Isotopic evolution of snowmelt 2. Verification and parameterization of a one-dimensional model using laboratory experiments

Abstract

Three controlled cold room experiments were conducted to verify and parameterize a one-dimensional (1-D) model that simulates the isotopic composition of meltwater exiting the base of a snowpack. In the model, snow melts at the surface at a constant rate, and water percolates down the column while exchanging isotopically with ice. The effective rate of isotopic exchange and hence the isotopic composition of the melt at a given time is determined by the exchange rate constant kr, the height of the original snowpack, the percolation velocity u*, and the liquid to ice ratio in the exchange system. The experiments were designed to have different effective rates of exchange by varying the height of the snow column and the melt rate. Fitting the model to each of the experiments yielded kr values that fall in a narrow range, 0.14 to 0.17 hr-1, confirming that kr is an intrinsic rate constant for isotopic exchange. Knowing this value is important for developing future models, in which more complicated hydrological conditions are considered.