CHEMICAL WEATHERING AND GEOCHEMICAL MODELING WITHIN GLACIAL MELT WATER STREAMS, WRIGHT AND TAYLOR VALLEY, ANTARCTICA

The McMurdo Dry Valleys, Antarctica, are the coldest and driest region on Earth, thus making them an extreme end-member climate for the study of chemical weathering. Recent studies have investigated weathering reactions within this polar desert and the relationship between glacial and stream chemistry, including the interactions occurring between the water and the stream channel. The only water input for the stream is limited to the 6-12 week austral summer. The catchments in the targeted areas drain granitoid basement and then flow through drifts with clasts of variable lithology. This research examines the stream chemistry within glacial drainages in Wright and Taylor Valley in conjunction with geochemical modeling in order to assess the weathering processes occurring within polar drainages.

Analyses of stream water from Clark glacier in Wright Valley and Howard glacier (Delta stream) in Taylor Valley show an increase in solute concentrations as a function of distance from the glacier, confirming chemical weathering is occurring within melt water streams. Downstream increases in several cations (Ca²⁺, Na⁺, K⁺, Mg²⁺) occur in each drainage, but trends between the two streams differ. Clark glacier stream contains more Na⁺ than Ca²⁺ whereas Howard glacier contains more Ca²⁺ then Na⁺ distally; both cations increase in both streams as a function of distance.

Geochemical reaction path modeling for Clark glacier shows increasing concentrations of Ca²⁺, Na⁺, and Mg²⁺ over the reaction progress, paralleling the results of field data from Clark stream. Models of Delta stream show an increase in several cations; however Na⁺ concentrations are higher than Ca²⁺_, differing from the observed field data. Potential explanations for the differences between Na⁺ and Ca²⁺ concentrations include varying drift lithology between the two valleys or their proximity to the Ross Sea and thus marine aerosol flux. Both drift chemistry and Ross Sea aerosol input could affect stream chemistry and both are currently being incorporated in low-temperature modeling for each stream. Based upon this research, we confirm that chemical weathering is occurring within the melt water streams. Further geochemical modeling will further constrain the geochemical processes which lead to differences observed between Wright and Taylor Valley.