Black Sea thermohaline properties: Long-term trends and variations

3D velocity (m/s), temperature (°C) and salinity fields for the Black Sea are simulated by the use of the General Estuarine Ocean Model (GETM) and General Ocean Turbulence Model (GOTM). Data sets consists of monthly mean value on a horizontal grid of 423x172 data points (2 longitude minutes x 2 latitude minutes) and 70 vertical levels. Simulations are performed for the period from 1960 to 2015 (56 years). The 3D monthly mean vertical coordinate, temperature and salinity are stored in monthly NetCDF data files available for download.

Detailed description: The 3D hydrodynamic model comprises of 3D GETM and 1D GOTM initialized on high resolution 2 x 2 min latitude–longitude horizontal grid. The model bathymetry grid is produced from ETOPO1 global bathymetric grid with horizontal resolution of 1 min. Linear programming procedure was applied to smooth slightly the bathymetry. The maximum depth of the model domain is 2200 m with a 70 levels general vertical grid which is compressed towards the surface. A detailed description of the GETM equations can be found in Stips et al. [2004].One way to minimize dissipation and dispersion is to use a numerical method which satisfies the Total Variation Diminishing (TVD) property. Flux-limiter methods satisfy the TVD property and switch between a second-order approximation when the field is smooth and a first-order approximation when it is near a discontinuity. Flux-limiter methods have been applied to the different numerical approaches so that oscillations present in the numerical solution can be minimized. The second-order monotone scheme with the Superbee limiter is used herein [Burchard and Bolding 2002]. The meteorological forcing from the European Centre for Medium Range Weather Forecast (ECMWF) available from http://www.ecmwf.int, has been applied, namely, ERA-40 project (1958-2001) and ERA-Interim project (1979-2015). Two model runs have been chosen: Run1 with ERA-40 (1958-1979) followed by forcing with ERA-Interim (1980-2015) and Run2 forced with ERA-Interim (1979-2015), in order to study the effect of the starting year and forcing data and to identify possible artificial trends due to computational and forcing uncertainties. Freshwater input has been evaluated using the values from the Global Runoff Data Centre (GRDC, http://www.bafg.de/GRDC) runoff. Being an estuarine basin, the Black sea is very sensitive to variations in the fresh water input. The resulting buoyancy flow induced by the river runoff is essential for establishing the basin circulation. Comparison between runoff data sets from different data centres has revealed similar climatological mean annual cycles for all rivers considered herein [Miladinova-Marinova et al., 2016]. The mode has been forced the GRDC data because it contains long term daily records of the Danube River. Water exchange in the Bosphorus and Kerch Straits is simulated as a river flow that contains surface outflow/inflow and bottom inflow/outflow. Assuming the long term steady state water and salt budgets in the Black Sea, the monthly averaged volume fluxes have been estimated [Miladinova-Marinova et al., 2016] and used further as a forcing condition. The model is initialized by means of temperature and salinity 3D fields coming from the project MEDAR/MEDATLAS II (http://www.ifremer.fr/medar). The MEDAR data set for the Black Sea reflects the main features known from observations – the strong halocline at 70-150 m, the CIL at approximately 25-70 m and the doming of the isohalines due to the cyclonic Rim current. The detailed model setup and an extended validation is presented in Miladinova-Marinova et al. [2016]. Burchard, H., and K. Bolding (2002), Getm: A general estuarine transport model. Scientific documentation, Joint Research Centre Ispra Tech. Rep. EUR 20253 EN, Eur. Comm; Stips, A., K. Bolding, T. Pohlmann, and H. Burchard (2004), Simulating the temporal and spatial dynamics of the North Sea using the new model GETM (General Estuarine Transport Model), Ocean Dynam., 54, 266-283; Miladinova-Marinova S., A. Stips, E. Garcia-Gorriz, D. Macias Moy (2016), Black Sea ecosystem model: setup and validation, EUR 27786, doi: 10.2788/601495

Simulation zip files from Run1, BLACK_SEA_HYDRO1_YEAR_MONTH.zip, and simulation zip files from Run2, BLACK_SEA_HYDRO2_YEAR_MONTH.zip, are stored herein.