Coastal–open Ocean Exchange in the Black Sea: Observations and Modelling

The interaction between physical and biological processes in the areas of continental margins governs the variability of ecosystems. The complexity of processes in these areas requires detailed studies combining modelling and surveying efforts. One promising step in this direction was undertaken in the framework of the EROS 21 project, focusing on the shelf part of the north-western Black Sea. In the present paper, we focus on the results of physical studies aiming to improve the understanding of the fundamental exchange processes in the ocean margins, as well as to quantify some of them in the Black Sea. We illustrate the capabilities of circulation models to reproduce physical processes with different time- and space-scales: coastal waves, internal waves, baroclinic Rossby and topographic waves. Another class of important phenomena in the coastal zone is associated with convection. Sources at the sea surface and in the outflow areas give rise to plume dynamics that play a crucial role in the vertical mixing and provide the mechanism for water-mass formation. Most of the results are illustrated for the shelf part of the Black Sea. The verification of simulations is performed by comparison with survey data, altimeter data from the Topex/Poseidon mission and radiotracer observations. The latter, in combination with simulations from circulation models, are used to trace the penetration of tracers into the intermediate and deep layers. We show that although most 90Sr is introduced by river runoff, large amounts of this signal penetrate the halocline in the Bosphorus Straits area and along the southern coast. Another important fraction of the river water penetrates the intermediate layers at the shelf edge in the north-western Black Sea.