Seasonal overturning circulation in the Red Sea: 2. Winter circulation

Abstract

The shallow winter overturning circulation in the Red Sea is studied using a 50 year highresolution MITgcm (MIT general circulation model) simulation with realistic atmospheric forcing. The overturning circulation for a typical year, represented by 1980, and the climatological mean are analyzed using model output to delineate the three-dimensional structure and to investigate the underlying dynamical mechanisms. The horizontal model circulation in the winter of 1980 is dominated by energetic eddies. The climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24 N. The overturning is accomplished through a cyclonic recirculation and a cross-basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model's winter overturning circulation. The simulated water exchange is not hydraulically controlled in the Strait of Bab el Mandeb; instead, the exchange is limited by bottom and lateral boundary friction and, to a lesser extent, by interfacial friction due to the vertical viscosity at the interface between the inflow and the outflow.

Carbon and nitrogen stable isotope ratios of pelagic zooplankton elucidate ecohydrographic features in the oligotrophic Red Sea

“…The low salinity water in the south appears to be Gulf of Aden surface water that is depleted in primary nutrients, well oxygenated (not shown), and has relatively low chlorophyll concentrations. This is consistent with the inflow of Gulf of Aden surface water during the winter described by Smeed (2004) and Yao et al (2014b).…”

“…The observed elevation of the isopycnals toward the North (Fig. 2) suggests that this cyclonic eddy likely influences primary productivity by injecting nutrients from the deep water into the euphotic zone (McGillicuddy et al, 1998;Li and Hansell, 2008;2014b). Further, the eddy transports water and concomitantly disperses nutrients from the coastal coral reefs toward the open sea off Duba (Eshel and Naik, 1997;Acker et al, 2008).…”

“…Remote sensing and modelling efforts indicated deep convection during the winter and the presence of a recurrent cyclonic gyre in the North. These mechanisms may transport small amounts of nutrients from coastal (reef-borne) sources and upwelling (Acker et al, 2008;Yao et al, 2014b). The Gulf of Aden Water, however, is the primary source of nutrients for the whole Red Sea.…”

The Gulf of Aden Intermediate Water Intrusion Regulates the Southern Red Sea Summer Phytoplankton Blooms

“…The model employed a 10-year spin up period, using the atmospheric conditions of 1952. The results and validation of these simulations were presented in Yao et al [27,28]. Of specific interest for the current study, the seasonal exchange flow patterns and the volume transports at the strait of Bab-el-Mandeb, as well as the structure of the intruding flow, were found to be robust features of the 50 year run and consistent with available observations [27].…”

“…The model was specifically configured to study of the general circulation of the Red Sea and presented in Yao et al [27,28]. The hydrodynamics were simulated using the MIT General Circulation Model (MITgcm) over a 50-year period between 1952 and 2001.…”