The Black Sea Upwelling System: Analysis on the Western Shallow Waters

Upwelling is due to the combined effect of the coastal divergence process and Ekman pumping. The author aims to investigate two new upwelling indices for the Black Sea, derived from climate reanalysis models and the following in situ data: (a) the Coastal Upwelling Transport Index (CUTI) that estimates the rate of vertical volume transport and (b) the Biologically Effective Upwelling Transport Index (BEUTI) that estimates the nitrate flux into the surface mixed layer. Average monthly wind by the European Centre for Medium-Range Weather Forecasts (ECMWF) and Copernicus Marine Services for the Black Sea basin is used to calculate the CUTI and BEUTI Indexes for over 26 years (1993–2019) to analyse the sites along the North-Western Black Sea where changes in divergence phenomena occur. From 2000 to 2018, 31 divergence processes were observed based on daily in situ data from the coastal monitoring stations, with significant predominance in late spring and early summer. Nitrate supply by coastal upwelling has been estimated by combining sea surface temperature and salinity for the in situ data for the North-Western Black Sea shallow waters, and BEUTI indices were determined. Comparing 18 years of data results, the calculated indices and the observed upwelling events showed significant correlations.