Interhemispheric coupling, the West Antarctic Ice Sheet and warm Antarctic interglacials
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 preindustrial (CO2 280 ppm) in each of the last four interglacials. During the previous three interglacials, this anomalous warming was short lived (3000 years) and apparently occurred before the completion of Northern Hemisphere deglaciation. Hereafter, we refer to these periods as “Warmer than Present Transients” (WPTs). We present a series of experiments to investigate the impact of deglacial meltwater on the Atlantic Meridional Overturning Circulation (AMOC) and Antarctic temperature.
It is well known that a slowed AMOC would increase southern
sea surface temperature (SST) through the bipolar seesaw
and observational data suggests that the AMOC remained
weak throughout the terminations precedingWPTs, strengthening rapidly at a time which coincides closely with peak Antarctic temperature. We present two 800 kyr transient simulations using the Intermediate Complexity model GENIE-1 which demonstrate that meltwater forcing generates transient southern warming that is consistent with the timing of WPTs, but is not sufficient (in this single parameterisation) to reproduce the magnitude of observed warmth. In order to investigate model and boundary condition uncertainty, we 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 BP. Only with consideration of the possible feedback of West Antarctic Ice Sheet (WAIS)
retreat does it become possible to simulate the magnitude of
Authors: Holden, P.B., Edwards, N.R., Wolff, Eric W., Lang, Nicola J., Singarayer, J.S., Valdes, P.J., Stocker, T.F.