The Curious Case of the Mono Lake Laminae

Mono lake is a closed basin, hypersaline, alkaline lake; the deepest part of the lake currently deposits distinctive, finely laminated sediments. Combined with the unusually good preservation of organic matter, intact cells, and DNA in these sediments, the laminae may provide a unique opportunity to reconstruct the biogeochemistry of Mono Lake over the past ~300 years. Importantly, this includes the interval over which lake salinity has doubled due to anthropogenic activities, which had presumed marked impacts on lake ecology. However, the origin and timing of the laminations has yet to be resolved. At the broadest scale, X-Ray fluorescence (XRF) and photographic analysis demonstrate an increase in authigenic mineral fraction over the past ~100 years, around the time the lakes volume began to drop, and act as a potential marker of anthropogenic disturbances. We also attempted to describe the nature of the individual laminae using chlorophyll analyses, fluorescence and optical microscopy, x-ray diffraction (XRD), and XRF. High resolution XRF (0.2mm) and XRD show no systematic elemental or mineralogic differences between layers, except for a slight correlation between white layers and increased carbonate. Chlorophyll concentrations decrease downcore in the lighter bands, while remaining relatively constant downcore in the darker bands. Microscopy revealed a slightly higher concentration of phototrophic diatoms in the dark layers, often with chloroplasts still intact. However, due to sampling bias and low sampling resolution, these analyses remain inconclusive and require further exploration. We tentatively hypothesize that the visible layering primarily represents differences in organic content, with timing and size related to the seasonal blooms of phytoplankton and brine shrimp, implying annual lamination. If confirmed, the laminae would provide a rich record of lake ecology and how said ecology was impacted by the recent drop in water level.