9631364 H. Wright The proposed research will investigate the nature and timing of climatic transitions in the Northern Rocky Mountains while assessing the reliability of small lakes in mountainous regions to record regional climate. The study is aimed at refining the scope and chronology of climatic events described in earlier glacial and pollen studies by identifying annual to century-scale variations that were previously too fine to be described. To do so, the project will use a high-resolution, multi-proxy approach, with emphasis on two innovative techniques for the region: stable-isotopic composition of bio-induced carbonates and dating with varved sediment. The research strategy includes calibrating proxy data from single varves to the instrumental climate record, interpreting and dating short-term climatic variations for the last 12,000 years, producing a detailed time series to analyze frequencies of change, and comparing a small varved site (Marl Lake) with a larger lake (Flathead) to assess the ability of small lakes in complex climatic regimes to record a regional signal. Climatic interpretations from Marl Lake will rely principally on the stable-isotopic composition of authigenic carbonates, changes in diatom assemblages associated with salinity changes, sediment characteristics, and trace-elements of ostracodes. A pollen profile will be constructed for correlation with regional vegetation studies. Climatic interpretations from the larger Flathead Lake will rely on isotopic- and lake-level fluctuations. The combined sediment-core and seismic records will be used to infer the timing and duration of drought. Synthesis of effective-moisture estimates and drought frequency for the two lakes will be beneficial in the assessment of long-term water yield of major rivers, such as the Columbia, which are critical sources of irrigation. A secondary benefit from the seismic survey of Flathead Lake is the opportunity to reconstruct the history of Glacial Lake Missoula in the Mi ssion Valley region. The results will provide guidelines regarding the regional accuracy of data collected from small basins and can be used to test the fidelity of a new generation of climate models. ??
