Establishment and Evolution of Stable Water Isotopes in Seasonal Alpine Snow

Stable water isotopes are splendid passive tracers, not only suited to show hydrogeological flow paths but also to determine - and possibly quantify - processes at catchment scale, such as evaporation and sublimation. In alpine hydrology, snow largely contributes to groundwater recharge, therefore understanding how the water isotopes in snow are shaped and how they change over time is key. In this study we discuss the potential driving forces of snow isotopic composition in individual snow events, through correlating snow isotopy to several individual meteorological parameters at the field site and at the location of moisture origin using a back trajectory model. Furthermore, in this study we discuss the results of weekly field observations at three sites along an elevational transect within an East Austrian cirque (7 km²), where snow pack melt water and high-resolution snow pack layers isotopy were sampled. Weekly isotopic changes of isotopic snow pack layers are correlated to potential driving forces. Considering the thermal induced snow metamorphism, we installed an array of snow thermometers in the snow throughout the season to correlate the isotopic changes to the snow temperature and thermal gradient. First order isotopes (δ²H and δ¹⁸O) show to be significantly correlated to local meteorological conditions like the cloud top pressure, and cloud temperature. The second order isotope, Deuterium excess (dxs), is significantly correlated to the relative humidity and temperature at the moisture origin. Weekly changes in first order isotopes of the seasonal snowpack could be correlated to the average global radiation of the period between sampling, and to the net radiation 24 hours before sampling. Changes in dxs only showed significance to the temperature gradient. Isotopic gradients (i.e., the gradient of snow isotopy above and below a monitored layer) did appear to significantly affect the isotopic change, both for the first and second order isotopes.  This research highlights the local and non-local establishment of meteoric stable water isotopes in winter and proposes that more research needs to be conducted towards isotopic snow profile evolution in a seasonal snowpack.