Collaborative Research: A 50,000-year continuous record of the Indian Summer Monsoon from Loktak Lake, NE India

最近巴基斯坦的洪水以及来自缅甸和孟加拉国的气候移民例证了印度夏季风（ISM）强度的突然和巨大变化所造成的巨大社会后果。然而，我们并不完全了解在不同时间尺度（1000 ~ 100年）上不同因子对ISM渐变和突变的相对重要性。该项目将从一个沉积物堆积率异常高且对ISM变化敏感的地点生成长（5万年）湖泊沉积物记录，从而实现对过去湖泊水位和环境变化的高分辨率重建。对古湖泊系统的分析将为当前和预估的ISM变化提供重要的视角，从而验证以下假设：1)温室气体浓度在加强ISM方面比太阳能更重要；2)大西洋深部环流的减弱削弱了ISM； 3)太平洋和印度洋环流模式的频率和强度的变化导致孟加拉湾变暖，削弱了ISM。该项目的预期智力成果是提高对ISM对未来温室气体增加和相关全球变化的反应的理解。与靠近湖泊的曼尼普尔大学建立的伙伴关系将通过互惠的公众和利益相关者参与研讨会得到加强，并提高社区对项目成果的理解。洛克塔克湖面积大、面积浅，沉降速度快、连续，约6 cm/世纪，是亚世纪尺度区域降水-蒸发平衡变化的敏感记录者。洛克塔克湖的初步工作表明，湖泊水位在几个全球气候状态（温室气体浓度和夏季日照）中发生了大幅度的变化，并伴随有机和无机地球化学信号的变化。为了验证上述假设，将收集沉积物岩心并进行沉积学、地球化学（ICP-OES）、扫描x射线荧光（XRF）、长链和中链蜡的氢（δ2H）和碳（δ13C）同位素、有机质的碳和氮（δ15N）同位素、孢粉学、硅藻、水生活动和陆地生态系统变化的生物标志物的分析。代用解释将通过分析支持同位素的气候模式模拟来辅助。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。

Recent floods in Pakistan and climate migrants from Myanmar and Bangladesh exemplify the enormous societal consequences of abrupt and large magnitude change in the strength of the Indian Summer Monsoon (ISM). However, we do not fully understand the relative importance of different factors on gradual and abrupt ISM change at different timescales (1000s to 100 years). This project will generate long (50,000 years) lake sediment records from a site that has an unusually high rate of sediment accumulation and is sensitive to changes in the ISM, enabling high resolution reconstructions of past lake levels and environmental changes. This analysis of the paleo lake system will provide important perspective on present and projected changes in the ISM, allowing the following hypotheses to be tested: 1) greenhouse gas concentrations are more important in strengthening the ISM than solar energy, 2) a weakening of deep Atlantic Ocean circulation weakens the ISM, and 3) changes in the frequency and intensity of Pacific and Indian Ocean circulation patterns cause warming in the Bay of Bengal, weakening the ISM. The expected intellectual outcome of this project is an improved understanding of the ISM response to future increased greenhouse gases and associated global changes. Established partnerships with Manipur University, located proximal to the lake, will be strengthened through reciprocal public and stakeholder engagement workshops and enhance community understanding of the project findings.Loktak Lake is large, shallow, and has a fast, continuous sedimentation rate of ~6 cm/century, making it a sensitive recorder of regional changes in precipitation-evaporation balance at sub-century scales. Preliminary work from Loktak Lake indicates large magnitude lake level variations across several global climate states (greenhouse gas concentrations and summer insolation) with attendant changes in organic and inorganic geochemical signals. To test the aforementioned hypotheses, sediment cores will be collected and analyzed for sedimentology, geochemistry (ICP-OES), scanning X-ray fluorescence (XRF), hydrogen (δ2H) and carbon (δ13C) isotopes of long- and medium-chain waxes, carbon and nitrogen (δ15N) isotopes of organic matter, palynology, diatoms, and biomarkers for aquatic activity and terrestrial ecosystem changes. Proxy interpretation will be aided by analysis of isotope-enabled climate model simulations.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.