Brief communication: Unabated wastage of the Juneau and Stikine icefields (southeast Alaska) in the early 21st century

Etienne Berthier,Christopher Larsen,William J. Durkin,Michael J. Willis,Matthew E. Pritchard

doi:10.5194/tc-12-1523-2018

Abstract

Abstract. The large Juneau and Stikine icefields (Alaska) lost mass rapidly in the second part of the 20th century. Laser altimetry, gravimetry and field measurements suggest continuing mass loss in the early 21st century. However, two recent studies based on time series of Shuttle Radar Topographic Mission (SRTM) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation models (DEMs) indicate a slowdown in mass loss after 2000. Here, the ASTER-based geodetic mass balances are recalculated carefully avoiding the use of the SRTM DEM because of the unknown penetration depth of the C-band radar signal. We find strongly negative mass balances from 2000 to 2016 (−0.68 ± 0.15 m w.e. a−1 for the Juneau Icefield and −0.83 ± 0.12 m w.e. a−1 for the Stikine Icefield), in agreement with laser altimetry, confirming that mass losses are continuing at unabated rates for both icefields. The SRTM DEM should be avoided or used very cautiously to estimate glacier volume change, especially in the North Hemisphere and over timescales of less than ∼ 20 years.

Highlights

The Juneau Icefield (JIF) and Stikine Icefield (SIF) are the southernmost large icefields in Alaska (Fig. 1)
We find strongly negative mass balances from 2000 to 2016 (−0.68 ± 0.15 m w.e. a−1 for the Juneau Icefield and −0.83 ± 0.12 m w.e. a−1 for the Stikine Icefield), in agreement with laser altimetry, confirming that mass losses are continuing at unabated rates for both icefields
We find an excellent agreement between repeat laser altimetry survey and our multi-temporal analysis of ASTER digital elevation models (DEMs) in term both of mass balances and of the pattern of dh/dt with altitude for the JIF and SIF since 2000

Summary

Introduction

The Juneau Icefield (JIF) and Stikine Icefield (SIF) are the southernmost large icefields in Alaska (Fig. 1). The JIF covers about 3800 km and the SIF close to 6000 km at the border between southeast Alaska and Canada (Kienholz et al, 2015) Together they account for roughly 10 % of the total glacierized area in Alaska. Both icefields experienced rapid mass loss in the second part of the 20th century (Arendt et al, 2002; Berthier et al, 2010; Larsen et al, 2007). The last survey used in Larsen et al (2015) was flown in 2012 for all glaciers During these varying time intervals, nine glaciers experienced strongly negative mass balances (between −0.51 and −1.14 m w.e. a−1), while Taku Glacier, which alone accounts for one-fifth of the JIF area, experienced a slightly positive mass balance (+0.13 m w.e. a−1). The trend toward enhanced mass loss is observed on Taku Glacier, for which the mass balance was posi-

Results

Discussion

Conclusion