Effect of phytoplankton adaptation on the distribution of its biomass and chlorophyll a concentration in the surface layer of the Black Sea

Using the field data collected in the Black Sea in September 2005-May 2013, the authors studied the spatial variability of the ratio of organic carbon to chlorophyll a (C:Chl a) in the sea surface layer (0-1 m). The C:Chl a ratio is an important parameter that reflects the phytoplankton adaptation to abiotic factors. Its maximum variations occurred in September-October 2005 and October 2010 when the highest spatial variability of average light intensity and nitrogen concentration was observed in the upper mixed layer. As a result, the maps of phytoplankton biomass differed from chlorophyll maps. In August 2011, no effect of light or nitrogen on the spatial variability of the C:Chl a ratio was found. Changes in the contribution of dinoflagellates to the total phytoplankton biomass affected the C:Chl a ratio variability, which was two times lower compared to September-October 2005 and October 2010. Also, the spatial distribution of phytoplankton biomass differed from the distribution of chlorophyll a concentration only in some areas of the sea. In May 2013, environmental factors slightly varied across the study area and the spatial variability of the C:Chl a ratio was insignificant. Therefore, the map of phytoplankton biomass indicated similarities with the chlorophyll map.