Mapping of Water under a Part of the Greenland Ice Sheet Using Ice-Penetrating Radar

Sammanfattning: The contribution to the global sea level change from the large ice sheet of Greenland and Antarctica if both ice sheet where to melt completely, is estimated to be approximately 70 meters. How much the actual contribution would be, is due to complex ice dynamics still unclear. It is crucial to gain knowledge about the spatial distribution of wet and frozen beds, in order to increase the understanding of ice-sheet flow. There are yet no complete models available that can fully explain and describe ice sheet motion and the feedback mechanisms that are involved, making this topic important for future predictions and modelling of the impact of a warming climate. Radar sounding can be used for distinguish the different reflectivity between wet and frozen beds, this is however limited by uncertainties caused by scattering and attenuation. To be able to map the spatial distribution of subglacial water, attenuation needs to be taken into account. Here, mapping of water under a smaller part of the Greenland ice sheet was performed, and three different methods for acquiring attenuation values was used to obtain a suitable value of the attenuation. A CMP analysis, an attenuation model based on temperature data and an attenuation estimation derived from common-offset radar data, the mean attenuation value from these methods was used for the determination of the reflectivity. Hydraulic potential calculations was also performed, analyzed and compared with the result from the mapping of the reflectivity. Higher reflectivity was observed closer to the front of the glacier, indicating wetter basal condition in that area. This area did also have more moulins and sinks which could lead water from the surface down to the base of the ice.