Doctoral Dissertation Research: Changing Spatial Patterns of Rocky Mountain Snowpack During the Holocene and Their Effects on Ecological Boundaries

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Snowpack is a vital water resource in the West, but little is know about its variation beyond the past 60 years. Vegetation and lake level studies from the Rocky Mountains indicate significant changes in precipitation regimes, including changes in snowpack, during the past 11,000 years. In order to examine the patterns of precipitation change in the past, and to provide long-term context for understanding present and future changes, this doctoral dissertation research project aims to quantify millennial-scale changes in seasonal precipitation patterns over the Holocene and their relation to ecological changes at several sites across the West. Multiple lines of independent evidence from fossil pollen, hydrogen and oxygen isotopes, and lake sediment stratigraphies will be used to reconstruct past moisture, vegetation and fire regime gradients. A survey of modern lake water isotopic values across a gradient of seasonal precipitation regimes will provide a baseline for understanding the sensitivity of lake isotopic budgets to changes in seasonal contributions of precipitation. This baseline will be used to calibrate a hydrologic model that includes lake water and isotopic budgets that will aid in quantifying paleoclimatic records of snowpack. Water budgets, informed by past lake-level data, will determine estimates of overall moisture availability. Isotopic budgets will inform estimates of the contributions of seasonal precipitation to lake-water volume, and of the amount of evaporation. By investigating variations in the spatial patterns of seasonal precipitation over the past 11,000 years in the Rocky Mountains, we will examine the linkages between snowpack change, atmospheric circulation, ecotone shifts, and fire regimes. Annual snowpack is the largest reservoir of fresh water in the West, study results will be especially crucial for evaluating water resources and the possible effects of future climate change in the West. Research sites span key spatial gradients in modern precipitation to investigate the stability of these gradients over time in order to provide a context for understanding recent changes in spatial and volumetric distribution of snowpack in the West. Study results will also evaluate the potential effect of snowpack changes on forest distributions and wildfire regimes. Because the Holocene contains periods of different El-Nino frequency and intensity than today and periods that were likely warmer than today, studying Holocene snowpack distribution may reveal insight into the potential for future changes and their ecological effects. As a Doctoral Dissertation Improvement award, this project will enable a strong student to develop a promising and independent career.