Terminus Ablation Rates for the Glaciers in Kalaallit Nunaat (Greenland) from 2013 to 2023

The marine-terminating glaciers on Kalaallit Nunaat (Greenland) have undergone accelerated mass loss since the 1990s, with a substantial portion due to the effects of dynamic ice loss. Conventional assessments of dynamic mass loss, however, often ignore the influence of terminus change on the timing of mass loss from the terminus. Here we construct and analyze a decadal (2013--2023) record of monthly ice flux driven both by temporal variability in ice flow (i.e., discharge) and terminus position change -- collectively called terminus ablation -- for 49 marine-terminating glaciers in Greenland. We calculate terminus ablation rates using open-source datasets of terminus position, surface elevation, ice thickness, and glacier speed in order to facilitate the extension of the terminus ablation time series as more data become available. During 2013--2023, we observe coincident seasonal variations in terminus position and discharge that produce a pronounced summer peak in terminus ablation. However, for 8 glaciers we find that the terminus ablation time series has more erratic seasonality than would be estimated from discharge alone. Additionally, 4 glaciers exhibited seasonality superimposed on large inter-annual fluctuations likely due to surging or disappearance of floating tongues. At regional scales, the magnitude of seasonal oscillations in terminus ablation are much larger than discharge: for the northwest and central west sectors, where the fraction of outlet glaciers included in our estimates is greatest, seasonal oscillations in terminus ablation are ~45 gigatonnes per year (Gt/yr) and ~25 Gt/yr, respectively, compared to less than 10 Gt/yr for discharge. Our terminus ablation time series do not include every outlet glacier, but they suggest that terminus position change is the dominant contributor to dynamic mass loss at seasonal time scales, in contrast with its decadal-scale contributions. Since seasonality in mass loss from Greenland can influence the fate of meltwater, it is essential that future research on the ocean impacts of Greenland mass loss account for seasonal terminus position change.