Effect of Bed Topography and Basal Friction Weakening on Glacier Flow: Implications for Campbell Glacier Tongue, East Antarctica

Glacier flow is an important indicator of ice sheet mass balance and subsequent global climate change. Previous studies suggested that bed topography and basal friction weakening due to subglacial lakes control glacier deformation. However, there is a lack of quantitative analyses for the interplay of these factors. Recent geophysical observations using DDInSAR reported two circular velocity anomalies with a width of ~1.5 km in Campbell Glacier Tongue, East Antarctica. Constraining the amplitude and time variation of these circular anomalies provides an insight on the relationship between glacial surface deformation and basal conditions. Here we developed 2D and 3D numerical models for the vertical and horizontal motions of glaciers using open-source finite element software, Elmer/ice, to quantify the contribution from the factors controlling ice flow. We conducted a series of parametric calculations over a wide range of bed topography and basal friction. First, we tested the effect of bed slope on the glacier flow with an idealized geometry. When the bed slope increases, the glacier flows just become faster without any signal of circular anomalies. The basal Gaussian-shaped obstacles were adopted to investigate the effect of the shape and arrangement of obstacles on surface glacier deformation. We found the localized (in 2D model) and circular (in 3D model) velocity anomalies when the topography of obstacles are high and tip. Then, we adopted the model geometry using Bedmap2 data of Campbell Glacier regions. Our results exhibit that no pronounced circular velocity anomalies appear, which means that the basal obstacles high enough to interrupt ice flow do not exist.Thus, we hypothesize the effect of friction heterogeneity along the ice base, which can be varied with time due to subglacial lake level change and pressure-induced melting of ice. We searched for the best-fit distribution of friction heterogeneity to constrain the observed circular anomalies. As a result, we argued that the friction heterogeneity can explain the anomalies, which implies that the basal frictional weakening by subglacial lake plays a more dominant role than basal topography.