Variations des bilans de masse des glaciers alpins et scandinaves sur les dernières décennies, leurs relations avec l'Oscillation du climat de l'Atlantique Nord

Alpine and Scandinavian glaciers mass balances, their relations with the North Atlantic Oscillation

¹ Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS 54 rue Molière, Domaine Universitaire, BP 96, 38402 Saint Martin d'Hères Cedex, France - Tél. : 04 76 82 42 05
² Université Joseph Fourier, Grenoble 1, 38402 Saint Martin d'Hères Cedex, France

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Abstract

Nowadays, different studies try to understand the relations between the main climate variables and the climatic archives available on the Earth. In this study, we explained relations between Alpine and Scandinavian glaciers and the North Atlantic Oscillation, to understand the recent evolution observed in these areas. The annual glacier mass balance variable is known as a good climatic local indicator. Earlier studies show that mass balance distributions are really representative of their own mauntainous area, on distances lower than 500 km. However, observations show that when mass balance is higher than the mean in the Alps, it tends to be lower in Scandinavia, and conversely. In order to understand this behaviour, we then studied the variability of the North Atlantic Oscillation. Overall, the NAO index has a high inter-annual variability. However, dominant positive or negative phases can be observed for some long periods. For instance, indexes are in an exceptionally positive phase for the last ten years. The direct correlations between annual North Atlantic Oscillation index and annual mass balances are low, and slightly better for Scandinavian glaciers. In order to take away annual noise, we then tried to remove high signal frequencies with triangular filter,calculated on five years. Alpine glaciers and NAO indexes are anti-correlated, whereas Scandinavian glaciers and NAO index are positively correlated. Furthermore, the relation is more apparent with Scandinavian glaciers than with those of the Alps. This could be principally explained by the geographical distribution of the glaciers, and the greater importance of maritime precipitations on Scandinavian glaciers. Glaciers are still complex systems and the simple NAO index can not explain their entire hydrological cycle. Because of the low correlations, it is not possible to reconstruct past glaciers mass balances, nor to predict these mass balances thanks to NAO indexes.