Diel Cycling of as, Cu, Fe, Mn, and V In McMurdo Dry Valley, Antarctic Streams: Identifying Controls on Metal Geochemistry

We present data on dissolved (0.4 µm) and environmentally available, unfiltered-acidified, concentrations of As, Cu, Fe, Mn, and V within two McMurdo Dry Valley, Antarctic streams: Canada Stream and Andersen Creek. These streams both originate from Canada Glacier melt but differ in their geomorphology and biological composition. Flow and melt travel time controlled more than 33% of the diel variability observed in dissolved metal, major ion, and Si in these streams. Discharge (r²³ 0.56) significantly correlated (n= 24, µ=0.05) with the percentage of environmentally available metals that are adsorbed within each stream. Temperature also correlated with the amount of As and Cu adsorbed on particulate matter in Andersen Creek (r²= 0.83, 0.46) and Fe and Mn adsorbed in Canada Stream (r²=0.69, 0.49). Greater heterogeneity of environmentally available metal translated to greater heterogeneity in the amount of metal adsorbed. For example, environmentally available Cu concentrations in Canada Stream ranged from 2 to 88 nM with adsorbed Cu ranging from 13-88%, whereas Cu in Andersen Creek ranged from 1 to 5 nM with adsorbed Cu ranging from 88 to 99%. Silicate weathering controls approximately 20% of the chemical variability observed in both streams. In Andersen Creek increasing Si is associated with increasing Cu, Fe, and V with no relation to discharge.  However, in Canada Stream increasing Si is associated with decreasing discharge, Cu, Mn, and major cations. It is likely that in Andersen Creek Cu, Fe, and V are released via silicate weathering. Yet, metals are not released, and/or are adsorbed during silicate weathering within Canada Stream. This may be the result of greater hyporheic exchange, or biological activity occurring within Canada Stream. This study provides baseline data to understand hyporheic-groundwater controls on metal geochemistry and data illustrates the high rate of metal denudation from Antarctic Streams.