Temperature and vapour-trajectory controls on the stable-isotope signal in Canadian Rocky Mountain snowpacks

The effects of temperature and seasonal air-mass trajectories on stable water isotopes in alpine snowpacks are investigated using meteorological and snow-pit data at two alpine field sites in the Canadian Rocky Mountains: Haig Glacier, Alberta, and Opabin Glacier, British Columbia. Snow pits were sampled through three accumulation seasons (October-June, 2004/05, 2005/06 and 2006/07) for delta O-18, delta D, temperature and density. The isotopic characteristics of precipitation over these time periods, including the local meteoric waterline and average delta O-18, delta D and deuterium excess, were defined using this dataset. Individual snowfall events over the three seasons were identified in the accumulation records from both sites and then fit to snow-pit stratigraphies to determine their mean isotopic characteristics. A trajectory classification was produced for all events, and the key meteorological characteristics of each trajectory class were 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 O-18 between storm classes. However, the separation appears to be driven primarily by the mean temperature of each class rather then being a direct effect of vapour pathway.