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The three main Taylor Valley lakes (Bonney, Hoare, and Fryxell) have been the subject of study since the discovery of the dry valleys by members of R.F. Scott's expedition in 1903 (Scott 1905, pp. 214-215). Since this time, bathymetric mapping of the lakes has been carried out by various investigators while conducting limnological studies. Standard "lead-line" sounding was the technique used for determining lake depth, but this technique limits the amount of data acquired to the number of holes that can be made in the 3-5-meter (m) thick perennial ice covers. Problems exist with all three bathymetric maps in general use today. The Lake Bonney map is based on 1963 soundings, which are marked without data in the original publication (Angino, Armitage, and Tash 1964), and the shoreline is significantly distorted (likely from parallax error in the air photo interpretation). The existing Lake Hoare map (Wharton and McKay 1986) is the most detailed of the three and includes sounding points and data. The Lake Fryxell map contains a great amount of detail (Lawrence and Hendy 1985), but the original sounding points and data are not available.
Modeling of hydrological and geochemical fluxes in these lake systems has been limited in the past by the lack of good morphometric and bathymetric data. Therefore, during November and December 1995, a geophysical study was conducted to improve the bathymetric and morphologic detail for all three Taylor Valley lakes. In this article, we report on new bathymetric maps for Lakes Bonney, Hoare, and Fryxell that were created from a combination of
The GPR measurements were best over the shallow moat areas and in isolated spots elsewhere. Prior to this study, it was thought that the high salinity of the lakes would be the largest obstacle to using GPR, but our survey suggests that trapped gas bubbles in the thick ice cover limit the GPR survey. Moat ice allows excellent penetration into subbottom sediments, but perennial ice obscures signals with backscattering and rapidly attenuates radar energy. The amplitude of this scattering is most extreme at Lake Hoare, followed by Lake Bonney, and then Lake Fryxell. Interestingly, when we performed GPR surveys on Lakes House and Vida, which were formerly believed frozen solid (our survey suggests a saline water body exists in Vida at approximately 19 meters), good detail of the ice structure for its entire thickness was obtained. It may be that the ice covers of Lakes Vida and House do not have the same bubble structure as, for examples, Lakes Fryxell, Bonney, and Vanda, because they are formed by the freezing of annual floodings on the ice surface.
To produce the maps presented in this paper, the lake margins were defined by digitizing the shoreline from the 1993 aerial photography and rectifying this to GPS perimeter surveys performed in November 1995. A GPS survey was not performed for Lake Fryxell, so the shoreline was established with an integration of the 1993 aerial photography and the 1:50,000 USGS topographic map. The lake margin was used in the contouring process as points with zero water depth. In addition, the aerial photographs show a distinct transition from the moat ice to the older white ice covering most of the lake. The 1995 radar data indicate that this corresponds closely to a "grounding line" where the floating ice changes into grounded ice. This grounding line was also digitized and assigned a depth as determined by the radar data.
The new bathymetric maps are shown in figures 1 to 3, and the resulting morphometric data are presented in the table. An interesting result of this study is the liquid-to-frozen water content in each of the lakes. Lake Fryxell is very different from the other two lakes in this respect, having more ice volume than liquid water volume. This finding has profound implications for both the comparative chemistry and hydrology of the lakes. For instance, if climatic warming were to cause the lake ice covers to melt, Lake Fryxell's salinity would decrease approximately 3.5 times more than Lake Bonney's (not accounting for the change in stream input). Therefore, we might expect the ecological impact caused by a warming to be greater in Lake Fryxell than in Lake Bonney. The mean depth (lake volume divided by lake area) also points to some interesting differences in the lakes. Lake Fryxell has a substantially larger evaporative surface area compared to volume than the other two lakes. This proportion should mean that Lake Fryxell's level is far more susceptible to changing climate than are the other two lakes. When just considering lake morphometry, Lake Fryxell's lake level should drop faster than either Lakes Bonney or Hoare during a dry-climatic period. Once the level dropped so that Lake Fryxell was contained in the west basin, all three lakes would behave similarly (since the mean depths would be more similar).
The full report is available at http://mcm.maxey.dri.edu/lter.
This research was funded by National Science Foundation grant OPP 92-11773. We also thank the sponsorship of Golder Associates, Ltd., and the National Research Council of Canada.
References
Angino, E.E., K.B. Armitage, and J.C. Tash. 1964. Physicochemical limnology of Lake Bonney, Antarctica. Limnology and Oceanography, 9(2), 207-217.
Lawrence, M.J.F., and C.H. Hendy. 1985. Water column and sediment characteristics of Lake Fryxell, Taylor Valley, Antarctica. New Zealand Journal of Geology and Geophysics, 28, 543-552.
Scott, R.F. 1905. The voyage of Discovery (Vol. 2). London: McMillan.
Wharton, R.A., and C.P. McKay. 1986. Oxygen budget of a perennially ice-covered antarctic lake. Limnology and Oceanography, 31(2), 437-443.