Forest and lake dynamics in response to temperature, North American monsoon and ENSO variability during the Holocene in Colorado (USA)

Learning how terrestrial environments responded to past temperature and precipitation variations can help anticipate how these environments will respond to natural climate variability upon which human induced climate change is superimposed. Here we present a detailed multi-proxy analysis of a sediment core from Emerald Lake, located at the montane-subalpine forest transition in west-central Colorado. The record tracks changes in the lake environment, vegetation and fire activity mostly related to climate change for the latest Pleistocene and Holocene, and complements the previously published lake-level reconstruction from the same site. Vegetation and lake level show similar patterns with insolation changes and other regional paleoclimate records for temperature, with coldest conditions during the Younger Dryas (YD), warming in the early Holocene - thermal maximum reached around 6800 cal yr BP – and cooling in the middle and late Holocene. This record also shows how subalpine environments reacted to Holocene moisture dynamics for both summer, related to the North American Monsoon (NAM), and winter precipitation that could be associated with El Niño Southern Oscillation (ENSO), indicating that Emerald Lake was sensitive to long-term and millennial-scale regional and global climate changes. Climatic perturbations, generally cold and/or arid events and low lake levels at ca. 8200, 4200, 1200-1000 cal yr BP influenced the vegetation around Emerald Lake in association with well-known worldwide climatic events.