Seasonality in Terminus Ablation Rates for the Glaciers in Kalaallit Nunaat (Greenland)

Abstract. Marine-terminating glaciers of 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 advance or retreat on the timing of mass loss. Here we construct and analyze a decade (2013–2023) 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, including terminus position, ice surface elevation, ice thickness, and glacier speed, to facilitate the continuation of the terminus ablation time series as more data become available. For the majority of glaciers, 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 has more erratic seasonal variability compared to discharge. 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, the average difference between the annual maximum and minimum in terminus ablation are ∼51Gt/yr and ∼25Gt/yr, respectively, compared to only ∼5Gt/yr for discharge. While our terminus ablation time series do not include every outlet glacier, they suggest that terminus position change is the dominant contributor to Greenland glacier dynamic mass loss at seasonal time scales, in contrast with the relatively small influence of terminus change on decadal-scale mass loss. Since seasonality in mass loss can influence the fate of freshwater fluxes and can affect areas where seasonal accuracy is essential, such as downstream ecosystem, fjord productivity and ocean circulation, it is essential that future estimates of Greenland mass loss account for seasonal terminus position change.