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Abstract:
The Southern Hemisphere Westerly Winds (SWW) drive upwelling south of the Antarctic Polar Front (PF) that vents CO2 to the atmosphere. During the ice ages, a northward (equatorward) shift of the PF may have reduced this CO2 venting, helping to explain the lower atmospheric CO2 concentration of those times. However, evidence of PF migration is lacking. Here, we report biomarker–based sea surface temperature (SST) reconstructions from two marine sediment cores at different latitudes in the Southern Indian Ocean across the last glacial cycle. Using a quantitative framework for the effect of the PF on meridional SST gradient, we show that the PF underwent an equatorward shift during the ice ages. The PF latitude reconstruction, when compared with other data, also suggests a role for Earth’s axial tilt in the strength and latitude range of SWW-driven upwelling, which may explain previously noted deviations in atmospheric CO2 from a simple correlation with Antarctic climate.
