Toward a Multi-Proxy Database of Pleistocene Water Isotope Records; Differentiating Precipitation Isotopic Composition from Precipitation Amount in the Asian Monsoon System

季风降雨对生活在南亚和东亚的数十亿人来说至关重要。因此，重要的是要了解季风的可变性以及季风随时间变化的方式和原因。该项目将分析印度洋大陆架的一个岩芯，以记录过去64万年的季风。这些记录将包括风、降雨量和河流径流的变化。这些记录将与已知的温度变化、温室气体和其他潜在的季风强迫机制的记录进行比较。这种比较将有助于理解气候对季风变化的影响。这些记录还将为用于预测未来气候变化的数值气候模型提供现实世界的测试。该项目将资助一名女研究生。它还将为从地球科学中代表性较低的群体招收的本科生提供研究经验。两个参数是理解气候变化的关键-温度和降雨量。温度重建现在是定量的，通过一些独立的方法完成，并直接与气候模拟相比较。即使在最先进的气候模型中，降雨量也是一个很难模拟的参数，因为，例如，大多数降雨量发生的空间尺度远远小于模型现在和可预见的未来所能容纳的范围。重建过去的降雨量同样困难，而且在这一点上，是定性的。这项研究是一个较长期目标的一部分，该目标侧重于解决重建降雨的一个关键缺陷，即区分降雨同位素组成的变化与通常用于重建降雨的水同位素代用品(即洞穴δ18O、海水δ18O和叶蜡δ2Η)的降雨量的能力。降雨的同位素组成和降雨量都很重要。前者产生有关水汽从源头到汇(大规模环流)的源区、输送路径和动态的信息。后者提供了关于地方和区域范围内降雨量变化的信息。这些代理的有用性取决于知道重建中表达了什么规模。这项研究建立在过去工作的基础上，这里的重点是叶蜡δ2Η。来自安达曼海U1448站南亚夏季风的叶蜡δ2H的64万年记录将以名义上2000年的样本分辨率重建。支持记录、海底δ18O(年表)和叶蜡δ13C(植被结构)将以相同的分辨率生成。最终的记录将使用时间序列分析技术进行定量评估，以确定相对于南亚和东亚季风系统的现有海水δ18O、洞穴δ18O和叶蜡δ2Η记录，对日照、冰量、海平面和温室气体的敏感性及其时间(相位)。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。

Monsoon rainfall is critical to billions of people living within South Asia and East Asia. It is thus important to understand monsoon variability and how and why monsoons may change over time. This project will analyze a core from the Indian Ocean continental shelf to produce records of the monsoons over the last 640,000 years. The records will include changes in winds, rainfall, and river runoff. These records will be compared with records of known changes in temperature, greenhouse gases, and other potential monsoon forcing mechanisms. That comparison will help to understand the influence of climate on monsoon variability. Those records will also provide real-world tests for the numerical climate models used to predict future climate change. The project will support a woman graduate student. It also will provide research experiences for undergraduates recruited from groups typically underrepresented in the earth sciences.Two parameters are key to understanding climate change - temperature and rainfall. Temperature reconstructions are now quantitative, accomplished by a number of independent means, and directly comparable to climate simulations. Rainfall is a difficult parameter to simulate even in the most advanced climate models because, for example, most rainfall happens at spatial scales far smaller than models can accommodate now and for the foreseeable future. Reconstructing rainfall in the past is similarly difficult and, at this point, qualitative. This research is part of a longer-term objective that focuses on resolving a key shortcoming in reconstructing rainfall, the capacity to differentiate changes in the isotopic composition of rainfall from rainfall amount in water isotope proxies commonly used to reconstruct rainfall (i.e. speleothem δ18O, sea water δ18O, and leaf wax δ2Η). Both the isotopic composition of the rainfall and the rainfall amount are important. The former yields information on source areas, transport paths, and dynamics taking place as moisture travels from source to sink (large-scale circulation). The latter provides information on changes in rainfall amount at the local to regional scale. Usefulness of these proxies depends on knowing what scale is expressed in the reconstruction. This research builds on past work, focusing here on leaf wax δ2Η. A 640,000-year record of leaf wax δ2H from the South Asian summer monsoon at Andaman Sea Site U1448 will be reconstructed at a nominal 2,000-year sample resolution. Supporting records, benthic δ18O (chronology), and leaf wax δ13C (vegetation structure) will be generated at the same resolution. The resulting records will be quantitatively assessed using time-series analytical techniques to determine the sensitivity to insolation, ice volume, sea level, and greenhouse gases as well as their timing (phase) relative to existing seawater δ18O, speleothem δ18O and leaf wax δ2Η records from the South- and East-Asian monsoon systems.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.