ALASKA’S TAKU GLACIER REVEALS ACCELERATED ADVANCE -- A SIGNAL OF GLOBAL WARMING

On-going measurements of the behavior of Taku Glacier, the largest glacier on Alaska’s Juneau Icefield reveal evidence of major climate change. Unlike most other glaciers along the 1,400-km-long Alaskan Panhandle, the 360 km² Taku Glacier has been vigorously advancing since 1890. During the past two decades this advance has been characterized by an accelerated forward thrusting at the glacier terminus. The ice front now shows a strongly convex upward profile and is moving forward >1.1 m/d in spite of summer ablation of ~1 m/d. Excessive summer melt results from the terminus being at sea level in Taku Inlet.

There is presumed linkage to notable increases in El Nino’s effect on the coastal climate and therefore on glacier regime changes in recent decades. High spatial-resolution surveys since the 1980s do not detect notable increases in surface ice flow in the source areas, but physical evidence at the terminus supports a significant increase in glacier activity and the continuing advance.

Year round meteorological records collected on the Juneau Icefield document that unusual warming conditions have occurred over the past 20 yr with minimum winter temperatures on the source névés being 25 to 30 degrees warmer than recorded 30 to 50 yr ago. This warming condition has resulted in a rise of the icefield’s regional freezing level and a substantial increase in snowfall on the higher névés. Annually, ~60 m of snow accumulates at the 1,500-2,000 m elevation where the largest and highest source névés lie. About half of this snowpack is annually retained, adding to the glacier’s volume and affecting the longitudinal stress trajectory in the lower glacier sectors. In considering the glacier’s flow lag, some of the terminal thrust fracturing may reveal kinematic energy release, a possibility difficult to document. The measured terminal thrusting is interpreted as a global warming effect in recent decades through inland displacement of the Arctic Front and upward shifting of the regional freezing level. The implication with respect to global climate change has encouraged the Juneau Icefield Research Program to continue to emphasize the need for careful monitoring of the glacier’s annual mass balance and the annual measurement of longitudinal GPS-controlled surface profiles to document the intensity and rapidity of related climate change.