Latest Neogene monsoon of the Chotanagpur Plateau, eastern India, as revealed by fossil leaf architectural signatures

Abstract

A fossil leaf assemblage from latest Neogene (Pliocene) sediments exposed in Jharkhand of Chotonagpur Plateau, eastern India, is subjected to a CLAMP (Climate Leaf Analysis Multivariate Program) analysis using a new high spatial resolution (~1 km2) WorldClim2 gridded climate data and PhysgAsia2 calibration. The CLAMP analysis of 80 different morphotypes of fossil leaves indicates a mean annual temperature (MAT) of 21.9 °C ± 2.3 °C; a cold month mean temperature (CMMT) of 16.7 °C ± 3.5 °C and a warm month mean temperature (WMMT) of 26.9 °C ± 2.9 °C. Precipitation estimates have high uncertainties but suggest a weak monsoon with a growing season (11.7 ± 1 months) precipitation (GSP) of 201.2 ± 64.3 cm. The new calibration also provides for the first time in India more detailed insights into the hydrological regime through the return of annual and seasonal vapour pressure deficit (VPD) and potential evapotranspiration (PET) estimates, as well as new thermal overviews through measures of thermicity and growing degree days. The new results confirm the overall warmth of the region. Although rainfall estimates have large uncertainties due to year-round wet soils, measures of VPD and PET show persistent high humidity, but with higher evaporative stress in the summer during late Neogene times than now.