Comparative characterization of humic substances from the open ocean, estuarine water and fresh water

• Published in: Organic Geochemistry
• Main Authors: Esteves, Valdemar I., Otero, Marta, Duarte, Armando C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2009
• Subjects: Morena; North Atlantic
• Online Access: http://hdl.handle.net/10773/5504; https://doi.org/10.1016/j.orggeochem.2009.06.006

Humic substances were isolated from ocean, estuarine water and fresh water using a two column array of XAD-8 and XAD-4 resins in series. The extracted fulvic acids and XAD-4 fraction from different origins were characterized using UV–vis., molecular fluorescence, Fourier transform infrared (FTIR) spectroscopy and cross polarization magic angle spinning (CPMAS)-13C nuclear magnetic resonance (NMR) spectroscopy. The isolation procedure allowed us to obtain the necessary amount of sample for characterization, even in the case of open ocean water, which has a very low amount of dissolved organic carbon (DOC). Humic substances from the open ocean showed the lowest chromophore and fluorophore contents and showed relatively greater fluorescence at lower wavelengths than those from fresh water. FTIR and 13C NMR spectra highlighted the idea that humic substances from a marine environment have a more branched aliphatic structure and less aromatic structure than those highly influenced by terrestrial sources. The spectra also suggest that the open ocean humic substances have a higher content of olefinic carbons than aromatic- or alkyl-substituted carbons. CEE MAST-0019-C: Biogeochemical Carbon Cycling in Coastal Zones CEE MAS2-CT93-0065: Multidisciplinary Oceanographic Research in the Eastern Boundary of the North Atlantic (MORENA)