A RECORD OF VOLUME IN THE GREAT SALT LAKE OVER THE HOLOCENE AND ITS CONNECTION TO PACIFIC CLIMATE MODES

In the modern climate system, the El Nino/Southern Oscillation (ENSO) dominates the climate in the Southwestern US. We present records of carbonate oxygen and carbon isotopes; hydrogen and oxygen isotope variability in brine shrimp cysts; and variability in mineralogy from reflectance spectrometry in a core spanning 9 to 2 ka bp from the Great Salt Lake, UT (GSL). The isotopic composition of lake waters are inferred from the cyst isotope records. The oxygen isotopic composition of cysts decreases slowly by about 2 permil from the beginning of the record (approx. 9 ka bp) to about 6 ka, and then is highly variable after about 4500 ybp. This slow decrease suggests decreased water input into the GSL up to the Mid-Holocene and more variable inputs after. Some portion of the decrease is likely attributable to a reestablishment of equilibrium with local precipitation sources following the rapid evaporation of Lake Bonneville at the end of the Pleistocene. Carbonate oxygen and carbon isotope ratios co-vary before 6 ka and after 4.5 ka, and are anti-correlated between, suggesting a major restructuring of the hydrologic regime in the Mid-Holocene. Based on reflectance spectrometry, the ratio of aragonite to illite increases abruptly at about 6 ka, which is consistent with increased carbonate precipitation from a more concentrated brine. We find a consistent pattern in our multi-proxy reconstruction of relatively wet conditions in the early Holocene, a dry mid-Holocene, and finally a wet and more variable late Holocene in the GSL catchment. We interpret high variability in the isotopic record since 4500 ybp as consistent with other studies that suggest a strengthening of the ENSO cycles in the late Holocene.