Researchers: Joseph S. Levy, University of Texas Institute for Geophysics, Austin, TX, Andrew G. Fountain, Department of Geology, Portland State University, Portland, OR, James L. Dickson and James W. Head, Department of Geological Sciences, Brown University, Providence, RI, Marianne Okal, UNAVCO, Boulder, CO and Jaclyn Watters, Department of Earth and Environment, Boston University, Boston, MA.
Written by Linda Rowan
4 October 2013
A coastal valley in Antarctica has been a natural laboratory for decades for studies of land surface changes, rates of erosion, polar environments, and rates of ice loss. The Garwood Valley has abundant thermokarst, a unique cold region landscape, consisting of land surface disrupted by melting ground ice. Terrestrial laser scanning (TLS) imaging of an ice cliff in the valley over a two-year period shows a much higher rate of erosion than previously estimated. The thermokarst is not evolving at a constant rate instead it is eroding at a more rapid rate due to higher insolation driven melting and higher sediment/albedo feedbacks. So Antarctica is changing more rapidly as the result of climate change and the landform changes will yield similar landscapes to the Arctic periglacial terrains by the end of the century.
The Garwood Valley is a coastal valley in the McMurdo Dry Valleys of Southern Victoria Land, Antarctica. The valley has been studied for decades, partly because of its convenience to McMurdo Station, the U.S. base for research and partly because it is an excellent example of thermokarst and related polar landscapes. The valley consists of permafrost and is partially filled by a remnant of the Ross Sea Ice Sheet. Ablation till consisting of sand and silt covers much of the valley and is in turn covered by some pebble-sized desert pavement. The ablating buried ice mass produces the thermokarst, including the Garwood Valley Ice Cliff.
The ice cliff stands tall where a remnant of the Ross Sea Ice Sheet connects with the Garwood River. The ice cliff consists of 10 to 15 meters of ice capped by 2 meters of ice-cemented glacial till and river sediments. The top 20 centimeters thaws in the summer time. A continuous monitoring station measured air temperature, relative humidity, ice cliff surface temperatures via infrared radiometry, range to the ice cliff via an ultrasonic distance sensor, wind speed and direction and radiation balance from November 2010 to January 2012. A time-lapsed camera system (i.e., image every 10 minutes from January 10 to 28 of 2012) and twice a year terrestrial laser scanning (TLS) of the ice cliff augmented the continuous measurements. Airborne LiDAR data was collected between 2001 and January of 2012.
The observations show that the ice cliff has been eroding at a rapid rate since 2001 and that the rate of erosion has been increasing over the past decade. Since 2001, a total of 44,900 ± 900 cubic meters of the ice cliff has eroded away with an average of 5,000 ± 100 cubic meters per year from 2001 to 2012. Over the last two years of observations, the rate increased. From November 2010 to January 2011 about 6,700 ± 130 cubic meters of material was removed and from January 2011 to January 2012 about 11,300 ± 230 cubic meters of material was removed. The erosion rate from 2001-2012 is five times greater than the erosion rate in the late Holocene (past 6,000 years), the rate from 2010-2011 is six times greater than the late Holocene rate and the rate from 2011-2012 is ten times greater than the late Holocene rate. Two factors contribute to the high rate of erosion based on all of the measurements: 1. Periods of positive total net radiation cause extensive melting of the ice cliff and 2. Sediments transported by weathering onto the ice cliff surfaces lowers the albedo and during periods of intense insolation, these sediments heat the ice cliff causing additional melting and erosion. The results suggest that coastal Antarctica is rapidly changing due to climate change and may have degraded permafrost landscapes similar to those in the Arctic by the end of the century.
Publications: Levy, J.S. et al. Accelerated thermokarst formation in the McMurdo Dry Valleys, Antarctica. Sci. Rep. 3, 2269; DOI:10.1038/srep02269 (2013).
Thermokarst, permafrost, albedo, insolation, total net radiation
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