Mid-Holocene Indian Summer Monsoon variability off the Andaman Islands, Bay of Bengal

摘要

A sediment core retrieved from the Andamans Forearc Basin (AFB) near Landfall Island, North Andaman, provides a record of sediment provenance and climate change during the mid to late Holocene. Radiocarbon ages ranging from 6078 to 1658 indicate that the core represents the interval from 6500 BP to the present. Grain size variation indicates a cyclic variation of wetter and drier conditions corresponding to changes in intensity of the Indian Summer Monsoon (ISM), which was at greatest intensity near 6400, 5300 and 3300-3000 BP. Geochemical parameters including abundance of CaCO_3, eNd and δ~(18)O in Globigerinoides ruber are consistent with a long-term trend from cooler, wetter conditions to the warmer, drier conditions at present Chemical weathering intensity, which lags behind climate changes on land, shows a pulse of highly weathered sediment deposited at about 4000 BP. During the short-duration pulses of intense monsoon activity, sandy sediment was supplied from the Andaman Islands. The Irrawaddy, Salween, and Sittang rivers of Myanmar are the secondary sediment sources for the study area.