Revisiting ice sheet mass balance: insights into changing dynamics in Greenland and Antarctica from ICESat-2

Abstract. The time series of observations from NASA’s latest satellite laser altimetry, the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) are now mature to revisit the methodology for estimating surface elevation change and mass balance of ice sheets as proposed by Sørensen et al. (2011). Following the original ICESat study, we combine the derived ICESat-2 surface elevation change estimates with modelled changes of both the firn and the vertical bedrock to derive the total mass balance of the ice sheets, during the northern hemisphere mass balance years of October 2018 to September 2021. The method of converting the surface elevation change to mass balance change has been refined to obtain more reliable mass balance results for both ice sheets. From 2018 to 2021, we find that the grounded ice sheet in Antarctica has lost 135.7±27.3 Gt year^-1, and the Greenland ice sheet 237.5±14.0 Gt year^-1. Compared to 2003–2008, the ICESat-2 derived mass change of the Greenland ice sheet has a similar magnitude; however, the spatial pattern is changed and we observe reduced ice loss around Jakobshavn Isbræ and in the southeast accompanied by increased loss almost everywhere else and especially in the northern sector of the ice sheet. Our results show pervasive ice sheet loss across much of Greenland in recent years and an increase in loss from Antarctica compared to earlier studies. Parallels between the two ice sheets revealed by ICESat-2 data reflect atmospheric and oceanic drivers and show the importance of understanding ice sheets as components within the Earth system.