The glaciers of Glacier National Park are retreating rapidly and may disappear entirely within the next few decades. This situation has galvanized public attention, because glacier retreat provides an iconic manifestation of global climate change, because it is intuitive that glacier retreat is a response to rising temperatures, and because national parks are revered as places where geoecosystems are considered protected in their natural state. Relatively little is known about the history of glaciers in Glacier National Park between the end of the Ice Age (roughly 20,000 years ago) and the Little Ice Age, which ended about AD 1860. more specifically, little is known about when the park's glaciers formed and how they fluctuated before the historic period. To rectify this shortcoming, the U.S. Geological Survey provided logistical support in the summer of 2007 for the retrieval of sediment cores from a lake below Agassiz Glacier, a large glacier in the northwestern corner of the park. This Small Grant for Exploratory Research will provide support to measure sedimentary properties in lake cores already extracted from an important site in Glacier National Park. The cores will be analyzed for organic matter, biogenic silica, mineral phosphorous content, and grain-size distribution. Color spectrophotometry will be applied to assist in identifying changes in core sedimentology. Terrestrial organic fragments suitable for AMS 14C dating will be removed and stored for future analysis. In addition, samples from the uppermost few decimeters of the two surface cores will be submitted for 210Pb dating to develop a chronology for sedimentation during the past 200 years or so. Overall this multi-proxy approach involving multiple lab methods and geochronologic tools will allow development of a detailed Holocene history of the Agassiz Glacier.
This project will use known relationships between sediment deposition and glacier behavior, plus refined dating techniques, to develop a detailed chronology for Holocene glaciation in Glacier National Park. The disappearance of glaciers in that national park has drawn much popular attention in debates about climate change, even though no studies have dated past shifts in glacial ice to put the recent melting into perspective. The organic matter and biogenic silica content of the sediment should vary inversely to glacier extent because colder, more turbid water would decrease productivity in the lake. In contrast, mineral phosphorous should be directly proportional to glacier extent because a larger glacier would generate more silt containing phosphorous. Grain-size analysis will be used to quantify the abundance of rock flour in the sediment as a proxy for glacier presence/absence, and for glacier extent. The resulting improved understanding of Holocene glacial fluctuations will also aid efforts to reconstruct climate variability in this region over millennial, centennial, and decadal timescales. This project also will provide ecological and management information for the national park because glaciers are crucial components of the ecosystem, providing reliable sources of water to streams and wetlands during periods of drought, and driving disturbance and succession patterns through their advance and retreat.
