Browsing by Author "Shekhar, Mayank"

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    Tree-Ring Isotopic Records Suggest Seasonal Importance of Moisture Dynamics Over Glacial Valleys of the Central Himalaya
    (Frontiers Media S.A., 2022) Singh, Nilendu; Shekhar, Mayank; Parida, Bikash Ranjan; Gupta, Anil K.; Sain, Kalachand; Rai, Santosh K.; Br�uning, Achim; Singh Charkaborty, Joyeeta; Sharma, Vikram; Kamal Tiwari, Reet; Chauhan, Pankaj; Montagnani, Leonardo
    Accelerated glacier mass loss is primarily attributed to greenhouse-induced global warming. Land�climate interactions have increasingly been recognized as an important forcing at the regional-local scale, but the related effects on the Himalayan glaciers are less explored and thought to be an important factor regulating spatial heterogeneity. The aim of the present study is a multi-decadal approximation of glacier�hydroclimate interaction over the western region of the central Himalaya (WCH). Multi-species, highly coherent, tree-ring cellulose ?18O chronologies from three sites across the WCH were used to derive atmospheric humidity (Atmospheric Moisture Content: AMC) record of the last four centuries. Annual-scale AMC reconstruction implies a decreasing regional atmospheric moisture since the mid-19th century and a sharp decline in recent decades (1960s). Coherency analyses between regional AMC and glacier mass balance (GMB) indicate an abrupt phase-shift in the relationship after the 1960s within a common record of the last 273�years. To ascertain the cause of this phase-shift, annual AMC was disintegrated into seasonal-scale, utilizing ?200�years of ?18O record of a deciduous tree species. Seasonal (winter: October�March; summer: April�September) AMC reconstructions and disaggregation results indicate higher sensitivity of regional ice-mass variability to winter moisture dynamics than summer.Winter season AMC reconstruction confirms a revival of winter westerlies-driven moisture influx in the region since the 1970�s. Meanwhile, the record for the summer season AMC indicates a gradual decline in moisture influx from the beginning of the 20th century. Interestingly, despite a prominent decline in Indian summer monsoon (ISM) precipitation after the mid-20th century, the summer season AMC�GMB relation remained stable. We hypothesize that decadal-scale greening, and consequently increased evapotranspiration and pre-monsoon precipitation might have been recycled through the summer season, to compensate for the ISM part of precipitation. However, isotope-enabled ecophysiological models and measurements would strengthen this hypothesis. In addition, high-resolution radiative forcing and long-term vegetation greening trends point towards a probable influence of valley greening on GMB. Our results indicate that attribution of ice mass to large-scale dynamics is likely to be modulated by local vegetation changes. This study contributes to the understanding of long-term hydroclimate�ice mass variability in the central Himalaya, where predictions are crucial for managing water resources and ecosystems. Copyright � 2022 Singh, Shekhar, Parida, Gupta, Sain, Rai, Br�uning, Singh Charkaborty, Sharma, Kamal Tiwari, Chauhan and Montagnani.