HOLOCENE CLIMATE AND STRATIFICATION HISTORY OF ISLAND LAKE, WYOMING

Island Lake is located in the Shoshone National Forest near Cody, Wyoming, at an elevation of 3,048 meters. Positioned centrally in the Beartooth Mountains, Island Lake is an alpine lake of glacial origin. Like many alpine lakes, Island Lake is highly transparent, with a deep chlorophyll maximum, and a maximum water depth of 33 m, and is thus ideally suited to study the relationships between ecological bioindicators and geochemical proxies. Here we explore preliminary paleolimnological data from a sediment core measuring 1.54 meters, which was collected in the summer of 2013. Two planktonic diatom genera, Discostella and Aulacoseira, were abundant throughout the core. Both of these genera have known ecological associations with stratification and destratification, respectively, in low-nutrient lakes from this region. Based on the relative abundances of fossil diatom species in each group, we created a diatom-inferred stratification index to reconstruct changes in lake stratification patterns over the Holocene. Detailed phosphorus geochemistry and bulk metal geochemistry were also analyzed to reconstruct landscape evolution and biogeochemical cycling with respect to potential changes in lake stratification patterns. A sequential extraction for phosphorus (SEDEX) was used to identify phosphorus associated with oxides, mineral phases, and organic matter. Together, these paleo-environmental indicators show a record of substantial changes throughout the Holocene at Island Lake, and provide context for other regional records of climate change in the Rocky Mountain region.