In-situ high-resolution stable water isotope measurements of snowpacks in cold environments: opportunities for better understanding dynamic snowpack processes

Snow is a major component of the hydrological cycle in cold environments. Snowpacks not only directly contribute to the local water cycle through snowmelt in late winter, but also constantly interact with local atmospheric water vapor through sublimation and vapor exchange throughout the winter. However, the widely used ‘traditional’ snow water isotope sampling method is destructive and temporally discrete, which limits the ability to capture the highly dynamic snow-liquid-vapor process within snowpacks. Therefore, at the Julinia site in Finland, we conducted the first winter field deployment of an innovative in-situ water isotope probe (WIP) system to sample cold and dry water vapor from snowpack layers and ambient air, where WIP was originally designed for use in trees and soils to study tree water uptake during the growing season. Water vapor sampled in-situ based on the direct vapor equilibrium method was continuously measured by a laser spectroscopy isotope analyzer (Picarro). Combined with ‘traditionally’ sampled water isotopes from event-based snowfall and snowpack layers, the temporal variation of δ¹⁸O and δ²H in different snowpack layers formed by different snowfall events illustrate the isotopic process of snowpack compaction, vapor exchange within the snowpack, and snowmelt. This approach provides an opportunity to better understand the long-overlooked isotopic difference between snowfall, snowpack, and snowmelt water, which can lead to non-negligible bias in partitioning ‘blue water’ and ‘green water’ in snow-dominated regions when using the stable water isotope techniques.