The carbon budget of Mono Lake

Abstract

Radiocarbon measurements suggest that 14C‐free carbon enters from beneath Mono Lake at a rate of about 1 mol/m2/yr. An input of this magnitude should be manifested in the inorganic carbon budget of the lake and with this in mind we have devised a model to reconstruct the evolution of the partial pressure of CO2 (pCO2) over the past 150 years. This encompasses a period (1945 to present) during which major diversions of source waters via the Los Angeles aqueduct have been in effect, significantly increasing the salinity of the lake and hence its pCO2. The model has been constrained by experimental characterization of the carbonate chemistry of the lake water, by the temperature dependence of pCO2 for the lake water, and by pCO2 measurements made on the lake water in 1966, 1969,1981, and 1989. Our calculations suggest that prior to 1945 the pCO2 of Mono Lake water was about 1.3 times the atmospheric value. To produce this excess, an input of CO2 of about 3.3 mol/m2/yr is required. Volcanic activity beneath the lake is a probable source of this input.