Diatom​ Records of Peat Sequence From the Late Quaternary to Reconstruct Paleoenvironmental Changes in Baspa Valley, NW Himalaya

📝 Executive Abstract

Studying paleomonsoon proxies is essential for understanding the spatial and temporal evolution of the Indian Summer Monsoon (ISM). The present study examines hydro climatic variability over the past~21 ka BP (Late Quaternary) using a biological proxy (diatom PCA/assemblage composition) supported by a multi-proxy approach (i.e., stable carbon isotopes (δ13C), total organic carbon (TOC), environmental magnetism (χlf)) from a 100 cm peat sequence of the Baspa Valley, NW Himalaya, located at~3450 mamsl in the Higher Himalaya. The chronology of the studied peat profile, constrained by six AMS radiocarbon (14C) ages, indicates that peat development in the region commenced around 21 Ka BP. The results show that the δ13C values range from − 27.34 to − 25.32‰, TOC from 0.32 to 1.5 wt% and the χlf from 0.41 to 0.72 (10−8m3kg–1). The dominant diatom genera identified in the Baspa peat profile are Caloneis, Cocconeis, Diploneis, Encyo- nema, Epithemia, Geissleria, Hantzschia, Navicula, Pinnularia, Pseudostaurosira, Rhopalodia, Punctastriata, Staurosira, Tabellaria, Staurosirella, Ulnaria, and Nitzschia. Enrichment in δ13C, low TOC, suppressed diatom PCA scores, and lower χlf indicated cold-dry climate, and vice-versa. The multi-proxy data indicate four major episodes of alternating weak and strong ISM phases: weak during ~ 21–15 Ka BP and ~ 11–1.6 Ka BP, and strong from ~ 15–11 Ka BP and ~ 1.6 Ka BP to Present. The warm-moist and cold-dry phases correspond to strengthening and weakening of the ISM , respectively, and thesephases correlate with variations in the Northern Hemisphere summer insolation.