Southern Ocean contribution to both steps in deglacial atmospheric CO rise.

The transfer of vast amounts of carbon from a deep oceanic reservoir to the atmosphere is considered to be a dominant driver of the deglacial rise in atmospheric CO. Paleoceanographic reconstructions reveal evidence for the existence of CO-rich waters in the mid to deep Southern Ocean. These water masses ventilate to the atmosphere south of the Polar Front, releasing CO prior to the formation and subduction of intermediate-waters. Changes in the amount of CO in the sea water directly affect the oceanic carbon chemistry system. Here we present B/Ca ratios, a proxy for delta carbonate ion concentrations Δ[CO], and stable isotopes (δC) from benthic foraminifera from a sediment core bathed in Antarctic Intermediate Water (AAIW), offshore New Zealand in the Southwest Pacific. We find two transient intervals of rising [CO] and δC that that are consistent with the release of CO via the Southern Ocean. These intervals coincide with the two pulses in rising atmospheric CO at ~ 17.5-14.3 ka and 12.9-11.1 ka. Our results lend support for the release of sequestered CO from the deep ocean to surface and atmospheric reservoirs during the last deglaciation, although further work is required to pin down the detailed carbon transfer pathways.