LINKAGES BETWEEN BIOGENIC SILICA AND DIATOM INDICES IN MONITORING ENVIRONMENTAL CHANGE IN BEAR LAKE, UTAH-IDAHO

Biogenic silica and diatom assemblages are commonly used as paleoenvironmental proxies in paleolimnological studies. It has often proved difficult, however, to establish direct links between biogenic silica and diatom assemblages or climatic indicators. We examined these issues in a multi-proxy, paleolimnological study of sediment cores retrieved from Bear Lake, in order to infer past environmental and climate change. Bear Lake is a large (282 km2), deep (63 m) lake situated on the border of Utah and Idaho and is dimictic, mesotrophic, and alkaline. Before the 20th century, Bear Lake was a terminal lake, but today it serves as a reservoir connected by canals to the Bear River. Sample scores (fossil diatom data) on the first axis of a principal components analysis (PCA) are correlated with biogenic silica contents and oxygen isotope ratios. In combination, these indicators suggest that variations in effective moisture during the Holocene have impacted diatom productivity, probably through nutrient availability. Diatom diversity is inversely correlated with biogenic silica, an intriguing relationship that may reflect shifts in lake trophic levels. Fluctuations observed using these methods are striking and indicate significant and relatively frequent (100-1000s of years) changes in environmental conditions at Bear Lake.