grant NE/J010545/1. J.L. was supported by Marie Curie Fellowship FP7-PEOPLE-2013-IEF (Marie Curie proposal 622483). S.L.J. was funded through the Swiss National Science Foundation (grant PP00P2-144811). C.W. acknowledges support from the European Research Council grant ACCLIMATE/no 339108. This is LSCE contribution no. 4488. This is the final version of the article. It first appeared from Nature Publishing Group via https://doi.org/10.1038/ncomms11539
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