The Greenland Ice Sheet discharges ice to the ocean through hundreds of outlet glaciers. Recent acceleration of Greenland outlet glaciers has been linked to both oceanic and atmospheric drivers. Here, we leverage temporally dense observations, regional climate model output, and newly developed time series analysis tools to assess the most important forcings causing ice ﬂow variability at one of the largest Greenland outlet glaciers, Helheim Glacier, from 2009 to 2017. We ﬁnd that ice speed correlates most strongly with catchment-integrated runoff at seasonal to interannual scales, while multiannual ﬂow variability correlates most strongly with multi-annual terminus variability. The disparate time scales and the inﬂuence of subglacial topography on Helheim Glacier’s dynamics highlight different regimes that can inform modeling and forecasting of its future. Notably, our results suggest that the recent terminus history observed at Helheim is a response to, rather than the cause of, upstream changes.
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