Intra- and inter-annual variability in dynamic discharge from the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, and its role in modulating mass balance

We determined ice velocities for the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during November 2016-November 2017, by feature-tracking 54 pairs of Sentinel-1 synthetic-aperture radar images. Seasonal velocity variations with amplitudes up to 10% of the yearly-averaged velocity were observed. Shorter-term (<15 d) intra-annual velocity variations had average and maximum deviations from the annual mean of up to 16 and 32%, respectively. This indicates the errors that could be incurred if ice discharge values determined from a single pair of images were extrapolated to the whole year. Average ice discharge for 2016-2017 was 1.93 +/- 0.12 Gt a(-1). The difference from an estimate of similar to 1.4 Gt a(-1) for 2003-2009 was attributed to the initiation of ice stream flow in Basin BC. The total geodetic mass balance over 2012-2016 was - 1.72 +/- 0.67 Gt a(-1) (- 0.31 +/- 0.12 m w.e. a(-1)). The climatic mass balance was not significantly different from zero, at 0.21 +/- 0.68 Gt a(-1) (0.04 +/- 0.12 m w.e. a(-1)), and has remained near zero at decadal-scale for the last four decades. Therefore, the total mass balance has been controlled largely by variations in ice discharge, whose long-term changes do not appear to have responded to environmental changes but to the intrinsic characteristics of the ice cap governing tidewater glacier dynamics.