ALBERT

Description: Totten Glacier is the principal source of ice loss from the East Antarctic Ice Sheet. Although the East Antarctic Ice Sheet as a whole has remained approximately in balance, the response of Totten Glacier to climate forcing remains a key source of uncertainty in predicting its future contribution to sea level rise. Here, we compare and combine estimates of the mass change of Totten Glacier and it's surrounding region from satellite measurements of changes in its volume, ice speed and gravitational potential acquired over the past two decades between 2002 and 2022. Ice losses from the Totten Glacier catchment and two surrounding areas – the Vincennes Bay region and the Moscow University catchment – have doubled since 2002 from 8.5 ± 0.7 Gt/yr to 20 ± 1.5 Gt/yr. We find the largest disagreement in Vincennes Bay, which remains a challenging region in which to monitor mass changes - likely a combination of a paucity in observations of ice thickness, and the regions’ small mass imbalance compared to local SMB fluctuations. Using a regional climate model, we show that only Totten Glacier is losing ice due to it flowing faster than it’s equilibrium state, although the rate of its dynamic ice loss has slowed by 60 %. In total, the region has lost 285 ± 19 Gt of ice and raised the global sea level by 0.8 ± 0.1 mm, with the majority (62 %) of this loss originating from Totten Glacier itself.

Description: Satellite gravimetry as realized by the GRACE and GRACE-FO missions (both referred to as GRACE in the following) is a major observation for ice mass balance estimates. Thereby, GRACE-based studies were often conducted separately for either the Antarctic Ice Sheet, the Greenland Ice Sheet, or the global glacier domain or selected glacier regions. The start of the Glacier Mass Balance Intercomparison Exercise (GLAMBIE) in addition to the Ice-sheet Mass Balance Intercomparison Exercise (IMBIE) gives new impetus to questions about the consistency between GRACE-based estimates for different land ice domains and about the sensitivity of the estimates to methodological choices. We report investigations on a consistent land ice mass balance estimate based on our tailored sensitivity kernel approach previously applied to the Antarctic Ice Sheet and the Greenland Ice Sheet. In the tailored sensitivity kernel approach the sensitivity kernel of the mass change estimator is directly optimized in a formal minimization of propagated GRACE solution errors and leakage errors. The focus on specific regions is realized by 'tailoring' the method to the signal of interest based on available signal covariance information of mass changes, without violating global consistency of the analysis. We show via a sensitivity analysis how different parameters of the estimation method (such as weighting of GRACE error covariance information, degree of external information employed for the signal covariance information, and accounting for sea-level fingerprints) influence the resulting mass change estimates.

Description: In 2019 the Combination Service for Time-variable Gravity fields (COST-G) started operation with the release of the complete time-series of combined GRACE monthly gravity fields COST-G GRACE RL01. Meanwhile additional time-series of monthly GRACE gravity fields have become available, mainly from Chinese analysis centers. The COST-G quality control confirms the high quality of these solutions that are derived with independent analysis tools. In the frame of the Horizon 2020 project Global Gravity-based Groundwater Product (G3P) the weighting scheme of the monthly GRACE-FO gravity fields was adapted to take into account the limitations on the solution space imposed by the specific observation geometry of the GRACE/GRACE-FO missions. We present the new COST-G GRACE RL02 combination, based on an extended set of time-series including COST-G's new Chinese partners, and combined applying the G3P weighting scheme.