Impacts of Atmospheric Moisture Transport Extremes on Antarctic Ice Sheet Mass Balance

Abstract

Projections of future rates of sea level rise have large uncertainties. These arise in part from an incomplete understanding of the atmospheric moisture transport processes affecting the difference between mass gained on and lost from the Antarctic Ice Sheet. Events of extreme atmospheric moisture transport, also called atmospheric rivers, can both add mass to and remove it from the Antarctic Ice Sheet when they make landfall. However, the net impact of atmospheric river landfalls on the mass balance of the Antarctic is unclear. Accumulation due to elevated snowfall conditions associated with atmospheric river landfalls over the ice sheet increases its mass, but the intensity and spatial extent of those impacts are unknown. On the other hand, extreme conditions associated with the presence of atmospheric rivers over Antarctic ice shelves may contribute to accelerated iceberg calving from them. Here, we describe research which clarifies both of these areas of uncertainty. First, we examine the association between atmospheric river landfalls with snowfall rates and frequency over the Antarctic Ice Sheet in spaceborne observations. We show that atmospheric rivers correspond with statistically significant snowfall rate and frequency increases over two key regions of the Antarctic Ice Sheet, which persist deep into its interior. We next explore the relationship between atmospheric rivers over Antarctic ice shelves and the timing of tabular iceberg calving from them. We demonstrate a statistically significant relationship between atmospheric rivers and the onset of iceberg calving for certain ice shelves. We then show that iceberg calving events associated with atmospheric rivers tend to feature short-term increases in near-surface air temperature, but not decreases in sea ice concentration, nor changes in near-surface wind speed. We further find that extremes in near-surface air temperature show a statistically significant relationship with the timing of iceberg calving iceberg calving. We affirm that a link between environmental extremes resulting from atmospheric rivers and the onset iceberg calving is plausible. The strongest links we find, however, are between snowfall and atmospheric river landfalls over Antarctica.