Abstract

This study provides a detailed characterization of spatiotemporal variations of stable water ¹⁸O and ²H isotopes in both snowpack and meltwater in a subarctic catchment. We performed extensive sampling and analysis of snowpack and meltwater isotopic compositions at 11 locations in 2019 and 2020 across three different landscape features: (a) forest hillslope, (b) mixed forest, and (c) open mires. The vertical isotope profiles in the snowpack’s layered stratigraphy presented a consistent pattern in all locations before snowmelt, and isotope profiles homogenized during the peak melt period; represented by a 1–2‰ higher δ¹⁸O value than prior to melting. Our data indicated that the liquid-ice fractionation was the prime reason that caused the depletion of heavy isotopes in initial meltwater samples prior to the peak melt period. The liquid-ice fractionation was influenced by snowmelt rate, with higher fractionation during slow melt. The kinetic liquid-ice fractionation was evident only in close examination of meltwater lc-excess values, not δ¹⁸O values alone. Meltwater was isotopically heavier and more variable than the depth-integrated snowpack; the weighted mean of meltwater isotope values was higher by 0.62–1.33‰ δ¹⁸O than the weighted mean of snowpack isotope values in forest hillslope and mixed forest areas, and 1.51–6.37‰ δ¹⁸O in open mires. Our results reveal close to 3.1‰ δ¹⁸O disparity between the meltwater and depth-integrated snowpack isotope values prior to the peak melt period, suggesting that proper characterization of meltwater δ¹⁸O and δ²H values is vital for tracer-based ecohydrological studies and models.