Seasonal Variability of Dissolved Organic Carbon in the North-Eastern Black Sea in 2012

The article examines and discusses the seasonal and spatial variability of dissolved organic carbon (DOC), apparent oxygen utilization (AOU), chlorophyll a (chl a), and the proportion of pheophytin in the sum of chl a and pheophytin a (pheo a) along a 5-mile transect opposite Golubaya Bay at stations with depths of 10, 25, 50, 100, and 500 m (Gelendzhik, northeastern Black Sea). Sampling was carried out in 2012 from April to November inclusive with a frequency of one to two times per month. Statistical analysis of the weight average concentrations of DOC and chl a calculated for the entire data set demonstrated a relationship between the seasonal dynamics of DOC and chl a. The Spearman correlation coefficient was R = 0.59 with n = 49. Analysis of the seasonal dynamics of the weight average concentrations of DOC and chl a at individual stations showed the highest relationship between the parameters at the station with a depth of 50 m (R = 0.85, n = 10), quite remote from both continental runoff and the influence of the Rim Current. No significant relationship was found between the temporal dynamics of DOC and pheo a. Considering that the concentration of chl a is an indirect characteristic of the abundance of active autotrophic phytoplankton and pheo a is an indicator of the physiological state of microalgae, it can be suggested that the biomass of autotrophic phytoplankton has a greater impact on the dynamics of DOC than its physiological state (activity).