LATE HOLOCENE CLIMATE RECONSTRUCTION AND LAKE BASIN EVOLUTION OF COSLEY AND GLENNS LAKES, MT

Glenns and Cosley Lakes, located in Glacier National Park, have a unique lake morphological history. At one time, they were a single lake, roughly 6.5 km in length. Now they are separated by an alluvial fan that formed after a landslide during the Holocene. Water still flows from Glenns Lake to Cosley Lake via a stream. Cosley Lake has one additional source of water from Whitecrow Creek where the alluvial fan originates.

Lake level and thermal mixing depth often increase or decrease with changes in temperature and wind strength. For example, the phenology of lake ice cover is usually substantially altered with changing temperature. Such changes commonly have a profound effect on the ecology and community structure of limnobiota in the ecosystem, specifically the diatoms and other primary producers in lakes.

In 2013, we collected short sediment cores from Cosley and Glenns Lakes to analyze for a record of climate changes associated with lake level and mixing depth by utilizing known ecological relationships in planktic diatoms. Three planktic taxa present in the lakes with known ecological preferences for mixing depth when nutrient conditions are well constrained were identified in these cores: Discostella stelligera, Cyclotella comensis, and Cyclotella bodanica var. lemanica. Neoecological research from other lakes in the region have successfully inferred changes in wind intensity, temperature, and water clarity associated with changes in mixing depth over the last several centuries. These lakes are viable for this ongoing research to resolve the primary drivers of the mixing changes based on these three planktonic diatoms.