Modern-day mass gains over East Antarctica exceed the two decades prior

The recent Ice sheet Mass Balance Inter-comparison Exercise (IMBIE) suggests that between 2012 and 2017 the East Antarctic Ice Sheet was approximately in balance, experiencing a rate of mass change of 23 ± 38 Gt yr-1. While this study provided an important statistical reconciliation of various studies across several techniques, the root cause of the differences amongst the estimates remains unresolved. Satellite gravimetry provides a direct measurement of mass change; however, it is sensitive to all mass changes, and the necessary corrections for solid earth changes are substantial and poorly constrained. Satellite altimetry provides measurements of volume change, which includes changes in ice mass and non-ice mass. The latter is largely driven by changes in the density of the snow and firn requiring poorly constrained models for conversion to mass. Here, rather than deriving ice-sheet mass balance using a single technique, we use both satellite gravimetry and altimetry to better: (1) reconcile mass balance estimates between the two techniques, (2) improve constraint on firn dynamics, and (3) attempt to partition the driver of change. Because these two measurements are sensitive to different processes, using them in conjunction provides additional constraint of the most unknown processes. Our new technique solves for the change in total firn air content through time for the entire Antarctic Ice Sheet that provides a best-fit mass solution between altimetry and gravimetry. In such a way, we produce ice-sheet mass change at the fine-scale resolution of ice elevation measurements (10 km) that best matches the coarsely resolved (>100km) mass change from gravimetry. Our results indicate that during the ICESat-2 era (April 2019 through June 2023), the East Antarctic Ice Sheet gained mass at a rate of 160 Gt yr-1, three times the average mass gain over the two decades prior (52 Gt yr-1). The sector that spans 60E to 130E received the largest anomalous gains in mass (precipitation). These gains, in conjunction with minor gains from the Antarctic Peninsula (23 Gt yr-1), fully balance the continued mass losses from West Antarctica (-139 Gt yr-1). Large precipitation events over both East Antarctica and the Antarctic Peninsula are driving the mass gains; however, more time is needed to determine whether these changes are long-term or only short-lived given the ICESat-2 time series is just over 4 years in length. These results suggest that atmospheric dynamics play a key role in driving the mass balance of the East Antarctic Ice Sheet and have potential to rapidly change the overall mass balance of the ice sheet.