An imbalancing act: the delayed dynamic response of the Kaskawulsh Glacier to sustained mass loss

Abstract

The Kaskawulsh Glacier is an iconic outlet draining the icefields of the St. Elias Mountains in Yukon, Canada. We determine and attempt to interpret its catchment-wide mass budget since 2007. Using SPOT5/6/7 data we estimate a 2007–18 geodetic balance of −0.46 ± 0.17 m w.e. a−1. We then compute balance fluxes and observed ice fluxes at nine flux gates to examine the discrepancy between the climatic mass balance and internal mass redistribution by glacier flow. Balance fluxes are computed using a fully distributed mass-balance model driven by downscaled and bias-corrected climate-reanalysis data. Observed fluxes are calculated using NASA ITS_LIVE surface velocities and glacier cross-sectional areas derived from ice-penetrating radar data. We find the glacier is still in the early stages of dynamic adjustment to its mass imbalance. We estimate a committed terminus retreat of ~23 km under the 2007–18 climate and a lower bound of 46 km3 of committed ice loss, equivalent to ~15% of the total glacier volume.

Surface Mass-Balance Gradients From Elevation and Ice Flux Data in the Columbia Basin, Canada

“…Ice velocity estimates are becoming increasingly widespread and accurate (Heid and Kääb, 2012;Burgess et al, 2013;Dehecq et al, 2019;Gardner et al, 2020), suggesting that velocity can be reasonably determined for many glaciers. While ITS_LIVE velocities were not successful here for most years, we emphasize that our glaciers have complex topography and geometries, and are relatively small, so suggest that ITS_LIVE velocities, or similar resolution products, may perform well for glaciers with simpler geometry and in particular, for larger, faster flowing glaciers (e.g., Young et al, 2020). When extending a mass-continuity approach over accumulation zones, we recommend estimating firn column depth and density to inform total ice column density, and find this to be more important than accounting for firn compaction.…”

“…We suspect that for slightly larger glaciers, or glaciers with a simple geometry, velocity products like ITS_LIVE may be readily applicable. ITS_LIVE velocities worked well for a similar approach on the large (1,096 km 2 ) Kaskawalush Glacier (Young et al, 2020).…”

“…To address uncertainty in our depth-averaged velocity (we approximate depth-averaged velocity as 85% of surface velocity), we consider full slip (depth-averaged velocity is 100% of surface velocity) and no slip (depth-averaged velocity is 80% of surface velocity) to produce a σ Φ gate for each velocity, and take the maximum σ Φ gate (Young et al, 2020). For a given flux bin σ Φ from the gate at the top of the bin represents the uncertainty on flux in (σ Φin ) and σ Φ from the gate at the bottom of the bin represents uncertainty on flux out (σ Φout ).…”

“…Fewer than 1% of glaciers worldwide have long-term mass-balance observations (WGMS, 2018) or observations of subglacial topography (GlaThiDa, 2019). The lack of subglacial topographic information limits calculation of ice flux to relatively few glaciers (e.g., Berthier et al, 2003;Vincent et al, 2009;Belart et al, 2017;Rabatel et al, 2018;Bisset et al, 2020;Young et al, 2020). Previous efforts to infer the spatial distribution of mass balance from ice flux have primarily focused on glacier tongues (e.g., Gudmundsson and Bauder, 1999;Kääb and Funk, 1999;Berthier et al, 2003;Vincent et al, 2009Vincent et al, , 2021Berthier and Vincent, 2012;Gao et al, 2020), where ice thickness, glaciological balance and ice velocity measurements are most numerous, density is assumed to be that of ice, and glacier geometry is simplest.…”

“…Flux gates provide the relation of mass balance to altitude by inferring the average surface mass balance between (or above or below) selected cross sections where the bedrock topography is known. This approach does not yield a complete spatial coverage of glacier mass balance, but is simpler and less data demanding than alternative methods (e.g., Hubbard et al, 2000;Sold et al, 2013;Belart et al, 2017;Young et al, 2020), and thus easier to apply for more glaciers. We collected field observations of surface mass balance (b a ) coincident with the ALS surveys (Pelto et al, 2019), and use these data to assess the accuracy of our flux-derived b a .…”