Geochemical processes in the Lake Fryxell Basin (Victoria Land, Antarctica)

Abstract

Major ion, nutrient, transition metal, and cadmium concentrations are presented for nine meltwater streams flowing into Lake Fryxell, a permanently stratified lake with an anoxic hypolimnion in Taylor Valley, Antarctica. For the major ions, stream compositions are considered in terms of dissolution of marine-derived salts and chemical weathering of local rocks. Although Lake Fryxell has undergone significant evaporative concentration, only calcite, of the simple salts, is predicted to precipitate. Geochemical budgets indicate, however, that large quantities of K, Mg, and SO₄ have also been removed from the lake. Reverse weathering may be an important sink for K and Mg, although magnesium removal with calcium carbonate phases is also likely. Assuming constancy of composition over recent geologic time, all of the salts in the Fryxell water column could have been delivered under present flows in about three thousand years (chloride age).

Comparison of nutrient concentrations in these meltwater streamsn with other flowing waters in the world reveals that the Frywell streams are strikingly deficient in NO₃-N but not PO₄-P. The apparent nitrogen deficiency in Lake Frywell itself can be attributed to the low annual stream loadings of this nutrient.

Stream concentrations and loadings are also presented for Mn, Fe, Co, Ni, Cu, and Cd. “Dissolved” metal concentrations correlate roughly with average crustal abundances, suggesting that chemical weathering is the major source for these elements. Vertical metal profIles within Lake Fryxell itself appear to be governed by the formation of insoluble sulfide phases, or, in the case of Mn, by MnHPO₄. However, dissolved nickel levels in sulfide-bearing waters are much higher than can be explained in terms of metal-sulfide equilibria, and we suspect that significant organic complexing of this metal is occurring in the deeper waters.