Spatiotemporal distribution of the upper ocean temperature and salinity in the Bay of Bengal during 1980–2022 and its implications on the mixed layer dynamics
摘要
This study investigates the spatiotemporal distribution of the upper ocean temperature and salinity of the Bay of Bengal (BoB) during 1980–2022 and its implications on the mixed layer dynamics. Available reanalysis/modelling datasets and altimeter observations are used for the analysis with a quantitative approach. The results show that the surface temperature has increased 0.6 °C in last 43 years and indicates the deepening of near surface isothermal layer by ~ 10–15 m. On the contrary, the near surface isohaline layer depth is reduced by 5–10 m over the analysis period. The empirical orthogonal function analysis shows maximum spatial surface temperature (salinity) variation of 79–84% (70–81%) over the northern-northwestern (northern) BoB where the highest temporal contribution comes from Winter (Autumn) followed by Spring (Spring). The maximum (~ 8–10 × 10− 5 kg/m2/s) freshwater influx in the northern BoB during Summer spreads towards south during Autumn controlling the upper layer salinity, which further determine the stratification and associated stability. High stratification (Energy Required for Mixing > ~ 9000 J/m2) in the northern BoB during Autumn significantly reduces the mixed layer depth (~ 10 m) and increases the static stability (Square of Brunt Vaisala frequency > 5 × 10− 4 s− 2). The net ocean heat content in the upper ocean (100 m) is seen increasing consistently with the temperature and is seasonally highest in Spring (~ 3.4 × 1019 J) when the downward net heat flux is also maximum (~ 85 W/m2). Therefore, this study suggests that the spatiotemporal inhomogeneity in the distribution of temperature and salinity over the BoB mostly determine the mixed layer characteristics here.