In this study, we reconstruct high-resolution vegetation and climate variability over the past 6100 years using a multi-proxy approach (i.e., pollen, stable organic carbon isotopes (δ13C), and environmental magnetic parameters) from an alpine peat sequence of the Dayara meadow, located at ∼3430 m altitude in the upper Bhagirathi basin of the Central Higher Himalaya. The chronology of the studied lake-peat sequence, constrained by four radiocarbon (14C) ages, indicates that peat development in the region commenced around 6100 cal yr BP. Pollen combined with δ13C results reveal a significantly warmer and wetter climate between ∼6100 and 5300 cal yr BP, corresponding to the late phase of the Holocene Climate Optimum (HCO) in the upper Bhagirathi basin. Around ∼5300 cal yr BP, an abrupt climate shift occurred, which led to a prolonged dry spell between ∼4800 and 3400 cal yr BP. This dry spell was characterized by a decline in arboreal tree taxa, particularly Quercus, Alnus, and Betula, the complete disappearance of Juglans, and a notable increase in drought-tolerant herbs, such as Chenopodiaceae-Amaranthaceae and Ephedra. This prolonged cold-dry phase is correlated with a weakening of the Indian summer monsoon (ISM) intensity, as previously recorded in the core summer monsoon zone, in response to regional warming of the Indo-Pacific Warm Pool. Subsequent increase in arboreal tree taxa and moisture-loving pollen taxa, along with a reduced representation of drought-tolerant herbs, suggests a warm and wet climate between ∼3400 and 1600 cal yr BP (Roman Warm Period ∼2200 to 1600 cal yr BP), ∼1000 to 500 (Medieval Climate Anomaly), and from ∼130 cal yr BP to the Present (Current Warm Period). In contrast, the intermittent periods between ∼1600 and 1000 (Dark Ages Cold Period) and ∼ 500 to 130 cal yr BP (Little Ice Age, LIA) were dominated by cold and drought-tolerant desert steppe vegetation. The highest concentration of pollen and fern, especially from sub-alpine tree taxa, between ∼6100 and 5300 cal yr BP, suggests an upward shift of the tree line beyond its modern-day position, reflecting optimal climatic conditions. Conversely, during the LIA, the tree line descended to its lowest elevation in the past ∼6100 years. The strengthened ISM episodes during the middle to late Holocene likely provided the moisture necessary for the glacier advances in the upper Bhagirathi catchment.
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