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Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship
THE DISCOVERY OF SUBGLACIAL LAKES
The continent of Antarctica is formed from a fragment of the Gondwana super-continent, which included the continental masses of Africa, South America, Australia, Antarctica, and India. This supercontinent began to break apart in Early Cretaceous time (around 130 million years), and full isolation of Antarctica from other Gondwana fragments, and the associated possibility of circum-Antarctic ocean circulation, was achieved by 30 million years (Early Oligocene). Although there is evidence for alpine glaciation in Antarctica from Cretaceous time, it seems that a large ice sheet did not come into existence until around 35 million years (Anderson 1999). Since its formation the ice sheet has not entirely disappeared, although its eastern and western parts have experienced substantial fluctuations in volume.
The earliest attempts to measure ice depth in Antarctica used seismic sounding from the surface of the ice sheet where the reflection of shock waves generated by explosives was measured. Admiral Byrd’s expedition to the Antarctic in 1939-1941 conducted trials of such a system, but the Norwegian-British-Swedish expedition in 1951-1952 pioneered the scientific use of this technique in the Antarctic. Although the technique proved cumbersome and slow, it was the best technique available at the time and was used during the International Geophysical Year (IGY) in 1957-1968 by several countries to provide important data about the underlying topography. The IGY data provided many interesting insights into the subglacial structures in the interior of the Antarctic, but the technique was too unwieldy to be extended across the whole continent.
The recognition that radio waves at very high frequencies could penetrate ice but were reflected by rock changed this approach and lead to the development of Antarctic airborne radio-echo sounding by the Scott Polar Research Institute in the 1960s. Use of this technique across the Antarctic ice sheet provided, for the first time, the possibility of mapping the whole of the underlying continental rock (Robin 1972). The principal intention was to enable glaciologists to calculate more accurately the total mass of the ice sheet by measuring its thickness; however, the data collected provided valuable information to a wide range of scientists with many interests. By 1980, RES had been collected from more than 400,000 km of flight track, covering approximately 50 percent of the 13.5 × 106 km2 Antarctic ice sheet. This coverage, however, was concentrated in only few areas, and despite continued survey work there are still many areas of the Antarctic continent for which no RES data exist (Figure 1.1). In some areas of the continent, flight lines are so widely spaced that subglacial features cannot be adequately mapped.
Compilation of all available data by the Scientific Committee on Antarctic Research (SCAR), however, resulted in the publication of the first detailed sub-ice topographic map (Lythe et al. 2001), which was critical in the developing search for subglacial water.
The possibility of the existence of subglacial water was first identified by Robin and others in 1968. They noted that in places the RES signal changed from one characteristic of an ice-rock interface to one indicative of an ice-water interface, which suggested that there could be water trapped between the bedrock and the bottom of the ice sheet. The first subglacial lake reported was located beneath Sovetskaya Station; water was also indicated under Vostok Station (Robin et al. 1970).