Mono Lake, a major closed-basin alkaline salt lake in eastern California, derives its water from a mixture of creeks and springs, with the former providing in excess of 75% of the total. The Li isotopic composition of lake water has not varied significantly over a 4 year meromictic period (delta(7)Li similar to + 19.5). Springs are isotopically distinct: groundwater springs and seeps carry water enriched in isotopically heavy Li whereas thermal springs supply isotopically light (delta(7) Li < lake), but 10 times more Li-rich, water. Isotopic fractionation during crystallization of carbonate tufa and evaporitic salt appears to be insignificant, and thus cannot be called on as a principal control of the isotopic balance of Li of the lake. Isotopic differences between the end-member source components permit a water budget to be calculated, suggesting (1) springs provide > 50% of the Li to the lake; (2) the Li budget is sensitively balanced on small thermal spring contributions, < 3% of the total spring inflow; and (3) the residence time of Li in the lake is 28 ka. Other Great Basin closed lakes have variable Li isotopic compositions ( δLi-7 from + 16.7 to +23.7), all of which differ significantly from those of several major takes and seawater (homogeneously &SIM; +32). Copyright © 2003 Elsevier Science Ltd.
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