First data on dissolved black carbon in the coastal Northwestern Mediterranean Sea

The spatial distribution of dissolved black carbon (DBC) concentrations was investigated using the benzene-polycarboxylic acid (BPCA) method applied to 28 subsurface seawater samples collected in the Rhone-Fos-Marseille area (Northwestern Mediterranean Sea, Southern France), a coastal zone heavily influenced by the Rhone River and maritime traffic. DBC concentrations, ranging from 9 to 27 µg C L^-1, showed clear spatial differences across the sampling sites. Significantly higher concentrations were observed at the mouth of the Rhone River and in the harbour areas. The DBC/dissolved organic carbon (DOC) ratio ranged from 0.9 to 2.8%, while the B6CA/B5CA ratios, ranged from 0.14 to 0.21, potentially reflecting a diversity of sources of BC in this area. DBC concentrations were significantly correlated with the combustion fluorescence index (COX). Overall, this study highlights the presence of DBC at substantial concentrations in the Rhone-Fos-Marseille area, emphasizing the need for further research to identify its sources and assess its impacts on marine ecosystem.