Projections of sea-level rise contributions from West Antarctica's dynamically thinning ice streams contain high uncertainty because some of the key processes involved are extremely challenging to observe. An especially poorly observed parameter is sub-decadal stability of ice-stream beds, which may be important for subglacial traction, till continuity and landform development. Only two previous studies have made repeated geophysical measurements of ice-stream beds at the same locations in different years, but both studies were limited in spatial extent. Here, we present the results from repeat radar measurements of the bed of Pine Island Glacier, West Antarctica, conducted 3–6 years apart, along a cumulative ∼ 60 km of profiles. Analysis of the correlation of bed picks between repeat surveys shows that 90 % of the bed displays no significant change despite the glacier increasing in speed by up to 40 % over the last decade. We attribute the negligible detection of morphological change at the bed of Pine Island Glacier to the ubiquitous presence of a deforming till layer, wherein sediment transport is in steady state, such that sediment is transported along the basal interface without inducing morphological change to the radar-sounded basal interface. Given the precision of our measurements, the upper limit of subglacial erosion observed here is 500 mm a−1, far exceeding erosion rates reported for glacial settings from proglacial sediment yields, but substantially below subglacial erosion rates of 1.0 m a−1 previously reported from repeat geophysical surveys in West Antarctica.
Bibliographical noteDD was supported by NERC Training Grant NE/K011189/1 to RGB. All fieldwork was supported by funding from the UK Natural Environment Research Council (NERC) iSTAR Programme Grants NE/J005665 (RGB/ECK/AMS/AMB/DGV) and
NE/J005681 (AEH), NERC grants NE/B502287 (ECK/AMS) and NE/J004766 (MS), and the British Antarctic Survey (BAS) Polar Science for Planet Earth Programme. We would like to thank all members of the iSTAR traverses of Pine Island Glacier for assistance with field-data acquisition in 2013/14 and 2014/15; M. Baird, T. Gee, J. Wake and J. Yates for field-operational support during iSTAR; F. Buckley, C. Griffiths and J. Scott for field assistance in 2007/08 and D. Routledge for field assistance in 2010/11. We are especially grateful for the dedicated and professional support of BAS Operations and Logistics without whom this study would not have been possible.
Data availability. All the data in this paper are available from
the lead author by request and will be made available on the
NERC/iSTAR GIS site, http://gis.istar.ac.uk/.