Meltwater Streams, Taylor Valley

The principal meltwater streams in Taylor Valley are identified by name in Fig. 19.46 which was prepared by Lyons et al. (1998a). The geochemical evolution of 

The relationship between the chemical compositions of the lakes in Taylor Valley and their respective tributaries became even more apparent in the subsequent study of Lyons et al. (1998). These authors demonstrated that a remarkable geochemical continuum exists between concentrations of the major ions in the meltwater 

The chloride ion in the streams and lakes of the ice-free valleys is conservative which means that it accumulates in the lakes because the chloride salts of most major as well as trace metals are highly soluble. Consequently, the flux of chloride ions that enter a lake annually and the total inventory of chloride in the lake can be used to calculate the chloride age of the lake which is defined by  

The importance of chemical weathering in the geochemistry of the ice-free valleys of southern Victoria Land is also indicated by the presence of bicarbonate ions and of molecular silicic acid (H SiO ) in the streams and lakes of this area. These constituents are released into solution in surface water by the incongru-ent dissolution of alumino-silicate minerals such as microcline  

Reactions of this kind are by far the most important source of silicic acid in solution in natural waters because the solubility of quartz (SiO ) is very low. The hydrogen ions (H+) that are consumed by this reaction originate by dissociation of carbonic acid which forms when carbon dioxide of the atmosphere dissolves and reacts with molecules of water  

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McKnight, D. M., and C. M. Tate. 1997. Canada Stream A glacial meltwater stream in Taylor Valley, South Victoria Land, Antarctica. In Stream Organic Matter Budgets (J. R. Webster and J. L. Meyer, Eds.), pp. 14-17. Journal of the North American Benthological Society 16 3-161. 

Fig. 19.47 A log-log plot of the concentrations of sodium and chloride ions (in millimoles per liter) of glacial ice, meltwater streams, saline lakes, and the brine discharged by the Blood Falls of the Taylor Glacier form a quasi-linear array. The ions of the other major elements form similar arrays. The coherence of these data is caused by the complex processes that progressively increase the concentrations of the water in the streams and in the lakes of Taylor Valley (Adapted from Lyons et al. 1998)...

Equation 19.5 demonstrates why the presence of bicarbonate ions and molecular silicic acid in the streams of Taylor Valley is evidence that chemical weathering of feldspar and other silicate minerals is occurring in spite of the harsh climatic conditions. The only prerequisite to chemical weathering of minerals on the surface of the Earth as well as in the subsurface is the presence of liquid water. The work of Nezat et al. (2001) has demonstrated that silicic acid and bicarbonate ions are present in all meltwater streams in the watersheds of Lake Bonney, Lake Hoare, and Lake Fryxell. 

The regional variation of Sr/ Sr ratios in the lakes and leached from soil of Taylor Valley reported by Jones and Faure (1968, 1978) in Fig. 19.45 was confirmed and elaborated and by Lyons et al. (2002) who measured the Sr/ Sr ratios of 15 meltwater streams identified in Fig. 19.46. The data are listed in Appendix 19.9.4 and are presented graphically in Fig. 19.49. The Sr/ Sr ratios of the meltwater streams in each drainage basin of Taylor Valley range both above and below the Sr/ Sr ratio of the respective lakes and thereby reveal the existence of differences in the ages... 

The strontium in each meltwater stream in Taylor Valley is derived by chemical weathering of the silicate minerals in the soil and contains varying proportions of marine strontium that is transported into Taylor Valley by the wind in the form of snow flakes and atmospheric particulates. The Sr/ Sr ratios of the lakes in Fig. 19.49 decrease from west to east in Taylor Valley from Lake Bonney (0.71187, west 0.71204, east) to Lake Hoare (0.71057), and to Lake Fryxell (0.70895). This trend is caused by the increasing abundance of marine strontium with decreasing distance from the coast that is also evident in Fig. 19.45. The elevated Sr/ Sr ratios in the lakes and tributaries in the central and western parts of Taylor Valley confirm that most of the strontium originated by chemical weathering of silicate minerals in the soil. 

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