Fluorescence and absorption properties of chromophoric dissolved organic matter (CDOM) in coastal surface waters of the northwestern Mediterranean Sea, influence of the Rhône River

Abstract

(350) could be determined. By contrast, the spectral slope of CDOM absorption (S CDOM ) was significantly higher (0.023 ± 0.003 nm −1 ) in summer than in fall and winter periods (0.017 ± 0.002 nm −1 ), reflecting either CDOM photobleaching or production in surface waters during stratified sunny periods. The CDOM fluorescence, assessed through excitation emission matrices (EEMs), was dominated by protein-like component (peak T; 1.30-21.94 QSU) and marine humic-like component (peak M; 0.55-5.82 QSU), while terrestrial humic-like fluorescence (peak C; 0.34-2.99 QSU) remained very low. This reflected a dominance of relatively fresh material from biological origin within the CDOM fluorescent pool. At the end of summer, surface CDOM fluorescence was very low and strongly blue shifted, reinforcing the hypothesis of CDOM photobleaching. Our results suggested that unusual RhôneCorrespondence to: R. Sempéré (sempere@univmed.fr) River plume eastward intrusion events might reach Marseilles Bay within 2-3 days and induce local phytoplankton blooms and subsequent fluorescent CDOM production (peaks M and T) without adding terrestrial fluorescence signatures (peaks C and A). Besides Rhône River plumes, mixing events of the entire water column injected relative aged (peaks C and M) CDOM from the bottom into the surface and thus appeared also as an important source of CDOM in surface waters of the Marseilles Bay. Therefore, the assessment of CDOM optical properties, within the hydrological context, pointed out several biotic (in situ biological production, biological production within Rhône River plumes) and abiotic (photobleaching, mixing) factors controlling CDOM transport, production and removal in this highly urbanized coastal area.

Floodplain influence on dissolved organic matter composition and export from the Mississippi—Atchafalaya River system to the Gulf of Mexico

“…Similar observations can be gleaned from comparisons of CDOM from other free-flowing and regulated rivers. Higher CDOM absorption coefficients and DOC-normalized yields were observed in the Congo (Spencer et al 2009), Orinoco (Battin 1998), Mackenzie (Osburn et al 2009), Yukon (Spencer et al 2008), and Atchafalaya Rivers (this study), compared to regulated rivers like the Yangtze (Guo et al 2007), Mississippi (this study), and Rhô ne Rivers (Para et al 2010). Additional studies are needed to gain further insights about the roles of floodplains in shaping the concentrations and compositions of DOM in rivers.…”

Functioning of the planktonic ecosystem on the Gulf of Lions shelf (NW Mediterranean) during spring and its impact on the carbon deposition: a field data and 3-D modelling combined approach

“…B2). A contribution of CDOM absorption was furthermore introduced from in situ optical measurements (Para et al, 2010) in the Rhone River (Eq. B2).…”

The composition and flux of particulate and dissolved carbohydrates from the Rhone River into the Mediterranean Sea

“…However, these investigations focused on measurements of POM, DOM, nutrients, dissolved inorganic carbon (DIC), chromophoric dissolved organic matter (CDOM), total suspended matter (TSM) fluxes, and freshwater discharges (Coste and Raimbault, 1993;Sempéré et al, 2000;Pont et al, 2002;Para et al, 2010); therefore, little information regarding labile biochemicals (e.g. carbohydrates) in both particulate and dissolved fractions is currently available.…”