Post-depositional modification of stable water isotopes in winter snowpacks in the Canadian Rocky Mountains

To assess the seasonal stability of the δ18O stratigraphy in winter snowpacks in the Canadian Rocky Mountains, snow pits were sampled over three accumulation seasons at two field sites. These sites, Opabin and Haig Glaciers, are ~160km apart at similar elevations and represent windward and lee-slope environments respectively. At both sites, snow pits were sampled at one glacier and one forefield location throughout each accumulation season. Intra-seasonal changes in δ18O at each site were examined to determine the extent of post-depositional modification of isotope stratigraphies. At both glacier sites, there was minimal temporal change before the onset of spring melt in all years. In addition, the similar structure of δ18O profiles from both glacier sites suggests that regional controls govern the isotopic composition of solid-phase precipitation across the study area. At forefield locations, the absence of an insulating layer of ice at the base of the snowpack allowed for vapour transport and post-depositional modification of the seasonal δ18O signal. This did not result in consistent changes to the mean δ18O, deuterium excess and δD–δ18O regression line slopes in the lower layers of snow, and the observed smoothing of δ18O profiles was less than that simulated by applying a diffusion model to these snowpacks.