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

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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.