DIATOM ASSEMBLAGES OF SILICEOUS SPIRES IN YELLOWSTONE LAKE, WYOMING

Yellowstone National Park contains the largest concentration of terrestrial hydrothermal features on Earth, and Yellowstone Lake is a key hydrothermal basin, with more than 650 vent structures on the lake floor. Hydrothermal spires - hard, porous, laminated structures associated with inactive vents - on the floor of Yellowstone Lake are hypothesized to form when convective cooling near hydrothermal vents precipitates amorphous silica. Two complete siliceous spires were photographed and retrieved from the lake floor in 1997 and 2016. These structures were collected from approximately 15-meters water depth and were dated to ~11 ka using uranium-isotope disequilibria. Fossils diatoms, microscopic siliceous algae commonly used as paleoenvironmental indicators, are preserved within the spire structures. Diatom assemblage composition indicates that diatom frustules were entrained from nearby sediment or grew directly on the structures. The assemblage throughout is dominated by small benthic species, including Staurosirella pinnata and Pseudostaurosira brevistriata. The planktonic species, Aulacoseira subarctica, is also abundant in assemblage counts. Diatom assemblages vary throughout the record, an indication of changing lake level, turbidity, or hydrothermal activity through time. Future research includes comparing spire and proximal sediment core assemblages to assess variations in community characteristics with increasing distance from hydrothermal vents.