GFI/BCCR Seminar: Unforced Southern Ocean deep convection as a driver of millennial-scale Antarctic warming

Joel Pedro (NBI, København Universitet):

Unforced Southern Ocean deep convection as a driver of millennial-scale Antarctic warming

Abstract
Antarctic Isotope Maxima (AIM) – centennial-to-millennial-scale warming events observed in Antarctic ice cores during the last glacial period – are conventionally explained by changes in northward ocean heat transport during Dansgaard-Oeschger events. We propose an alternative mechanism in which internal atmosphere–sea-ice–ocean processes at southern high latitudes play the central role.

Simulations with a free-running coupled climate model show that heat release associated with Southern Ocean deep convection variability can drive Antarctic temperature variations of 0.5–2.0 °C. The mechanism involves three steps: (1) Preconditioning: heat accumulates at depth in the stratified glacial Southern Ocean; (2) Convection onset: wind and/or sea-ice changes (potentially remotely triggered) tip the preconditioned system into the convective state; (3) Antarctic warming: fast sea-ice–albedo feedbacks (on annual–decadal timescales) and slower Southern Ocean frontal and sea-surface temperature adjustments to convective heat release (on multidecadal–centennial timescales), drive an increase in atmospheric heat and moisture transport over Antarctica.