Ventilation of a Monsoon-Dominated Ocean: Subduction and Obduction in the North Indian Ocean

Abstract

Based on the characteristics of oceanic circulation in a monsoon-dominated ocean, a new framework of annual ventilation, including subduction and obduction, is postulated and applied to the North Indian Ocean based on both SODA and GODAS. It is revealed that besides the winter season, ventilation can also occur in summer. Considering the horizontal resolution, SODA results are mainly discussed, with GODAS results given for validity of key conclusions. The annual subduction/obduction rate in the North Indian Ocean based on SODA is estimated at 10.2 Sv/11 Sv averaged from 1960 to 2009, with 4.2 Sv/6.2 Sv occurring during winter monsoon period and 6 Sv/4.8 Sv during summer monsoon period, respectively. Both subduction and obduction feature great interannual variability, with the vertical pumping term of decisive importance. Furthermore, the concepts of the penetration depth through subduction and the origin depth through obduction are postulated. The penetration depth in the Arabian Sea is on the order of 50 to 200 m; the origin depth through obduction in the Arabian Sea is deeper than that in the Bay of Bengal, with the deepest on the order of 200 to 250 m along the western boundary.