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Zusammenfassung:
The Southern Westerly Winds (SWW) drive upwelling south of the Antarctic Polar Front that vents CO2 to the atmosphere. During the ice ages, a northward (equatorward) shift of the Antarctic Circumpolar Current (ACC) fronts may have reduced this CO2 venting, helping to explain the lower atmospheric CO2 concentration of those times. However, direct evidence of frontal migration is scarce. In this study, we report biomarker-based surface layer temperature reconstructions from 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 ACC fronts on meridional SST gradient, we show that the ACC was ~2° equatorward relative to its modern position during the ice ages and ~4-6° poleward than its modern position at the end of the last two glacial terminations, consistent with ACC migration playing a role in glacial-interglacial CO2 change. Further comparison of the temporal evolution of ACC latitude with other observations posits a role for Earth’s axial tilt in the strength and latitude range of SWW-driven upwelling. This has implications for past and future atmospheric CO2 concentrations and may explain previously noted deviations in atmospheric CO2 from a simple correlation with Antarctic climate.
