Collaborative Research: P2C2--Speleothem Constraints on Seasonal Hydroclimate Variability in Mainland Southeast Asia since the Late Pleistocene

本项目旨在利用从老挝和越南这两个具有非常独特的季节性降雨气候的国家之间跨越关键地理分界线的洞穴中获得的一套洞穴记录，描述过去~ 45,000年间亚洲夏季和冬季季风环流和东南亚大陆（MESA）当地水文气候的特征。这项工作的总体目标是探索夏季和冬季亚洲季风变率对变化的外部驱动因素（如日照）和内部气候变率的动态响应，这将有助于提高对脆弱地区大规模水文变率的理解。具体来说，研究人员将开发一套新的过去气候记录，利用多种环境示踪剂（碳和氧同位素，微量元素，如镁/钙，放射性碳），在精确定年的洞穴中，至少跨越过去~ 45000年。此外，一项详细的洞穴监测计划将有助于解释从洞穴中获得的数据。这些结果将与过去气候变率的其他区域和全球记录以及最先进的气候模式模拟相结合，以诊断MESA地区在次年代际到千年时间尺度上驱动水文气候变率的主要机制。这项研究将涉及以下具体目标：(1)确定MSEA水文气候夏季和秋季/冬季对轨道强迫和千年强迫的响应；(2)确定MSEA水文气候对年代际至多年代际海温变率的响应；(3)将现有资料与其他资料综合起来，阐明MSEA水文气候的时空格局，并结合古气候模式分析。将使我们能够研究夏季和秋季/冬季季风变化的动力机制。来自三个研究地点的洞穴氧同位素记录将作为夏季季风强度的代表，由印度洋上游降雨的程度主导，微量元素测量将为每个洞穴地点过去当地水平衡的变化提供有力的证据，老挝地点记录夏季降雨量，越南地点记录秋冬降雨量。潜在的更广泛的影响包括，通过从洞穴中产生定量的、年代准确的几千年气候记录，更好地了解脆弱地区的季风动力学和相关水文气候。该项目将为三所大学（包括两所少数民族服务机构）的几名本科生（包括暑期研究经历）和一名研究生（博士）以及一名博士后研究员提供科学培训、指导和专业发展。此外，该项目将支持一名早期职业科学家。该项目的结果将成为美国和研究地区（老挝/越南）正在进行的和新开发的公共宣传活动的一部分，涉及学生和博士后。该项目还将促进包括与当地社区在内的国际和跨学科合作。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。

This project aims to characterize the Asian summer and winter monsoon circulation and local hydroclimate across Mainland Southeast Asia (MESA) during the last ~45 thousand years using a suite of speleothem records from caves that extend across a critical geographical divide between Laos and Vietnam, two countries with very distinct seasonal rainfall climatologies. The overarching goal of this work is to explore the dynamic response of summer and winter Asian monsoon variability to changing external drivers, such as insolation, and internal climate variability which will contribute to improved understanding of large-scale hydrological variability in a vulnerable region. Specifically, the researchers will develop a new set of past climate records utilizing multiple environmental tracers (Carbon and Oxygen isotopes, trace elements such as Magnesium/Calcium, radiocarbon) in precisely dated speleothems spanning at least the last ~45 thousand years. Additionally, a detailed cave monitoring program will aid the interpretation of data obtained from the speleothems. The results will be integrated with other regional and global records of past climate variability and state-of-the-art climate model simulations to diagnose the dominant mechanisms driving hydroclimate variability on sub-decadal to millennial timescales in the MESA region. The research will address the following specific objectives: (1) Determine the summer and fall/winter response of MSEA hydroclimate to orbital and millennial-scale forcing, (2) Determine the response of MSEA hydroclimate to decadal to multidecadal scale sea surface temperature variability, and (3) Synthesize data with other available records to elucidate the spatiotemporal patterns of MSEA hydroclimate, which, combined with paleoclimate model analyses, will allow us investigation of the dynamical mechanisms underlying summer and fall/winter monsoon variability. Speleothem oxygen isotope records from three study sites will serve as a proxy for summer monsoon intensity, dominated by the degree of upstream rainout over the Indian Ocean and trace element measurements will provide robust evidence for past variations in local water balance at each cave site, with Laos sites recording summer rainfall and Vietnam sites recording fall/winter rainfall.The potential Broader Impacts include a better understanding of the monsoon dynamics and related hydroclimate in a vulnerable region by generating quantitative and well-dated multi-millennial climate records from speleothems. The project will provide scientific training, mentorship and professional development for several undergraduate (including summer research experience) and one graduate (Ph.D.) students, as well as one postdoctoral researcher at three universities including two minority serving institutions. Additionally, the project will support an early career scientist. The results of the project will be part of ongoing and newly developed public outreach activities both in The US and the study region (Laos/Vietnam) involving students and postdocs. The project will also foster international and transdisciplinary collaborations including with local communities.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.