A Continuous Late Holocene Record of Paleoclimate Change from Grinnell Lake Sediment Cores, Glacier National Park, Montana

Grinnell Lake is a glacially-fed alpine lake in the northern Rocky Mountains of Montana. Limnological parameters and radiocarbon ages from a ~1.17 -meter-long sediment core from Grinnell Lake provide a ~1,200 year-long climate record. The objective of this thesis is to develop a multi-proxy record of glaciation by distinguishing periods of positive and negative mass balance chronologically. Two overlapping sediment cores (1P-1B-1 and 1C-2B-1) were described, photographed, and sampled at 0.5 cm, 1 cm, and 5 cm intervals and analyzed for % organic carbon, % inorganic carbon, mineral composition, bulk density, biogenic silica, and clastic sediment flux. Glacial fluctuations were identified based on downcore plots of these parameters, and correlated with previously constructed glacial and climate records from the Canadian Rockies. The results indicate that cold conditions ~1100 AD initiated the "Little Ice Age" and the expansion of the Grinnell Glacier. A warmer climate persisted from ~1120-1450 AD however two or three periods of glacial advance are possible during this time period. A subsequent cold climate ~1450-1900 AD coupled with increased precipitation ~1600-1900 AD initiated significant ice expansion reaching its maximum extent ~1900 AD. Anomalously high 20th century temperatures resulted in rapid glacial recession and mark the end of the "Little Ice Age". These results contribute to existing climate records from the Little Ice Age period and will help to analyze small scale forcing mechanisms driving climate change and how these changes might spread globally.

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