Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO₂ changes

摘要

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 14C 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.