MINOR CATIONS WITHIN ANTARCTIC STREAM WATER: DETERMINING THE ROLE OF THE HYPORHEIC ZONE

The McMurdo Dry Valleys, Antarctica, are a polar desert containing ephemeral streams driven by glacial melt that flow 4-12 weeks in the austral summer. These streams contain a shallow area of porous sediment known as the hyporheic zone, where there is interaction with the stream bed and water can be temporarily stored. Major cations have been analyzed in these streams every year since the McMurdo Dry Valleys Long Term Ecological Research (MCM LTER) program began in 1992, but only one other study has analyzed minor cations (Li, Rb, Sr, Ba) in these waters. This study is the first to examine minor cation concentrations versus flow and downstream profiles. Transect samples were collected at three streams that flow into the ocean: Wales, Commonwealth, and Miers, and diurnal samples were collected at a more inland stream, Von Guerard. Streams were analyzed for Li, Sr, Rb, and Ba, and concentrations range from 0.056-2.78 µM, 0.193-3.54 µM, 5-25 nM, and 0.005-3.00 µM, respectively. Downstream profiles show an overall increase in Li, Rb, and Sr with stream length, suggesting chemical weathering input. Ba concentrations decrease with stream length, suggesting it is less soluble than the others. Commonwealth stream shows an increase in K:Rb and Na:Li but decreases in Ca:Sr. Wales increases in K:Rb and Ca:Sr, but decreases in Na:Li. Miers stream flows though Miers Lake, where there is a sharp decrease in Ca:Sr. This decrease is likely due to precipitation of calcium carbonate within the lake. Diurnal sampling at Von Guerard stream shows no linear correlation between minor cation concentrations and discharge, as previously seen with major cations. This suggests that concentrations are controlled by rapid dissolution and hyporheic exchange. Hysteresis plots show Na⁺, Rb⁺, and Li⁺ rotate clockwise, while Ca²⁺ and Sr²⁺ move in a counterclockwise rotation. It is thought that Na⁺, Rb⁺, and Li⁺ concentrations increase in concentration on the rising limb due to rapid salt dissolution, while Ca²⁺ and Sr²⁺ concentrations increase on the falling limb due to chemical weathering in the hyporheic zone. This information is useful in understanding chemical weathering and hyporheic exchange within these streams as well as estimating the input of these elements into the ocean.