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 Measured
Climate Induced Volume Changes of Three Glaciers and Current
Glacier-Climate Response Prediction
by D.C. Trabant, R. S. March, L. H. Cox, W. D. Harrison, and E.G.
Josberger
SEARCH Open Science
Meeting,
Arctic Research Consortium of the United States (ARCUS)
October 27, 2003, Seattle, Washington, USA
ABSTRACT
Two small but hydrologically significant shifts in climate have
affected the rates of glacier volume change at the three U.S. Geological
Survey Benchmark glaciers. Rate changes are detected as inflections in the
cumulative conventional and reference-surface mass-balances of Wolverine
and Gulkana Glaciers in Alaska and South Cascade Glacier in Washington.
All mass-balance trends and inflection points are strongly correlated with
the 1976/77 and 1989 interdecadal climate-regime shifts that are
recognized in several climate indices for the North Pacific and the
National Center for Environmental Prediction (NCEP) re-analysis data.
Wolverine Glacier is a south-facing valley glacier on the Kenai Peninsula
in south-central Alaska. Gulkana Glacier is a south-facing branched valley
glacier on the southern flank of the Alaska Range in interior Alaska,
about 350 kilometers northeast of Wolverine Glacier. South Cascade Glacier
is in the North Cascade Mountains of northern Washington. The cumulative
mass balances are robust and have recently been corroborated by geodetic
determinations of glacier volume change. Furthermore, the four-decade
length of record is unique for the western hemisphere. Balance trends at
South Cascade Glacier in Washington are generally in the opposite sense
compared with Wolverine Glacier in Alaska; NCEP correlation of winter
balance with local winter temperatures is positive at 0.59 for Wolverine
and –0.64 for South Cascade Glacier. At Wolverine Glacier, the
negative trend of cumulative mass balances, since measurements began in
1965, was replaced by a growth trend (positive mass balances) during the
late 1970s and 1980s. The positive mass-balance trend was driven by
increased precipitation during the 1976/77 to 1989 period. At Gulkana
Glacier, the cumulative mass-balance trend has been negative throughout
its measurement history, but with rate-change inflection points that
coincide with the interdecadal climate-regime shifts in the North Pacific
indices. At South Cascade Glacier, the mass-loss trend, observed since
measurements began in 1953, was replaced by a positive trend between 1970
and 1976 then became strongly and continuously negative until 1997 when
the rate of loss generally decreased. Since 1989, the trends of the
glaciers in Alaska have also been strongly negative. These loss rates are
the highest rates in the entire record. The strongly negative trends
during the 1990s agree with climate studies that suggest that the period
since the 1989 regime shift has been unusual.
Volume response time and reference surface balance are the current
suggested methods for analyzing the response of glaciers to climate.
Volume response times are relatively simple to determine and can be used
to evaluate the temporal, areal, and volumetric affects of a climate
change. However, the quasi-decadal period between the recent
climate-regime shifts is several times less than the theoretical volume
readjustment response times for the benchmark glaciers. If hydrologically
significant climate shifts recur at quasi-decadal intervals and if most
glaciers’ volume-response times are several times longer (true for
all but a few small, steep glaciers), most medium and large glaciers are
responding to the current climate and a fading series of regime shifts
which, themselves, vary in magnitude. This confused history of driver
trends prevent conventional balances from being simply correlated with
climate. Reference-surface balances remove the dynamic response of
glaciers from the balance trend by holding the surface area distribution
constant. This effectively makes the reference surface balances directly
correlated with the current climatic forcing. The challenging problem of
predicting how a glacier will respond to real changes in climate may
require a combination of the volume response time and reference surface
mass balances applied to a long time-series of measured values that
contain hydrologically significant variations.
Trabant, D.C., March, R.S., Cox, L. H., Harrison, W.D, and Josberger,
E.G., 2003, Measured Climate Induced Volume Changes of Three Glaciers and
Current Glacier-Climate Response Prediction, SEARCH Open Science
Meeting, Arctic Research Consortium of the United States (ARCUS), October
27, 2003, Seattle, Washington, USA (abstract available at
http://siempre.arcus.org/4DACTION/wi_pos_displayAbstract/7/1050
[Full Poster, Acrobat PDF
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Maintainer: Rod March
Last update:
Wednesday, January 03, 2007 12:46 PM
URL: http://ak.water.usgs.gov/glaciology/reports/2003.10
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