Frank Pattyn @ ULB
Glacier fluctuations in the Altai (Russia)
Global mean temperatures have risen over the past 100 years by about 0.6°C. Over half of the increase has occurred in the last 25 years (IPCC). Glaciers all over the world react to these variations in background temperature, primarily by retreating (this is valid for most glaciers outside Antarctica or Greenland). They are therefore considered to be potentially good climatic indicators.
One way to determine the state of a glacier is by determining its mass balance. During winter, a glacier gains mass from accumulating snow. During the following summer some, and sometimes all, of that winter accumulation is lost due to melt. The difference between the accumulation and melt (or ablation) describes the annual net mass balance, which is equal to change in glacier volume.
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Mass balance measurements on more than 280 glaciers all over the world indicate that in most regions of the world, glaciers are shrinking in mass. More information of the website of the State of the Cryosphere and the Mountain glacier fluctuations.
Glaciological measurements on Sofiyskiy Glacier
The majority of source information with respect to the dynamic response of temperate glaciers with changing climate comes from European and, to a lesser extent, North-American glaciers, while the share of the European glaciers in the world glacier area consists of only 3%. Hence, our knowledge on the glaciers of remote and hardly accessible mountain regions, often characterized by a high degree of glacierization, is rather limited. This biased distribution of glaciological source information severely constrains present attempts to assess the impact of climate change on the global glacier volume. It also hampers a full understanding of glacier dynamics and the impact of different climatic conditions. This project intends to expand the current global glaciological record by presenting and analyzing data gathered on Sofiyskiy Glacier, located in the Russian Altai Mountains, and collected during four consecutive summer field seasons in the period 1997-2000.
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The climate of the Altai Mountains exhibits two important characteristics which contribute to the specific interest of this study area. First, the extreme continentality gives rise to aridity and large diurnal and seasonal temperature range. Second, owing to the coincidence of both accumulation and ablation season in summer, we can characterize the Altai glaciers as summer-accumulation type glaciers. Although current knowledge on the behaviour of these glaciers is limited, they are reported to be more vulnerable to the current global warming trend than the better known (maritime) winter-accumulation type glaciers. During this project, the basic characteristics of Sofiyskiy Glacier were investigated, such as surface mass balance and velocity, and the historical front variations. To gain a better understanding of the glacier's dynamics, we also performed a force-balance analysis and an analysis of basal conditions using a three-layer reflectivity model for electromagnetic pulses.
Recent glacial history
Sofiyskiy Glacier (49º47'N, 87º46'E) is one of the major glaciers in the central part of the South Chuya Range, a mountain chain within the Altai mountain belt, situated in the border region between Russia and Mongolia. The SW--NE oriented Sofiyskiy Glacier is approximately 7 km long and has an average width of 1.7 km. The head of the glacier is located near Mt. Brat (3876 m a.s.l.), one of the highest peaks of the range. A steep ice fall is situated between 2800 and 3000 m a.s.l. Below this ice fall, the glacier terminates in a relatively flat tongue.
During the 20th Century, several front-position markers were recorded. The earliest records are from field markers and aerial photographs. During each of the 1997-2000 field seasons, the snout position was mapped with differential GPS. The historical record is further extended back in time by radio-carbon dating of wood fragments collected in three different former front moraines of Sofiyskiy Glacier. On comparison to Maliy Aktru Glacier, a glacier located in the North Chuya Range some 30 km to the northwest, it is clear that both glaciers retreated steadily since the beginning of the 20th Century. Their average retreat rates are 9.6 m/a for Maliy Aktru Glacier and 18.3 m/a for Sofiyskiy Glacier, based on re-measurement of field markers and our own measurements of the front position. The most rapid retreat of both glaciers occurred between 1900 and 1940.
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Surface mass balance
Based on our DGPS measurements, a mean mass-balance reference profile for the period 1997-2000 was constructed using a linear parameterization. Excluding the short 1999-2000 balance season, the Equilibrium Line Altitude (ELA) and the slope of this reference profile are 3179 m and 73.1 cm/a w.e. per 100m, respectively. The figure below also shows the mass balance reference profile for Maliy Aktru Glacier, based on a 38-year mass balance record (1962-1999: World Glacier Inventory).
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Radio echo sounding (RES)
Radio-echo sounding measurements were carried out with a 5MHz (central frequency) Ice Penetrating Radar (Narod and Clarke, 1994). The system consists of a monopulse transmitter generating 1600 V pulses across a resistively-loaded 10m dipole antenna, and an airwave-triggered oscilloscope receiver connected to a palmtop computer for digital data recording. Pulses are generated at 512 Hz and have a bandwidth of 1-200 MHz.
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Numerical modelling
A successful simulation of the observed historical front variations was accomplished by dynamic calibration. This resulted in the reconstruction of the recent mass-balance history of the glacier, showing a distinct drop of surface mass-balance conditions in the second half of the 19th Century, slightly higher balance conditions at the beginning of the 20th Century, followed by a steady decrease towards present conditions.
The future response of Sofiyskiy Glacier was projected for six 21th Century climate scenarios. Under a “no-change” scenario, the glacier retreats with more than 2 km by 2100. If air temperature would gradually rise with more than 5°C during this Century, the glacier would vanish near 2100.
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References
Pattyn, F., B. De Smedt, S. De Brabander, W. Van Huele, A. Agatova, A. Mistrukov and H. Decleir (2003) Ice dynamics and basal properties of Sofiyskiy Glacier (Altai, Russia) based on DGPS and radio-echo sounding surveys. Annals of Glaciology 37: 286-292.
De Smedt, B. and F. Pattyn (2003) Numerical modelling of historical front variations and dynamic response of Sofiyskiy glacier, Altai Mountains, Russia. Annals of Glaciology 37: 143-149.
Acknowledgements
This research forms a contribution to the project `Glacier Fluctuations and Climatic Change in South Siberia' (Federal Office for Scientific, Technical and Cultural Affairs), Contract IN/RU/006 (1998-2000), and the research project `Climatic Change in the Altai Mountains' (FWO-Vlaanderen), Contract G.0120.97 (1998-2000).