Stable isotope studies on the origin and geological history of water and salts in the Lake Vanda area, Antarctica.

Abstract

Abstract-Possible origins of lake water, salts dissolved in water of a saline lake , Lake Vanda, those contained in cored sediments of the lake and those distributed on the ground surface in the adjacent area were investigated on the basis of the stable isotope compositions, 13C/12C, 180/160 and 34S/325 .The lake water is concluded to be neither marine nor volcanic in origin but surface fresh water such as glacial melt water, because of the low 8180 values ranging from -30.3 to -31.9%0. On the other hand, sulfate in lake water and in cored sediments from Lake Vanda shows 834S values similar to that of sea water sulfate. Therefore, it is supposed to be marine in origin.Salts distributed on the ground surface near the lake consist mainly of calcite, gypsum, thenardite, sodium niter and halite. The isotopic compositions of carbonate and sulfate minerals range from -14.4 to +17.6%o for 813C and from -0.4 to +22.3%o for 81,10 of calcite and from +14.1 to +20.3 %o for 834S of gypsum. From the isotopic compositions of calcite and gypsum, three different origins, hydrothermal, marine and marine aerosol are considered according to their occurrences and localities. Salts distributed in this area , however, do not constitute the source for those contained in Lake Vanda .The genesis and historical events of the saline lake also were examined. The lake was once a fjord containing sea water and was isolated from the ocean by glaciation after the Tertiary. After the isolation of the lake from the ocean, evaporation of lake water in cold climate and supply of glacial melt water in warm climate have alternately taken place several times.

Isotopic Evolution of Saline Lakes in the Low-Latitude and Polar Regions

“…Lake Bonney in Taylor Valley and Lake Vanda in Wright Valley retain hypersaline deep waters with salinities above 100 g/kg (L Bonney, west lobe and L Vanda) and 200 g/kg (L Bonney, east lobe). Based on the chemical and isotopic profiles of these lakes, several investigators (Hendy et al 1977;Lyons et al 1998a;Matsubaya et al 1979;Nakai et al 1975;Ragotzkie and Friedman 1965;Torii and Yamagata 1981) interpreted that the saline, deep waters were formed as a result of the evaporation of lakes to small hypersaline icefree ponds or perhaps to near dryness during a colder and drier climate in the past. Lake Bonney is at least 300-ky old and Lyons et al (2005) suggested that the hypolimnia of Lake Bonney are remnants of a marine fjord of Miocene time.…”

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“…Salt residues from wind-blown sprays are a widespread phenomenon on Antarctic boulders and within soils. Carbon and oxygen isotopic measurements (Nakai et al, 1975) of surficial calcite coatings on rocks from the Wright Dry Valley region of Antarctica display a range in Ol3C (-14.4 to + 17.60/00) and 0 18 0 (-0.4 to + 22.30/00), with different boulders from the same locality showing a large variation. The total range easily encompasses the values obtained for the first generation of bicarbonates from LEW 85320 measured by this study and Gooding et al (1988b), and its local inconsistency may explain the discrepancy between the results obtained by the two sets of investigators.…”

Carbon isotopic compositions of Antarctic carbonaceous chondrites with relevance to the alteration and existence of organic matter.

“…2) On the contrary, it may be argued that Antarctic meteorites are subjected to terrestrial carbonate contamination with heavy S13C by weathering (e.g., Velbel et al, 1991;Miyamoto, 1991). Most S13C values of surface carbonate on terrestrial Antarctic materials are lower (-14.4 to +17.6%o; Nakai et al, 1975) than those of indig enous carbonate in carbonaceous chondrites (+20 to 60%o, Clayton, 1963;Grady et al, 1988). Grady et al (1988) (Table 2).…”