Lake water level monitoring of glacier fed lakes in the Dry Valleys

Monitoring of the lake level and lake ice ablation rates of lakes in the Dry Valleys was monitored from the 1969/70 summer until the 1990/91 season. The data was used to contribute to the understanding of the mass balance of the glacier-river-lake systems in the Dry Valleys because these fluctuations are indicators of climate change in this part of Antarctica. Most of the work was concentrated on Lake Vanda. The actual water level of the lake was first measured in November 1969 by surveying using shore bench marks. In December of that year a sudden surge of the lakes water level was observed. Measurements established the existence of a seiche like movement of the lake. A water flow recorder was installed at the lake edge to obtain a continuous record of the water level changes. Continuous readings, accurate to 0.001 of a metre, were then taken over complete seasons at Lake Vanda. In addition, to establish whether the ice cover rose and fell in direct relationship and to the same degree as the free water, an instrument was anchored to the lake bed, and direct measurements made of the rise and fall of the ice surface. Because Lake Vanda water levels are a reflection of coastal climatic trends (the source water comes from a coastal glacier), it was decided that spot lake levels be taken on other lakes in the Dry Valleys to compare the variations of coastal glacier fed lakes with inland glacier fed lakes. Several lakes in the McMurdo Dry Valleys were visited and their fluctuations recorded to compare these variations with respect to climate including Lake Vanda and Lake Brownworth in the Wright Valley, Lake Vida and Upper Victoria Lake in Victoria Valley, Lake Vashka and Lake Webb in the Barwick Valley, Lake Fryxell, Lake Chad (Hoare), Lake Henderson and Lake Bonney in the Taylor Valley, Lake Joyce and Lake House in the Pearce Valley and Lake Miers in the Miers Valley. (Not every lake was measured every season). Water levels at the beginning and end of the melt season were levelled to a benchmark at each lake, thus recording the summer and winter fluctuations. In the 1980/81 season, a water level recorder was installed at Don Juan Pond to monitor water level fluctuations from the beginning of the summer season and throughout the winter. This monitoring was continued every season afterwards. In addition to lake level measurements, the lake ice ablation rates were measured on Lake Vanda starting in the 1969/70 season. Initially bamboo poles were placed on the lake surface, but as the summer progressed, they began to melt into the ice causing the measurements to be inaccurate. Numerous methods were tried to rectify this problem. In the 1975/76 season, two new methods were tried. An ice pit was dug and allowed to refreeze and theoretically at the end of the summer the difference in height from the bottom of the pit to the top would determine ablation, but the 'glasshouse effect' had produced large bodies of water beneath the apparently solid lake ice surface making any measurement useless. The other was to drill a hole and put down a nicrome wire with an ice thickness device from the under surface ice to the upper surface. Before and after measurements were collected to obtain an ablation rate. Ice thickness and ablation rates were measured every season after this. In the 1988/89 season, a three year project was undertaken to extend the spatial scale of the study. The aim was to extend the river flow/lake level record in Wright Valley to permit identification of any secular change in hydrologic behaviour of the Lower Wright Glacier - Onyx River - Lake Vanda system and to provide data on hydrological behaviour in widely separate sites in the Dry Valleys to enable identification of spatial variations in hydrological behaviour and definition of the representativeness of the Wright Valley. Stream flow monitoring stations were erected near the outlet of the Upper Victoria Lake in Victoria Valley, downstream from the Garwood Glacier Lake in the Garwood Valley and at three sites on the Adams and Miers streams in the Miers Valley so that lake level monitoring could be compared with the corresponding lakes and glaciers measurements.