VARIATION IN GLACIER LENGTH AND ICE VOLUME OF RABOTS GLACIÄR IN RESPONSE TO CLIMATE CHANGE, 1910 - 2003

Keith A. Brugger, Kurt A. Refsnider, and Matthew F. Whitehill, 2006, Annals of Glaciology v. 42.

ABSTRACT

Rabots Glaciär, like many other glaciers in the Swedish Arctic, retreated from its last maximum extent in response to a 1 °C warming that occurred around 1910. Historical records, photographs, and measurements of the glacier's terminus document a slow initial rate of retreat of about 1.6 m a-1 between 1910 and 1933. Thereafter the average retreat rate abruptly and substantially increased to 10 m a-1 and remained essentially constant into the mid-1980s. Concomitant decreases in glacier volume during this time were estimated using a reconstruction of the glacier's 1910 surface and topographic maps of the 1959 and 1980 glacier geometry. Ice volume decreased 1.9 x 107 m3 between 1910 and 1959, corresponding to a rate of volume loss of 3.9 x 105 m3 a-1. Between 1959 and 1980 the glacier's volume decreased by an additional 4.9 x 107 m3, equivalent to a rate of 2.3 x 106 m3 a-1. This roughly order-of-magnitude increase in the rate of volume loss coincides with an interval of relatively constant and rapid retreat of the glacier. Measurement of the terminus position throughout the 1980's and 1990's indicated that the glacier continued to retreat at rates comparable to that from 1933 to 1980. However, an analysis of ice surface elevations surveyed in 1998 suggested that the rate of volume loss since 1980 had slowed considerably to about 1.2 x 106 m3 a-1. This estimate is somewhat problematic in that it was based on fewer than 50 measurements of ice surface elevation.

During the summer of 2003, nearly 1000 measurements of the location of the glacier's margin and elevation of the present ice surface were made using differential GPS survey techniques. The rate of ice retreat remains about 10 m a-1. Preliminary analysis of the changes in surface elevations between 1980 and 2003 shows that the glacier's volume has decreased by approximately 3.0 x 107 m3. This equals a rate of 1.3 x 106 m3 a-1 that again indicates a significant reduction in the rate of ice loss, and may furthermore imply the glacier is beginning to complete its response to the climatic warming of the early 20th century. This conclusion is also supported by numerical modeling which suggests that in the absence of concurrent climate change, Rabots Glaciär should be: (1) essentially half-way through its response to the earlier climate warming; and (2) currently experiencing a rate of volume change comparable to that measured.