Atmospheric drying as the main driver of dramatic glacier wastage in the southern Indian Ocean

Abstract

The ongoing retreat of glaciers at southern sub-polar latitudes is particularly rapid and widespread. Akin to northern sub-polar latitudes, this retreat is generally assumed to be linked to warming. However, no long-term and well-constrained glacier modeling has ever been performed to confirm this hypothesis. Here, we model the Cook Ice Cap mass balance on the Kerguelen Islands (Southern Indian Ocean, 49°S) since the 1850s. We show that glacier wastage during the 2000s in the Kerguelen was among the most dramatic on Earth. We attribute 77% of the increasingly negative mass balance since the 1960s to atmospheric drying associated with a poleward shift of the mid-latitude storm track. Because precipitation modeling is very challenging for the current generation of climate models over the study area, models incorrectly simulate the climate drivers behind the recent glacier wastage in the Kerguelen. This suggests that future glacier wastage projections should be considered cautiously where changes in atmospheric circulation are expected.

High-resolution dynamical downscaling of re-analysis data over the Kerguelen Islands using the WRF model

“…The warmest regions of the islands referred above have the lowest total amounts of precipitation for all seasons, comparable to those over the surrounding waters. The precipitation results are consistent with Favier et al (2016) who found a significant correlation between precipitation and elevation. Figure 7 shows the results for the 10-m horizontal wind.…”

“…Unlike the other modes, SAM has a direct effect on the seasonal mean climate of the Kerguelen Islands as it is related to variations in the position and strength of the storm track that impacts the islands. As discussed in Favier et al (2016), the recent increase in the SAM index and resultant poleward shift of the storm track has led to generally drier conditions in the islands. As seen in Fig.…”

“…Favier et al (2016) showed that changes in the SIOD and SAM lead to variations in the storm track which impacts the Kerguelen Islands. Their influence is analysed here.…”

“…Recently, Favier et al (2016) has shown that the glacier wastage in the Kerguelen Islands during the 2000s was among the most dramatic on Earth. These authors have also found that most of the climate models from the Coupled Model Intercomparison Project 5 (CMIP5; Taylor et al 2012) cannot reproduce properly the observed atmospheric conditions over the islands, in particular the precipitation.…”

“…Favier et al (2016) showed that an increase in the Southern Annular Mode (SAM; Marshall 2013) index, the principal mode of atmospheric circulation variability in the Southern Hemisphere, since the mid-1970s has led to a poleward shift of the storm track with higher surface pressures and drier conditions around the Kerguelen Islands and equatorward. Before 1975, the temperature pattern over the southern Indian Ocean resembled the Subtropical Indian Ocean Dipole (SIOD; Behera and Yamagata 2001).…”