Location of Subglacial Lakes and Ice Sheet Thermal Conditions

Subglacial lakes are evidence for melting at the ice-sheet base. They can, therefore, be used to validate the thermal conditions calculated by ice-sheet models. Over 145 subglacial lakes have been identified at the base of the

13 million km2 Antarctic Ice Sheet (Siegert et al., 2005a). The bulk of the lakes are located in the interior of the Antarctic Ice Sheet, at or close to ice divides in the form of domes and ridges, where ice velocity is low (Dowdeswell and Siegert, 1999). Almost 60 per cent of lakes are found within 200 km of an ice crest, remembering that ice flowlines from divide to coastal margin are often over 1,000km long in Antarctica (Fig. 6.3). Only about 15 per cent of subglacial lakes are positioned more than 500 km from an ice divide. At least 16 subglacial lakes occur at locations which are near the onset of enhanced ice flow, some hundreds of kilometres from the ice-sheet crest. An example is provided by three subglacial lakes near the onset of fast flow into Byrd Glacier. Byrd Glacier is fast flowing and drains a very large interior ice-sheet drainage basin into the Ross Ice Shelf. These subglacial lakes are similar in size and depth to the small and probably shallow lakes found in major subglacial basins in the ice-sheet interior. Siegert and Bamber (2000) recognized subglacial lakes at the heads of ice stream tributaries (some of which are several hundred kilometres in the ice-sheet interior) as being evidence of warm-based conditions along the entire length of the enhanced flow unit.

Huybrechts (1990) used the location of subglacial lakes, as evidence of warm-based conditions, to verify the broad-scale thermal character of the icesheet base across East Antarctica. Basal melting conditions were predicted across both the centre of East Antarctica and at the base of ice streams. However, because of the smoothed bedrock topography used as model input, individual lakes, or the outline of specific lake regions, were not able to be matched well. There is, therefore, plenty of scope to better use subglacial lakes in the future verification of ice-sheet model thermal conditions.

Further validation of the ice-sheet thermal regime can be made by comparing results with temperature profiles from ice cores. However, this comparison is limited by the small number of deep ice cores and the lack of penetration to the lower layers of the ice sheet in most cases.

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