Abstract
AbstractWe present ice velocities observed with global positioning systems and TerraSAR‐X/TanDEM‐X in a land‐terminating region of the southwest Greenland ice sheet (GrIS) during the melt year 2012–2013, to examine the spatial pattern of seasonal and annual ice motion. We find that while spatial variability in the configuration of the subglacial drainage system controls ice motion at short timescales, this configuration has negligible impact on the spatial pattern of the proportion of annual motion which occurs during summer. While absolute annual velocities vary substantially, the proportional contribution of summer motion to annual motion does not. These observations suggest that in land‐terminating margins of the GrIS, subglacial hydrology does not significantly influence spatial variations in net summer speedup. Furthermore, our findings imply that not every feature of the subglacial drainage system needs to be resolved in ice sheet models.
Highlights
One potential dynamic thinning mechanism of the Greenland ice sheet (GrIS) is surface melt-induced acceleration of ice motion [Zwally et al, 2002; Parizek and Alley, 2004; Andersen et al, 2010]
We find that while spatial variability in the configuration of the subglacial drainage system controls ice motion at short timescales, this configuration has negligible impact on the spatial pattern of the proportion of annual motion which occurs during summer
We have examined spatial variability in surface melt-induced ice motion in a land-terminating region of the southwest GrIS
Summary
One potential dynamic thinning mechanism of the Greenland ice sheet (GrIS) is surface melt-induced acceleration of ice motion [Zwally et al, 2002; Parizek and Alley, 2004; Andersen et al, 2010]. The spatial coincidence of faster flowing areas with surface drainage routing suggests that localized meltwater input to the ice bed, and the associated changes in subglacial water pressure, is the likely cause of the flow enhancement. Point-based observations from the same region have shown that net annual ice motion is insensitive to these short-term variations in ice flow [van de Wal et al, 2008; Sole et al, 2013; Tedstone et al, 2013], except possibly at high elevations well above the equilibrium line altitude [Doyle et al, 2014]. No study to date has combined the required spatial and temporal coverage and resolution to investigate whether the insensitivity of net annual ice motion to short-term variations in ice flow holds across broader spatial scales, so the impact of spatially variable subglacial drainage and potential related flow enhancement on net annual regional ice motion remains unquantified
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