In May 2015, the Shirshov Institute of Oceanology conducted a field survey in
the area. By means of direct measurements at a mooring station deployed at a depth
of 22 m on the shelf just west of the strait outlet, it was observed that the
cross-shore components of the current velocity in the surface and the bottom layers
were strongly anti-correlated during the periods of stratifications, and completely
uncorrelated during the periods when stratification relaxed. This suggests that the
buoyant discharges from the Kerch Strait may enhance wind-driven currents on the
eastern Crimean shelf. If so, this may represent an important mechanism responsible for cross-shelf exchanges in the region.
Browsing through the literature, we encountered some reports on the influence of
stratification generated by continental discharges on the one hand and the
wind-driven cross-shelf flows on the other. For example, as argued by [2], both
observations and numerical modeling of the Pearl River plume in the South China
Sea shelf showed that the enhancement of stratification by the plume thins the
surface frictional layer and enhances the cross-shelf circulation in the upper water
column so that the surface Ekman current and compensating flow beneath the
plume are indeed amplified. Some related issues were discussed in early papers
dedicated to the theory of upwellings (e.g., [1, 3]). However, to our knowledge, the
ability of a buoyant Sea of Azov plume to enhance the upwelling-downwelling type
wind-driven cross-shelf circulations in the Black Sea has not been investigated.
In what follows, we first describe the observational evidence that gave motivation to this paper. Then, we present two simple, semi-analytical 2D models of
wind-driven flow on the Crimean shelf, aimed to simulate the effect of damping
vertical mixing on the cross-shelf transport. One model represents the two-layered
stratification and the other one the continuous stratification with eddy viscosity
linearly decreasing downwards.
Observations
The map of field measurements on May 18–24, 2015, was shown above in Fig. 1.
The mooring station indicated by the blue star was deployed at a depth of 22 m and
functioned during 6 days. It was equipped with acoustic Nortek Aquadopp current
meter at a depth of 5 m and mechanical Sea Horse tilt current meter at the bottom,
and had also temperature sensors at the same depths. All data were recorded as
1 min averages.
The CTD profiling by SBE19plus instrument conducted on May 20, 2015, at
four stations situated along a north-to-south transect from the Cape Chauda as
indicated in Fig. 1, gives an idea of the vertical distributions of thermohaline fields
(Fig. 3). It exhibits a pronounced two-layer stratification, with a warm (up to 16 °C)
and relatively fresh (below 17.8 psu), 10–15 m thick upper layer formed by
admixture of Sea of Azov water above the colder (below 13 °C) and saltier (up to
18.2 psu) Black Sea water. Between the two layers, there was a steep picnocline.
Sea of Azov Waters in the Black Sea …
463
the area. By means of direct measurements at a mooring station deployed at a depth
of 22 m on the shelf just west of the strait outlet, it was observed that the
cross-shore components of the current velocity in the surface and the bottom layers
were strongly anti-correlated during the periods of stratifications, and completely
uncorrelated during the periods when stratification relaxed. This suggests that the
buoyant discharges from the Kerch Strait may enhance wind-driven currents on the
eastern Crimean shelf. If so, this may represent an important mechanism responsible for cross-shelf exchanges in the region.
Browsing through the literature, we encountered some reports on the influence of
stratification generated by continental discharges on the one hand and the
wind-driven cross-shelf flows on the other. For example, as argued by [2], both
observations and numerical modeling of the Pearl River plume in the South China
Sea shelf showed that the enhancement of stratification by the plume thins the
surface frictional layer and enhances the cross-shelf circulation in the upper water
column so that the surface Ekman current and compensating flow beneath the
plume are indeed amplified. Some related issues were discussed in early papers
dedicated to the theory of upwellings (e.g., [1, 3]). However, to our knowledge, the
ability of a buoyant Sea of Azov plume to enhance the upwelling-downwelling type
wind-driven cross-shelf circulations in the Black Sea has not been investigated.
In what follows, we first describe the observational evidence that gave motivation to this paper. Then, we present two simple, semi-analytical 2D models of
wind-driven flow on the Crimean shelf, aimed to simulate the effect of damping
vertical mixing on the cross-shelf transport. One model represents the two-layered
stratification and the other one the continuous stratification with eddy viscosity
linearly decreasing downwards.
Observations
The map of field measurements on May 18–24, 2015, was shown above in Fig. 1.
The mooring station indicated by the blue star was deployed at a depth of 22 m and
functioned during 6 days. It was equipped with acoustic Nortek Aquadopp current
meter at a depth of 5 m and mechanical Sea Horse tilt current meter at the bottom,
and had also temperature sensors at the same depths. All data were recorded as
1 min averages.
The CTD profiling by SBE19plus instrument conducted on May 20, 2015, at
four stations situated along a north-to-south transect from the Cape Chauda as
indicated in Fig. 1, gives an idea of the vertical distributions of thermohaline fields
(Fig. 3). It exhibits a pronounced two-layer stratification, with a warm (up to 16 °C)
and relatively fresh (below 17.8 psu), 10–15 m thick upper layer formed by
admixture of Sea of Azov water above the colder (below 13 °C) and saltier (up to
18.2 psu) Black Sea water. Between the two layers, there was a steep picnocline.
Sea of Azov Waters in the Black Sea …
463