Collaborative Research: Spatial and Temporal Patterns of Drought in Western North America during the Holocene

这笔赠款是根据2009年《美国复苏和再投资法》(公法111-5)提供的。这笔赠款产生的古气候数据集记录了从太平洋西北部到加拿大北极的北美西部科迪拉拉地区一对开放和闭合的泥晶盆地上干旱循环的时间、持续时间、频率和规模。该项目使用水文和稳定同位素质量平衡模型来提供对降水和相对湿度变化的定量估计。该项目探索了干旱的时间-地理模式在全新世期间是如何变化的，并使用先进的数据处理技术来检验关于古气候档案中的周期性的假设。这些结果被用来推断太平洋变化的潜在模式的性质，并记录它们如何随着时间的推移而变化。该项目测试了有关研究区域在全新世期间气候变化的原因和大小的假设。该项目还将文献中的数据与热带南美洲正在进行的工作相结合，以调查一系列时间尺度上的大规模太平洋强迫。这些记录的综合将导致对太平洋气候系统的更好的理解和对北美西部干旱循环的更好的可预测性。在过去的6ka期间，沿着西部科迪拉拉的湖泊水位一直相对稳定，在最密集的研究期间创造了高分辨率的档案。在全新世早期，大干旱显着降低了区域水位，从而将分辨率限制在十年至世纪尺度前约6ka。地质年代学由~(137)Cs、~(210)Pb、~(14)C、Tephra年代学和地磁对比提供。在所有研究地点都采用相同的方法，以简化数据解释并增加结果的稳健性。多代理研究将包括稳定同位素、灰度级、漫反射光谱、XRF、磁性测量以及点火损失的有机和无机碳。该小组与不列颠哥伦比亚大学合作，后者使用摇摆体组合来重建古温度。然后，将几千年的亚十年分辨率水文记录与普渡大学的一个合作者目前正在进行的高分辨率耦合海洋大气GCM模拟进行比较。这项工作与北美西部有关，那里的人口迅速增长，水资源紧张。该区域相对稀少的仪器前气候记录表明，该区域对太平洋变率以及PDO和AMO之间的相互作用高度敏感。需要更深入地了解这些变异性模式的过去行为，以提高预测能力。其目标是以与人类社会相关的时间分辨率调查气候变化，并回答以下问题：干旱和暴雨的强度和周期性在全新世期间发生了怎样的变化？这一时期北美西部干旱循环的空间格局是什么？与极端干旱和暴雨有关的边界条件和强迫因素是什么？

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This grant produces paleoclimate datasets recording the timing, duration, frequency and magnitude of aridity cycles on a network of paired open and closed micritic basins along the western cordillera of North America from the Pacific NW to the Canadian Arctic. The project employs hydrologic and stable isotope mass balance models to provide quantitative estimates of precipitation and relative humidity changes. The project explores how the temporal-geographic patterns of aridity changed during the Holocene and uses advanced data processing techniques to test hypotheses concerning the periodicities in the paleoclimate archives. These results are used to infer the nature of potential modes of Pacific Ocean variability and to document how they have changed over time. The project tests hypotheses concerning the causes and magnitude of climate variability in the study region during the Holocene. The project also synthesizes data from the literature with ongoing work in Tropical South America to investigate large-scale Pacific Ocean forcing over a range of timescales. Synthesis of these records will result in a better understanding of the Pacific climate system and improved predictability for aridity cycles in western North America.Lake levels along the western cordillera have been relatively stable during the past ~6ka creating high resolution archives during the period of time targeted for most intense study. During the early Holocene megadroughts significantly lowered water levels regionally thereby limiting the resolution to multi-decadal to century scale prior ~6ka. Geochronology is provided by 137Cs, 210Pb, 14C, tephra chronology and geomagnetic correlation. The same methods are applied at all study sites to simplify data interpretation and increase robustness of findings. Multiproxy studies will include stable isotopes, grayscale, diffuse spectral reflectance, XRF, magnetic measurements, and organic and inorganic carbon by loss on ignition. The group collaborates with the University of British Columbia, who use chironomid assemblages to reconstruct paleotemperatures. The multi-millennial hydrologic record with sub-decadal resolution is then compared with high resolution coupled ocean atmosphere GCM simulations currently being conducted by a collaborator at Purdue University.The work is relevant to western North America where populations are rapidly expanding and water resources are stressed. The relatively sparse preinstrumental climate records for this region indicate that it is highly sensitive to Pacific Ocean variability and to the interaction between the PDO and AMO. A deeper understanding of the past behavior of these modes of variability is needed to improve predictive capabilities. The goal is to investigate climatic change at a time-resolution relevant to human society, and answer questions such as: How have the intensity and periodicity of droughts and pluvials changed during the Holocene? What is the spatial pattern of aridity cycles in western North America during this period? What boundary conditions and forcing factors are related to extreme droughts and pluvials?