Interhemispheric coupling, the West Antarctic Ice Sheet and warm Antarctic interglacials

Abstract

Abstract. Ice core evidence indicates that even though atmospheric CO 2 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 (CO 2 ∼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 preceding WPTs, 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

How warm was the last interglacial? New model–data comparisons

“…It also enhances the MAT warming over East Antarctica but only by a few tenths • C, still greatly underestimating the warming indicated by the ice cores. Simulations with HadCM3 [17] suggest that in addition to the WAIS retreat, freshwater input to the North Atlantic from the Laurentide and Eurasian ice sheets during the termination is needed to produce MAT warming that is consistent with the ice core data. This is consistent with evidence of persistent iceberg melting at high northern latitudes at the beginning of the LIG [55].…”

“…AOGCMs though have not been able to produce the warming indicated by the East Antarctic ice cores when forced by orbital forcing changes only [17,18]. Transient simulations for the LIG with intermediate complexity models [19] suggest that Arctic warming peaked early in the interglaciation because obliquity peaked earlier than precession [20], while meltwater forcing introduced to the North Atlantic can generate an early Antarctic warming [17].…”

The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles

“…While in the model they are only slightly warmer than the present interglacial, the reconstructions suggest that previous interglacials were warmer by about 4 • C (Jouzel et al, 2007). Much warmer conditions in Antarctica during previous interglacials can be attributed to the disappearance of the West Antarctic ice sheet (Holden et al, 2010) and the initial temperature overshoot due to the mechanism of the bipolar seesaw (Ganopolski and Roche, 2009). The first mechanism is not taken into account in our simulations since we did not include changes in the Antarctic ice sheet.…”

The last interglacial climate: comparing direct and indirect impacts of insolation changes

“…Merz et al (2014), however, find a very stable response of the large-scale circulation in their AGCM simulations with a variety of last interglacial Greenland ice sheet reconstructions. For Antarctica, previous studies indicate that reduction of the West Antarctic ice sheet could cause additional local warming over the Antarctic continent Holden et al 2010;Otto-Bliesner et al 2013).…”