Characterization of biotic and abiotic signatures of modern lake sediments of western India, and its palaeo-environmental implications

Abstract

A multi-proxy study of biotic and abiotic components was conducted on surface sediment samples from six lakes/wetlands located along the western transitional boundary of the contemporary Indian Summer Monsoon (ISM) in the Indian Subcontinent. The primary goal is to assess the suitability of various proxies as representatives of modern vegetation, environmental and climatic conditions. The collected data indicate significant variations in the composition and density of pollen in response to climate-induced and anthropogenic ecological changes throughout the northwest India transect. The palynological studies from eastern Rajasthan shows high forest elements in comparison to western Haryana and western Uttar Pradesh. In addition, the palynological data was juxtaposed with other biotic proxies such as diatom and isotopic studies, along with geochemical proxies and paleomagnetic data of the surface lake sediments. The presence of marker pollen taxa including Cerealia type Poaceae, Chenopodiaceae, and Brassicaceae, allows for distinct recognition of anthropogenic activities throughout the whole transect. The diversity and distribution of diatoms also support the palynological data in response to climate-induced and anthropogenic ecological changes. Furthermore, grain size, geochemistry (TOC/TN ratio with stable carbon isotope), and magnetic susceptibility data offer crucial insights about the sediment's depositional settings and general mineralogical composition. Stable carbon isotope data shows C3 dominance in relatively humid areas and C4 dominance in semi-arid areas, suggesting climate-driven control over sediment organic matter composition. Canonical correspondence analysis (CCA) indicates that biotic variables (pollen, diatom, stable isotopic composition) are significantly controlled by modern precipitation and temperature. Redundancy analysis reveals a significant influence of current average temperature and precipitation on major element oxide variations in surface lake sediments. Therefore, we propose using palynological, stable carbon isotope, diatom data, along with grain size, environmental magnetism, and geochemistry, to establish a multiproxy modern analogue for quantitative palaeoclimatic reconstructions. As a result, this study provides the first modern analogues from a climate-sensitive region that separates the area under ISM influence from an area with meager precipitation in western India.