Geochemical flux on Commonwealth glacier


As part of a geochemical study of the Commonwealth Glacier in Taylor Valley, Antarctica, two 3-meter snow pits were dug in the accumulation zone and analyzed for major ions by ion chromatography. This dataset shows the mean annual atmospheric flux of chloride, sulfate, nitrate, and calcium to the Commonwealth Glacier. Determination of the atmospheric flux of these ions to the glacier surface aids in assessing the chemical composition of precipitation to the McMurdo Dry Valleys and the role of glaciers in the geochemical cycles of the region.

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Chemical measurements from two snow pits on the Commonwealth Glacier were obtained in this work. After the initial excavation of the snow pit using standard avalanche shovels, the sampling wall face was scraped off using polypropylene shovels that had been cleaned by successive soakings in 18 Mohm MilliQ water. The snow was prepared for sampling by using a Teflon spatula to loosen the section. A Teflon sampling device was then slid into the snow layer and gently manipulated to loosen the compacted snow. The snow sample was placed into a 500 mL HDPE container that had been previously soaked overnight and rinsed three times with 18 Mohm MilliQ water at Crary Laboratory and transported to the field site empty. Samples remained frozen until immediately prior to analysis at McMurdo Station using a Dionex DX-120 ion chromatograph (IC). The technique, a modification of Welch et al. (1996), implements a sample loop of approximately 400 uL for all standards and samples. A Dionex IonPac AS14 analytical column (4x250 mm) and AG14 guard column (4x50 mm) were used with an ASRS Ultra Anion Self-Regenerating Suppressor to analyze major anions. The eluent was a 3.5 mM Na2CO3 and 1.0 mM NaHCO3 solution with a pump flow-rate of 1.2 mL min-1. Cations were analyzed using the Dionex IonPac CS12A analytical column (4x250 mm), a CG12A guard column (4x50 mm), and a CSRS Ultra Cation Self-Regenerating Suppressor. The 1.3% methanesulfonic acid eluent had a flow-rate of 1.2 mL min-1. A stock standard solution was created from several single-element standards. The multi-element stock standard was diluted to produce six calibration standards with a range of concentrations that covered the estimated concentrations of the samples. Analytical and filtration blanks were run before, during, and after samples. An independent multi-element standard was analyzed after creating a calibration curve to satisfy quality assurance and quality control. Several sample duplicates were analyzed for recovery comparisons and were used for precision analysis. Maximum analytical variability between samples was +/-3.3% for Cl-, +/-10.9% for Ca2+, and +/-14.4% for NO3-. The snow pits were dated with a +/- 1 year accuracy using Na+ peaks, which commonly define the austral autumn when low sea-ice extent and high maritime winds deposit large amounts of sea salt on glacial surfaces (Legrand and Mayewski, 1997). The assigned dates were compared to physical mass balance measurements made since 1993 by the MCM LTER. Annual accumulation in water equivalents was calculated using measured density and snow layer thickness. Flux data were calculated, Fj = Cj*Bj where Fj is the flux for any given year, Cj is the average concentration for a given year, and Bj is the accumulation rate in water equivalents for that year. This procedure was applied for all annual layers in both snow pits. The calculated values for corresponding years were then averaged between the two snow pits.


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