Collaborative Research: Early-Versus Late- Holocene Drought Variations in the Northern Rocky Mountains

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This study proposes to investigate high-frequency drought events in northwestern Montana for two time intervals: 0-2000 and 7000-9000 14C yr BP. The principal goals are to reconstruct the timing, severity, and cyclicities of shifts in effective moisture so that we may address the following questions: 1) Are drought frequencies correlative in time with known solar and/or oceanic-atmospheric frequencies? 2) Does the frequency of drought change over the last 10 ka BP and are these changes correlative with changes in the climatic boundary conditions? 3) Does the timing of drought in the Northwest have a defined relationship to that of adjacent regions?Three climatic proxies preserved in lake sediments-- the d18O of carbonates, diatom assemblages, and charcoal-will be used to answer these questions. The combined use of d18O and diatoms potentially provides an innovative technique for estimating the severity, as well as the seasonal timing of drought. The addition of charcoal analyses permits the study the effects of drought on both aquatic and terrestrial ecosystems. The study aims to reconstruct high-frequency climatic variations at decadal to sub-decadal resolution. The records will be dated with a combination of varve counts and multiple 14C dates to ensure as accurate and detailed a chronology as possible. Three sites were chosen for analysis to mediate potential complications caused by local climatic effects in mountainous regions.