A dense water dome generated by Ekman suction in the Adriatic Sea

An experiment is being carried out in the Adriatic Sea, in the area between the Island of Blitvenica close to the east coast and the Island of Jabuka in the open sea. CTD and ADCP data are collected during cruises and are supplemented by temperature, pressure and dissolved oxygen time series recorded at the sea bottom, by SST satellite data, and by meteorological time series originating from permanent coastal stations. Moreover, high-resolution, 2-km meteorological (ALADIN) and oceanographic (ROMS) models are used to reproduce and interpret the experimental findings. Thus far, the most interesting finding was a dense water dome documented in some detail by the yo-yo CTD profiler on 28 May 2017. Its center was observed at a distance of 15-20 km from the coast and the dome extended farther offshore than onshore. The dome left its mark on the sea surface, with the temperature above its center being slightly lower than in the surrounding areas, as documented by both in situ and remotely-sensed data. Shipborne ADCP measurements suggested that the surface circulation around the dome was cyclonic. A simple calculation, based on the meteorological model results, showed that the winds supported divergence of surface transports close to the dome center on 25, 26 and 27 May 2017 and that the resulting vertical current speeds could explain the observed rising of the pycnocline. It therefore appears that Ekman suction was responsible for the formation of the dense water dome. However, the agreement between the observed and calculated shape of the dome is less than perfect, suggesting that the process provides a strict test of the meteorological model and its ability to accurately reproduce the wind shear. The test is even more severe when it comes to the oceanographic model, because the first simulations failed to reproduce the dome and thus led to a reexamination of the role of lateral friction.