CAVE SEDIMENT CORE PRESERVES 2200 YEARS OF ALPINE WILDFIRE HISTORY IN NORTHERN UTAH, USA

High-elevation alpine caves can trap sediment in environments that are otherwise erosional regimes, and therefore have the potential to record important paleoecological and paleoenvironmental conditions. Many such caves have small collection basins and seasonal flooding acting as a filter, and therefore could provide a uniquely granular view of a local region’s environmental history. In contrast, the complex hydrological systems of many caves mean that sediment records could be repeatedly removed by erosion or reworked. To test whether alpine cave sediments can preserve a reliable and detailed record of fire history, we examined Boomerang Cave located in Logan Canyon, northern Utah, U.S.A. at ~2230 m elevation. This cave is positioned along the boundary of two different climate modes created by the El Niño - Southern Oscillation within western North America, and the surrounding drainage basin floods seasonally, predominantly from spring snow melt, transporting sediments into the cave. To examine whether these cave sediments are a useful paleoecological and paleoenvironmental record, we recovered a short continuous sediment core from the Dome Room, where fine sediments accumulate at the bottom of the chamber. The core is 78.5 cm long with an age of 2190 ± 20 ¹⁴C years BP (2308 to 2121 cal BP) at its base. Charcoal samples were collected and analyzed at 0.5 cm resolution from the entire core, which preserves at least three large wildfire episodes based on charcoal particle abundance, with each pulse separated by ~25 cm. These charcoal pulses correlate to changes in bulk magnetic susceptibility and elemental abundances measured using X-ray fluorescence, with Al/Si ratios and bulk magnetic susceptibility values increasing during each pulse. We hypothesize these results might indicate increased erosion and runoff after the removal of vegetation by major wildfire event(s). Our data suggest that this late Holocene sediment record preserves past wildfire events from the surrounding area, and sediment cores from alpine caves have the potential to be valuable archives of local paleoenvironmental history.