MOUNTAIN SNOWPACK VARIABILITY AND ALPINE ECOSYSTEM SHIFTS IN THE ROCKY MOUNTAINS, USA DURING THE HOLOCENE

The western United States, a region characterized by high spatial and temporal precipitation variability, relies on mountain snowpack water resources to sustain human and ecological systems. The ongoing, widespread decline of snowpack across the region therefore raises serious concerns. Geologic archives of past winter precipitation trends and associated environmental responses provide valuable context for anticipated future hydroclimate changes and their potential impacts on sensitive alpine ecosystems. Previous work suggests that the western US experienced substantial hydroclimate fluctuations during the Holocene. However, few existing records are seasonally sensitive, continuous, and/or document the attendant ecological responses to snowpack variability. Here, we present an ~11,000-year lake sediment record of mountain snowpack and vegetative changes from a suite of lakes in the Teton Range, Grand Teton National Park, WY. We use traditional sedimentary parameters, including accumulation rate, sediment grain size, and clastic flux, to infer changes in snowpack-derived runoff. We then assess alpine ecological changes in high-elevation catchments by integrating biological sedimentary analyses (biogenic silica (Si/Ti), ∂13C ratios) with novel biomolecular (ancient sedimentary DNA) techniques at Lake Solitude (43.7926, -110.8448) [2761 m a.s.l; 0.15 km²; max depth, ~10.5m], a non-glacial, cirque lake located in the central Tetons. Our results reveal variations in Holocene winter precipitation and lake ice duration, with consistently low snowpack persisting in the early Holocene until a pronounced and sustained increase in the mid Holocene, which aligns with shifts in aquatic productivity, vegetative community composition, and the onset of regional neoglaciation and lake level rise. Snowpack then remains high but variable during the past ~4,000 years. Ultimately, the Lake Solitude record provides crucial context for understanding contemporary snowpack trends, which threaten sensitive alpine ecosystems in Grand Teton National Park and the broader western US.