MEROMIXIS IN HYPERSALINE MONO LAKE, CALIFORNIA .1. STRATIFICATION AND VERTICAL MIXING DURING THE ONSET, PERSISTENCE, AND BREAKDOWN OF MEROMIXIS

Changes in vertical mixing in hypersaline Mono Lake, California, are described for the onset, persistence, and breakdown of meromixis, 1982 through 1990. In 1982 and 1983 exceptionally large runoff led to a 2.6-m rise in surface elevation and the onset of meromixis. Chemical stratification accounted for a density difference between 2 and 28 m of 1.2-1.5 x 10(-2) g cm-3 in 1984; the midsummer density difference between 2 and 28 m due to temperature was approximately 0.5 x 10(-2) g cm-3. Salinities ranged from 77 to 98 g liter-1; sodium, chloride, sulfate, and carbonate are the major ions. The flux-gradient heat method corrected for solar heating was used to calculate vertical mixing during the period from April to October. The eddy diffusivity at the thermocline ranged from molecular to 26 x 10(-6) m2 s-1 and averaged 3.4 x 10(-6) m2 s-1. Eddy diffusivity was found to regress on N2, the Brunt-Vaisala frequency squared, to the -0.58 power, suggesting turbulence is generated by local shear rather than large-scale processes.