The Mass of McCall Glacier. Its Regional Relevance and
Climatological Implications for Climate Change in the Arctic
Bernard T. Rabus and Keith Echelmeyer
University of Alaska-Geophysical Institute
McCall Glacier has the only long-term mass balance record in Arctic Alaska. Mean annual balances over the periods 1958-71 and 1972-93 were -0.13 m and -0.33 m respectively; recent annual balances (1992-95) are around -0.6 m. For an arctic glacier with low mass exchange rate this marks a dramatically negative trend. Elevation profiles and terminus outlines, recently acquired with airborne and ground-based GPS methods on McCall and ten other glaciers of various sizes and aspects within a 30 km radius, were compared with topographic maps made several decades earlier. Comparison of the elevation changes of McCall and the other glaciers from 1956 to present show no major differences in the common parts of their elevation ranges. During this time span most glaciers have cumulative balances between -10 and -13 m (McCall: -12m). This indicates that McCall Glacier is representative for the region. Contrary to the cumulative balances which are similar for the different glaciers, the changes in terminus position vary markedly. This complicated regional pattern is dominated by effects of glacier geometry and flow dynamics in the terminus region. To estimate mass balance disturbances from fractional length changes is not possible in this area.
To show that the mass balance of McCall Glacier detects climate change on a larger synoptic scale we show results from a simple two parameter degree day/accumulation model. The model uses radiosonde temperature and ground precipitation data from coastal weather stations at Barrow (Alaska) or Inuvik (Canada) as input and is calibrated with a subset of the known annual mass balances of McCall Glacier. Positive degree days and accumulation calculated by the model show significantly different trends for Barrow and Inuvik; Inuvik data reproduce all measured annual mass balances of McCall Glacier within a 20% error band and also quantitatively reproduce the long-term trend towards negative balances. Barrow data on the other hand fail to reproduce either annual balances or the long term trend within reasonable error. Contrary to measurements, balances modeled from Barrow data are generally too negative except for a short period of positive balances in the 1970's. For their limited time range, 1948 to 1989, Kaktovik (Alaska) data gave results similar to those obtained with the Inuvik data. We speculate that the average location of the Arctic front in summer which separates Inuvik, Kaktovik and McCall Glacier from Barrow creates distinct climatic regions with non-identical climate change scenarios that explain the observed differences in modeled degree days and accumulation.
Given our results, we conclude that McCall Glacier is representative of a synoptic scale region and its mass balance record is an important measure of ongoing climate change in the Arctic. [an error occurred while processing this directive]