Paleoenvironmental Change over the last 4000 years in Glacier National Park, Montana: Carbon and Nitrogen in Lake Cores from Lake Josephine and Swiftcurrent Lake

Lake cores record regional environmental and climate change, as well as stochastic changes in local surface processes. The climate and geomorphic history in the Northern Rocky Mountains is not well known, and analysis of lake cores is useful to further our understanding of Holocene climate change in the region. We analyzed a 4m long core from Lake Josephine and a 5m long core from Swiftcurrent Lake, downvalley from Grinnell Glacier, in an effort to constrain environmental change in the region. The Lake Josephine core is approximately 3000 years old, while the Swiftcurrent Lake core is approximately 4000 years old. C/N analysis was performed to quantify terrestrial versus aquatic input sources using an Elemental Analyzer. Percent TOC data was retrieved through carbon coulometry to consider its relevance as a proxy for climate change through solar forcing. Results show that there is a visual relationship between the variance of solar forcing and %TOC in Lake Josephine that should be verified through spectral analysis. C/N ratios reveal an increase of terrestrial inputs and rooted aquatic material in Lake Josephine and Swiftcurrent Lake over time. Percent TIC and dolomite act as proxies for intensity of glacial erosion and glacier fluctuation in Lake Josephine. Dolomite presence in Swiftcurrent Lake might act as a proxy for a threshold of glacial activity. Regional climate variability as recorded in C/N ratios were compared to Holocene climate periods, with good correlation during the Little Ice Age and the Medieval Climate Anomaly