Paleomonsoon variability during the past seven centuries: Insights from a northwest Himalayan lake

Abstract

Monsoon rainfall in the northwest (NW) Himalaya is influenced by a complex interplay of various forcing factors, controlling diverse agrarian practices. The NW Himalaya receives the bulk of its rainfall from the Indian summer monsoon (ISM) with a small amount of precipitation originating from the westerlies during winter. To understand ISM variability in the last millennium, a 1 m long core was raised from Tikkar Taal Lake in the Panchkula district of Haryana, India and examined for multiple proxies (grain size, major and trace element ratios, stable isotope (δ¹³C_org) and Total Organic Carbon (TOC Wt). The statistical analyses, including End Member Modelling (EMM), correlation matrix, spectral analysis, Wavelet Transform Coherence (WTC) Analysis along with Continuous Wavelet Transform (CWT) analysis reveal significant changes in the Little Ice Age (LIA) and Current Warm Period (CWP). Accelerator Mass Spectrometry (AMS) ¹⁴C dates of three bulk sediment and two gastropod samples give an age range of ∼700 years. Pacific Decadal Oscillation (PDO) along with El Niño -Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) are the forcing factors for changes in precipitation. Two climatically significant intervals are identified, LIA (∼1296–1850 CE) with a moderately wet and humid phase from ∼1296 to 1500 CE, followed by a moderately dry phase from ∼1500 to 1850 CE overlapped by the Maunder Minimum (∼1645–1710 CE). The CWP is characterized by humid conditions (1850 CE onwards) coinciding with human-induced changes in the environment. The spectral analysis shows NAO and PDO like cyclicities of 15, 16, 18,19,22 and 28 yrs.