SULFUR, NITROGEN, AND CARBON IN THE BIOSPHERE 185 



TABLE 1 



LIMNOLOGICAL AND ISOTOPIC DATA 8 FROM GREEN LAKE, 



FAYETTEVILLE, N. Y., JUNE 30, 1962 



This depletion confirms what the vertical gradients also show, that the lake is a 

 trap for total sulfur but loses 4 S. Isotopic fractionation between sulfide and 

 sulfate is maximal, averaging 57 per mil, in the monimolimnion. But light ( 32 S 

 enriched) sulfide is reoxidized in the upper lake (the mixolimnion), and export 

 via the outlet results in a slight net loss of heavy 34 S. 



We noted that the model suggested by these data is a reflux system with a 

 leak near the top. We also compared the lake to a salt dome, where bacterial 

 production of free sulfur preferentially removes 32 S from seawater, and the 

 associated sulfate deposits 15 are strongly enriched in 34 S. There are coupled 

 biological processes that fractionate the carbon isotopes, 16 and Green Lake 

 carbonate, like the carbonate in the caprock of a salt dome, is strongly depleted 

 in C 



Green Lake is certainly not a typical lake. It owes its meromixis to deep 

 seepage of exceptionally saline groundwater, entering a basin of unusual shape 

 and depth that was formed as the plunge basin of a late glacial waterfall. It 

 differs from more ordinary lakes in its initially high sulfate content — about a 

 hundred times that of Linsley Pond. Moreover, apparently because there is so 

 much more sulfur than iron, H 2 S is free to diffuse upward, and the mud of 

 Green Lake is not a trap for sulfide in the form of FeS, as Linsley Pond is. 

 Neither lake appears to liberate sulfide to the atmosphere, the "leak at the top" 

 of Green Lake being an outlet to water, not to the air. So the main conclusion of 

 my limnological excursion is not what the atmospheric scientists mav have 

 hoped. If massive quantities of sulfur enter the atmosphere from reduced 

 hypolimnia, enabling geochemists to balance the global sulfur budget, 18 I 

 cannot prove it and do not claim it. All I claim is that the metabolism of sulfur, 

 on an areal basis, can be about a tenth as active as the metabolism of carbon; but 



