[1] Closely spaced CTD transects performed in the summertime reveal simultaneous downward/upward bendings of temperature/salinity contours in the seasonal thermocline/ permanent halocline of the Stolpe Channel and the Gulf of Gdansk, which may be interpreted as geostrophically balanced cyclonic eddies in the intermediate layer. To examine processes capable of forming the observed cyclonic eddies, a numerical simulation based on the Princeton Ocean Model (POM) has been initiated. The subsurface cyclones in the Stolpe Channel were satisfactory simulated in model runs under easterly/ northerly wind conditions. Their formation was shown to result from the adjustment of the high potential vorticity (PV) outflow (from the Bornholm Basin via the Stolpe Sill) to low potential vorticity environment by vortex stretching (so-called the PV outflow hypothesis by Spall and Price [1998]). In accordance with the real wind conditions, a cyclonic eddy observed in the intermediate layer of the Gulf of Gdansk was satisfactorily reproduced in a model run with the westerly wind shutdown, which implies westward transport throughout the Stolpe Channel and thereby excludes the PV outflow hypothesis. The subsurface cyclone simulated in the Gulf of Gdansk was traced to form in the course of relaxation of the coastal downwelling baroclinic jet.

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[1] A data set of closely spaced CTD profiling performed aboard Russian and Polish research vessels during 1993-2009 and numerical modeling are applied to study the variability in the asymmetric transverse structure of salinity/density in the Słupsk Furrow (SF) overflow of the Baltic Sea. The numerical simulations show that, on the one hand, the overflow may be dynamically treated within the SF as a subcritical, eddy-producing gravity current in a wide channel, and on the other, at the sill displays some features peculiar to frictionally controlled rotating flows. Comparison between the field measurements and the simulation results indicates that the variability of the cross-channel density structure is caused mainly by meandering of the gravity current and mesoscale eddies -mostly above-halocline cyclones and intrahalocline anticyclones. The meanders and eddies are found to be strongly affected by the bottom topography and wind-forcing.

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