Modelling of Long-term Variability of the Black Sea Dynamics and Changes of Ecosystem Characteristics

A three dimensional coupled physical-biological model of the Black Sea is provided to investigate the long-term changes of its ecosystemcharacteristics under the synergic impact of eutrophication, climatic changes and population outbreak of the gelatinous invader Mnemiopsis leidyi.The circulation model fields are simulated using a high frequency ERA40 atmospheric forcing as well as assimilation of the available hydrographicand altimetry sea level anomaly data for a 30-year period (1971-2001). The circulation model resolves well different temporal and spatial scalesfrom mesoscale to the sub-basin scale and from the seasonal peaks to the decadal scale trend-like changes. The biogeochemical model includes themajor vertical biological and chemical interactions, and the processes up to the anoxic interface zone. Its food web structure is represented by twophytoplankton- and zooplankton-size groups, bacterioplankton, gelatinous carnivores Mnemiopsis and Aurelia, and opportunistic species Noctilucascientillans.The nitrogen cycling is accommodated by the particulate and dissolved organic nitrogen compartments and the dissolved inorganicnitrogen in the forms of ammonium, nitrite and nitrate. The ecosystem model can simulate successfully the major observed features and trends ofthe intense eutrophication phase (from the early seventies to early nineties), but also can be modified for better simulating the ecosystem conditionsof the post-eutrophication phase.