Stable isotope-vapour trajectory relationships in Rocky Mountain snowpacks

To assess the relationships between vapour trajectories and stable water isotopes in the Canadian Rocky Mountains, snow pits were sampled over three accumulation seasons (2004/05, 2005/06 and 2006/07) at two field sites. These sites, the 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 for delta 18O, deltaD, temperature and density. Intra-seasonal changes in delta18O are examined to determine the extent of post-depositional modification of isotope stratigraphies. At forefield sampling locations, vapour transport within the snowpack caused a significant amount of post-depositional modification of the seasonal delta18 O signal. At glacier sites there was minimal temporal change before the onset of spring melt in all years, and the comparative structure of delta 18O profiles from both glacier sites suggests that regional controls govern the isotopic composition of solid-phase precipitation in the Rocky Mountain region.;The seasonal stability of isotope profiles at glacier sites enables individual snowfall events to be identified within isotope stratigraphies. A trajectory classification is produced for all events and the key meteorological, synoptic and isotopic characteristics of each trajectory class are investigated using data from alpine field sites and a suite of meteorological records from the region. An analysis of the relative influences of temperature and air-mass trajectory on snow-isotope ratios reveals some separation in mean delta 18O between storm classes, but the separation appears to be primarily driven by the mean temperature of each class rather than being a direct effect of vapour pathway.;To further investigate the effect of storm trajectory on stable isotope ratios in this region, the isotopic evolution of precipitation along storm trajectories from 2006/07 is modelled using a single stage Rayleigh distillation model coupled to a simple orographic model. Isotopic data from alpine snow pits, along with an additional dataset from a sampling transect in southern British Columbia, are used to constrain and test the model. The addition of an orographic component is an improvement over a conventional Rayleigh model, and there is a good model fit to alpine isotope data for most storms.