Glacial water mass structure and rapid δ18O and δ13C changes during the last glacial termination in the Southwest Pacific

- A vertical transect of marine isotope records anchored in a robust age model.
- A detailed record of the deglaciation fills gaps in depth & time in the SW Pacific.
- Wind-driven mixing ventilated the shallow Southern Ocean in early deglaciation.
- Winds combined with thermohaline transport to drive CO2 release.
- A combination of oceanic triggers achieved pulsed release of CO2 from the ocean.

Changes in ocean circulation are thought to have contributed to lowering glacial atmospheric CO2 levels by enhancing deep ocean sequestration of carbon that was returned to the atmosphere during glacial terminations. High-resolution benthic foraminiferal δ13C and δ18O records from a depth transect of cores in the Southwest Pacific Ocean presented here provide evidence that both wind- and thermohaline-driven circulation drove CO2 from the ocean during the last deglaciation. Shallow geochemical stratification in the glacial Southern Ocean was followed by a short pulse of rapid δ13C enrichment to intermediate water depths during Heinrich Stadial 1, indicative of better-ventilated intermediate waters co-occurring with documented wind-driven upwelling in the Southern Ocean. Intermediate depth δ13C enrichment paused at the start of the Antarctic Cold Reversal (∼14.7 ka), implying a brief shallow restratification, while deeper layers were progressively flushed of δ13C-depleted and δ18O-enriched waters, likely caused by the increasing influence of deep waters sourced from the North Atlantic. The coincidence of atmospheric CO2 increases with these geochemical shifts in both shallow and deep cores suggests that shifts in both atmospheric and oceanic circulation contributed to the deglacial rise of CO2.