Physicochemical Limnology of Lake Bonney, Antarctica

Abstract

Lake Bonney is a permanently ice-covcrcd lake of 3.2 km2 in upper Taylor Valley, Victoria Land, Antarctica.The mean depth, without ice cover, is 18.7 m. Thk lake probably occupies a glacially ovcrdccpcncd valley. The lake is meromictic. The maxirhal temperature of 7C coincides with the chcmoclinc at about 15 m; the tempcraturc decreases to a range of +2 to -4C in the bottom waters and to less than 1C bcncath the ice. Calculations of supcrficial water inflow and of water loss by sublimation of ice indicate that the lake is slowly shrinking.Old shorelines above the prcscnt lake level attest to shrinkage. Part of the difference between water gain and water loss is made up by inflow of warm-spring water at depth. Such springs are probably the major source of heat for the lake. Total solids in the monimolimnion range up to 407.3 g/liter, Sodium and magnesium chloride account for 96,s of the dissolved salts. An analysis of ionic ratios suggests that the lake waters may consist of trapped scawatcr highly modified by subscqucnt concentration by evaporative processes, by addition of ions from surrounding soils, and by addition of warm-spring water. The ionic concentrations arc altcrcd in part by the precipitation of CaSOe, CaC03, and Na2SOh.

Dating of geochemical events in Lake Bonney, Antarctica, and their relation to glacial and climate changes

“…Neither of these theories, however, can completely account for the composition of the two lobes of Lake Bonney. The bottom waters of the West Lobe show a remarkable similarity to that of sea water in the ratios of all the major ionic species except for depletions in HC0 3 -, SO/-, and Ca2+ (Angino et al 1964). These depletions can be accounted for by the observed precipitation of calcium carbonate and gypsum on the bottom of this and other Antarctic lakes (e.g., Angino et al 1964;Pewe 1960;Nelson & Wilson 1972).…”

“…East Lobe, however, shows some interesting differences in composition from that of sea water. The ratio of sodium to magnesium, the two major cations in the lake, is reduced to less than a sixth of that of sea water, while potassium to sodium ratios are doubled (Angino et al 1964;Boswell et al 1967). The ratios of the trace elements Zn, Mn, Pb, Bi, and Fe to total dissolved solids, although closer to those of sea water than other Antarctic lakes, are all enriched with respect to sea water (Boswell et af.…”

“…Oxygen and carbon isotopic ratios were determined by standard procedures using a Nuclides Analysis Associates 6-60 double collector, double inlet mass spectrometer. Many writers have speculated on the history of Lake Bonney (Armitage & House 1962;Angino & Armitage 1963;Angino et al 1964;Hoare et al 1964;Shirtcliffe 1964;Shirtcliffe & Benseman 1964;House et al 1966;Boswell et al 1967). It has been suggested that the salts represent trapped sea water which has been somewhat modified by later processes of evaporation, addition of ions from surrounding soils and warm spring water, and the precipitation of CaS0 4, CaC0 3, and Na 2S0 4 (Angino et al 1964).…”

“…Many writers have speculated on the history of Lake Bonney (Armitage & House 1962;Angino & Armitage 1963;Angino et al 1964;Hoare et al 1964;Shirtcliffe 1964;Shirtcliffe & Benseman 1964;House et al 1966;Boswell et al 1967). It has been suggested that the salts represent trapped sea water which has been somewhat modified by later processes of evaporation, addition of ions from surrounding soils and warm spring water, and the precipitation of CaS0 4, CaC0 3, and Na 2S0 4 (Angino et al 1964). House et al (1966) believed that the salts came from the sea indirectly, via sea spray and snow, and have been transported to the lake by meltwater over a long period of time.…”

“…Similarly if the ratio was as high as 0'5, a 7 % contribution would be sufficient. Using the bathymetric measurements of Angino et al (1964) and our chemical analyses we have calculated that the total dissolved salts in the bottom 17 m of East Lobe of Lake Bonney is 1·1 X 10 1 0 kg.…”