Water Mass Intrusion from Arabian Sea to the Bay of Bengal during summer; Experimental Observations in August 2015

S.U.P Jinadasa, Ocean University of Sri Lanka, Department of Physical Oceanography, Colombo, Sri Lanka; The Ocean University of Sri Lanka, Oceanography, Colombo, Sri Lanka, Gayan Pathirana, University of Ruhuna, Sri Lanka., Oceanography and Marine Geology,, Colombo, Sri Lanka, Anusha Priyanthi Wijesundara, National Aquatic Resources Research and Development Agency, Colombo, Sri Lanka, Hemantha W Wijesekara, Naval Research Lab Stennis Space Center, Stennis Space Center, United States and Harindra J.S. Fernando, University of Notre Dame, Notre Dame, United States
Abstract:
Abstract

Arabian Sea (AS) and Bay of Bengal (BoB) are two subdivisions of northern Indian Ocean, which are in unique characteristics. Both basins are influenced by Indian Ocean monsoon and the surface circulation characterizes with seasonally reversing currents as a response to the seasonal winds. Seasonal freshwater influx and evaporation forced the changes in salinity level and the variations observed suggest that the region consist of high/ low salinity waters. High evaporation rates over the AS and remarkable amount of freshwater flux to the BoB creates a hydrological imbalance between two basins. Observations and model simulations of previous studies pointed out that south west monsoon currents (SMC) brings high saline AS waters into the BoB during summer and west ward flowing of northwest monsoon currents (NMC) carries low saline BoB waters into the AS during winter.

The current experiments on intrusions of AS waters in to BoB were carried out using R/V Roger Revelle cruise during 4th-15th August 2015. The study mainly focused on the conductivity temperature depth (CTD) observations during the cruise. The CTD data were incorporated with current derived from surface drifters, Ocean Surface Current Analyses Real-time (OSCAR) temperature salinity (T-S) data from 1990 – 2016.

The result consistent with the previous studies on SMC flows eastward around Sri Lanka serving as an open ocean link to connect AS with BoB during summer monsoon. Further, it was noted that SMC is strong during the early August with a speed of 0.8 – 1.2 m/s and reduces to 0.6 – 0.7 m/s at the end of the month. The CTD observations in southern BoB clearly indicated that the presence of AS waters at the depths of 96 – 135 m where estimated salinity was at 34.86 – 35.2 psu which provides the evidences for the intrusion of ASW into the BoB. Furthermore, the analysis indicated that four salinity extreme layers between 103 – 162 m depths with a thickness of 10 – 20 m in upper 200 m east of Sri Lanka point out the importance of subsurface mixing associated with temperature salinity (T-S) properties of the water column.

Key words:Arabian Sea, Bay of Bengal, Summer monsoon currents, Water mass exchange

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