Seasonal Speedup Along the Western Flank of the Greenland Ice Sheet

Abstract

It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (<15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow.

Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

“…We hope that this work will provide motivation for further study of near-terminus subglacial hydrology at tidewater glaciers. Joughin and others (2008) have suggested that surface melt induced speed-up of tidewater glaciers is of only small relative magnitude near the terminus and therefore less important than other processes such as terminus retreat. However, it remains possible that increased surface melting may be the driver of terminus retreat; increased surface melt entering a pervasive distributed drainage system will lead to increased basal lubrication, and subsequently acceleration and thinning.…”

“…Since 2000, KNS has undergone acceleration and thinning, but only modest retreat averaging ∼100 m a −1 (Rignot and Kanagaratnam, 2006;Thomas and others, 2009;Lea and others, 2014). Previous hydrological study has inferred that seasonal evolution of ice velocity >35 km inland from the (Joughin andothers, 2010, 2011). Note the logarithmic velocity colour scale.…”

“…1, Sole and others (2011)), which provides information on channelisation of subglacial hydrology higher up in the catchment, and ice velocities over the wider glacier ( Fig. 1) from the NSIDC MEaSUREs dataset (Joughin andothers, 2010, 2011). Unfortunately, subglacial topography is poorly constrained near to the terminus of KNS (Morlighem and others, 2014), preventing the meaningful modelling of drainage pathways for comparison with the observed plume locations (e.g.…”

The seasonal cycle and interannual variability of surface energy balance and melt in the ablation zone of the west Greenland ice sheet

“…Strong interactions exist between surface meltwater production and the sliding behaviour of the ice sheet in west Greenland (Zwally et al, 2005;Van de Wal et al, 2008;Joughin et al, 2008;Shepherd et al, 2009), a process that is linked to the formation and decay of subglacial meltwater channels (Schoof, 2010). The increase in runoff since 1990, following atmospheric warming (Box and Cohen, 2006;Hanna et al, 2008), explains more than half of the recent mass loss of the GrIS ( Van den Broeke, 2009a).…”

Arctic Climate Tipping Points

“…This is part of a longer-term trend of increasing melt extent since the 1970s. Recent observations show that seasonal surface melt has led to accelerated glacier flow (Joughin et al 2008;van de Wal et al 2008). The surface mass balance of the GIS is still positive (there is more incoming snowfall than melt at the surface, on an annual average), but the overall mass balance of the GIS is negative due to an increased loss flux from calving of glaciers that outweighs the positive surface mass balance.…”