Late Quaternary vegetation shifts and climate change in the sub-alpine belt of the Parvati Valley, Himachal Pradesh, India

Abstract

Pollen, sediment texture, moisture, organic/inorganic carbon content and geochemical analyses of a 1.2m in-depth sediment profile from upper Tundabhuj Lake in the Parvati Valley show that the region supported alpine-scrub vegetation. The forest elements largely consisted of Betula and its broad-leaved allies viz., Quercus, Corylus and Carpinus interspersed with meadow grasses, Asteraceae, Impatiens, etc. under a warm and moderately humid climate from around 17,100 to 14,700 cal yr BP. Additionally, the increase in organic carbon, enrichment of immobile elements (TiO2, Al2O3, Fe2O3) and moderate values of the Chemical Index of Alteration (CIA = ~72) reinforce the warm and moderately humid climate in the catchment. Subsequently, at around 14,700 to 10,600 cal yr BP, an increase in alpine-scrub vegetation dominated by Betula, Corylus and Carpinus was observed. The enrichment of (TiO2, Ni and Cr) and slightly higher CIA values (72–78) indicated relatively more humid conditions than earlier climatic conditions. The climate turned cold and dry between 10,600 and 5400 cal yr BP as deduced from the abrupt reduction in the alpine-scrubs and meadow constituents. During this period immobile elements (Al2O3, TiO2, Fe2O3, and Cr) also decreased. In contrast, mobile elements (CaO, Na2O, Sr, and Ba) increased along with a gradual decrease in CIA (minimum at 42.5 cm) and organic carbon content supporting cold and dry climatic conditions. From around 5400 until ~1600 cal yr BP, the region saw a return of alpine-scrubs and conifers, indicating a relatively warm and humid climate. Increasing CIA values, organic carbon, and concentration of immobile elements also reaffirm relatively warm and humid climatic conditions. In the most recent phase (around 1600 cal yr BP to present), the climate deteriorated as reflected by the depletion of Betula and broad-leaved associates and an increase in dry elements such as Juniperus and Ephedra. The decrease in CIA values, organic carbon and immobile elements (TiO2, Al2O3, and Fe2O3) substantiate this observation.