Glacier, climate signal, mass balances, ablation rate, front fluctuations.

France, Swiss and Austria

1.Glaciers of Claridenfirn (46°40’N; 8°50’E)
2. Aletsch (46°30’N; 8°02’E),
3. Hintereisferner (46°48’N; 10°46’E)
4. St Sorlin (45°10’N; 6°10’E)
5. Sarennes (45°07’N; 6°07’E)

1 : E  
2 : S-E to S
3 : E to N- E
4 : N to E 
5 : S

1. 2540-3240m
2. 1556-4160m 
3. 2430-3710m 
4. 2700-3400m
5. 2850-3150m.

1 : 1914-2002 
3 : 1953-2002 
4 : 1957-2002 
5 : 1949-2002.

The 1953-1999 average rate of decrease :
• 2: -0.32 m water equivalent yr-1
• 3: -0.45 m w.e. yr-1
• 4: -0.33 m w.e. yr-1
• 5: -0.62 m w.e. yr-1

The cumulative centered mass balance series show a strikingly common feature between the respective behaviours of the 1, 3, 4 and 5 glaciers. Mass balance fluctuations of the Aletsch glacier show some discrepancies, especially between 1957 and 1980. It could be a consequence of the difference of methods used to obtain the data.

Explained variance between mass balance terms :
• Summer mass balance represents 76% of the annual mass balance for the 5 glacier (against 30% for winter mass balance);
• Summer mass balance represents 68% of the annual mass balance for the 1 glacier (against 42% for winter mass balance).

The summer mass balance term represents by far the largest contribution to the annual mass balance. The comparison of the standard deviations of each mass balance term leads to the same conclusion and shows that the winter mass balance contribution to the annual mass balance is greater on the 1 glacier than on the 5. It is consistent with the fact that 1 observations are from the accumulation zone only and the decreasing variability of mass balance with elevation. The summer mass balance explains by far the largest part of the annual mass balance correlation between the 1 and 5 glaciers.
The cumulative winter mass balance relative to the 1954-1981 period show strong differences between the 1 and 5 glaciers. The winter mass balance for 1 shows no trend whereas that shows a strong positive trend over the last 20 years for 5 (increase by an average of 30 cm w.e./yr), in total opposition with the annual mass balance trend. Concerning the summer mass balance, the comparison between 1 and 5 shows a striking feature: the variation pattern is very similar and the cumulative ablation follows the same trend, with very similar melting rate changes over the last 50 years.
Comparison between average summer mass balances of the two glaciers shows that the ablation from the 1st June to September has increased similarly between 1954-1981 and 1982-2002 periods for the two glaciers (0.6 m w.e./yr).

Mean ablation rate on the 5 glacier increased significantly from 1954-1981 to 1982-2002 with regards to both snow and ice ablation periods (0.5 cm w.e./day for snow and 0.3 cm w.e./day for ice). The snow ablation period has decreased by 4 days and the ice ablation period has risen from 27 to 43 days. The snow ablation rate increase is very similar for the 1 glacier.

For the 5 glacier, between 1954-1981 and 1982-2002, the calculated energy variations are 20 and 11 W m-2 for the snow and ice ablation periods respectively. The air temperature increase between the same periods explains the largest part of the ablation rise.

Winter and summer mass balance series of Claridenfirn and Sarennes have been used to investigate the possibility of a common climatic signal throughout the Alps.

First, the overall mass balance variations since the beginning of the 20th century have been compared for 4 glaciers (2, 3, 4, 5). They are obtained from stakes inserted in the ice in the ablation area and from drilled cores in the accumulation zone. Total cumulative annual mass balances of the Sarennes and St Sorlin glaciers have been extended to cover the entire 20th century using old maps with elevation contours and recent geodetic measurements. For the Aletsch glacier, data have been obtained since 1923 by an indirect method using hydrological data (water flux measurements and precipitation data).

The 1953-1999 average rate of decrease has been removed, i.e., each glacier mass balance has been reduced by subtracting the 1953-1999 average mass balance of each glacier from the annual values (cumulative centered mass balance). Data from Claridenfirn have been also included.

Then, a detailed analysis of winter and summer separate mass balance observations of the 1 and 5 glaciers over the last 50 years has been conducted. Measurements at only one stake were selected on each glacier (at 2900 m a.s.l.) : the highest stake of 1 (accumulation zone) and a stake located in the middle of the 5 glacier and representative of the overall glacier mass balance. The cumulative winter and summer mass balance variations centered with respect to the 1954-1981 period (marked by a sharp reduction in glacier mass) have been compared for the two glaciers.

Finally, using the latent heat of fusion, the snow and ice ablation rates have been converted into energy assuming that the ablation is due only to melting.

(4) - Remarques générales