High-resolution mascon solutions reveal glacier-scale mass changes over the Greenland Ice Sheet from 2002 to 2022

SUMMARY As the main contributor to global sea-level rise, the Greenland Ice Sheet (GrIS) has undergone significant mass change over the last two decades. The satellite mission of GRACE (Gravity Recovery And Climate Experiment) and its follow-on mission (GRACE-FO) provide accurate observations but low-spatial resolution. In contrast, satellite altimetry provides observations at a high-spatial resolution but with large uncertainties, limiting the understanding of glacier-scale mass change. To derive accurate and high-spatial resolution mass change estimates from GRACE/GRACE-FO observations, we present a novel constraint mascon method in which the regularization matrix is constructed with the signal variances from satellite altimetry. Based on the proposed method, we derive a series of high-resolution (25 km × 25 km) monthly mascon solutions from 2002 April to September. The glacier-scale estimates from the input–output method agree better with those from our mascon solutions than those from the global mascons of CSR (Center for Space Research, the University of Texas), JPL (Jet Propulsion Laboratory), and GSFC (Goddard Space Flight Center), with a higher linear regression coefficient of 0.71. Benefitting from the greatly improved spatial resolution, our estimates provide the first accurate monthly glacier-scale mass change estimates from GRACE/GRACE-FO observations over the GrIS, to our knowledge. The results show that 20 of the 260 glaciers contributed to more than 42 per cent of the ice loss in the GrIS from 2002 to 2022. Most strikingly, the mass loss of Jakobshavn Isbrae was the most significant at –18.7 ± 0.05 Gt yr−1, accounting for 7.4 per cent of the total in the GrIS during the study period. Furthermore, we find that the SMB (surface mass balance) and ice-dynamics-related mass changes contribute nearly equally to the observed mass changes, but the corresponding spatiotemporal characteristics differ. SMB contributed the most to the mass change in 2019, while ice dynamics played the most dominant role in 2018. Moreover, the SMB effect is widespread, and ice-dynamics-related mass loss is mainly concentrated in five small areas.