P2C2: Dry or Wet in East Asia During Heinrich Events? New Perspectives from Multiproxy Cave Records and Coupled Model Simulations

该项目旨在利用长江中游中国中东部的一套洞穴，将大尺度亚洲季风环流与上一次冰川周期的北大西洋冷却事件(即海因里希事件)期间的局地水文气候变率区分开来。该项目为威廉·帕特森大学(William Paterson University)的博士后研究员和丰富的本科生研究经验提供支持。威廉·帕特森大学是一所以本科教学为主的大学，学生群体多样化(由美国农业部指定的西班牙裔服务机构)，包括许多第一代上大学的学生。耦合的大气环流模型(CGCM)模拟表明，东亚可能会随着气候变暖而变得更加潮湿，但这些预测仍然存在很大的不确定性，这在很大程度上是由于模型模拟之间缺乏一致。减少这些模型偏差是现代气候科学更具针对性和挑战性的方面之一，以此来提供战略，以满足未来在食物、水、能源和生物多样性方面的需求。目前，对于中国中部的当地降水变化对亚洲季风的区域扰动有多敏感，缺乏一致的理解，因为对东亚中部季风的了解主要依赖于氧同位素记录，根据新的研究，氧同位素记录不一定反映当地的水气候。因此，本项目旨在通过解决以下问题来建立中国中东部局地降水变率的更完整的图景：(1)是否可以使用微量元素(镁、锶、钡)等洞穴喷发替代物来解除东亚区域大气环流与当地水文的卷积。如果是这样的话，(2)这些替代指标给我们提供了什么关于中国中东部当地水文气候的信息，以及解释这种替代推断变化的机制是什么。(3)代理重建结果与耦合大气环流模式(CGCM)的古模拟结果吻合程度如何。该项目的主要目标包括：(1)利用来自长江中游四个洞穴的一套测年准确的洞穴洞穴，重建海因里希事件1-6期间中国中东部的当地水文；(2)利用共同体地球系统模型CGCM模拟，描述在代理中观测到的水文模式的机制；为了解决上述目标，研究人员旨在检验以下假设：(1)尽管印度季风减弱，但中国中心在海因里希事件期间更潮湿，从而挑战了东亚季风在北大西洋(NA)冷却期间变弱的长期范式；(2)中国中东部的降雨量最好地可以用季风演变的季节性滞后来解释。在NA降温期间较晚出现梅雨到盛夏将导致盛夏阶段较短，使中国中南部潮湿，以至北部干旱条件为代价；(3)Heinrich事件期间撒哈拉/萨赫勒地区植被死亡和随后更高的沙尘排放，影响了ITCZ的位置，从而放大了假说(2)中概述的响应；(4)洞穴旋体假替代时间序列(由PSM生成)与东亚的测量记录进行比较，将有助于确定洞穴旋体三角洲18-氧的主要控制因素。它还可能允许对模型技能进行更可靠的评估，并帮助更好地评估突发气候变化事件中的任何模型代理偏差。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 disentangle large-scale Asian monsoon circulation from local hydroclimate variability during North Atlantic cooling events of the last glacial cycle (i.e., Heinrich events) using a suite of speleothems from the middle reaches of the Yangtze River in central-eastern China. The project provides support for a postdoctoral research fellow and extensive undergraduate research experience for students at William Paterson University as a primarily undergraduate teaching university with a diverse student body (Hispanic Serving Institution designated by USDOE), including many first generation to attend college.Coupled General Circulation Model (CGCM) simulations suggest that East Asia is likely to get wetter with climatic warming, yet there is still much uncertainty in these projections due in large part to the lack of agreement among model simulations. Reducing these model biases is one of the more pertinent and challenging aspects of modern climate science as a means to provide strategies to meet the future needs in food, water, energy, and biological diversity.Currently, there is a lack a consistent understanding of precisely how sensitive local rainfall variability in central China is to regional perturbations in the Asian monsoon because knowledge of the monsoon in central East Asia principally relies upon oxygen-isotope records which, according to new research, may not necessarily reflect local hydroclimate. Therefore, this project aims to build a more complete picture of local rainfall variability in central-eastern China by addressing the following questions: (1) Can speleothem proxies, such as trace elements (Magnesium, Strontium, Barium) be used to deconvolve regional atmospheric circulation from local hydrology in East Asia. If so, (2) what do these alterative proxies inform us about local hydroclimate in central-eastern China and what are the mechanisms to explain the proxy-inferred changes. (3) How well do the proxy reconstructions match the paleo-simulations from coupled general circulation models (CGCMs). The main objectives of the project include: (1) reconstruct local hydrology in central-eastern China during Heinrich events 1-6 utilizing speleothem trace elements and isotope ratios from a suite of well-dated speleothems from four caves located in the middle reaches of the Yangtze River; (2) delineate the mechanisms for the hydrologic patterns observed in the proxies using the Community Earth System Model CGCM simulations; and (3) conduct model-proxy syntheses in space and time by directly comparing speleothem pseudoproxy time series--constructed using climate model output coupled with Proxy System Models (PSMs)--with measured isotope profiles.To address the above objectives the researchers aim to test the following hypotheses: (1) Despite a weakened Indian monsoon, central China was wetter during Heinrich events thereby challenging the longstanding paradigm that the East Asian Monsoon (EASM) became weaker during North Atlantic (NA) cooling; (2) The higher rainfall in central-eastern China can best be explained by a seasonally-lagged onset of the mei-yu stage of monsoon evolution. A later onset of mei-yu to midsummer during NA cooling would have resulted in a shorter midsummer stage, leaving south-central China wet at the expense of dry conditions to the north; (3) Vegetation demise and subsequent higher dust emissions from the Sahara/Sahel regions during Heinrich events, affected the position of the ITCZ and thus amplified the response outlined in hypothesis (2); (4) Comparison of speleothem pseudoproxy time series (generated from PSMs) with measured records from East Asia will help to identify the dominant controls on speleothem delta 18-Oxygen. It may also allow a more robust assessment of model skill and help to better evaluate any model-proxy biases through abrupt climate change events.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.