Collaborative Research: P2C2--Western United States Hydroclimate during the Last Interglacial: Developing Proxy Records and Using Model Intercomparison to Glimpse the Future

在美国西部干旱至半干旱地区，淡水供应对农业、能源和城市系统至关重要。量化过去温暖时期的水文气候变化，如末次间冰期（LIG；距今12.9万年至11.6万年），对于评估地球过去的气候模型模拟至关重要。该项目旨在重建美国西部在全球温度与21世纪低端预估相当的LIG期间降水的空间和季节分布变化。该项目将包括应用新方法（钙和三氧同位素）对沙斯塔湖洞穴（加利福尼亚州北部）和泰坦洞穴（怀俄明州北部）的石石柱，并将在东北大盆地（犹他州/爱达荷州的熊湖和犹他州/内华达州的邦纳维尔盆地）和西南大盆地/莫哈韦沙漠（曼尼克斯湖和欧文斯湖，加利福尼亚州）的四个湖泊站点提供新的时间数据和新测量（碳酸盐团块和三氧同位素）。该项目的预期结果是过去温度、降雨量、湿度来源和季节性变化的记录。这些新的过去气候记录将被整合到一个区域代理数据网络中，用于对末次间冰期（127 ka）的气候模式模拟进行基准测试。气候模拟界的古气候模式比对（PMIP4）和耦合模式比对项目（CMIP6）的工作包括将Tier 1 LIG （127ka）模拟作为CO2水平相似、轨道构型不同、地形不变和海平面较高的模式的基准目标。利用气候模型在区域尺度上验证水文气候相关变量需要可靠的年代和空间分布的古气候观测，以便将美国西部的LIG水循环置于地质和未来气候变化的背景下。然而，对这一区间的古气候的定量估计很少，这也给地质年代学带来了挑战，因为它超出了放射性碳年龄控制的极限。该项目旨在通过提供：1)洞穴记录的新观测，2)现有湖泊岩心的新U-Th定年，以及3)在洞穴和湖泊沉积物中应用新的温度、降水和湿度半定量代用物来提高我们对美国西部LIG气候的理解。通过从洞穴和湖泊沉积物中开发新的高分辨率代理时间序列，我们将为过去温暖期北美季风的行为提供新的见解，并重建第二次消冰期（Termination II）和海洋同位素阶段5 （MIS5）期间气候突变事件的水文气候响应。这项研究使用了以前由美国国家科学基金会和美国地质勘探局资助的大陆钻探项目恢复和存档的现有湖泊岩心，以及最近收集的已知跨越MIS5和LIG大部分地区的洞穴主题。潜在的更广泛的影响包括量化过去温暖期的区域水文气候变化，以及为末次间冰期的气候模式模拟设定基准。其他更广泛的影响包括将项目研究成果转化为研讨会（从古气候到政策），该研讨会召集了水资源管理者、政府机构（如美国地质勘测局）、气候和天气风险评估和预测公司以及来自美国各地的早期职业古气候研究人员。该研讨会将强调陆地过去气候记录(湖泊沉积物、树木年轮、洞穴主题)可以提供水文气候数据，超出决策者评估气候变率和干旱和洪水等极端事件所需的仪器记录。这组科学家将编写一份白皮书、水资源管理者的政策简报，并在一个科学会议（美国地球物理联合会）的教育和推广会议上发表一份报告。该项目将为两名研究生和一名博士后提供科学培训、指导和专业发展。通过联合实地考察和合作，这些学生和博士后将有机会在气候档案、新型代理系统、地质年代学和模型代理比较方面发展跨学科的专业知识。此外，研究人员将招募本科生完成与该项目相关的暑期实习。本科学生将通过以下方式招募：(1)范德比尔特大学和田纳西州立大学（一所历史悠久的黑人大学）之间的Earth Horizons项目和合作伙伴关系；(2)由NSF-REU-EPSCOR资助的布朗大学领导联盟项目。本科学生将被鼓励在区域、国家和国际科学会议（如AGU、GSA）上进行研究报告。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Freshwater availability is critical to agricultural, energy and urban systems in the arid to semi-arid western U.S. Quantifying hydroclimate change during past warm periods, such as the Last Interglacial (LIG; ~129,000-116,000 years before present), is essential for evaluating climate model simulations of Earth’s past. This project aims to reconstruct variations in the spatial and seasonal distribution of precipitation in the western U.S. during the LIG during which global temperature are comparable to low-end 21st century projections. The project will include the application of novel methods (calcium and triple oxygen isotopes) on stalagmites from Lake Shasta Caverns (northern California) and Titan Cave (northern Wyoming), and will provide new chronological data and novel measurements (carbonate clumped and triple oxygen isotopes) at four lake sites in the northeast Great Basin (Bear Lake, Utah/Idaho and Bonneville Basin, Utah/Nevada), and southwest Great Basin/Mojave Desert (Lake Manix and Owens Lake, California). The anticipated results of this project are past records of changes in temperature, rainfall amount and moisture source and seasonality. These new past climate records will be integrated into a regional proxy-data network used to benchmark climate model simulations of the Last Interglacial period (127 ka).The paleoclimate modeling intercomparison (PMIP4) and coupled model intercomparison project (CMIP6) efforts of the climate modeling community include Tier 1 LIG (127ka) simulations as a benchmarking target for models with similar CO2 levels, different orbital configuration, unchanged topography and higher sea