Transition of flow regime along a marine-terminating outlet glacier in East Antarctica

摘要

We present results of a multi-methodological approach to characterize theflow regime of West Ragnhild Glacier, the widest glacier in Dronning MaudLand, Antarctica. A new airborne radar survey points to substantially thickerice (>2000 m) than previously thought. With a discharge estimateof 13–14 Gt yr−1, West Ragnhild Glacier thus becomes of thethree major outlet glaciers in Dronning Maud Land. Its bed topography isdistinct between the upstream and downstream section: in the downstreamsection (<65 km upstream of the grounding line), the glacieroverlies a wide and flat basin well below the sea level, while the upstreamregion is more mountainous. Spectral analysis of the bed topography alsoreveals this clear contrast and suggests that the downstream area is sedimentcovered. Furthermore, bed-returned power varies by 30 dB within20 km near the bed flatness transition, suggesting that the watercontent at bed/ice interface increases over a short distance downstream,hence pointing to water-rich sediment. Ice flow speed observed in thedownstream part of the glacier (~250 m yr−1) can only beexplained through very low basal friction, leading to a substantial amount ofbasal sliding in the downstream 65 km of the glacier. All the abovelines of evidence (sediment bed, wetness and basal motion) and the relativelyflat grounding zone give the potential for West Ragnhild Glacier to be moresensitive to external forcing compared to other major outlet glaciers in thisregion, which are more stable due to their bed geometry (e.g. ShiraseGlacier).