Detecting high spatial variability of ice-shelf basal mass balance (Roi Baudouin ice shelf, Antarctica)

Abstract

Abstract. Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e., the difference between refreezing and melting. Here, we present a novel technique – based on satellite observations – to capture the small-scale variability in the BMB of ice-shelves. As a case study we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica and derive its yearly-averaged BMB at 10 m horizontal gridding. We use mass conservation within a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which avoids spatial averaging hence loss of spatial resolution. Our BMB field exhibits high detail and ranges from −14.8 to 8.6 m a−1 ice equivalent. Highest melt rates are found close to the grounding line where the basal ice-shelf slope is the steepest. The BMB field agrees well with on-site measurements from phase-sensitive radar, although unresolved spatial variations in firn density determined from profiling radar occur. We show that the surface expression of an englacial lake (0.7 × 1.3 km2 wide and 30 m deep) lowers by 0.5 to 1.4 m a−1, which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice-shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice-shelf channels advect passively toward the ice-shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.