Permafrost distribution and active‐layer depths in the McMurdo Dry Valleys, Antarctica

Abstract

AbstractThe McMurdo Dry Valleys (MDVs) constitute the largest ice‐free area (6700 km2) in Antarctica. Permafrost is ubiquitous in the region and is present as ground ice or buried ice, ice‐cemented permafrost and dry‐frozen permafrost. Using a combined dataset that includes more than 800 shallow (<1.5 m) excavations, we provide a map at a scale of 1:2 million showing the distribution of permafrost in the MDVs. Our data suggest that about 55% of the permafrost is ice cemented, 43% is dry frozen and ground/buried ice comprises at least 2% of the area. Permafrost form is related to climatic zone, age of sediments and local site factors. Ice is present in ice‐cored alpine moraines and coastal tills of Holocene age in hummocky drifts of late Quaternary age (ca. <115 ka); however, it is also present in Miocene‐aged sublimation till in Beacon Valley. Ice‐cemented permafrost is present not only in coastal areas (subxerous climatic zone) and in sediments of late Quaternary age, but also in soils of pre‐Quaternary‐age in ultraxerous regions along the polar plateau. Dry‐frozen permafrost exists along the floors and lower sidewalls of larger ice‐free valleys (xerous climatic zone) in sediments of pre‐late Quaternary age. Dry‐frozen permafrost, which may be unique to Antarctica, appears to form from sublimation of moisture in ice‐cemented permafrost over time. Active‐layer depths are 45 to 70 cm in coastal areas and in the eastern half of Wright and Taylor Valleys, 20 to 45 cm in other ice‐free areas within 60 km of McMurdo Sound, and <20 cm along the polar plateau. Copyright © 2007 John Wiley & Sons, Ltd.