Paleoclimatic and diagenetic history of the late Quaternary sediments in a core from the southeastern Arabian Sea: geochemical and magnetic signals

The geochemical and rock-magnetic investigations were carried out on a sediment core collected from the SE Arabian Sea at 1420 m depth in oxygenated waters below the present day oxygen minimum zone. The top 250 cm sediments of the core represent the last 35 kaBP. The δ18O values of Globigerinoides ruber are heaviest during the Last Glacial Maximum (LGM) and appear unaffected by low-saline waters transported from the Bay of Bengal by stronger northeast monsoon and West Indian coastal current. The signatures of Bφlling-Allerφd and Younger Dryas events are distinct in the records of magnetic susceptibility, organic carbon (OC) and δ18O. Glacial sediments show higher OC, CaCO3, Ba, Mo, U and Cd, while the early to late Holocene sediments show increasing concentrations of OC, CaCO3, Ba, Cu, Ni and Zn and decreasing concentrations of Mo, U and Cd. Productivity induced low-oxygenated bottom waters and reducing sedimentary conditions during glaciation and, productivity and oxygenated bottom waters in Holocene are responsible for their variation. The core exhibits different stages of diagenesis at different sediment intervals. The occurrence of fine-grained, low-coercivity, ferrimagnetic mineral during glacial period is indicative of its formation in organic-rich, anoxic sediments, that may be analogous to the diagenetic magnetic enhancement known in sapropels of th