TEMPORAL VARIABILITY OF DISSOLVED INORGANIC CARBON IN STREAMS AT THE MCMURDO DRY VALLEYS, ANTARCTICA

The McMurdo Dry Valleys (MCM) are the largest relatively ice-free area in Antarctica, named for their low humidity and lack of ice cover. In Taylor Valley, one of the McMurdo Dry Valleys, meltwater generated from glaciers is the primary source of water, and the ephemeral streams transport this meltwater to the ice-covered, closed basin lakes. The streams typically flow for six to ten weeks during the Austral summer. My work has been done to ascertain the controls on the concentration and distribution of alkalinity (dissolved inorganic carbon) in the streams on various temporal scales. The solutes in the streams are derived from three primary sources: dissolution of marine derived salts, dissolution of calcite coatings derived from bedrock weathering, and direct weathering of silicate rocks. Many observations of stream flow have been made, revealing that flow varies throughout the day and is not consistent for streams in the same lake basin. Other factors contributing to differences in stream chemistry include atmospheric input, stream geomorphology, and hyporheic zone exchange. Two streams, Von Guerard and Andersen Creek, were sampled for cation, anion, and alkalinity concentration. Von Guerard is longer and has more hyporheic zone interaction than Andersen. Results show that both streams are undersaturated with respect to CaCO₃, with Saturation Indices (SI) ranging from -5.25 to -0.81, averaging -2.44. Stream samples from December 2010 had higher ion activity products (IAP) and lower SI values. In January 2011, concentrations of Ca²⁺ were highest, reaching 504 µM in Andersen Creek, resulting in SI values that approach equilibrium. Hourly differences in SI from 22:00 to 08:00 local can be attributed to lower temperature, due to the inverse solubility relationship CaCO₃ has with temperature. For samples taken at the same day and time, Von Guerard exhibited higher Ca²⁺ and stream temperature than those from Andersen, resulting in a higher CaCO₃ saturation. Due to the differences observed in the temporal variability of inorganic carbon between Andersen and Von Guerard, it is likely that these two streams have significantly different controls on their stream chemistry, but both streams provide environments for CaCO₃ dissolution.