A 10-yr record of stable isotope ratios of hydrogen and oxygen in precipitation at Calgary, Alberta, Canada

Short-term (0.5–3 d) precipitation samples were collected from January 1992 to December 2001 in Calgary, Alberta, Canada, and the stable isotope ratios of hydrogen (²H/¹H) and oxygen (¹⁸O/¹⁶O) for these samples were determined. The 10-yr amount-weighted average δ²H and δ¹⁸O values of precipitation were −136.1‰ and −17.9‰, respectively. Consistent with International Atomic Energy Agency (IAEA) established practice, the following local meteoric water line (LMWL) for Calgary was derived using amount-weighted monthly average δ²H and δ¹⁸O values: δ²H = 7.68 δ¹⁸O − 0.21 (r² = 0.96, n = 104). The correlation equation between δ²H and δ¹⁸O values from individual samples was found to be δ²H = 7.10 δ¹⁸O −13.64 (r² = 0.95, n = 839), which is different from the LMWL, exhibiting lower slope and intercept values. A comparison of δ²H and δ¹⁸O correlation equations with temperature during precipitation events showed a trend of decreasing slopes and intercepts with increasing temperature. Our data suggest that this is caused by incorporation of moisture derived from evaporation from water bodies and soils along the storm paths and by secondary evaporation between the cloud base and the ground during precipitation events. These processes compromise the usefulness of d-excess values as an indicator for the meteorological conditions in the maritime source regions. The δ¹⁸O temperature dependence at Calgary was found to be ~ 0.44‰ °C⁻¹. The study shows that short-term sampling of individual precipitation events yields valuable information, which is not obtainable by the widely used monthly collection programs.