A Regional Intercomparison of Ice Sheet Mass Balance Estimates of the Northwest Greenland Ice Sheet

Abstract

Changes in ice sheet mass manifest as changes in ice flow, ice thickness, and gravitational attraction. These parameters can be measured from space and used to track Greenland's contribution to sea level rise independently from each other. While an excellent level of agreement between these satellite techniques has been demonstrated at the ice sheet scale, less attention has been paid to whether this agreement is maintained at regional and local scales. However, regional mass balance assessments are key to validating and calibrating ice sheet models, ensuring they can accurately reproduce the spatial distribution of ice losses. Here, we compare mass balance estimates derived from satellite altimetry, satellite gravimetry, and the input‐output method in Northwest Greenland, which we find to agree within 6 Gt yr ⁻¹ during their overlap period (2010–2019). We further investigate local sources of discrepancies between techniques and find that 55% of the remaining difference between our altimetry and input‐output estimates can be explained by discrepancies at 2 of the sector's 74 glaciers, likely due to poor knowledge of ice thickness. Finally, owing to the good regional agreement between our estimates, we construct a reconciled mass balance record, showing that the Northwest sector contributed 5.1 ± 0.2 mm to sea level rise between 1972 and 2024. The pace of ice loss was fastest in the 2010s, with a record high mass loss rate of 65 ± 4 Gt yr ⁻¹ , before slowing down to 41 ± 10 Gt yr ⁻¹ in the last 4 years of our survey.