Spatiotemporal characteristics and mechanisms of upper water exchange between the Arabian Sea and the Bay of Bengal in the North Indian Ocean

Defu ZhengYanzhao FuJunru GuoJun Song^*Yu Cai

• Dalian Ocean University, Dalian, China

Abstract：The distribution state and water exchange characteristics of the Arabian Sea Water (ASW) and the Bay of Bengal Water (BBW) in the North Indian Ocean during seasonal and interannual variations were studied by combining the spectral clustering method, with emphasis on the analysis of the spatiotemporal variations and control mechanisms of water fluxes in two main channel sections: the mouth of the Bay of Bengal (6° N) and the central equatorial seas (81° E). The results indicate that the eastward water flux driven by the Southwest Monsoon Current and Wyrtki jets averages 13.93±2.50 Sv (1 Sv = 10 6 /m 3 ) in summer and autumn, and the distribution range of ASW reaches the peak during this period, which can be extended to the north of 10° N in the Bay of Bengal. The winter-spring BBW incursion into the region west of 73° E in the Arabian Sea and the transport of the Northeast Monsoon Current reach 16.43±1.48 Sv, showing obvious seasonal changes. Changes in water fluxes across the Bay mouth and equatorial channels show a general positive correlation during 2001-2020, with water exchange in the equatorial region being more complexin the seasonal process, possibly related to changes in the intensity of the Wyrtki jets. The Bay mouth channel shows that the average low salinity water outflow from the Bay of Bengal is 6.03±1.50 Sv and is larger in summer than in winter, corresponding to the process of massive diffusion of BBW in the east from July to October. Affected by the monsoon transition process and the equatorial half-year Kelvin wave, water flux changes exhibit obvious half-year and one-year cycles over time. The time series of low salinity water transport anomaly and Dipole Mode Index (DMI) in the Bay mouth and equatorial region are negatively correlated (-0.30 and -0.42), indicating that water exchange is also moderated by Indian Ocean Dipole (IOD) events on the interannual scale, and the process in the equatorial region is more sensitive to IOD events, reflecting a more complex 2-3 year cycle in water flux changes.