The Cryosphere Discussions
www.the-cryosphere-discuss.net
1994-0432
1994-0440
1
1
2007
10.5194/tcd-1-169-2007
http://www.the-cryosphere-discuss.net/1/169/2007/
http://www.the-cryosphere-discuss.net/1/169/2007/tcd-1-169-2007.html
http://www.the-cryosphere-discuss.net/1/169/2007/tcd-1-169-2007.pdf
169
212
2007-07-09
Improving estimation of glacier volume change: a GLIMS case study of Bering Glacier System, Alaska
M. J. Beedle
beedlem@unbc.ca
M. Dyurgerov
W. Tangborn
S. J. S. Khalsa
C. Helm
B. Raup
R. Armstrong
R. G. Barry
National Snow and Ice Data Center, 449 UCB, University of Colorado – Boulder, CO 80309-0559, USA
Institute of Arctic and Alpine Research, University of Colorado – Boulder, CO 80309-0450, USA
HyMet Inc., 13629 Burma Rd. SW, Vashon Island, WA 98070, USA
Geography Program, University of Northern British Columbia, 3333 University Way, Prince George, B.C. V2N 4Z9, USA
The Global Land Ice Measurements from Space (GLIMS) project has developed
tools and methods that can be employed by analysts to create accurate
glacier outlines and resultant measures of glacier extent. To illustrate the
importance of accurate glacier outlines and the effectiveness of GLIMS
standards we have conducted a case study on Bering Glacier System (BGS),
Alaska. BGS is a complex glacier system aggregated from multiple drainage
basins, numerous individual ice streams, and many accumulation areas.
Published measurements of BGS surface area vary from 1740 to 6200 km<sup>2</sup>, depending on how the boundaries of this system have been defined.
Utilizing GLIMS tools and standards we have completed a new outline and
analysis of the area-altitude distribution (hypsometry) of BGS using Landsat
images from 2000 and 2001. We compared this new outline (3632 km<sup>2</sup>)
with three previous outlines to illustrate the errors that result from the
widely varying estimates used in previous analysis of BGS area. The use of
different BGS outlines results in highly variable measures of volume change
and net balance (b<i><sub>n</sub></i>). Outline variability alone results in a net
balance rate range of –1.0 to –3.2 m/yr water equivalent (W.E.), a volume
change range of –4.2 to –8.2 km<sup>3</sup>/yr, and a near doubling in
contributions to sea level equivalent (SLE), 0.0122 mm/yr to 0.0236 mm/yr. A
study of three different models of BGS net balance leads us to favor
estimates of b<sub><i>n</i></sub> of –1.2 m/yr W.E. and total volume change of –4.2 km<sup>3</sup>/yr for the period 1950–2004. These estimates result in a near
doubling of contributions to sea level equivalent when compared with
previous studies. While current inaccuracies in glacier outlines hinder our
ability to fully understand glacier change, there is no reason why our
understanding of glacier extents should not be comprehensive and accurate.
Such accuracy is possible with the increasing volume of satellite imagery of
glacierized regions, and recent advances in tools and standards.
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