The overturning circulation in the Arabian Gulf

The Arabian Gulf is a relatively small marginal sea but shows a very wide range of salinity and, hence, density from intense evaporation. Observations and previous numerical modeling studies show the inflow/outflow near the surface/bottom of the Strait of Hormuz, compensating the freshwater loss in the Gulf. We revisit this topic using approximately 2 km horizontal resolution ocean circulation model and compute the zonal and meridional overturning circulations to obtain a 3-dimensional ocean circulation picture. The surface current in the Gulf responds to the northwesterly wind and flows southeastward, creating southward flow at the surface and returning flow near the bottom. The buoyancy flux shows clear seasonal variability. Even with excessive evaporation in summer, the incoming shortwave radiation reduces the surface density, leading to surface warming in the central Gulf. The density decrease in the Gulf triggers the volume influx from the Arabian Sea through the Strait of Hormuz. With the outflow near the bottom of the Strait, there is a counterclockwise zonal overturning circulation. In winter, the latent heat flux exceeds the incoming solar radiation, resulting in a positive water-mass transformation. The heat loss is slightly greater to the east of the Strait, driving the volume flux into the Gulf, which encounters outflow in the Gulf. There is also a counterclockwise zonal overturning circulation, but it does not penetrate the Gulf as much as in summer. The lower branch of the overturning circulation settles near 200 m in the Arabian Sea and interacts with clockwise/counterclockwise overturning circulation in summer/winter associated with the Asian monsoon. Our finding shows the buoyancy flux that drives the ocean circulation in the Arabian Gulf, highlighting the importance of the flux observations at the interface of atmosphere and ocean for better estimation of the ocean circulation.