230 Th in the Andaman Sea: Rapid deep-sea renewal

[1] 230Th activities were determined in seawater collected from the Bay of Bengal and the Andaman Sea. The Andaman Sea is a semi-closed basin that is isolated from the Bay of Bengal by the Andaman-Nicobar Ridge. The noticeable trend in the vertical distribution of 230Th activity in the Andaman Sea is its uniformity below 1250 m depth. We applied the scavenging-mixing model to this vertical profile in the Andaman Sea, and estimated the upper limit of renewal time to be 6 yr. We compared 210Pb/226Ra ratios among deep waters of various oceanic basins to constrain the application of 230Th as a tracer of deep-water renewal. The 210Pb/226Ra ratios were almost identical for the deep-water of the Andaman Sea and the inflow water from the Bay of Bengal, suggesting that the deep water in the Andaman Sea is replaced rapidly without bottom scavenging effects on the 210Pb/226Ra ratio.