Quantification of the surface mixed-layer lateral transports via the use of a HF radar: Application in the North-East Aegean Sea

High Frequency (HF) radars, if properly located, can prove to be a valuable tool in areas of specific oceanographic interest, like Straits connecting two contrasting Ocean Basins, as in the case of the Turkish Straits connecting the Mediterranean and the Black Sea. The two basins' exchange generates a surface inflow and current into the North Aegean Sea that determine its characteristics and variability. Thus it is of prime importance to monitor and quantify the lateral advection of Black Sea waters (BSW) after their exit through the Dardanelles Straits. Here, we exploit surface velocity maps obtained through a HF radar in an effort to estimate (a) mixed-layer depth and (b) surface layer volume fluxes with unprecedented high spatiotemporal resolution. Comparison of the results of the hereby introduced method to estimates of the Dardanelles inflow into the Aegean Sea, or to independent estimates of the BSW advection volume fluxes in the interior of the basin, reveal consistently smaller values obtained with the new method. The difference is attributed to the fact that the HF radar method corresponds solely to advection within the surface mixed-layer, which is only a fraction of the total volume influx of Black-Sea waters into the Aegean. Testing this hypothesis on hydrographic measurements from a section further down the flow certifies that the quantity of BSW within the mixed-layer corresponds to a fraction of the total inflow of BSW.