Abstract
Abstract. Refined temporal signals extracted from a winter and summer mass balance series recorded at Glacier de Sarennes (French Alps) using variance decomposition are related to local meteorological data and large-scale North Atlantic Oscillation (NAO) anomalies in terms of interannual variability, trends of the low-frequency signals, and breaks in the time series. 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° N latitude south-facing glacier has a 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 correlation of winter and summer mass balance terms with NAO anomalies is investigated. Singularly, highest values are obtained between winter NAO anomalies and summer balance. Winter NAO anomalies and winter balance and precipitation are almost disconnected. However, these results strongly depend on how the NAO signal is smoothed, so that the link between Sarennes mass balance seasonal terms and NAO signal remains tenuous and hard to interpret.
Highlights
Mountain glaciers are recognised as excellent indicators of climate change over the last few centuries (Oerlemans and Fortuin, 1992; Haeberli, 1995; Vincent, 2002; IPCC, 2007)
This is understandable since the Atlantic Multidecadal Oscillation (AMO) is physically based on temperature and, despite being an oceanic oscillation mode, positive AMO phases are effectively related to positive near-surface air temperature anomalies in continental Europe
Summer balance at Sarennes is significantly anti-correlated with North Atlantic Oscillation (NAO) anomalies (r = −0.33), and similar significant positive correlations are observed with Lyon temperature (r = 0.41), as expected from the high anti-correlation between summer balance and temperatures (Table 2)
Summary
Mountain glaciers are recognised as excellent indicators of climate change over the last few centuries (Oerlemans and Fortuin, 1992; Haeberli, 1995; Vincent, 2002; IPCC, 2007). As pointed out by Harrison et al (2009) and Huss et al (2012), the combination of these effects can have different results on glacier-wide balance from one glacier to another To overcome these artifacts, Elsberg et al (2001) proposed to relate mass balance to a constant geometry correcting for surface and altitude changes. The special location of Sarennes at the climatic boundary between the southern and northern French Alps and its long record of seasonal balances led us to extend such analyses, focusing on how this link splits for summer and winter mass budgets For both local and large-scale atmospheric covariates, correlations are investigated for annual values and for the trends of the low-frequency signals. After a presentation of the site and of the method used to process the data (Sect. 2), this analysis is conducted and discussed for the winter (Sect. 3) and summer (Sect. 4) mass balance components
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