Characterization of dissolved organic matter fluorescence in the South Atlantic Bight with use of a PARAFAC model:

Systematic water sampling for characterization of chromophoric dissolved organic matter (CDOM) in the coastal South Atlantic Bight was conducted as part of the long term Coastal Ocean Research and Monitoring Program (CORMP). Water samples were collected during a 3.5 year period, from October 2001 until March 2005, at the vicinity of the Cape Fear River (CFR) outlet and in adjacent Onslow Bay (OB). In this study, we investigate the use of the CDOM absorption coefficient at 350 nm - aCDOM(350), and CDOM Excitation Emission Matrix (EEM) fluorescence in estimating annual fluxes of the Dissolved Organic Carbon (DOC) from the Cape Fear River to Long Bay in the South Atlantic Bight. Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra and six components were identified: three terrestrial humic-like, one marine humic-like and two protein-like components. We have derived empirical relationships between DOC concentration and the aCDOM(350), total fluorescence intensity and the intensities of respective EEM components derived from the PARAFAC model. DOC concentration and CDOM optical parameters were very well correlated and R2 ranged between 0.77 and 0.90. Regression analysis revealed that the offset in DOC concentration estimations with the use of CDOM optical parameters varies with the qualitative composition of CDOM. The relationships between DOC concentration and intensity of the humic-like CDOM components characterized by excitation maximum at longer wavelengths have significantly higher DOC estimation offsets compared to analogous relationships between DOC and intensity of the humic-like CDOM components characterized by excitation maximum at shorter wavelengths. The relationships between DOC concentration and intensity of one of the protein-like components resulted with no offset in DOC concentration estimation. We have investigated the influence of the CDOM composition on the value of the organic carbon-specific CDOM absorption coefficient, a*CDOM(350), and fluorescence intensity. This data suggests that the relative proportion of humic-like CDOM components (characterized by excitation maximum at longer wavelengths) and the main protein-like component have the biggest impact on the values of a*CDOM(350). Based on the relationships between aCDOM(350) and Caper Fear River flow and aCDOM(350) and DOC concentrations DOC fluxes were estimated for 2002, 2003 and 2004. The DOC fluxes varied between 1.5 ÷ 6.2 1010 gCyr-1, depending on the river flow.