| Description |
The focus of this research is to infer past environments and climate from diatoms preserved in sediments deposited in Bear Lake, Utah/Idaho. Bear Lake is a larger (282km2), deep (maximum depth=62 m) lake. In 1996 three cores were retrieved using a Kullenberg corer. In 1998, short cores were katen from three sites in the lake, and in 1999, 22 samples from six surface sites were retrieved. Diatom stratigraphies were constructed using two long cores (96-1, 96-2) and one short core (98-10), and a composite stratigraphy was created by splicing together the three cores. Results from the surface samples provided useful ecological information that was used to interpret the fossil diation communities in the cores. A ratio of planktonic to nonplanktonic diatoms and the Simpson Index of Diversity were computed for each sample in the composite stratigraphy. Principal Components Analysis (PCA) of the composite stratigraphy and Correspondence Analysis (CA) of the surface sample were used to identify similarities among species and to group samples from the cores and the surface samples. Analysis of the fossil diation community composition indicates that Bear Lake experienced readily available nutrients and lower alkalinity from the base of the record, ~15,000 calendar years BP until ~7,000 calendar years BP, suggesting a connection with Bear River. This would have resulted from deglaciation and moist climate conditions that combined to create a large, fresh lake. As the climate warmed, the connection between the lake and river ended, and the lake became a closed system that was susceptible to fluctuations in effective moisture. Variations in moisture and temperature caused fluctuations in lake levels that were relatively minor in compartison to the changes that occurred before ~7,000 calendar years BP. A period of broken diatoms occurred from 1,00 calendar years BP until the present, making conclusions regarding recent climate change difficult. Current diatom community composition reflects the artifiects the artificial diversion of the river into the lake in 1912. Comparison with studies of other lakes in the western United States sugest similarities in the pattern of regional environmental and climatic change, |
