Abstract
Abstract. We present results of a multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (>2000 m) than previously thought. With a discharge estimate of 13–14 Gt yr−1, West Ragnhild Glacier thus becomes of the three major outlet glaciers in Dronning Maud Land. Its bed topography is distinct between the upstream and downstream section: in the downstream section (<65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level, while the upstream region is more mountainous. Spectral analysis of the bed topography also reveals this clear contrast and suggests that the downstream area is sediment covered. Furthermore, bed-returned power varies by 30 dB within 20 km near the bed flatness transition, suggesting that the water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~250 m yr−1) can only be explained through very low basal friction, leading to a substantial amount of basal sliding in the downstream 65 km of the glacier. All the above lines of evidence (sediment bed, wetness and basal motion) and the relatively flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region, which are more stable due to their bed geometry (e.g. Shirase Glacier).
Highlights
The overall mass balance of the Antarctic ice sheet is dominated by a significant mass deficit in West Antarctica (Rignot et al, 2008; Pritchard et al, 2012)
East Antarctica is mainly continental, limited observations in Dronning Maud Land (DML), show that the ice sheet seaward of the inland mountains lies on a bed well below sea level (BEDMAP2; Fretwell et al, 2013) and most of the ice from the polar plateau is discharged through numerous glaciers in between coastal mountain ranges
The high bed reflectivity in the zone immediately upstream of the grounding line may eventually point to wet bed conditions
Summary
The overall mass balance of the Antarctic ice sheet is dominated by a significant mass deficit in West Antarctica (Rignot et al, 2008; Pritchard et al, 2012). Based on the ice thickness data presented in this paper, we estimate the grounding line mass flux to be 13– 14 Gt yr−1, which constitutes roughly 10 % of the total discharge from DML (Rignot et al, 2008) This is of the same order of magnitude as Shirase Glacier (13.8 ± 1.6 Gt yr−1; Pattyn and Derauw, 2002) and Jutulstraumen (14.2 Gt yr−1; Høydal, 1996), the other two major outlet glaciers in the DML region. While rapid changes at the marine boundary have not yet been observed, Rignot et al (2013) point to an exceedance of basal melt (underneath the ice shelf and at the grounding line) over calving for several ice shelves in DML (including Roi Baudouin Ice Shelf, downstream of West Ragnhild Glacier). We subsequently discuss the consequences of a marine-terminating East Antarctic outlet glacier, characterized by a wet sediment and dominated by basal motion/sliding
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