Seasonal Dynamics and Estimation of the Annual Primary Production of Phytoplankton in the Black Sea

Seasonal variations in the surface chlorophyll a concentrations (Chl(s)) and the integrated primary production (PPinf) were investigated for ten regions of the Black Sea based on long term observations (1973-1997). Two or three maximums of both Chl(s) and PPinf were registered in most of the shelf regions (SR, < 200 m), the continental slope (CS, 200-1500 m), and the deep regions (DSR > 1500 m) in February-March, June-August, and October-November. Such a pattern suggests that the seasonal dynamics of PPinf strongly depend on the Chl(s) variability. The mean annual values of the PPinf comprised 130-420, 130-150, and 140-150 g C m(-2) in the SR, CS, and DSR, respectively. These values are mainly typical of the eutrophic layer and the transition between the eutrophic and mesotrophic waters (SR) or for the upper boundary of the mesotrophic waters (CS and DSR). The maximal contribution of the wintertime (December-March) to the total PPinf values (40-42%) was observed in the DSR. In the SR and the adjacent eastern CS areas, the proportion of the PPinf summertime production (June-September) reaches 40-60% and is higher than the wintertime production. The lowest values of PPinf (9-17%) were produced in the spring and autumn periods. The total annual values of PPinf in the Black Sea are close to 50-70 Mt C.