CO2 concentrations in perennially ice-covered lakes of Taylor Valley, Antarctica

Abstract

Lakes in Taylor Valley, southern Victoria Land,Antarctica, are unusual in that they areperennially covered by a 3–5 m thick ice layer.Previous work on gas concentrations in theselakes has shown that the surface waters aresupersaturated with respect to O2,N2O, as well as the noble gases. Our datashow that the dissolved CO2 (CO2(aq))concentrations, calculated from pH andΣCO2, can be highly undersaturatedat shallow depths of the lakes. CO2partial pressure values (pCO2) are as lowas 10−4.3 atm and 10−4.2 atm in theeast and west lobes of Lake Bonney,respectively, and 10−3.8 atm in LakeHoare. CO2(aq) depletion occurred only inthe uppermost part of the water column, inassociation with elevated primary productivity(PPR). The upward diffusion of CO2(aq)from the aphotic zone, and the annual input ofCO2 via glacial meltwater can notreplenish the amount of CO2(aq) annuallylost to primary productivity in the uppermostmeters of the water column. Calcification is alimited source of CO2(aq), since the lakesare undersaturated with respect to calcitethrough portions of the austral summer.Preliminary respiration rates have been used toobtain an annual inorganic carbon balance.Further down in the water column, at the sitesof the deep-water maximum in primary production(PPRmax), which in Lakes Bonney andFryxell is associated with nutrient gradients,CO2(aq) is not undersaturated. A largeupward flux from CO2-supersaturatedaphotic waters provides a surplus ofCO2(aq) at the PPRmax. Lake Fryxell,unlike the other lakes, is supersaturated withCO2(aq) throughout the entire water column.