Terrigenous influx from Peninsular Indian Rivers in response to climatic variability since the Last Glacial Maximum

Abstract

The contribution of rivers from peninsular India to the sediment load of the continental shelf in south-eastern India, the western Bay of Bengal, is relatively less understood. Here, we present a record of a sediment core from the continental margin off Kalpakkam, located in the western Bay of Bengal, inferring detrital influx, palaeo-weathering, and palaeo-monsoonal conditions over the past 23,000 years. We used a multi-proxy approach that included mineral magnetism, particle size, geochemical analyses, stable isotopic (δ¹³C and δ¹⁵N), and diffuse reflectance spectroscopic analyses to decipher the sediment supply from the Palar River and the depositional history of the southeastern continental shelf in response to variations in the monsoon during the late Quaternary. Radiocarbon (¹⁴C) dating of sediment samples was carried out using Accelerator Mass Spectrometry (AMS), based on five sample analyses. Organic carbon samples were collected at different core depths to establish a precise chronology of climatic and sedimentary changes over the last 23,000 years, covering key periods such as the Last Glacial Maximum, the Bølling-Allerød, and the Younger Dryas. The magnetic mineral concentration (SIRM, χ_ARM, χ_lf) and mineralogy (HIRM) varied in response to terrigenous influx, chemical weathering, monsoon strength and shifts in provenance of sediments. The magnetic data is corroborated by other proxies, such as hematite/goethite ratio, particle size distribution (percentages of sand, silt, clay), CaCO₃, C/N ratio, and carbon and nitrogen isotopes. A gradual increase in the northeast monsoon is documented during 22,000–15,000 cal. Years B·P. (Last Glacial Maximum), followed by a slight decline during 15,000–10,000 cal. Years B·P. A brief decline in northeast monsoon rainfall is observed at around ∼13,900 cal. Years B·P. (Bølling-Allerød), with an increase during ∼12,900–11,800 cal. Years B.P. (Younger Dryas). The Early Holocene period was characterized by increased detrital influx to the core site, strong pedogenesis, and chemical weathering in the continental areas in response to high rainfall conditions. A significant increase in terrigenous input, linked to the shifting and upliftment of the Palar River basin, is observed around 4900 cal. Years B.P. These findings provide valuable insights into the Late Quaternary evolution of riverine sediment dynamics of peninsular India and monsoon variability in the western Bay of Bengal.