Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice mélange in northwest Greenland

Abstract

Glacier ice discharge, which depends on ice velocity and terminus fluctuations, is a primary component of Greenland Ice Sheet mass loss. Some research suggests that ice mélange influences terminus calving, in turn affecting glacier velocity. The details and broad spatiotemporal consistency of these relationships, however, is undetermined. Focusing on 16 northwestern Greenland glaciers during 2009 through summer 2014, we examined seasonal surface velocity changes, glacier terminus position, and sea ice and ice mélange conditions. For a longer‐term analysis, we also produced extended records of four glaciers from 1999 to 2014. There is a strong correspondence between seasonal near‐terminus sea ice/mélange conditions and terminus change, with rigid ice mélange conditions associated with advance and open water associated with retreat. Extended sea ice‐free periods and reduced rigid mélange are also linked with anomalously large terminus retreat. In all but one case, sustained multiyear retreat of greater than 1 km during both the 15 year and 6 year records was accompanied by interannual velocity increases. Seasonal velocity patterns, however, correspond more strongly with runoff changes than terminus behavior. Projections of continued warming and longer sea ice‐free periods around Greenland indicate that notable retreat over wide areas may continue. This sustained retreat likely will contribute to multiyear speedup. Longer melt seasons and earlier breakup of mélange may also alter the timing of seasonal ice flow variability.