Permafrost distribution and active-layer depths in the McMurdo dry valleys, Antarctica

The McMurdo Dry Valleys (MDVs) constitute the largest ice-free area (6700 km(2)) 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 (c) 2007 John Wiley & Sons, Ltd.