Basal heterogeneity of Thwaites Glacier, Antarctica: Results from advanced ice penetrating radar data

Thwaites Glacier dominates the mass balance of the northern West Antarctic Ice Sheet. Subglacial topography and crustal variability strongly control the organization of flow in this catchment, and will likely dictate the response of this glacier to climate change. Basal roughness is symptomatic of the coupling between the ice sheet and the underlying crust, although causality can be unclear. Using airborne ice penetrating radar data collected In the 2004-05 austral summer, a comprehensive aerogeophysical survey was flown across the northern WAIS. The AGASEA/BBAS survey, (a collaborative effort between the University of Texas at Austin and the British Antarctic Survey) collected 50, 000 line kilometers of coherent radar data. We use this data to analyze the basal roughness of Thwaites Glacier using both along track slope statistics and lengthening of the bed echo in individual records. The first method applies to hectometer to decimeter length scales. We improve on initial efforts using low resolution unfocused radar data by using a new high resolution focused SAR algorithm, decreasing length scales of analysis from hundreds of meters to tens of meters. The second method, examining the length of the received bed echo, is instructive as to the distribution of slopes on the the scale of the radar carrier wave, integrated over the footprint of the radar. Overall, we find a self-affine landscape with a similar topological structure to that found in many erosional terrains. We find that large portions of Thwaites Glacier are underlain by very smooth material, which also corresponds to regions of low bed strength. Unlikely the Siple Coast ice streams to the south, however, we find little evidence of the downstream advection of this material. We suggest that the nature of ice sheet basal coupling in the Thwaites Catchment is different to that found on the Siple Coast.