Seasonal Evolution of Mixed Layers in the Red Sea and the Relative Contribution of Atmospheric Buoyancy and Momentum Forcing

The seasonal and spatial evolution of mixed layers (MLs) in the Red Sea (RS) is analyzed for the 2001-2015 period using the results of a high resolution (~1km horizontal, 50 vertical layers) ocean circulation model forced by a novel regional high resolution (5 km) atmospheric reanalysis dataset. The simulation reproduces the main features of the near-surface stratification, as described by the available observations. The seasonal evolution of the modeled mixed layer depths (MLDs) in the RS is predominantly driven by atmospheric buoyancy forcing, especially its heat flux component. Everywhere in the basin the model MLs are deepest in January and February. The deepest MLDs develop in the northern parts of the Gulf of Aqaba and in the western parts of the north RS. The MLDs gradually shoal towards the south, reflecting the meridional gradient of wintertime surface buoyancy loss. In spring and summer, the surface ocean heat gain increases the stratification and the MLs are becoming shallow everywhere in the basin. During this season wind may have a significant local impact on the MLD. Particularly important are strong winds channeled by topography, such as in the vicinity of the Strait of Bab-Al-Mandeb and the straits connecting the two gulfs in the north, and lateral jets blowing through mountain gaps, such as the Tokar jet in the central RS. The MLD distribution further suggests influence by the general and mesoscale circulation. The complex patterns of air-sea buoyancy flux, wind forcing, and the thermohaline and mesoscale circulation, are all strongly imprinted on the MLD distribution.

Red Sea Mixed Layer Dynamics Ocean Circulation