P2C2: Past Extension of the North American Monsoon System (NAMS) into the Great Basin Reconstructed from Cell-to-Ecosystem Dendrochronology

北美大流域地区供水的长期年度至年代际变化还没有得到很好的了解。根据长达一个世纪的树木年轮记录，对过去气候变化的更准确描述，可以改进对未来变暖情景下的供水和地下水补给的预测。晚材宽度和假年轮年表与夏季降水有关，因此可以提供几个世纪以来暖季湿度的记录。该项目将利用独特的潜力重建北美季风系统(NAMS)的过去可变性，北美季风系统是暖季水分输送到大盆地南部的关键机制之一。将使用新的环宽年代学结合对内华达州南部针叶树物种的解剖和稳定同位素分析来重建NAMS的北部延伸。细胞水平的树状气候学是一个不断发展的研究领域，对木材形成的详细研究将补充NAMS区域的现有项目。该项目将有助于澄清夏季环流模式与厄尔尼诺南方涛动(ENSO)之间的联系，以及在长期干旱期间季节性湿度制度的作用。预期的研究结果将完善对美国西南部、大盆地/莫哈韦沙漠和四角地区未来水资源可获得性差异的预测。这项研究的动机是迫切需要量化木材形成的环境控制和树枝气候代用品背后的机制。该项目由雷诺的内华达大学和魁北克大学合作，建立在最近建立的横跨大盆地两个山脉的最先进的仪器横断面上。具体的研究目标是：(1)从机械上确定位于北冰洋西北部的黄松种群早材/晚材和假年轮形成的气候驱动因素；(2)重建过去几个世纪以来北冰洋边界地区夏季风对树木生长的影响，作为北冰洋扩展及其年际变化的一个指标。实地采样将在绵羊范围内进行，在那里，“内华达州气候-生态水文评估网络”(NVERCAN)提供沿山谷到山顶样带的大气、土壤和植被变量的测量。通过将木材解剖测量与树木年轮中氧和碳的稳定同位素分析相结合，将实现对黄松树轮记录的详细校准。还将从土壤水、大气水蒸气和降水中测量稳定的氧同位素，以更好地校准树轮同位素测量。资金用于培训一名博士后研究员和一名研究生。研究成果将被整合到内华达大学里诺分校的研究生和本科生课程中，该校的学生数量和多样性不断增加。

Long-term annual to decadal variability of water supply in the Great Basin region of North America is not well understood. Predictions of water supply and groundwater recharge under future warming scenarios can be improved by providing more accurate representations of past climatic changes derived from multi-century-long tree-ring records. Latewood-width and false-ring chronologies have been linked to summertime precipitation, and therefore can provide a record of warm-season moisture over several centuries. This project will exploit a unique potential for reconstructing past variability of the North American Monsoon System (NAMS), one of the key mechanisms for warm-season moisture delivery to the southern Great Basin. New ring-width chronologies combined with anatomical and stable isotopic analyses of conifer species in southern Nevada will be used to reconstruct the northern extension of the NAMS. Cellular-level dendroclimatology is an evolving area of research, and detailed studies of wood formation will complement existing projects in the NAMS region. The project will help clarify the connection between summertime circulation patterns and the El Niño Southern Oscillation (ENSO), as well as the contribution of seasonal moisture regimes during prolonged drought episodes. Expected research results will refine predictions of future differences in water availability between the American Southwest, the Great Basin/Mojave Deserts, and the Four-Corners Region.This research is motivated by the pressing need to quantify the environmental controls of wood formation and the mechanisms underlying dendroclimatic proxies. The project, a collaboration between the University of Nevada, Reno, and the Université du Québec à Chicoutimi, builds on state-of-the-art instrumental transects recently established across two mountain ranges in the Great Basin. Specific research goals are: (1) to mechanistically determine the climatic drivers for earlywood/latewood and false-ring formation in populations of ponderosa pine located at the northwestern limit of the NAMS; and (2) to reconstruct summer monsoon influences on tree growth in this NAMS boundary region as an index of NAMS extension, and its interannual variability, over the past few centuries. Field sampling will take place in the Sheep Range, where the "Nevada Climate-ecohydrological Assessment Network" (NevCAN) provides measurements of atmospheric, pedologic, and vegetational variables along a valley-to-mountain-top transect. Detailed calibration of ponderosa pine tree-ring records will be achieved by combining wood anatomical measurements with stable isotopic analyses of oxygen and carbon from tree rings. Stable oxygen isotopes will also be measured from soil water, atmospheric water vapor, and precipitation to better calibrate the tree ring isotope measurements. Funding supports training of a postdoctoral researcher and a graduate student. The research results will be integrated into graduate and undergraduate level courses at the University of Nevada, Reno, a campus whose student population is constantly increasing in number and diversity.