Diatom-Inferred Records of Paleolimnological Variability and Continental Hydrothermal Activity in Yellowstone National Park, USA

Fossil diatoms were used to reconstruct paleoclimatic and hydrothermal conditions in Yellowstone National Park. First, an extensive literature review summarizes the current state of knowledge about eukaryotic organisms characteristic of continental hydrothermal environments. Eukaryotes in hydrothermal systems can live at extremes of acidity (pH \u3c 4.0) and alkalinity (pH \u3e 9.0), and at moderately high temperatures (\u3c 62 °C). Silicate and carbonate precipitation in continental hydrothermal environments is mediated by eukaryotic organisms, which are important members of biofilm communities. A case study of alkaline-chloride sinter deposits in Yellowstone Lake and the Upper Geyser Basin inferred in-situ diatom growth rather than post-depositional accumulation of valves settling from the water column. Conical spires from the floor of Yellowstone Lake contained opportunistic fossil diatom species indicative of relatively shallow and alkaline conditions during structure formation. Fossil diatoms of the Upper Geyser Basin were low-nutrient and aerophilic species and in various stages of diagenetic alteration. An analysis of fossil diatoms showed that assemblages of Yellowstone Lake were sensitive to both direct climate impacts on the lake’s physical and chemical structure and indirect impacts on catchment processes. A major shift in species composition occurred at approximately 6475 and 1500 cal years BP. The diatom species composition suggests that the early Holocene winters and springs were cooler than today, with a relatively short interval of spring mixing. In the middle Holocene, the diatoms composition indicates a transition to warmer winters and springs, but colder summer temperatures. Specifically, the diatom assemblage suggests earlier ice-out and delayed stratification that resulted in periods of extended spring mixing. The late-Holocene diatom assemblage is indicative of wetter springs and sustained spring mixing. The impact of hydrothermal explosion events was assessed on diatom communities using sediment cores from Yellowstone Lake and Cub Creek Pond. The impact of these events was more pronounced in the early Holocene sediment record of the shallower, smaller Cub Creek Pond than in Yellowstone Lake. Overall, diatom assemblages were generally resilient to disturbance via hydrothermal disturbance, with only short-duration changes in diatom assemblage