LACUSTRINE RECORDS OF POSTGLACIAL CLIMATE-HYDROTHERMAL-ECOSYSTEM CHANGE IN LOWER GEYSER BASIN, YELLOWSTONE NATIONAL PARK

The thermal basins of Yellowstone National Park are dynamic geo-ecosystems, with millennial- and centennial-scale climate change impacting hydrothermal systems and their surrounding ecosystems. Lake sediments provide a useful archive for understanding a thermal area’s geo-ecological development. Six lakes (>14,000 years in age) were cored between 2018 and 2023 within and near Lower Geyser Basin, the largest thermal area in Yellowstone National Park. Hydrothermal activity is reconstructed through analysis of sediment geochemistry (scanning XRF, ICP-MS, δ¹³C_sediment) and mineralogy (petrographic thin sections); pollen and charcoal analyses are used to reconstruct vegetation and fire, respectively. Shifts in sediment abundance of sulfur, arsenic, and antimony suggest that Goose, Feather, and Lower Basin lakes experienced significant shifts in hydrothermal activity in the last 4000 years. Goose Lake abruptly stopped receiving hydrothermal input after ca. 3800 years ago, while Feather Lake shows an increase in trace elements indicative of increased hydrothermal activity during the same period. Associated pollen and charcoal records indicate that these geochemical changes were associated with an opening of basin vegetation from forest to thermal grassland and a decrease in fire activity. Rush Lake currently contains dozens of sublacustrine thermal vents and geochemical data indicate that hydrothermal input to the lake has been stable since ca. 14,500 years ago. Gravel and sand deposits punctuate late-glacial Rush Lake stratigraphy, likely deposited through hydrothermal explosions and glacial outwash. Pollen data from Rush Lake suggest that little vegetation change occurred following the development of Pinus contorta (lodgepole pine) forest ca. 12,000 years ago. Taken together, the lake-sediment records of hydrothermal activity are seldom synchronous, revealing a dynamic geo-ecosystem shifting significantly in Lower Geyser Basin over the past 14,500 years.