Provenance of the Late Quaternary sediments in the Andaman Sea: Implications for monsoon variability and ocean circulation

We present a geochemical and Sr-Nd isotopic study on a sediment core collected from the Andaman Sea in an attempt to reconstruct the Late Quaternary weathering and erosion patterns in the watersheds of the river systems of Myanmar and understand their controlling factors. Age control is based on nine radiocarbon dates and O-18 stratigraphy. The rate of sedimentation was strongly controlled by fluctuations of the monsoon. We identify three major sediment provenances: (1) the Irrawaddy catchment, (2) the western slopes of the Indo-Burman-Arakan (IBA) mountain ranges and the Andaman Islands, and (3) the catchments of Salween and Sittang and the Bengal shelf, with the first two contributing 30-60% of the material. Enhanced contributions from juvenile sources and corresponding positive shifts of O-18 are observed at seven time periods (11-14, 20-23, 36, 45, 53, 57, and 62 ka) of which five are synchronous with cooling of the northern hemisphere, suggesting a link between the changes in sediment provenances and the shifting of the locus of the summer monsoon, southward from the Himalayas, without substantial reduction in intensity. Our data, and that from other cores in the region suggest that an eastward moving surface current disperses sediments, derived from the Bengal shelf and western margin of Myanmar, from the eastern Bay of Bengal into the western Andaman Sea and that its strength has increased since the LGM. The existence of this current during the LGM implies that the Andaman Sea and the Bay of Bengal were well connected during the last glacial period.