Eurico J. D’Sa, Edward B. Overton, Steven E. Lohrenz, Kanchan Maiti, R. Eugene Turner, Angelina Freeman

The characteristics of fluorescent components of dissolved organic matter (DOM) were examined using excitation emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) for seawater samples obtained from the northern Gulf of Mexico (NGoM) before, during and after the 2010 Deepwater Horizon (DwH) oil spill. An EEMs PARAFAC modeling of samples collected within 16 km of the well head during the oil spill in May 2010, which included one typical subsurface sample with a PAH concentration of 1.09 μg/L, identified two humic-like and two previously reported oil-like components. Compared to pre-spill levels, however, there were an order of magnitude higher fluorescence intensities associated with these components that are consistent with an oil spill source. The spectral decomposition of the EEMs data using individual and combined datasets from coastal and offshore waters impacted by the DwH spill further revealed the changing nature of fluorescent DOM composition. Although the PAHs concentrations were at pre-spill conditions after the spill in 2012 and 2013 near the DwH site, the variable and anomalous levels of fluorescence intensities and DOC concentrations three years following the spill suggest potential long-term persistence of the oil in the DOC pool in the NGoM.