Acceleration of surface lowering on the tidewater glaciers of Icy Bay, Alaska, U.S.A. from InSAR DEMs and ICESat altimetry

Much of the increasing rate of glacier wastage observed during the late 20th century is attributed to retreat and thinning of tidewater glaciers grounded below sea level in fiords. We estimate the area-average, i.e. the integrated volume change over glacier area, elevation changes on Guyot, Yahtse and Tyndall Glaciers, Icy Bay, Alaska. Our results indicate that from 1948 to 1999, the accumulation area of Guyot Glacier above 1220 m elevation lowered at an area-average rate of 0.7 ± 0.1 m/yr. The accumulation area of Yahtse Glacier, above 1220 m elevation lowered from 1972 to 2000 at an area-average rate of 0.9 ± 0.1 m/yr. On a same-area basis, Tyndall Glacier lowered from 1972 to 1999 at an area-average rate of 1.4 ± 0.2 m/yr; then accelerated substantially to 2.8 ± 0.2 m/yr from 1999 to 2002. From 2000 to 2003 the accumulation area of Yahtse Glacier lowered at 1.5 ± 0.3 m/yr, on average. The drawdown of these accumulation areas have occurred while snow accumulation at 5000+ m on Mt. Logan, Canada, has shown a strong increase from 1976 to 2000. Concurrently, coastal winter mean temperatures at Cordova and Yakutat, south-central Alaska, have increased to above freezing since about 1979. Retreat and surface lowering of the Icy Bay glaciers is attributed to tidewater glacier dynamics with climate warming effects superimposed.