level. The validation of hydroclimate-relevant variables at a regional scale using climate models requires robustly dated and spatially distributed paleoclimate observations in order to place the LIG water cycle in the western U.S. in the context of geologic and future climate change. Yet, few quantitative estimates of paleoclimate exist for this interval, which offers geochronologic challenges too as it is beyond the limit of radiocarbon age control. This project seeks to improve our understanding of LIG climate in the western U.S. by providing: 1) new observations from speleothem records, 2) new U-Th dating of existing lake cores, and 3) the application of novel semi-quantitative proxies for temperature, precipitation and humidity to speleothems and lake sediments. Through the development of new high-resolution proxy time-series from speleothems and lake sediments, we will provide new insight into the behavior of the North American Monsoon during a past warm period and reconstruct hydroclimatic response to abrupt climatic events during the penultimate deglaciation (Termination II) and Marine Isotope Stage 5 (MIS5). The research uses existing lake cores recovered and archived by previous NSF- and USGS-funded continental drilling projects, and recently collected speleothems known to span much of MIS5 and the LIG.The potential Broader Impacts include quantifying regional hydroclimate changes during past warm periods and benchmarking of climate model simulations for the last interglacial. Other Broader Impacts include translating the project research outcomes via a workshop (paleo to policy) convening water resource managers, government agencies (e.g., USGS), climate and weather risk assessment and projection companies and early career paleoclimate researchers from across the U.S. This workshop will emphasize on the information that terrestrial past climate records (lake sediments, tree rings, speleothems) can provide in terms of hydroclimate data beyond the instrumental records needed by policy makers to assess climate variability and extreme events such as drought and floods. The researchers will produce a white paper, policy briefs for water resource managers and a presentation at an education and outreach session at a scientific meeting (American Geophysical Union). The project will provide scientific training, mentorship and professional development for two graduate students and one postdoctoral researcher. Through joint field trips and collaborations, these students and postdoc will have opportunities to develop interdisciplinary expertise in climate archives, novel proxy systems, geochronology and model-proxy comparison. In addition, the researchers will recruit undergraduate students to complete summer internships related to the project. The undergraduate students will be recruited through (1) the Earth Horizons program and partnership between Vanderbilt University and Tennessee State University, a Historically Black University (HBCU); (2) the Leadership Alliance program at Brown University funded through NSF-REU-EPSCOR. The undergraduate students will be encouraged to develop their research into presentations at regional, national and international scientific meetings (e.g., AGU, GSA).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.