fueling alternative labile carbon source to sustain local carbon demand in addition to autochthonous carbon source derived from phytoplankton and heterotrophic microbial food web (Semp r et al., 2000) and increasing light attenuation ee (Blough and Del Vecchio, 2002; Nelson and Siegel, 2002). Chromophoric (or colored) dissolved organic matter (CDOM), which is the fraction of DOM that absorbs light over a broad range of ultraviolet (UV) and visible wavelengths, is essentially controlled by in situ biological production, terrestrial inputs (sources), photochemical degradation, microbial consumption (sinks), as well as deep ocean circulation (Siegel et al., 2002; Nelson et al., 2007; Coble, 2007) and upwelling and/or vertical mixing (Coble, 1996; Parlanti et al., 2000). CDOM is the major factor controlling the attenuation of UV radiation in the ocean (Kirk, 1994) and is highly photoreactive and efciently destroyed upon exposure to solar radiation (Mopper and Kieber, 2000, 2002). In the past 20 years, CDOM uorescence properties have been widely studied owing to excitation-emission matrices (EEMs). Coble et al. (1990) highlighted that the uorescence properties of the Black Sea CDOM came from two types of uorescent peaks (humic-like and protein-like). Protein-like uorescence, considered as a proxy for labile DOM (Yamashita and Tanoue, 2003), has been frequently reported (Mopper and Schultz, 1993; De Souza-Sierra et al., 1994; Determann et al., 1994, 1996; Coble, 1996; Mayer et al., 1999). The identication/quantication of humic-like and protein-like peaks from EEMs has thus allowed determining the dynamics of DOM in relation to its biological reactivity. In addition, uorescence indices have also been used to assess the origin and dynamics of uorescent CDOM, especially in the coastal areas subjected to freshwater inputs. The humication index (HIX, Zsolnay et al., 1999) and the biological index (BIX, Huguet et al., 2009) have been employed to determine the relative degree of humication and autotrophic productivity of uorescent CDOM, respectively. Freshwater inputs play a major role in the biogeochemistry of the coastal areas with a world annual fresh water discharge of 40 000 km3 , more than 25 billions tons of particulate and dissolved matter (Milliman et al., 1995) and transporting on average 1 ± 0.2 Gt of carbon per year in particulate and dissolved forms (Amiotte-Suchet et al., 2003). In the Mediterranean Sea, freshwater inputs enhance signicantly primary productivity (Cruzado and Velasquez, 1990; Joux et al., 2009). The annual uvial loading of TOC to the Mediterranean Sea comprises 0.08–0.3% of the standing stock of TOC in the whole Mediterranean Basin (Semp r et ee al., 2000), which is much higher than the average value reported for the World Ocean (0.024%, Smith and Hollibaugh, 1993). Since the damming of the Nile, the Rh ne River beo came the major source of fresh water and terrigenous particles to the Mediterranean basin (Margat, 1992). Its mean freshwater discharge is around 1700 m3 s1 , which represents 90% of the total freshwater input in the Gulf of Lion's continental shelf (Durrieu de Madron et al., 2003) and 3– Biogeosciences, 7, 4083–4103, 2010

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