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

最近发生在巴基斯坦的洪水以及来自缅甸和孟加拉国的气候移民证明了印度夏季风(ISM)强度的突然和大规模变化带来的巨大社会后果。然而，我们还没有完全了解不同因素在不同时间尺度(1000到100年)对ISM渐变和突变的相对重要性。该项目将从一个沉积速率异常高、对ISM变化敏感的地点生成长达50,000年的湖泊沉积物记录，从而能够高分辨率地重建过去的湖泊水位和环境变化。对古湖泊系统的分析将为现在和预测的ISM变化提供重要的视角，从而能够检验以下假设：1)温室气体浓度在加强ISM方面比太阳能更重要，2)大西洋深层环流的减弱削弱了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更好地理解国际安全管理对未来温室气体增加和相关全球变化的反应。与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，并增进社区对项目成果的了解。洛克塔克湖面积大、浅，沉积速度快，连续沉积速度约为6厘米/世纪，使其成为一个敏感的记录器，在亚世纪尺度上记录降水-蒸发平衡的区域变化。来自Loktak湖的初步工作表明，全球几个气候状态(温室气体浓度和夏季日照)的湖泊水位变化幅度很大，伴随着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，并对其进行沉积学、地球化学、扫描X射线荧光、长链和中链蜡氢(δ2H)和碳(δ13C)同位素、有机质碳和氮(δ15N)同位素、孢粉学、硅藻以及水生活动和陆地生态系统变化的生物标志物的分析。代理解释将通过分析启用同位素的气候模型模拟来辅助。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。

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.