Magnitude, Extent, and Impact of a Pre-Historical Multi-Century Drought in the Western US

该研究项目将调查北美西部在全新世晚期干旱期间发生的多世纪干旱的原因，并分析其地理范围和对居住在该地区的美洲原住民的影响。干旱是美国西部气候条件的一个常规特征，全球预测模型表明，干旱将在未来加剧。干旱通过农业损失、水资源限制以及对商业、公用事业和工业的一系列其他损害来影响社会。通过分析古气候模式，该项目将加强对造成美国西部持续干旱的海洋-大气动力学的基本理解。该项目将为史前人类应对这些恶劣环境变化所采用的策略提供新的见解。鉴于干旱对社会、经济和生态的破坏性影响，该项目将提供有关干旱动态和干旱响应的丰富见解。该项目还将通过实验室研究经验和在部落土地上的实地考察，为美国土著本科生和研究生提供教育和培训机会。在美国西部，晚全新世干旱期的降水模式呈现西南干燥西北湿润的持续偶极模式，类似于厄尔尼诺南方涛动的现代拉尼娜阶段所产生的模式。由于这些相似之处，晚全新世干旱期的古气候记录提供了对导致该地区长时间、高强度干旱的温度和降水剖面的见解。本项目将重点研究三个核心问题：(1)导致西南长期干旱和西北长期潮湿气候的双极条件的大气环流模式的时空范围是什么？(2)晚全新世干旱期的降水和温度变化是怎样的？(3)人类对长期环境变化的反应的性质和程度是什么？研究人员将分析从内华达州和爱达荷州沿南北样带的湿草地收集的沉积物芯中的花粉，以重建降水的时间变化。对残山艾树的碳氧同位素进行分析，重建降水和温度的季节模式。将使用高分辨率加速器质谱放射性碳技术重新确定关键考古遗址的收藏日期，以识别小型、短命的有机物，以重建美洲原住民对严重干旱时期的反应。这项研究的结果将增强对未来特大干旱和持续干旱条件进行建模的能力。

This research project will investigate the causes of a multi-century drought in western North America during the Late Holocene Dry Period and will analyze its geographic extent and impact on Native Americans living in the immediate area. Droughts are a regular feature of climatic conditions in the western U.S., and global prediction models suggest that they will intensify in the future. Drought impacts society through agricultural losses, water restrictions, and a range of other damages to businesses, utilities, and industry. By analyzing paleoclimatic patterns, this project will enhance basic understanding of the ocean-atmosphere dynamics that create persistent droughts in the western United States. The project will provide new insights into strategies employed by prehistoric populations to cope with these harsh environmental changes. Given the devastating social, economic, and ecological impacts of droughts, this project will provide rich insights regarding drought dynamics and responses to drought. The project also will provide education and training opportunities for Native American undergraduate and graduate students through laboratory research experiences and fieldwork on tribal lands.In the western U.S., precipitation patterns during the Late Holocene Dry Period had a persistent dipolar pattern of a dry southwest and a wet northwest, similar to the pattern produced during the modern-day La Nina phases of the El Nino Southern Oscillation. Because of these similarities, the paleoclimatic record for the Late Holocene Dry Period offers insights into the temperature and precipitation profiles that caused long-duration, high-intensity droughts in the region. This project will focus on three core questions: (1) What were the spatial and temporal extents of the atmospheric circulation patterns that resulted in the dipolar conditions of very long-term drought in the southwest and wet climate in the northwest? (2) What was the precipitation and temperature regime during the Late Holocene Dry Period? (3) What was the nature and extent of human response to an extended period of environmental change? The investigators will analyze pollen from sediment cores collected from wet meadows along a north-south transect in Nevada and Idaho to reconstruct temporal changes in precipitation. Carbon and oxygen isotopes will be analyzed from remnant sagebrush wood to reconstruct seasonal patterns of precipitation and temperature. Curated collections from key archaeological sites will be re-dated using high-resolution accelerator mass spectrometry radiocarbon to identify small, short-lived organics for reconstructing the responses of Native American populations to periods of intense drought. Findings from this research will enhance capabilities to model future megadroughts and persistent drought conditions.