Although the Arctic Ocean only comprises ∼1% of the global ocean volume, it receives about 10% of the global river discharge [Shiklomanov, 1998]. Therefore a greater influence of terrigenous organic matter from the river discharge is expected in the Arctic Ocean than in other ocean basins. Indeed, a strong terrestrial origin of dissolved organic matter (DOM) has been reported in the surface water of the Arctic Ocean [Opsahl et al., 1999; Amon et al., 2003; Amon and Meon, 2004; Guéguen et al., 2005].
 Colored dissolved organic matter (CDOM), which absorbs light in the UV–visible range, represents one fraction of the DOM pool (up to 25% [Benner, 2002]). Changes in CDOM fluorescence reflect the effects of physical and chemical processes that occur in the water column as well as variations in CDOM composition from different sources [Coble et al., 1990; Mopper and Schultz, 1993; Coble, 1996; Del Castillo et al., 2000; Guéguen et al., 2005].
 An important characteristic of the Arctic Ocean is its large continental shelf, which represents approximately 30% of its surface area. During sea ice formation in winter seasons, dense water cascading over the continental shelf around the Arctic Ocean could be an important transport pathway for DOM and other chemical species [Aagaard et al., 1985; Macdonald et al., 2002; Amon et al., 2003]. For example, sea ice formation could induce expulsion of sea salts, nutrients, and DOM from the shelf to the arctic basin [Giannelli et al., 2001; Thomas et al., 2001]. The Arctic Ocean is thus a region well suited to the study of the fate and transport of terrestrial organic matter and thus the shelf-basin interactions.
 Another important feature of the upper surface water column in the Arctic Ocean is the dominance of a strong halocline that separates the surface water from the underlying Atlantic-origin waters. In the Canada Basin, Pacific-origin waters [Roach et al., 1995] make up a substantial part of the upper halocline layer. This Pacific-origin water entering via the Bering Strait can be highly modified on the shelves by runoff, sea ice formation, and primary production. Associated with the upper halocline is a prominent nutrient maximum [Jones and Anderson, 1986] due to sea ice formation [Aagaard et al., 1981; Melling and Lewis, 1982] and interactions with sediments [Moore et al., 1983] on the shelves. Since these processes could be sources of DOM, a transport of organic matter into the halocline layer from the shelves to the arctic basin could be expected [Walsh, 1995; Walsh et al., 1997].
 In the Canada Basin, the occurrence of the nutrient-rich Pacific-origin waters coupled with large river inflows supports a substantial primary productivity on the western arctic shelves (360 and 40 g C m−2 yr−1 in Chukchi and Beaufort shelves, respectively [Fasham, 2003]). Surface layer biological productivity leads to the production of DOM, which can eventually be exported to depth [Melnikov and Pavlov, 1978; Bertilsson and Jones, 2003]. Because the arctic shelves are usually relatively shallow, the interactions with sediments and pore waters may also be an important source of CDOM [Skoog et al., 1996], particularly during the resuspension events caused by storms, ice rafting and bottom currents [Reimnitz et al., 1992; Eicken et al., 1997]. These different processes occurring on the arctic shelves may constitute substantial sources of CDOM, and therefore may play an important role in the cycling of DOM in the Arctic Ocean.
 In the present study, the nature and origin of CDOM in the western Arctic Ocean was investigated with a special emphasis on the influence of terrestrial DOM and implications for shelf-basin interactions. The Chukchi shelves with high in situ production, and Beaufort shelves with a strong influence of large river discharge, were compared in term of origin and behavior of CDOM. Specifically, three-dimensional excitation/emission matrices (3-D EEMs) were used to distinguish terrestrial from marine CDOM.