What processes control the net currents through shallow straits? A review with application to the Bohai Strait, China

Abstract

a b s t r a c tWe review the key processes controlling the net water circulation in shallow straits. The circulation is mainly barotropic, driven by the difference in mean sea level and tides on either side of the strait, the wind, the meandering of the currents in the adjoining seas, the bathymetry including the shape and width of the mouths and the presence of narrows, shoals, sills, islands, and lateral embayments. As the oceanography forcing can be non-synchronised on either side of the strait, the resulting net currents through the strait may appear chaotic. We apply these findings to the net circulation through the Bohai Strait in China using local wind, remote-sensing data of currents and sea level, and a hydrodynamic model. The net currents through the Bohai Strait were episodic. They were largest during winter storms when the wind generated a cyclonic coastal current in the northern Yellow Sea that flowed across the width of the Bohai Strait. Like the Luzon Strait, this current meandered and a branch of the current intruded into the northern Bohai Strait along the deeper channel. The wind set-up in the Bohai Sea and the wind-driven longshore current in the southern Bohai Sea generated a seaward flow through the southern Bohai Strait, somewhat like in Irbe Strait. As with the straits of the Seto Inland Sea, stagnation occurred in some embayments. As in the Torres Strait, the islands in the southern Bohai Strait retarded the net flow and increased the width of the outflow zone. These flows were also modulated at very long periods (~60 days) by long waves in the Yellow Sea, possibly generated by meandering of the Kuroshio Current that created an additional sea level slope through the strait. The transit time in the Bohai Strait was 60 and 10 days, respectively, during calm weather and winter storms. The residence time in the Bohai Sea was estimated to be about 1.68 years by the LOICZ model and 1.56 years by the hydrodynamic model, and the influence of the river runoff, including the Yellow River, was negligible.

Emergence of Summertime Hypoxia and Concurrent Carbonate Mineral Suppression in the Central Bohai Sea, China

“…From August 2011 to January 2016, the survey‐averaged salinity varied slightly from 29.4 ± 0.9 (August 2012) and 29.5 ± 1.5 (November 2012) to 30.5 ± 1.0 (August 2011 and May 2012) and 30.8 ± 0.5 (September 2015 and January 2016; Table ), which compares favorably with the decadal average of salinity of 29.9 in the Bohai Sea during 2002–2012 (Li et al, ). During our July 2016 and September 2017 cruises, however, the survey‐averaged salinity increased to 31.6 ± 0.5.…”

Novel, Repeated Surveys Reveal New Insights on Sediment Flux Through a Narrow Strait, Bohai, China

“…Given its special geographical location, the material fluxes through a sea strait bear major influences on two adjoining water bodies with impacts on mass, salt, pollutant, and energy budgets and thereby play a critical role in regional and global biogeochemical processes (Chung et al, 2001;Ferentinos & Kastanos, 1988;Hoshika et al, 1999;Wells, 1988). During the last several decades, investigations on water and sediments transport through sea straits have seen significant developments and received increasingly more attentions (Jordà et al, 2017;Li et al, 2015;Maren & Gerritsen, 2012;Pratt, 1990;Rossby & Flagg, 2012). Several international research projects, for instance, have focused on volume transport through the Strait of Gibraltar (connecting the Mediterranean Sea and the open Atlantic Ocean; Baschek et al, 2001;Jordà et al, 2017) and Otranto (connecting the Adriatic Sea and Mediterranean Sea; Ferentinos & Kastanos, 1988;Ursella et al, 2012).…”

Exploring Sources and Biogeochemical Dynamics of Dissolved Methane in the Central Bohai Sea in Summer

“…In summer, seawater from the North Yellow Sea enters the Bohai Sea through the northern strait, moves anticlockwise around the central basin, and finally flows out through the southern strait (Guan, 1994;Huang et al, 1999), involving riverine water discharges from the Yellow River and the Luanhe River (Figure 1). The hydraulic residence time of the entire Bohai Sea is estimated to be 1.6 years (Li et al, 2015).…”