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

积雪是西方一种重要的水资源，但在过去60年里，人们对其变化知之甚少。落基山脉的植被和湖泊水位研究表明，在过去的11000年里，降水制度发生了重大变化，包括积雪的变化。为了研究过去降水变化的模式，并为理解现在和未来的变化提供长期背景，本博士论文研究项目旨在量化全新世季节降水模式的千年尺度变化及其与西部几个地点生态变化的关系。来自化石花粉、氢和氧同位素以及湖泊沉积物地层学的多条独立证据将用于重建过去的水分、植被和火灾状况梯度。对不同季节降水制度梯度的现代湖水同位素值的调查将为了解湖泊同位素收支对降水季节性贡献变化的敏感性提供基线。这一基线将被用来校准一个水文模型，该模型包括湖泊水和有助于量化积雪古气候记录的同位素预算。根据过去的湖泊水位数据，水量预算将决定总体水分可获得性的估计。同位素预算将为估计季节性降水对湖泊水量的贡献以及蒸发量提供信息。通过调查过去11000年来落基山脉季节降水的空间模式的变化，我们将研究积雪变化、大气环流、交错带变化和火灾制度之间的联系。每年的积雪是西部最大的淡水蓄水池，研究结果对于评估水资源和西部未来气候变化的可能影响将特别关键。研究地点跨越现代降水中的关键空间梯度，以调查这些梯度随时间的稳定性，以便为了解西部积雪的空间和体积分布最近的变化提供背景。研究结果还将评估积雪变化对森林分布和野火状况的潜在影响。由于全新世的厄尔尼诺频率和强度与今天不同，而且可能比今天更温暖，研究全新世积雪分布可能会揭示未来变化的可能性及其生态影响。作为博士论文改进奖，这个项目将使一个强大的学生发展一个有前途的独立职业生涯。

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.