Paper No. 210-17
Presentation Time: 9:00 AM-6:30 PM
EVALUATING THE QUANTITY AND COMPOSITION OF SUSPENDED SEDIMENTS IN THE EPHEMERAL STREAMS OF TAYLOR VALLEY, ANTARCTICA
The McMurdo Dry Valleys are a polar desert and form the largest ice-free region of Antarctica. Ice-covered closed-basin lakes are found throughout the valleys, fed by glacial meltwater streams during the austral summer. Taylor Valley, one of the more well-studied valleys, contains numerous ephemeral streams which carry water from the glaciers to the lakes for four to ten weeks annually. While a substantial amount of research has been conducted on the aqueous geochemistry of the streams and lakes as well as the soil chemistry of Taylor Valley, a knowledge gap exists with regards to the quantity and quality of suspended sediments transported by these ephemeral streams. This study focused on Andersen Creek, a small stream draining the western side of Canada Glacier, with the following goals: 1) quantify the suspended sediment loads of this stream, 2) model past years sediment loads using previously collected hydrological data, and 3) determine the mineralogical composition, relative weathering state, and potential sources of the suspended sediments. Daily suspended sediment samples collected throughout the 2014-2015 melt season were supplemented with diurnal sampling events to build a robust sediment rating curve. Substitution of 15 minute interval discharge values into the resulting equation revealed a seasonal sediment flux of approximately 4 tons a-1. This rating curve was then used to back-calculate seasonal sediment fluxes from 1993 to 2015, with values ranging from 1 to 54 tons a-1. The flux calculation for the 1997-1998 melt season was twice as high as a previous estimate based on a few data points. Mostly consistent mineral compositions of sediments observed both over the course of a day as well as the austral summer suggests that wind is an important amalgamating factor in Taylor Valley. Relatively weathered volcanic ash material was also present in larger quantities than previously estimated, suggesting that it may be an important source of both silica and trace elements to the streams and lakes of Taylor Valley. Collectively, these revised suspended sediment flux estimates coupled with the relative abundance of volcanic ash indicate that leaching from suspended sediments may play a greater role in the geochemistry of Dry Valley streams and lakes than previously assumed.