Research Objectives:
This project is the glacier mass balance, melt and energy balance component of the McMurdo LTER. The glaciers of the McMurdo Dry Valleys are fundamental to the hydrology and biology of the valleys because they are the only significant source of water to the valley streams and lakes. Therefore, understanding the controls on the glacial extent and meltwater runoff is fundamental to a process-oriented approach to studying the dry valleys ecosystem.
The glacier studies currently in progress in the valleys include: mass balance measurements, GPS measurements, and ice radar on four glaciers, the Canada, Commonwealth, Howard, and Taylor glaciers; surface energy balance calculations on the Canada Glacier, applicable to all glaciers in the valley; and repeat photography for a subset of the glaciers to determine long-term change.
Mass balance measurements are based on an ablation stake network established in the 1993/94 austral summer. The stakes, approximately 130 spread over 4 glaciers, are measured twice a year, early November and late January, to establish winter and summer mass changes. Information from these measurements is being used to assess whether the glaciers are in balance with the current climate, how ablation is affected by surface slope and aspect, and to provide data for modeling glacial melt. This data also clarifies the spatial and temporal changes on the glaciers and with climate data furthers our understanding of how small changes in the climate can have large-scale affects on glacier runoff.
The mass balance work is supported by surface energy balance calculations which have been made on Canada Glacier starting in 1994/95. Results indicate that sublimation accounts for up to 80% of the total summer ablation. Snow cover on the glacier surface is perhaps the second largest control on glacier melt. Snow on glacier ice effectively shuts off radiation absorption into the ice, which is the dominant source of energy for melt. In these circumstances, such as snowy years or early and late in the season, streamflow is limited to melt from near vertical ice surfaces which do not accumulate snow, such as the ice cliffs that form the lower margin of the many glaciers. These results can be extrapolated to other glaciers in the valley using data from the LTER Automatic Weather Network of stations.
Other information being collected for the glaciers includes repeated GPS measurements of the ablation stakes to determine ice velocity. Radar measurements are being collected to establish the glacier thicknesses and shape of the glacier beds. Repeat photography of the glacier front is continuing to provide a more long-term perspective on glacier expansion or shrinkage. The repeat photography makes use of photos taken during Scott's expeditions to the valley, as well as more current photography in the 1970's to establish the behavior of these glaciers over the past 90 years.
