EAGER: 1500 Years of Indian Summer Monsoon Variabilty Reconstructed from High-Resolution Tibetan Lake Sediments

这项EAGER拨款利用青藏高原的湖泊沉积物，研究了过去1500年来印度夏季风的动态。具体来说，他们研究了辐射变率在以下目标事件中是否以及如何影响季风：中世纪气候异常（公元900年至1300年）、小冰期（公元1400年至1800年）和当前的温暖期。本研究以青藏高原东南缘的宁青唐吉拉山小高山湖泊（直径~400 m）为研究对象。这个地区是理想的，因为季风水汽在进入青藏高原之前从孟加拉湾经过年青坦吉拉山输送。因此，该地区湖泊的水文平衡应该对季风强度的变化高度敏感。该项目提供了有关季风变异性的宝贵信息，可用于探索该系统如何以及为何随时间变化。这项研究的结果将有助于了解维持敏感生态系统和超过10亿人口的季风如何对温室气体（即二氧化碳）辐射强迫的人为增加所驱动的未来变暖趋势作出反应。分析工作将集中在最高质量的沉积物上，并在可能的情况下使用自生或生物成因CaCO3测量的氧同位素（d18O）重建季风降雨，或者如果基岩地质排除了湖泊沉积物中CaCO3的保存，则使用侵蚀的地球化学指标和沉积物通量计算。研究结果将与青藏高原和喜马拉雅地区的冰芯和树木年轮记录以及中国西部的洞穴记录进行综合，以便从区域角度发展季风变化，并评估其与东亚季风变化在目标事件中的比较。尽管有重大发现的潜力，但该研究面临许多基于现场和分析的挑战，使其具有高风险。最重要的是，在该地区建立足够时间分辨率的年龄模型是出了名的困难，而这些模型需要对季风变率做出详细的说明。然而，主要研究人员在南美洲热带安第斯山脉高海拔地区的类似环境中研究类似湖泊系统的经验相当丰富。通过这项工作，他们成功地开发了沉积物测年技术。本研究直接解决了P2C2的研究目标，即了解季风系统对气候变化的响应，并确定这些系统对辐射强迫突变的敏感性，特别是在过去的暖期。这项研究提供了次十年分辨率的季风变率记录，可以详细分析过去1500年季风系统如何响应辐射强迫的变化，这将改善季风变率对变暖趋势的响应预测。拟议活动的更广泛影响这项研究将使依赖季风为生的10多亿人受益。有关季风动力学及其与辐射强迫关系的信息，将有助于预测和准备该系统由于人为温室气体增加而导致的全球气温上升的未来变率。随着对季风变异性认识的提高，可以制定有效的水资源管理战略，以应对未来潜在的水资源短缺和/或季风变异性的增加。

This EAGER grant investigates Indian summer monsoon dynamics during the last 1500 years using lake sediments from the Tibetan Plateau. Specifically, they examine if and how radiative variability impacted the monsoon during the following target events: the Medieval Climate Anomaly (AD 900 to 1300), Little Ice Age (AD 1400 to 1800), and current warm period. This research targets small alpine (~400 m diameter) lakes in the Nyainqentanglha Mountains, which are located at the southeastern edge of the Tibetan Plateau. This region is ideal because monsoon moisture is transported over the Nyainqentanglha Mountains from the Bay of Bengal before entering the Tibetan Plateau. As such, the hydrologic balance of lakes in this region should be highly sensitive to changes in the strength of the monsoon. This project provides valuable information about monsoon variability that can be used to explore how and why this system changes through time. The results of this study will aid efforts to understand how the monsoon, which sustains sensitive ecosystems and over 1 billion people, may respond to future warming trends driven by anthropogenic increases in radiative forcing from greenhouse gases (i.e. CO2).The analytical efforts will be focused on the highest quality sediment, and reconstructs monsoon rainfall using oxygen isotopes (d18O) measured on authigenic or biogenic CaCO3 where possible, or geochemical indicators of erosion and sediment flux calculations if the bedrock geology precludes the preservation of CaCO3 in lake sediments. The results will be synthesized with ice core and tree ring records from the Tibetan Plateau and Himalaya and speleothem records from western China in order to a develop regional perspective monsoon variability and assess how it compares with East Asian monsoon variability during the targeted events. Despite the potential for significant discovery, this research faces many field-based and analytical challenges that make it high risk. Most importantly, age models of sufficient temporal resolution that are needed to make detailed statements about monsoon variability are notoriously difficult in this region. However, the principal investigators have considerable experience working with similar lake systems in comparable environments in the high Andes of tropical South America. From this work, they have successfully developed techniques sediment dating. Intellectual Merit of the Proposed ActivityThis research directly addresses the P2C2 research objectives to understand the response of monsoon systems to climate change and to determine the sensitivity of these systems to abrupt changes in radiative forcing, particularly during past warm intervals. This research provides sub-decadally resolved records of monsoon variability that allow for a detailed analysis of how this monsoon system responded to changes in radiative forcing during the past 1500 years, which will improve forecasts of monsoon variability in response to warming trends.Broader Impacts of the Proposed ActivityThis research will benefit the more than 1 billion people who depend on the monsoon for their livelihood. The information about monsoon dynamics and their relationship with radiative forcing will be beneficial for forecasting and preparing for future variability in this system as a result of rising global temperatures from anthropogenic increases in greenhouse gases. With an improved understanding of monsoon variability, effective water management strategies can be developed to cope with potential future water shortages and/or increased monsoonal variability.