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Freiburger Geographische Hefte, Vol 56

Christoph Schneider (1998): Zur raumzeitlichen Differenzierung der Energiebilanz und des Zustandes der Schneedecke auf zwei Gletschern der Marguerite Bay, Antarktische Halbinsel


The Antarctic Peninsula is a region of special interest with respect to the regional impact of global climate change. With its large extent from north to south the mountain ridge constitutes the sole obstacle for the circumpolar west wind zone of the southern hemisphere. Teleconnections between lower latitude atmospheric circulation and the atmospheric circulation of Antarctica directly influence the circulation within the west wind zone and also the distribution of sea ice in this region. A warming trend of 2.5 Kelvin has been observed on the west side of the Antarctic Peninsula underlining the great significance of the issue. Furthermore, sea ice extension in the Bellingshausen Sea west of the Antarctic Peninsula has showed a negative trend during the last 25 years.

This study sets out to discuss the state-of-the-art knowledge and understanding of the regional climatology of Marguerite Bay on the west coast of the Antarctic Peninsula. The regional climate of the area is predominantly influenced by its sheltered situation through protection by large surrounding islands, - e.g. Alexander Island and Adelaide Island - and the mountain chain of the Antarctic Peninsula. Synoptic situations with advection of warm and moist air masses from the north west and situations with föhn-type winds from the east predominate meteorology. In the inner part of Marguerite Bay mean air temperatures during the summer months rise only slightly above 0°C. Therefore, until recently small ablation zones could only be observed on northward orientated glaciers.

Field work was carried out on the Northeast and McClary Glacier at 67° west and 68° south in Marguerite Bay. Three automatic weather stations were in operation on the Northeast - and McClary Glaciers in the summer of 1994/95. Furthermore, snow cover characteristics and snow cover development was observed by means of snow pits and ablation stakes. There was good agreement between the snow melt observed in summer and the snow melt calculated from micro-meteorological measurements by means of energy balance computations. It is shown that the summertime energy balance at the surface of the snow cover is predominated by turbulent heat fluxes. Energy input into the snow cover is mainly due to energy gain by sensible heat flux.

Spatial and temporal distribution of the energy balance was estimated using a simple model. This model is based on a digital elevation model and was developed to separate the snow cover into an currently wet snow zone and a percolation snow zone with snow that is currently completely frozen. This separation can also be obtained from radar satellite imagery. The altitude of the transition from wet snow to frozen snow was derived from meteorological data within the model for the summers of 1993/94 and 1994/95. The results were compared with radar satellite images. Results from both methods were consistent. The mean air temperature in summer was 1.2 Kelvin higher in summer 1994/95 compared to the summer of 1993/94. This resulted in the altitude of the transition between the two snow zones increasing by approximately 290 m.

Accumulation during winter varies considerably spatially. Readings in snow pits and at ablation stakes return values between 300 mm and 500 mm of water equivalent. The ablation in summer correlates with the mean air temperature and altitude. In the lowermost parts of the glaciers ablation amounts to 200 to 400 mm of water equivalent. The observations show that an ablation zone developed on the Northeast Glacier at the end of the summer of 1994/95. The equilibrium line altitude then was at 110 m above sea level.

Hence, further warming in summer in coastal regions will trigger the formation of large ablation zones on the glaciers. In the case of further warming, run-off from glaciers - as one part of the mass balance - will gain importance because the albedo of bare glacier ice in these ablation zones is much lower than the albedo of wet snow. In contrast to long-term adjustments of the glacial dynamic to climate variations, the changes in the snow cover have short-term consequences. The methods developed in this study enable the monitoring and analysis of these short-term changes.