Collaborative Research: A Continuous 60,000 Year Sediment Record Documenting Abrupt to Precession-Scale Climate Change and Ecosystem Response at Fish Lake UT, Upper CO River Basin

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Over the last several decades increased drought severity and wildfire intensity around the globe has drawn attention to a need for an improved understanding of how climate change over a human lifetime impacts people, ecosystems, and water resources. Rapid population growth in the arid western US combined with pervasive drought, temperature stress on forests, insect outbreaks, and unprecedented wildfires has negatively impacted people and the economy and focused attention on the need to improve our understanding of the controls and long-term consequences of increased climate stress on these valuable and unique ecosystems. This interdisciplinary project will place the 21st century drought and extreme fire seasons in western North America into a longer-term context as a means to identify likely future scenarios for climate change and ecosystem response. This research will use a long and continuous sediment lake record collected from a headwater lake in the upper Colorado River Basin to investigate past variations in precipitation and temperature, and the impacts these changes had on vegetation, wildfire, forest disturbance, and glaciation with special attention paid to periods of rapid climate change that has happened in the past over timescales relevant to people. This is possible because of the high accumulation rate of Fish Lake sediments of about 18.5 meters over the last 60,000 years producing a 60 foot high section of mud containing things like pollen, charcoal, bug parts, fish bones, and other fossils for researchers to study in addition to the sediment itself and the molecular fossils it preserves. The proposed work includes X-ray Fluorescence (XRF) and CT core scanning to identify abrupt sediment boundaries and characterize the sediment profiles at the highest possible resolution. Changes in precipitation and evaporation will be investigated by water isotope tracers, including leaf wax delta-2H (long and short chain) and chironomid delta-18O. Molecular fossils such as branched glycerol dialkyl glycerol tetraethers (brGDGTs) will be used as way to estimate past summer temperatures through time. Landscape and aquatic ecosystem responses will be studies by using pollen, charcoal, polycyclic aromatic hydrocarbons (PAHs), biogenic silica, and organic carbon, nitrogen and stable isotopes. Watershed erosion and glacial activity of the Fish Lake Plateau will be investigated in new detail with scanning XRF, grainsize, organic matter, biogenic silica, and bulk density. Successful dating of an 11-m long core recovered in 2014 has been demonstrated by radiometric methods, including 210Pb and AMS 14C of terrestrial macrofossils and charcoal, by tephrochronology, and by paleomagnetic measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.