Abstract
Abstract. Mass balance changes of the Antarctic ice sheet are of significant interest due to its sensitivity to climatic changes and its contribution to changes in global sea level. While regional climate models successfully estimate mass input due to snowfall, it remains difficult to estimate the amount of mass loss due to ice dynamic processes. It has often been assumed that changes in ice dynamic rates only need to be considered when assessing long-term ice sheet mass balance; however, 2 decades of satellite altimetry observations reveal that the Antarctic ice sheet changes unexpectedly and much more dynamically than previously expected. Despite available estimates on ice dynamic rates obtained from radar altimetry, information about ice sheet changes due to changes in the ice dynamics are still limited, especially in East Antarctica. Without understanding ice dynamic rates, it is not possible to properly assess changes in ice sheet mass balance and surface elevation or to develop ice sheet models. In this study we investigate the possibility of estimating ice sheet changes due to ice dynamic rates by removing modelled rates of surface mass balance, firn compaction, and bedrock uplift from satellite altimetry and gravity observations. With similar rates of ice discharge acquired from two different satellite missions we show that it is possible to obtain an approximation of the rate of change due to ice dynamics by combining altimetry and gravity observations. Thus, surface elevation changes due to surface mass balance, firn compaction, and ice dynamic rates can be modelled and correlated with observed elevation changes from satellite altimetry.
Highlights
Assessing and understanding ice mass balance of the Antarctic ice sheet (AIS) is challenging due to the remoteness and extensive ice cover of the continent, resulting in a sparse network of field observations to provide information about the climate, mass balance, and bedrock uplift rates
Any errors in the modelled surface mass balance (SMB) lead to differences in the ice dynamic estimates derived from Gravity Recovery And Climate Experiment (GRACE) versus altimetry
We showed that the differences between the old and new RACMO2 versions yield significantly different ice dynamic estimates, with RACMO2.3 producing smaller differences between the GRACE- and ICESat-derived estimates
Summary
Assessing and understanding ice mass balance of the Antarctic ice sheet (AIS) is challenging due to the remoteness and extensive ice cover of the continent, resulting in a sparse network of field observations to provide information about the climate, mass balance, and bedrock uplift rates. Temperature variations, overburden pressure, deformation, and repositioning of snow grains cause snow to densify until it reaches the density of glacier ice ( ∼ 917 kg m−3) (Herron and Langway, 1980) This results in a change in the ice sheet surface elevation without changing the mass of the ice sheet. Ice dynamics are not well known and information about ice dynamic variations is limited (Rignot, 2006; Rignot et al, 2008) This becomes an issue when assessing ice mass balance and surface elevation changes, or establishing ice sheet models. In this study we obtain an estimate of ice sheet dynamic elevation changes by combining modelled SMB rates using the Regional Atmospheric Climate MOdel (RACMO2); Gravity Recovery And Climate Experiment (GRACE); and laser altimetry observations from the Ice, Cloud, and land Elevation Satellite (ICESat). A study site in East Antarctica has been chosen due to the increase in mass that has been observed there by GRACE and altimetry, suggesting a thickening of the ice sheet
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