Meromixis in hypersaline Mono Lake, California. 3. Biogeochemical response to stratification and overturn

Mono Lake is a terminal, saline lake that became ectogenically meromictic in 1982–1983 and remained stratified until November 1988. During this period, the monimolimnion remained anoxic and nearly isothermal, while the upper mixolimnion was well oxygenated and exhibited a seasonal thermal regime. Dissolved sulfide and methane increased in the monimolimnion as a result of diffusive flux from the sediments. Winter mixing down to the chemocline distributed sulfide and methane throughout the mixolimnion. Lakewide inventories of dissolved sulfide and methane reflected the balance between increased concentrations and decreased monimolimnion volume over time. At overturn, the entire water column was isothermal and anoxic. Dissolved sulfide (380 × 10⁶ mol) was oxidized in 1 week by molecular oxygen. Methane (12 × 10⁶ mol) was removed more slowly by microbial oxidation and ventilation across the air‐water interface.