To date, there is a gap in the data about the state and mass balance of glaciers in the climate-sensitive subtropical regions during the Little Ice Age (LIA). Here, based on an unprecedented tree-ring sampling coverage, we present the longest reconstructed mass balance record for the Western Himalayan glaciers, dating to 1615. Our results confirm that the later phase of LIA was substantially briefer and weaker in the Himalaya than in the Arctic and subarctic regions. Furthermore, analysis of the time-series of the mass-balance against other time-series shows clear evidence of the existence of (i) a significant glacial decay and a significantly weaker magnitude of glaciation during the latter half of the LIA; (ii) a weak regional mass balance dependence on either the El Niño-Southern Oscillation (ENSO) or the Total Solar Irradiance (TSI) taken in isolation, but a considerable combined influence of both of them during the LIA; and (iii) in addition to anthropogenic climate change, the strong effect from the increased yearly concurrence of extremely high TSI with El Niño over the past five decades, resulting in severe glacial mass loss. The generated mass balance time-series can serve as a source of reliable reconstructed data to the scientific community.

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We reviewed the available climate records for the past 2 millennia based on the analyzed sediment and speleothem archives from different regions of South Asia. Speleothem records from the core-monsoon regions of the Indian sub-continent have revealed the Little Ice Age (LIA) as a climatically dry phase, whereas the same from the western and central Himalaya recorded LIA as wet. Moreover, the sediment-derived vegetation proxy records [pollen-spores and stable organic carbon isotope (δ13Corg)] from the western Himalaya also reported LIA as a dry phase. Heterogeneous results by different proxies during LIA enhanced our interest to understand the response of the proxies toward the primary precipitation sources, Indian summer monsoon (ISM) and winter westerly disturbances (WDs), over the Himalaya. We emphasize that in the Himalayan region, the vegetation predominantly responds to the ISM dynamics, whereas speleothem also captures the WD effect.

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This study highlights the modern pollen-vegetation relationships along an altitudinal gradient covering the lower temperate (~2,000 masl) to alpine vegetation zones (~3,800 masl) in the Bhagirathi valley, western Himalaya. The pollen dispersal dataset compared with the altitudinal vegetation distribution in the valley shows incoherency between the arboreal taxa and their respective pollen proportions. Discriminant analysis (DA) revealed the role of diurnal valley winds in pollen mixing between altitudinal vegetation zones. Pollen of arboreal taxa are transported profusely from the lower temperate vegetation zones to alpine zone. Whereas pollen of non-arboreal taxa, dominantly growing in the sub-alpine and alpine meadows, remain close to their source and represent the prevailing localized environmental conditions in the valley. Study revealed Pinus and Quercus as dominant arboreal pollen taxa throughout the altitudinal transect with a distinct transition in their representation between ~2,500 and 2,600 masl. High percentage of Pinus (Quercus) pollen below (above) this transition zone nearly corresponds with the present distribution of conifer (pine-oak) and broadleaved (oak-pine) forests in the valley and can be taken as a marker zone to infer palaeoecological changes. The sub-alpine and alpine krummholz, Juniperus and Ericaceae are found autochthonous in their pollen distribution that can serve as good indicators of relative tree-line and glacier dynamics in past. This pollen-vegetation relationship dataset could be an analogue for the interpretation of fossil pollen records in terms of extant vegetation in the mountain regions.