Monsoonal changes inferred from the Middle to Late Holocene sediments off Landfall Island, North Andaman

Abstract

In this paper, sediment texture, clay mineral composition, and δ18O data on Globigerinoides ruber of a sediment core collected from a water depth of 250 m near Landfall Island, Bay of Bengal, is presented to understand paleoenvironmental shifts during the Mid–Late Holocene period. From the sediment core, five organic carbon-rich samples were radiocarbon dated and the reservoir-corrected ages range from 6,078 to 1,658 years BP. The marine sediment core is represented dominantly by clayey silt with incursions of coarser components that occur around 6,000, 5,400, and 3,400 years BP. The sedimentation of the coarser detritus is due to strengthened southwest monsoon (SWM) since 6,500 to 5,400 years BP. Clay minerals are represented by smectite, illite, kaolinite, and chlorite in varying amounts. High kaolinite content and K/C ratio indicate intense SWM and strong bedrock weathering from the hinterland (~6,500–5,400 years BP). Incidence of smectite (48.82 to 25.09 %) and chlorite/illite (C/I) ratio (0.56 to 0.28) indicate an overall weakened southwest monsoon since 6,000 to 2,000 years BP with a brief incursion of extremely reduced SWM around 4,400 to 4,200 years BP. This is corroborated with the oxygen isotope on G. ruber that reveals a significant shift in the isotopic values ~4,300 years BP (−3.39 ‰), indicating weakening in SWM. Subsequently, fluctuations in the intensity of SWM are observed since 2,000 years to present.