INVESTIGATING CLIMATIC CHANGE IN THE DRY VALLEYS OF EASTERN ANTARCTICA WITH TEPHRACHRONOLOGY AND COSMOGENIC NUCLIDE SURFACE EXPOSURE DATING
PHILLIPS, William M., Department of Geography, Univ of Edinburgh, Edinburgh, EH8 9XP, United Kingdom, wmp@geo.ed.ac.uk, MARCHANT, David A., Department of Earth Sciences, Boston University, Boston, MA 02215, LEWIS, Adam R., Department of Earth Sciences, Boston Univ, Boston, MA 02155, LANDIS, Gary P., U.S. Geol Survey, Denver Federal Center, Denver, CO 80225, and VANDENHEUVEL, Brett, Department of Geological Sciences, University of Maine, Orono, Orono, ME 04469,

The present-day western Dry Valleys climate is characterised by mean annual temperatures of -30C to -35C and precipitation of less than 10 mm/yr. Cold-based glaciers, polygonal patterned ground, desert deflation pavements, and ventifacts typify this environment. Past climatic changes are recorded by surficial deposits and landforms documenting multiple alpine glacial advances. Dating these advances is central to understanding factors forcing climatic change in the Dry Valleys. Tephras erupted by volcanoes along the eastern Ross Sea embayment are interbedded with the surficial deposits and yield 40Ar/39Ar ages of about 4.3 to 15.0 Ma. The earliest ages are associated with deposits of warm-based glaciation and point to a major climatic shift between 10 to 15 Ma. After this time, alpine glaciation in the Dry Valleys became entirely cold-based and progressively more limited in extent. Dating of erratics deposited by small cold-based cirque glaciers with cosmogenic 3He is also in progress. Based upon relative weathering criteria and stratigraphic position, these advances reflect the latest period of major climate change to affect the western Dry Valleys. We are also investigating patterned ground formation with cosmogenic 3He depth profiles sampled through periglacial polygons developed in till overlying relic glacial ice. Preliminary results show the till to be a lag deposit produced by 10 to 15 m of sublimation. Patterned ground processes have been active over long time periods as shown by 3He exposure ages ranging from 1.14 Ma to 0.17 Ma. Convective churning of the till is absent as indicated by the progressive decrease of 3He concentrations from the surface downward.

Earth System Processes - Global Meeting (June 24-28, 2001)
Session No. G8
Timing and Rates in Earth System Processes
Edinburgh International Conference Centre: Sidlaw
1:30 PM-4:40 PM, Thursday, June 28, 2001