Interhemispheric coupling and warm Antarctic interglacials

Holden, P. B.; Edwards, N. R.; Wolff, E. W.; Lang, N. J.; Singarayer, J. S.; Valdes, P. J.; Stocker, T. F.
November 2009
Climate of the Past Discussions;2009, Vol. 5 Issue 6, p2555
Academic Journal
Ice core evidence indicates that even though atmospheric CO2 concentrations did not exceed ∼300 ppm at any point during the last 800 000 years, East Antarctica was at least ∼3-4 °C warmer than pre-industrial (CO2 ∼280 ppm) in each of the last four interglacials. During the previous three interglacials, this anomalous warming was short lived (∼3 000 years) and apparently occurred before the completion of Northern Hemisphere deglaciation. Hereafter, we refer to these periods as "Warmer than Present Transients" (WPTs). We here present transient 800 kyr simulations using the intermediate complexity model GENIE-1 which suggest that WPTs could be explained as a consequence of the meltwater-forced slowdown of the Atlantic Meridional Overturning Circulation (AMOC) during glacial terminations. It is well known that a slowed AMOC would increase southern Sea Surface Temperature (SST) through the bipolar seesaw. Observational data supports this hypothesis, suggesting that the AMOC remained weak throughout the terminations preceding WPTs, strengthening rapidly at a time which coincides closely with peak Antarctic temperature. In order to investigate model and boundary condition uncertainty, we additionally present three ensembles of transient GENIE-1 simulations across Termination II (135 000 to 124 000 BP) and three snapshot HadCM3 simulations at 130 000 Before Present (BP). These simulations together reproduce both the timing and magnitude of WPTs, and point to the potential importance of an albedo feedback associated with West Antarctic Ice Sheet (WAIS) retreat.


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