2002-2003 Science Planning Summary

Geology & Geophysics

Dr. Scott Borg
Program Manager

GO-074-O

NSF/OPP 00-87915
Station: McMurdo Station
RPSC POC: Ken Doggett
Research Site(s): Taylor Valley

Chemical weathering in Taylor Valley streams: Sources, mechanisms and global implications
Dr. W. Berry Lyons
Ohio State University
Byrd Polar Research Center
lyons.142@osu.edu

Deploying Team Members: Peter Cable . Carolyn B Dowling
Research Objectives: Geochemists study the process of "chemical weathering" whereby rocks and minerals are transformed into new, fairly stable chemical combinations, primarily by such chemical reactions as oxidation, hydrolysis, ion exchange and solution. Silicate hydrolysis is another such process, which may have an impact on the global climate by consuming carbon dioxide (CO2), an important greenhouse gas. Generally scientists have concentrated on more temperate climates to examine chemical weathering, because two of its most significant drivers are warmth and humidity.

However, recent data suggests that chemical weathering can and does occur in polar desert streams. At around 78°S, a number of ephemeral streams in the Taylor Valley that are associated with dry-based glaciers flow for four to ten weeks each year. Solutes produced from chemical weathering such as major cations, minor elements (for example, rubidium, cesium, lithium, strontium, and barium), bicarbonate, and dissolved reactive silica, as well as isotopes (87Sr/86Sr) have been found here. Although the mechanism/process of weathering is unknown, this project's researchers hypothesize that the high chemical weathering rates that have been computed derive either from the high coincidence of freezing/thawing cycles and/or the unusual hydrologic behavior of the hyporheic zone in these streams.

Building on the initial work of the McMurdo Dry Valleys Long Term Ecological Research team and others, researchers hope to better establish weathering rates and weathering mechanisms by examining the cryogenic processes whereby physical weathering may influence chemical weathering. To establish what materials are being weathered, project team members will analyze the suspended matter (in streams from the Lake Bonney basin in Taylor Valley and the Onyx Valley in Wright Valley) for their bulk chemistry and then compare these data to rock types in the valleys. To better ascertain solute sources, they will focus on uranium series geochemistry. Using major rock types from the Taylor and Wright valleys, they will also conduct laboratory experiments to establish how microfracturing from freeze-thaw cycles may affect chemical weathering. All of the data will be used to draw analogies to historic weathering regimes on Earth during colder, drier, climatic eras.


Field Season Overview:
Project team members will be based at the Lake Bonney field camp. They will travel by helicopter to outlying sampling areas where they will collect water, sediment, suspended load samples and rocks. Water samples will be processed in laboratories at Lake Hoare and Lake Bonney as well as at Crary Lab. Specimens will be transported back to the U.S. for further study.