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Abstract

Fire is a natural process, influenced by climate and vegetation (fuel source). The relationships between fire, climate and vegetation under changing climatic conditions are important to understand. Fire frequency in the western United States has significantly increased in the past three decades. This study examined the top two meters of a sediment core taken from the northern sub-basin of Swiftcurrent Lake, Glacier National Park, Montana, with the goal of using variability in charcoal flux into the lake as a proxy for fire history in the Grinnell Glacier and Swiftcurrent Valley drainage basins. Previous work suggests that an increase in fire-frequency occurred in the western United States over the more recent record, and because this core site has a higher sedimentation rate, the fire record will be more finely resolved in time. A preliminary model suggests that the core represents the last ~1700 years of sedimentation, at an average sedimentation rate of 1.2 mm/yr. Based on the sedimentation rates and the charcoal concentrations, charcoal accumulation rates (CHAR) range from 0 to 72 grains cm-2 yr-1. The 1700-year fire record shows a higher amount of fire events than previously found in a nearby, upvalley core. The fire return interval of the northern Swiftcurrent sub-basin is roughly 46 years between fires, whereas the southern sub-basin had an average return interval of 363 years between fires. The lower accumulation rates in the southern sub-basin could be due to the two large lakes (Lake Josephine and Lower Grinnell Lake) that serve as sediment sinks in the watershed, or it could be the result of the smaller drainage area. This shorter, more detailed record provides a new evaluation of the fire record of the Swiftcurrent Lake drainage basin.

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