Spatial distribution of stable water isotopes in alpine snow cover

Abstract

Abstract. The aim of this study was to analyse and predict the mean stable water isotopic composition of the snow cover at specific geographic locations and altitudes. In addition, the dependence of the isotopic composition of the entire snow cover on altitude was analysed. Snow in four Swiss catchments was sampled at the end of the accumulation period in April 2010 and a second time during snowmelt in May 2010 and analysed for stable isotope composition of 2 H and 18 O. The sampling was conducted at both south-facing and north-facing slopes at elevation differences of 100 m, for a total altitude difference of approximately 1000 m. The observed variability of isotopic composition of the snow cover was analysed with stepwise multiple linear regression models. The analysis indicated that there is only a limited altitude effect on the isotopic composition when considering all samples. This is due to the high variability of the isotopic composition of the precipitation during the winter months and, in particular in the case of south-facing slopes, an enrichment of heavy isotopes due to intermittent melting processes. This enrichment effect could clearly be observed in the samples which were taken later in the year. A small altitudinal gradient of the isotopic composition could only be observed at some north-facing slopes. However, the dependence of snow depth and the day of the year were significant predictor variables in all models. This study indicates the necessity to further study the variability of water isotopes in the snow cover to increase prediction for isotopic composition of snowmelt and hence increase model performance of residence time models for alpine areas in order to better understand the accumulation processes and the sources of water in the snow cover of high mountains.

Tracer-based analysis of spatial and temporal variations of water sources in a glacierized catchment

“…Moreover, snow samples plotted well on the LMWL (and therefore on the GMWL), as also confirmed by the slope and interception values very similar to those of the LMWL ( Table 4). This was also found for a set of snow-dominated catchments in Switzerland (Dietermann and Weiler, 2013) and indicates a similar geographical origin of precipitation during the winter with respect to the other seasons. However, we must mention that the range in the isotopic composition of snow samples was likely underestimated, due to the uncertainty associated with finding sampling locations representative for the isotopic signature of snowpack over the entire catchment.…”

“…However, we must mention that the range in the isotopic composition of snow samples was likely underestimated, due to the uncertainty associated with finding sampling locations representative for the isotopic signature of snowpack over the entire catchment. Indeed, in addition to altitude and seasonal effects, several other factors such as micro-and macro-topography, relocation of snow through wind drift and avalanches, and enrichment of heavy isotopes in upper layers of the snowpack depending on the sun exposure can contribute to significantly enhance the spatial and temporal variability of the isotopic composition of snowpack (Dietermann and Weiler, 2013). Samples collected from melting snow patches showed a wide isotopic range too (Fig.…”

Understanding snow hydrological processes through the lens of stable water isotopes

“…Here, the average isotope composition of precipitation shifts by 1.9‰/100/m for δ 2 H and 0.27‰100/m for δ 18 O, noting that in winter, above around 800 m asl, the precipitation is dominated by snow (Marty, 2008). Some version of this isotopic lapse rate is seen in almost all mountainous environments except on the leeward or "rain-shadow" side of mountains, which receive precipitation from clouds that have already passed over the highest elevation of the ridge and are no longer continuing to rise, keeping the cloud condensation temperature relatively stable (Bershaw, Penny, & Garzione, 2012;Dietermann & Weiler, 2013;Koeniger, Hubbart, Link, & Marshall, 2008;Moran, Marshall, Evans, & Sinclair, 2007;Wen, Tian, Weng, Liu, & Zhao, 2012;Winograd et al, 1998). Moran et al (2007) reported positive isotopic lapse rates (enrichment in heavier isotopes with increasing elevation) in snow samples on the leeward side of a glacierized valley in the Canadian Rockies (refer to Figure 4 in Moran et al (2007)), which may occur only if the warmer temperatures and hence smaller vapor-liquid or vapor-ice isotopic fractionation factors offset the "rain-out" effect.…”

“…It has been widely observed that early meltwater is more depleted in heavier isotopes and that, as the melt season progresses, both the residual snowpack and the generated meltwater become more enriched in heavier isotopes (Dietermann & Weiler, 2013;Taylor et al, 2001), which is also referred to as the melt-out effect (Ala-aho et al, 2017). To the best of our knowledge, the physical mechanisms of this melt-out effect are not well understood but likely involve the partial melting of snowpack which results in preferential loss of lighter isotopes in the early season meltwater.…”

The importance of snowmelt spatiotemporal variability for isotope-based hydrograph separation in a high-elevation catchment

“…The effect of the aspect of the hillslopes on isotopic variability and IHS results in topographically complex terrain has been rarely investigated. Dahlke and Lyon (2013) and Dietermann and Weiler (2013) surveyed the snowpack isotopic composition and showed a notable spatial variability in their data, particularly between north-and south-facing slopes. They conclude that the spatial variability of snowmelt could be high and that the timing of meltwater varies with the morphology of the catchment.…”