Remote sensing of surface meltwater routing in the Denmark Basin of the Northern Greenland Ice Sheet
Mass loss from the Greenland Ice Sheet(GrIS)has accelerated in recent decades,with profound effects on global sea-level rise.During each summer,the meltwater forms supraglacial rivers and then is transported to the proglacial zone,eventually flowing into the ocean and forming a continuous supraglacial-proglacial river system.This continuous supraglacial-proglacial drainage system directly results in the mass loss of the GrIS and has an important impact on the changes in the marine environment.Satellite images can directly observe the temporal and spatial distribution of supraglacial and proglacial rivers and have been widely used in the study of the GrIS.The satellite-derived observation can provide key information,such as the location,morphology,and dynamic changes of rivers.It has become an important way to analyze meltwater routing.In this study,361 scenes of Sentinel-2 and Landsat 8 satellite images are used to extract the supraglacial and proglacial rivers in the Denmark supraglacial-proglacial basin of the northeastern GrIS during the melt seasons(from July to August)and monitor their spatial distribution and dynamic changes.Furthermore,satellite-derived observation and meltwater runoff simulated by regional climate models(MARv3.12 and RACMO2.3p2)are compared and analyzed,and then the lag time of the supraglacial-proglacial drainage system is estimated.The main contents and conclusions of this study include the following three aspects:(1)The proglacial river width is in the range of 100-2000 m and experiences a seasonal trend.The ice surface meltwater shows similar variation characteristics,advancing to the high-altitude areas of the ice surface(up to～1400 m)at the initial stage of ablation,and then gradually receding to the edge of the ice sheet(up to～500 m).(2)A significant positive correlation is found between satellite-derived proglacial river width and meltwater on the ice surface(R=0.87,P＜0.01),forming a continuous supraglacial-proglacial drainage system that can effectively transport the meltwater each summer.(3)MARv3.12 and RACMO2.3p2 models can accurately simulate the meltwater runoff in the supraglacial-proglacial drainage system on a large area and long-term scale,and the simulated meltwater runoff and satellite-derived ice surface meltwater(MAR:R=0.87;RACMO:R=0.84,P＜0.01)and proglacial river width(MAR:R=0.89;RACMO:R=0.88,P＜0.01)have strong correlations.(4)The r between the simulated lagged meltwater runoff and satellite-derived proglacial river width(MAR:R=0.93;RACMO:R=0.92,P＜0.01)increased,which is significantly higher than that of the instantaneous meltwater runoff.The optimal lag time of the supraglacial-proglacial drainage system in the Denmark Basin is approximately 2 days.This lag time quantitatively represents the efficiency of meltwater routing in the supraglacial-proglacial drainage system.
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