Return to the Table of Contents for this chapter.
Three interconnected lakes lie in a dry valley just west of Mount Heekin, which is adjacent to the middle reaches of the Shackleton Glacier (figure 1, site A). At a little more than 85°S and at an elevation of about 945 meters (m), this may be the highest and most southerly occurrence of lakes in "dry valleys" on the antarctic continent; these lakes are at a significantly higher elevation than those of southern Victoria Land. On the Mount Goodale 1:250,000 topographic map quadrangle, lakes are indicated on moraines in Moraine Canyon and at a latitude marginally to the south of those near Mount Heekin. Aerial photos suggest that these "ponds" lack stream inflow from glaciers and hence are not comparable with the Mount Heekin locality.
The uppermost lake, about 30 m across, abuts the front of an ice tongue trending northeast off the Baldwin Glacier (figure 2); when water levels are sufficiently high, this lake drains into a second lake, measuring about 150 by 65 m; the second lake drains into a third, which is about 150 m in diameter. All three lakes are ice-covered except for small moats, 1-3 m in width. The moats were open on the first visit to the valley but covered by a veneer of ice on the second visit. The ice cover on each lake is domed slightly, suggesting that the ice is frozen to the bottom. Each lake is bordered by a shoreline (visible in figure 2) rising to about 50 centimeters (cm) above lake levels at the time of observation; across these shorelines, the loose rocks at the surface are covered with dried-out algal mud, suggesting higher lake levels earlier in the season. The mud forms mats that curl as they dry out. The rocks in the moats also are covered by algal mud. Thresholds for surface flow of water from the upper to the middle lake and from the middle to the lower lake are, respectively, about 50 cm and about 90 cm high. The differences in elevation of the water levels in the moats are about 1.5 m between the upper two and about 2.5 m between the lower two. Adjacent to the shoreline of the uppermost lake is a pronounced narrow zone with gypsum efflorescence. The floor of the valley appears to consist of a coarse lag resting on a light-colored, sandy, poorly consolidated till displaying polygons as much as 10 m across and outlined by surface fractures 20-30 cm deep.
Unfiltered waters from the three lakes have been analyzed for major ions and nutrients (table). In general, the nitrogen chemistry is markedly different from that in the dry valleys of southern Victoria Land. Nitrate, nitrite, and ammonia are all high; the strikingly high nitrate concentrations might suggest an unusually high atmospheric input. The marked reduction, from the uppermost lake to the lowermost lake, in nitrate, nitrite, and phosphate suggests biological activity, which is, of course, supported by the occurrence of algal mats. Low calcium-to-sodium ratios suggest the possibility of relatively high input of sodium from marine sources compared to that from chemical weathering.
In the same dry valley, a slightly sinuous stream course and small gravel fan (figure 3) indicate the former presence of another lake, which lies at a lower elevation than the third ice-covered lake. The stream course connects to a small snowfield that may be the remnant of another ice tongue, which is inferred from the presence of a lobe off the Baldwin Glacier. The snowfield is too small to provide enough meltwater to maintain a lake. Drilling of this small, former lake floor might reveal an interesting history of climate changes since deglaciation.
An adjacent valley to the west (figure 1, site B) is completely dry, and no signs of former lakes or stream courses were noted. Both that dry valley and the one with the lakes are closed depressions passing northeastward and northward, respectively, into a single bowl at a higher elevation; the northwestern flank of the bowl has low, wind-blown sand ridges oriented across valley.
A completely frozen lake measuring about 220 m by 65 m occurs in the next valley to the northwest (figure 1, site C), at an altitude of 1,294 m. The surface is flat, unlike the other lakes, but does have a series of irregular vertical cracks on the northwest flank. The ice in these cracks shows small vertically oriented columns suggestive of lake freezing. No evidence was noted of former shorelines. No glacier drains into the valley today, although a small tongue of the Baldwin Glacier probably did so in the past. Presumably the frozen lake is maintained, first, by annual snowfall and melting within the valley and, second, because the valley is narrow and, therefore, its floor is shielded from the Sun's heat by adjacent topography. Permafrost is very close to the surface upslope from the northeast end of the lake. The valley is closed off at its northeast end by a moraine with meter-size boulders.
These lakes are not obvious on air photos because of their small size, which may explain why, apparently, they were not seen and investigated on previous expeditions in the region.
Investigation of these lakes was dependent on the logistic support of U.S. Navy squadron VXE-6 and Helicopters New Zealand. Analytical data were obtained at the Crary Science and Engineering Laboratory by Dave Mikesell for anions and dissolved inorganic carbon and by Kathy Welch for cations. The x-ray determination of the gypsum salt effloresecence was made by Jeff Nicoll at Ohio State University. National Science Foundation grant OPP 94-20498 to Ohio State University provided support for David H. Elliot.