Poleward shift in the Southern Ocean westerlies synchronous with the deglacial rise in atmospheric CO2

The Southern Ocean westerly winds are hypothesised to play a key role in regulating atmospheric CO₂ over glacial-interglacial cycles; constraints on the paleo-latitude of the westerly winds have, however, remained allusive.  Here we use changes in the spatial pattern of planktic foraminiferal ∂¹⁸O to track changes in the latitude of the Southern Ocean polar and subtropical fronts over the last deglaciation, which are closely tied to the position of the westerly winds. We find a ~5° equator-ward shift in the position of the fronts (and thus westerlies) during the last glacial maximum relative to their Holocene position. Our reconstruction shows the poleward shift in the westerlies over deglaciation closely mirrors the sub-millennial scale variability seen in the rise in atmospheric CO₂. We propose that changes in the position of the westerly winds modulate CO₂ via changes in the extent of Southern Ocean sea ice and circulation of the abyssal ocean. Using climate model simulations, we explore the possibility of a feedback loop by which these CO₂/climatic changes may lead to further changes in the position of the westerly winds.