Seasonal Variations in the Barrier Layer and Its Formation Mechanism in the Northern Indian Ocean

Understanding the impact of the ocean barrier layer (BL) on regional ocean dynamics requires the knowledge of BL variability and the factors influencing it. Herein, using SODA reanalysis data sets, we systematically investigate the seasonal variations and formation mechanisms of BLs in the North Indian Ocean (NIO). Our results show that BLs are mainly found in the southeastern Arabian Sea (SEAS), Bay of Bengal (BoB), and the Eastern Equatorial Indian Ocean (EEIO), with the thickest BLs occurring in SEAS and BoB in January, and in EEIO in November. Seasonal BL variability is primarily driven by isothermal layer (IL) modulation. Further budget analysis reveals that the factors affecting seasonality of BL variability through modulating IL differ across the three regions. In the SEAS, BL variability is primarily modulated by ocean vertical processes, notably oceanic planetary waves and Ekman pumping. In the BoB, vertical dynamics, including Ekman pumping and oceanic planetary waves, are the primary determinant of BL variability, while horizontal advection affects the spatial extent of BL. In the EEIO, equatorial upwelling and oceanic planetary waves significantly affect BL variability. These results contribute to a better understanding of regional ocean dynamics and may improve the accuracy of ocean state estimates and representation of BL processes using ocean model simulations.