A 13,000year record of environmental magnetic variations in the lake and peat deposits from the Chandra valley, Lahaul: Implications to Holocene monsoonal variability in the NW Himalaya

An ~13,000year old record of in situ peat bog and lacustrine sediments from a post glacial lake in the Chandra valley of the Lahaul Himalaya is studied to generate the record of environmental magnetic signatures in response to Indian summer monsoon (ISM) variability in the NW Himalaya. The chronology of studied Chandra Peat Trench (CPT) profile is based on 9 AMS 14C calibrated dates (calyr BP). The piece-wise linear regression analysis of age-depth model indicates non-linear sedimentation with higher rates from ~4142calyr BP to the Present and lower accumulation during ~12,880–4142calyr BP. The mineral magnetism showed three dominant assemblages of magnetic minerals with varying concentrations in peat-lake sediment sequence i.e. (1) mixed ferri- and antiferromagnetic minerals between ~12,880 and 11,019calyr BP, (2) dominant antiferromagnetic mineralogy from ~11,019 to 3172calyr BP, and (3) significantly increased concentrations of mixed ferri- and antiferromagnetic minerals from ~3172calyr BP to the Present with characteristically increased ferrimagnetic concentrations after ~2032calyr BP. The characteristic increase in antiferromagnetic mineral concentration accompanied by decreased ferrimagnetic concentration from ~10,398 to 5770calyr BP suggest possible oxidation of magnetite to hematite under warmer climate conditions and corresponds to increased ISM intensity during early to mid-Holocene warm-wet climate in the NW Himalaya. The distinctly increased concentration of antiferromagnetic minerals from ~6732 to 5770calyr BP indicates mid-Holocene climate optimum (HCO) in the Lahaul Himalaya. The strengthening and weakening of ISM recorded in environmental magnetic signatures during ~1260–852calyr BP (~690–1098AD) and between ~852 and 239calyr BP (~1098–1711AD) corresponds to Medieval Warm Period (MWP) and Little Ice Age (LIA) events, respectively.