Complex multi-decadal ice dynamical change within the interior of the Greenland Ice Sheet

Observations of ice dynamical change in the interior of the Greenland Ice Sheet, at distances >~100 km from the ice-margin, are sparse, exhibiting very low spatial and temporal resolution (e.g. Sole et al., 2013; Doyle et al., 2014; Van de Wal et al., 2015). As such, the behaviour of interior Greenland ice represents a significant unknown in our understanding of the likely response of the ice sheet to oceanic and atmospheric forcing. The observation of a 2.2 % increase in ice velocity over a three-year period at a location 140 km from the ice margin in South West Greenland (Doyle et a., 2014) has been inferred to suggest that the ice sheet interior has undergone persistent flow acceleration. It remains unclear, however, whether this observation is representative of wider trends across the ice sheet.

Here, we investigate changes in ice motion within Greenland’s interior by utilising recent satellite-derived ice velocities covering the period 2013-2018 (Gardner et al., 2019) in conjunction with in-situ velocities collected at 30 km intervals along the 2000 m elevation contour during the mid-1990s (Thomas et al., 2000). Previous observations from the late-1990s/early-2000s through to late-2000s/early-2010s have revealed significant speed-up at many of Greenland’s tidewater glaciers (e.g. Bevan et al., 2012; Murray et al., 2015), in contrast to widespread deceleration within the ablation zone of the South West land-terminating margin (e.g. Tedstone et al., 2015; Van de Wal et al., 2015; Stevens et al., 2016). The recent availability of satellite data enables us to compare annual ice velocities from the period 2013-2018 to those collected at GPS stations in the mid-1990s, thereby enabling us to detect any long-term changes in ice-sheet wide inland ice motion during a period of considerable climatic and potentially significant dynamic change.

We observe multi-decadal interior ice acceleration of >15 % at Jakobshavn Isbrae, with similar inland accelerations at Kangerlugssuaq, Sermiligarssuk Brae and Narsap Sermia, and smaller velocity increases upstream of other marine-terminating outlets; these accelerations suggest that dynamic change at the margins has propagated considerable distances into the ice sheet interior. By contrast, ice velocities have slowed inland of some tidewater outlets such as Helheim Glacier, Umiamako Isbrae and Hagen Brae, confirming complex spatial variability in interior response to oceanic and atmospheric forcing. Furthermore, whilst prior work suggested that South West Greenland’s land-terminating sector experienced persistent interior speed-up between 2009 and 2012 (Doyle et al., 2014), our results reveal a >10% multi-decadal slowdown within the same sector, suggesting this region is resilient to recent increases in surface melt forcing.