DIATOM STRATIFICATION AND FIRE HISTORY RECONSTRUCTION OF ISLAND LAKE, WYOMING

Fire is a vital component of ecosystem functioning within boreal ecosystems. Reconstructing shifts in fire dynamics can provide information about changing climate. This study integrates sedimentary charcoal and fossil diatoms to reconstruct fire history and functions as an assessment of the effectiveness of combining multiple proxies on various temporal scales.

Island Lake, an alpine lake of glacial origin, is located in the Greater Yellowstone Ecosystem at an elevation of 3,048 meters. Island Lake has a maximum water depth of 33 m and is highly transparent with a deep chlorophyll maximum. Thus, it is ideally suited for investigating the relationships between paleolimnological tools for mixing depth and fire.

Preliminary diatom assemblage counts found two planktonic diatom genera with known ecological associations with stratification and mixing, Discostella and Aulacoseira, respectively, in abundance throughout the length of a sediment core. We created a diatom-inferred stratification index to reconstruct changes in lake stratification patterns over the Holocene. This stratification index was compared to dendrochronology fire history records of two nearby sites to assess whether mixing depth changes were correlated with terrestrial fire events indicated in a dendrochronology record. Preliminary results suggest that these paleolimnological indicators show substantial changes throughout the Holocene and provide greater context for other regional records of fire history.