01577nas a2200205   4500008004100000022001400041245007100055210006900126520095700195653001101152653001701163653002201180653002001202653002601222653001101248100002201259700002201281700002501303856004301328       2013                        eng d  a1944-800700aSummer melt regulates winter glacier flow speeds throughout Alaska0 aSummer melt regulates winter glacier flow speeds throughout Alas3 aPredicting how climate change will affect glacier and ice sheet flow speeds remains a large hurdle towards accurate sea level rise forecasting. Increases in surface melt rates are known to accelerate glacier flow in summer, whereas in winter, flow speeds are believed to be relatively invariant. Here we show that wintertime flow speeds on nearly all major glaciers throughout Alaska are not only variable but are inversely related to melt from preceding summers. For each additional meter of summertime melt, we observe an 11% decrease in wintertime velocity on glaciers of all sizes, geometries, climates and bed types. This dynamic occurs because inter-annual differences in summertime melt affect how much water is retained in the sub-glacial system during winter. The ubiquity of the dynamic indicates it occurs globally on glaciers and ice sheets not frozen to their beds and thus constitutes a new mechanism affecting sea level rise projections.10aAlaska10aIce Dynamics10aMountain Glaciers10aOffset Tracking10aSub-Glacial Hydrology10aWinter1 aBurgess, Evan, W.1 aLarsen, Chris, F.1 aForster, Richard, R.  uhttp://dx.doi.org/10.1002/2013GL058228