Spatial Distributions and Seasonal Variations of Dissolved Black Carbon in the Bohai Sea, China

To investigate the temporal and spatial variations of dissolved black carbon (DBC) concentrations in the Bohai Sea, China, 495 seawater samples on 141 sites were collected in different water depths and seasons in six cruises from 2010 to 2014 for DBC quantification by the molecular marker method-benzene polycarboxylic acid method. The average concentration of DBC was 96.6 +/- 32.9 mu g L-1 (n = 495) in the entire Bohai Sea, while it was 136. 2 +/- 33.7 mu g L-1 (n = 28) in the Laizhou Bay, 131.2 +/- 30.3 mu g L-1 (n = 44) in the Bohai Bay, 86.3 +/- 16.1 mu g L-1 (n = 66) in the Liaodong Bay, 89.6 +/- 19.8 mu g L-1 (n = 277) in the Central Bohai Basin and 57.8 +/- 8.6 mu g L-1 (n = 80) in the Bohai Strait respectively. DBC concentrations showed a distinct decreasing trend from coastal area to offshore area and from the internal Bohai Sea to the Bohai Strait in horizontal distribution although no significant differences(p > 0.1) was observed in the vertical water column. The average DBC concentrations of the Central Bohai Basin and the Bohai Strait in spring, summer, autumn and winter were comparable. However the DBC concentration patterns in different seasons varied significantly, such as the DBC concentrations were lower in the southern than northern of the Bohai Strait in spring, but it was inversed in autumn and winter. The seasonal variations of DBC concentration patterns followed the seasonal variations of ocean currents, suggesting that DBC would serve as a potential marker for the hydro-dynamics study.