Southern Ocean glacial conditions and their influence on deglacial events

The Southern Ocean is an important regulator of global CO₂ levels and likely had a key role in lowering atmospheric CO₂ levels during the Last Glacial Maximum (LGM) and driving the subsequent increase during the following deglaciation. Nonetheless, debate continues surrounding the relative importance of Northern versus Southern Hemisphere forcing during deglacial events. In this Review, we compare modern Southern Ocean conditions with those in the LGM and deglacial period, identifying factors that were critical in initiating the glacial termination. During the LGM, North Atlantic sourced waters appear to have shoaled and were largely absent from the glacial Southern Ocean. Increased ocean stratification, shoaling of the chemical divide and increased nutrient utilization at the surface contributed to glacial carbon sequestration in deep waters. Warming at mid-latitudes of the Southern Hemisphere and the Southern Ocean began at ~21 ka, preceding deglaciation, indicating insolation changes could have driven early atmosphere–ocean warming that initiated the shifting of ocean fronts leading to the release of carbon sequestered in the LGM. Southern Ocean dynamics appear to have been substantial, or even the critical, factors initiating the termination of the LGM before deepening of North Atlantic sourced waters. Future research should focus on better resolving deglacial chemical and physical changes in Southern Ocean waters and their representation in numerical models.