Seasonal and interannual variability of the barrier layer in the Bay of Bengal: characteristics and mechanisms

The Bay of Bengal (BoB) exhibits significant seasonal and interannual variability in barrier layer thickness (BLT). While previous studies have mainly provided qualitative insights into the dynamical mechanisms controlling the variabilities of BLT, quantitative assessments of the relative contributions of temperature and salinity remain unknown. To address this gap, this study employs a quantitative separation method​ to distinguish the roles of thermal and saline processes in regulating BLT in BoB, and combined with regression analyses of surface forcing fields to diagnose the dominant driving processes. Seasonally, thermal processes dominate BLT variability in most region and seasons via monsoon-driven ocean circulation and Ekman pumping that affects the isothermal layer depth, while saline processes only dominate the BLT thinning in the central BoB and western equatorial region during summer, mainly through the intrusion of high-salinity waters. Interannually, BLT variability is primarily controlled by thermal processes associated with Indian Ocean Dipole and El Niño-Southern Oscillation events, including remote Kelvin and Rossby wave propagation and local Ekman pumping that alter the ILD, while salinity advection modulates regional differences, particularly in the western BoB. The application of this quantitative framework clarifies previously ambiguous mechanisms, and supports the improvement of BLT simulation in ocean models.