Kinetics of solute acquisition from the dissolution of suspended sediment in subglacial channels

Twenty five laboratory dissolution experiments have been conducted to quantify rates of solute acquisition, measured as Ca 2+ concentration against time, from glacigenic sediments suspended in cold, dilute waters. Suspended sediment character was constrained by field‐calibrated ranges of both concentration in meltwater (g cm −3 ) and specific surface area by sediment mass (cm 2 g −1 ). This constraint yielded, for the first time in a glacier hydrochemical study, dissolution rate data as a function of the specific sediment surface area by water volume (cm 2 cm −3 ). The resulting experimental data are used to calibrate a kinetic dissolution model, where the rate of solute acquisition is considered in terms of three parameters: an initial concentration C 0 , reflecting rapid ion‐exchange reactions; an ultimate steady‐state concentration C s ; and a rate parameter k . Results indicate an excellent fit between the laboratory‐measured Ca 2+ concentrations and model output, with goodness‐of‐fit, expressed as χ 2 , reducing in all cases to less than 1·7 × 10 −14 following iterative curve fitting for each experiment. Plotting the resulting best‐fit equation parameters against specific surface area by water volume reveals a strong positive relationship for both C 0 and C s , respectively yielding straight‐line slopes of 4·2 × 10 −8 ( R 2 = 0·88) and 1·2 × 10 −7 ( R 2 = 0·77). However, k was found to be insensitive to changes in specific surface area by water volume ( R 2 = 0·00), largely reflecting the dominance of variability in C 0 and C s in this model.