LATE HOLOCENE HYDROLOGIC CHANGES IN THE EASTERN SIERRA NEVADA BASED ON AN ANALYSIS OF HIGH RESOLUTION GEOCHEMICAL DATA FROM JUNE LAKE (CA)

June Lake is a small glacial lake in the eastern Sierra Nevada of California, in the transitional region between the arid Great Basin to the east and the wetter Sierra Nevada to the west. June Lake is surficially hydrologically closed and a sensitive archive of climatic changes. We seek to determine the timing and periodicity of hydroclimatic changes over the late Holocene based on a 4.9 m sediment core covering the last ~4600 years. To that end, we employ high-frequency X-ray fluorescence and magnetic susceptibility (MS) data sets from the core. The strong correlation between the XRF record of Ca/Ti and lower resolution inorganic carbon data set suggests the calcium is associated with carbonate minerals, and we use this indicator to track lake level change. When carbonate accumulation is high, we interpret arid conditions that drive lake level lowering. The most prominent calcareous interval occurs between ~2700 and 1900 cal BP, which is known as an arid period in the Great Basin and Sierra. Another dry interval from ~1300-900 cal BP roughly coincides with the Medieval Climate anomaly. The fact that Ca/Ti and magnetic susceptibility, which is often high during episodes of enhanced runoff and precipitation, appear inversely correlated supports our interpretation of Ca/Ti as chiefly an indicator of lake level. Carbonate isotope data further elucidate climatic changes, and suggest intervals when June Lake’s hydrology may have been open. When δ¹⁸O and δ¹³C_CARB are highly correlated and Ca/Ti values are relatively high, we interpret a closed lake, similar to the modern system. Consequently, when correlation between carbonate isotope values is low, and carbonate precipitation declines, we suggest the lake may have been much larger and possibly hydrologically open, connecting with nearby Gull Lake. With few high resolution lake records for this time and region, this study helps to fill a significant knowledge gap that may prove relevant to resource planners, climate modelers and others concerned with anticipating and preparing for hydrologic variability in California’s headwaters.