Continental patterns of moisture anomalies associated with late Holocene mid-latitude megadroughts

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。与全球气候变化相关的气温变暖预计将导致许多中纬度地区出现更频繁、更严重的干旱。了解过去十年至几十年干旱的空间格局、强度和频率，以及这些格局与海洋-大气耦合系统动力学的联系，对于评估机制和为风险评估和预测提供基础至关重要。在潮湿地区，基于树木年轮的重建缺乏水文气候敏感性和/或时间深度，显然需要过去水文气候变化的记录。这项研究产生了一个北美潮湿地区过去3000年泥炭地水文气候记录网络。该网络与半干旱地区的树木年轮记录和其他干旱敏感记录一起使用，以确定过去湿度异常的大陆尺度足迹。对遗属变形虫、泥炭腐殖化和植物大化石的高分辨率分析为水文气候变化提供了详细的视角。在重要的中纬度干旱事件期间的高精度年表，特别是中世纪气候异常（MCA），为这些关键事件期间的湿度异常提供了强有力的描述。数据生成和综合与干旱、降水和海表温度（SSTs）的仪器记录分析相结合，以验证这样的假设，即像MCA期间的广泛干旱代表了20世纪水文气候变率的一种观测模式的放大或异常持续。在代理海温记录的约束下，利用数据模式比较和模拟实验来评估大西洋和太平洋对北美水文气候影响的相对重要性，以及气候系统对外部强迫变化的潜在动态响应。该研究提供了未充分研究区域的多年代际水文气候变率的时空重建，通过综合观测和模拟结果将这种变率与海洋-大气系统的动力学联系起来，并确定了过去3000年来影响北美大陆的最大干旱的机制和动力学。这项工作记录了全新世晚期干旱发生在通常被认为干旱风险较低的地区，这可能会改变科学和社会的看法。研究结果通过公开讲座、网站、大学层面的教学和咨询以及组织网络传播。数据通过NOAA古气候学项目以及其他渠道分发。该项目包括研究生的跨学科培训和众多本科生的研究经验。PI在招募女性方面有着良好的记录。PI将项目活动纳入课程材料和研讨会。该项目更新了PI和威斯康星大学CCR之间富有成效的合作，利用了全新世中期到现在的海洋-大气-陆地完全耦合模型瞬态运行所产生的丰富数据。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Warming temperatures associated with global climate change are expected to lead to more frequent and intense droughts in many mid-latitude regions. Understanding spatial patterns, magnitudes, and frequencies of past decadal-to-multidecadal droughts, and linkages of these patterns to dynamics of the coupled ocean-atmosphere system, is critical to assessing mechanisms and providing the foundation for risk assessment and prediction. There is a clear need for records of past hydroclimate variability in humid regions, where tree-ring based reconstructions lack hydroclimate sensitivity and/or temporal depth. This research produces a network of peatland-derived hydroclimate records spanning the past 3000 years in humid regions of North America. The network is used in conjunction with the tree-ring record of semi-arid regions and other drought-sensitive records to determine continental-scale footprints of past moisture anomalies. High-resolution analyses of testate amoebae, peat humification, and plant macrofossils provide detailed perspectives on hydroclimate variability. High-precision chronologies during significant mid-latitude drought episodes, particularly the Medieval Climate Anomaly (MCA), provide robust portrayals of moisture anomalies during these critical events. Data generation and synthesis is coupled with analyses of instrumental records of drought, precipitation, and sea-surface temperatures (SSTs) to test the hypothesis that widespread droughts like those during the MCA represented an amplification or unusual persistence of an observed mode of 20th century hydroclimate variability. Data-model comparisons and modeling experiments, constrained by proxy SST records, are used to assess the relative importance of Atlantic and Pacific Ocean influences on North American hydroclimate and the potential dynamic response of the climate system to changes in external forcing. The research provides spatial and temporal reconstructions of multidecadal hydroclimate variability in understudied regions, linking this variability to dynamics of the ocean-atmosphere system through synthesis of observational and modeling results, and identifying mechanisms and dynamics of the largest droughts to affect the North American continent in the last 3000 years. This work documents late Holocene droughts in regions conventionally assumed to have low drought risks, potentially transforming both scientific and societal perceptions.Results are disseminated through public lectures, a web site, teaching and advising at the University level, and organizational networks. Data is distributed through the NOAA paleoclimatology program, as well as other outlets. The project includes interdisciplinary training of graduate students and research experience for numerous undergraduates. The PI has a strong track record of recruitment of women. The PI incorporates project activities into course materials and seminars. The project renews a productive collaboration between the PI and the University of Wisconsin's CCR, taking advantage of the wealth of data created by the first mid-Holocene-to-present transient run of a fully coupled ocean-atmosphere-land model.