干旱区生态环境知识资源中心

The hyperarid polar desert of the McMurdo Dry Valleys contains an abundance of aeolian sedimentary deposits, the largest in Antarctica, providing a unique setting for studying cold climate aeolian processes and dune morphology. Meteorological controls on sand transport and changes in dune morphology were monitored for 11 days in November-December 2004 on a barchan dune in the Victoria Valley, McMurdo Dry Valleys. Sand transport in this environment was found to be influenced by, (1) interparticle cohesion (ice-bonding); (2) diurnal variations in the speed of thermally driven easterly valley winds due to reduced solar heating by ’night’; and (3) topographically modified foehn southwesterly winds. The threshold entrainment velocity during easterly valleys winds was 5.3 ms(-1) (at 0.4 m) +/- 0.21 m s(-1). Warm, dry and gusty fochn southwesterly winds were found to promote aeolian processes by dislodging surface sediments, with dune morphology responding rapidly. Importantly, no diurnal signal in sand transport was observed under these conditions when wind speed and sand transport occurred independently of solar heating. Measured changes in dune morphology indicate that the dune field of the Victoria Valley under current environmental conditions is in dynamic equilibrium, with frequent up-valley sand transport by thermally generated valley winds balanced by less frequent but greater magnitude down-valley sand transport by moderate to strong foehn southwesterlies. This results in little net movement of dunes and subsequent change in the position of the dune field. Accordingly, we believe that regional-scale shifts in climate that cause change in the synoptic circulation patterns of the Ross Sea region that affect the frequency of either the up-valley easterlies or down-valley foehn winds will result in a net change in the morphology of the Victoria Valley’s dune field. Such change in circulation may become apparent early as change in the morphology of the Victoria Valley sand dunes. We therefore suggest this site should be monitored as an indicator site for identifying change in regional weather and climate. Copyright (C) 2008 John Wiley & Sons, Ltd.