Identification of spatial variations in subglacial sediment discharge and basal slip from ground penetrating radar

Basal conditions that facilitate fast ice flow are still poorly understood and their parameterization in ice flow models results in high uncertainties in ice flow and consequent sea-level rise projections. One approach to understanding basal conditions is through investigating the basal landscape of ice streams and glaciers, which has been shaped by ice flow over the underlying substrate.

In this study, we map the subglacial landscape and identify basal conditions of Rutford Ice Stream (West Antarctica) using different visualisation techniques on high-resolution 3D radar data. Our novel approach reveals bedforms of < 300 m in length, surrounded by bedforms of > 10 km in length. We assume these variations in bedform dimension to reflect spatial variation in sediment discharge. We find no correlation to glaciological factors, but our radar data reveal a correlation between variation in bedform dimension to bed composition.

We thus developed a simple model relating sediment discharge (and hence, deformation) to inferred basal condition and measurements of basal effective pressure. The model implies that effective pressure and sediment properties (low-porosity material vs soft sediment) at the ice-bed interface are first-order controls on sediment discharge and thus bedform dimensions. This work highlights the small-scale spatial variability of basal conditions and its implications for basal slip.

Assuming glaciological factors to be constant this new approach, allows spatial variation in basal conditions and effective pressure to be identified from spatial variation in bedform dimensions, observed from high-resolution radar data. This will further allow the flow mechanism to be separated into basal slip and basal deformation and a better incorporation of their variation into numerical ice flow models.