Estimating Temporal Redistribution of Water in Upper Stratigraphy of the Juneau Icefield, Alaska

The redistribution of winter accumulation as surface melt into firn layers ("internal accumulation") remains a poorly understood parameter of glacier mass balance. Studies initiated following the onset of summer melt either... [ view full abstract ]

The redistribution of winter accumulation as surface melt into firn layers ("internal accumulation") remains a poorly understood parameter of glacier mass balance. Studies initiated following the onset of summer melt either neglect sources of internal accumulation or attempt to estimate melt through a variety of modeling methods. We employ ground­-penetrating radar repeat common midpoint (CMP) surveys to estimate temporal changes in water content within the upper annual layers of the Taku Glacier, Alaska. We assume density changes are temporally slow relative to water flow through the snow and firn pack, therefore inferring that changing radio­wave velocities measured by successive CMP surveys result from flux in surface melt through deeper layers. Preliminary CMP data yield radiowave velocities of 0.15 to 0.2 m/ns in snowpack densities averaging 0.56 g*cm-3, indicating partially to fully saturated snowpack (4­9% water content) and little water redistribution during the studied time span. This suggests that internal accumulation occurs very gradually over the course of a summer melt season, raising questions about how the rate of internal accumulation affects whole-glacier mass balance. We recommend that repeat CMP surveys be conducted over a longer timeframe, estimating stratigraphic water redistribution between the end of winter accumulation and maximum melt season.