Physical hydrology of the dry valley lakes

Abstract

This paper presents the results of 20 years of studies of the water levels and permanent ice covers of the dry valley lakes by New Zealand Antarctic Research Programme teams based at Vanda Station in Wright Valley. The different hydrological types of lakes and their relationships with climate are discussed. Since systematic level records commenced during the 1968-1969 summer season, the levels of all of the enclosed lakes have risen by varying amounts. A 1903 level available from Lake Bonney indicates that this rising trend has been continuing since that time. So sensitive is the balance between the highly variable summer inflows and the relatively constant annual sublimation losses that there are only poor correlations between the level changes of different lakes and between lake-level changes and measured climate parameters. All of the lakes have permanent ice covers which undergo a vertical turnover on approximately 1 O-year cycles as ablation loss from the surface is replaced by winter freezing onto the underside. The 2- to 5-m thickness of the permanent ice cover varies from lake to lake and is controlled by the annual ablation rate. The higher the ablation rate is, the thinner the ice cover is. Seasonal cycles of ice thickness reach a maximum at the end of winter in mid-November, and summer losses thin ice sheets by 12 to 30% by the end of January. Surface ablation losses average 0.3 m a-l; loss rates of 5.0 mm d -1 in summer lower to 0.6 mm d -1 in winter. Bottom melt accounts for some 45 to 55% of the total summer thinning of the ice cover. Level measurements made over winter at the hypersaline Don Juan Pond indicate that this lake receives groundwater inflow. The behavior of sediments carried by the ice covers is discussed, together with the behavior of lakes in contact with glaciers