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

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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.