Climatic drivers of seasonal glacier mass balances: an analysis of 6 decades at Glacier de Sarennes (French Alps)

Abstract

Abstract. Refined temporal signals are extracted from a glacier winter and summer mass balance series recorded at Glacier de Sarennes (French Alps) using variance decomposition. They are related to local and synoptic meteorological data in terms of interannual variability and structured trends. The winter balance has increased by +23% since 1976 due to more precipitation in early and late winter. The summer balance has decreased since 1982 due to a 43% increase in snow and ice melt. A 24-day lengthening of the ablation period – mainly due to longer ice ablation – is the main component in the overall increase in ablation. In addition, the last 25 yr have seen increases in ablation rates of 14 and 10% for snow and ice respectively. A simple degree-day analysis can account for both the snow/ice melt rate rise and the lengthening of the ablation period as a function of higher air temperatures. From the same analysis, the equilibrium line altitude of this 45° North latitude south-facing glacier has sensitivity to temperature of +93 m °C−1 around its mean elevation of 3100 m a.s.l. over 6 decades. The sensitivity of summer balance to temperature is −0.62 m w.e. yr−1 °C−1 for a typical 125-day long ablation season. Finally, the time structure of winter and summer mass balance terms are connected to NAO anomalies. Best correlations are obtained with winter NAO anomalies. However, they strongly depend on how the NAO signal is smoothed, so that the link between mass-balance seasonal terms and NAO signal remains tenuous and hard to interpret.