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 an improved 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 in 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 preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from −14.7 to 8.6 m a−1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) 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 (i.e. no melting nor refreezing) 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.
Highlights
74 % of the Antarctic ice sheet is surrounded by floating ice shelves (Bindschadler et al, 2011a) providing the interface for interactions between ice and ocean
For the 9227 km2 covered by the TanDEM-X digital elevation models (DEMs), net mass loss at the ice shelf bottom is 6.7 Gt a−1
The uncertainties of the absolute Lagrangian basal mass balance (LBMB) are typically higher than the LBMB itself, because errors unfavourably propagate in mass budgets (Moholdt et al, 2014)
Summary
74 % of the Antarctic ice sheet is surrounded by floating ice shelves (Bindschadler et al, 2011a) providing the interface for interactions between ice and ocean. Ice shelves that are laterally constrained through embayments (or locally regrounded from below), mitigate the marine ice sheet instability (Gudmundsson et al, 2012), regulating the ice flux from the inland ice sheet through buttressing. It is established that ice shelf integrity plays an important part in explaining sea-level variations in the past (Golledge et al, 2014; DeConto and Pollard, 2016), enabling improved projections of future sea-level rise (Golledge et al, 2015; Ritz et al, 2015)
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