The Large-Scale Climate in Response to the Retreat of the West Antarctic Ice Sheet

Abstract

Based upon coupled climate simulations driven by present day and conditions resembling the Marine Isotope Stage 31 (WICE-EXP), insofar the West Antarctic Ice Sheet (WAIS) configuration is concerned, we demonstrate that changes in the WAIS orography lead to noticiable changes in the oceanic and atmospheric circulations. Compared with the present day climate, the WICE-EXP is characterized by warmer conditions in the Southern Hemisphere (SH) by up to 5 • C in the polar oceans and up to 2 • C in the Northern Hemisphere (NH). These changes feed back on the atmospheric circulation weakening (strengthening) the extratropical westerlies in the SH (northern Atlantic). Calculations of the Southern Annular Mode (SAM) show that modification of the WAIS induces warmer conditions and a northward shift of the westerly flow, in particular there is a clear weakening of the polar jet. These changes lead to modification of the rate of deep water formation reducing the magnitude of the North Atlantic Deep Water, but enhancing the Antarctic Bottom Water. By evaluating the density flux we have found that the thermal density flux has played a main role in the modification of the meridional overturning circulation. Moreover, the climate anomalies between the WICE-EXP and the present day simulations resemble a bipolar seesaw pattern. These results are in good agreement with paleorecontructions in the framework of the Ocean Drilling and ANDRILL Programs.4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 442 rium in accelerated global oceanic models.

Oceanic response to changes in the WAIS and astronomical forcing during the MIS31 superinterglacial

“…2a) is substantially smaller than the results presented by Justino et al (2015). There are several factors related to these differences.…”

“…The ocean component has 31 vertical levels with layer thicknesses ranging from 10 m at the surface to 500 m at the ocean bottom (16 levels in the upper 200 m). Additional details of the ICTP-CGCM are described by Justino et al (2015) and Kucharski et al (2015).…”

“…TOPO applies the MIS31 WAIS topography as proposed by previous studies Justino et al, 2015); 2. AST is conducted with the astronomical configuration characteristics of 1072 ka (Berger, 1978;Coletti et al, 2015); 3. and MIS31 is the combined effect of the forcing described in TOPO and AST.…”

“…Previous work by Justino et al (2015) using a simplified lowresolution ocean model (3 • × 3 • ) has demonstrated that the incorporation of a modified WAIS topography, characteristic of the MIS31 interval, results in generally warmer global surface temperatures compared to the current climate with enhanced positive anomalies between 50 and 70 • S.…”

“…Modeled Weddell Sea warming in the TOPO simulation is related to weaker katabatic winds and reduced continental cold air advection due to a collapsed WAIS (Justino et al, 2015). During periods of reduced sea ice thickness, there is an increase in the heat flux from the ocean to the atmosphere.…”