Collaborative Research: Chemical Weathering in Taylor Valley Stream: Sources, Mechanisms and Global Implications

Tulane University, New Orleans LA

Investigators

Abstract

0087994 McKee This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a collaborative research program to study low temperature chemical and physical weathering processes in the Dry Valleys region of Antarctica. Chemical weathering is thought to affect global climate by consuming carbon dioxide (CO2) during processes such as silicate hydrolysis. This CO2 "buffer" can create climate change by controlling the atmospheric concentration of this important greenhouse gas. Because the principle controls on chemical weathering rates have been argued to be temperature and moisture, enhanced chemical weathering is thought to occur in warmer climates. The geochemistry of a number of ephemeral streams in Taylor Valley, Antarctica (~78 degrees) has been analyzed. These streams flow for 4 to 10 weeks per year and are associated with dry-based glaciers. Solutes produced from chemical weathering such as major cations, minor elements (e.g., rubidium, cesium, lithium, strontium, and barium), bicarbonate and dissolved reactive silica, as well as isotopes (87Sr/86Sr) indicate that chemical weathering does occur in these polar desert streams. Although the mechanism/process of weathering is unknown, it is hypothesized that either the high coincidence of freezing/thawing cycles and/or the unusual hydrologic behavior of the hyporheic zone in these streams are responsible for the high chemical weathering rates that have been computed. In this proposal, the plan is to build upon the initial work of the McMurdo Dry Valleys Long Term Ecological Research (MCM-LTER) team and others by better establishing weathering rates and weathering mechanisms by elucidating the role of physical weathering via cryogenic processes on chemical weathering. The suspended matter in streams from the Lake Bonney basin in Taylor Valley, and the Onyx Valley in Wright Valley will be analyzed for their bulk chemistry and compared to rock types in the valleys to establish what materials are being weathered. Emphasis will be placed on the utilization of uranium series geochemistry to better ascertain solute sources. The laboratory experiments will be done to establish the role of microfracturing via freeze-thaw cycles on chemical weathering. Major rock types occurring in Taylor and Wright Valleys will be used for these experiments. All of the data will be used to draw analogies to historic weathering regimes on Earth during colder, drier climatic regimes.