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 Ca2+ 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 (cm2 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 (cm2 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 C0, reflecting rapid ion‐exchange reactions; an ultimate steady‐state concentration Cs; and a rate parameter k. Results indicate an excellent fit between the laboratory‐measured Ca2+ concentrations and model output, with goodness‐of‐fit, expressed as χ2, 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 C0 and Cs, respectively yielding straight‐line slopes of 4·2 × 10−8 (R2 = 0·88) and 1·2 × 10−7 (R2 = 0·77). However, k was found to be insensitive to changes in specific surface area by water volume (R2 = 0·00), largely reflecting the dominance of variability in C0 and Cs in this model. Copyright © 2001 John Wiley & Sons, Ltd.