USING LAKE SEDIMENT RECORDS TO RECONSTRUCT POST-GLACIAL DUST DELIVERY TO HIGH-ELEVATION LAKES IN THE UINTA MOUNTAINS, UTAH

The Uinta Mountains of northeastern Utah rise above arid lowlands of the southwestern US. Previous work has shown that delivery of dust to these mountains has influenced pedogenesis, soil nutrient status, and surface water chemistry. An array of passive and active samplers in the alpine zone of the Uintas provides detailed information about contemporary dust fluxes, along with physical and geochemical properties of modern dust. However, reconstruction of changes in the dust system over time requires a continuous sedimentary archive sensitive to dust inputs. Radiocarbon-dated lake sediments records could potentially provide that archive. Cores collected from the subalpine Marshall and Bald Lakes extend from the late Holocene back to local deglaciation in the latest Pleistocene. Passive dust collectors in the vicinity of each lake constrain the geochemical properties of modern dust. Samples of regolith, retrieved from below surficial soil horizons in hand-dug pits and tree-tip mounds, and bedrock constrain properties of the local material within the watershed. Together these represent two end member sources of clastic sediment to each lake basin: allochthonous dust and autochthonous regolith. Geochemical analysis of sediment cores from each lake allows the relative contribution of local and exotic material to the lake to be considered as a time series covering the post-glacial interval. XRF and ICP-MS analysis reveal that the abundance of Ca in dust is greater than in local material. Conversely, the abundance of Al is greater in regolith and bedrock than in dust. As a result, the ratio Ca/Al is ~3x higher in dust than in local material. Plotting Ca/Al in Marshall Lake as a 12,000-year time series reveals that this ratio was relatively high post 2ka BP. Ca/Al was also high during the middle Holocene, at the same time that water levels were notably low at Bear Lake (Utah and Idaho) and Lake Tahoe (Nevada and California), suggesting that dust records from high-elevation lakes track regional aridity. Because the amount of dust entering the lake each year is likely small relative to the contribution of sediment from the local watershed, additional analysis of trace elements will potentially provide a more sensitive technique for identifying the influence of dust on lake sediment properties.