[en] Full text: Dissolved Inorganic Carbon (DIC) transported by rivers originates from three main sources : (1) the dissolution of carbonate rocks (with a δ¹³C close to 0 per mille); (2) the soil CO₂ derived from the degradation of organic matter and root respiration. This CO₂ participates, after forming carbonic acid in presence of water, to the alteration of silicate minerals. The isotopic signature of this source depends of the type of vegetation (around -26 per mille for C3 plants and -12 per mille in presence of C4 plants). The third source is the atmospheric CO₂, with a δ¹³C of -8 per mille. Within the frame of the PARAT project, the Patagonian rivers (Colorado, Negro, Chubut, Deseado, Coyle, Chico, Santa Cruz and Gallegos) have been sampled between September 1995 and November 1998 to determine their chemical and isotopic composition, the origin of the suspended and dissolved river load and their inputs to the South Atlantic Ocean. The results obtained for the δ¹³C_DIC at the mouth of these rivers varies between -12.8 per mille and -1.8 per mille. One can distinguish two groups of rivers : The Colorado, Negro, Chubut and Santa Cruz Rivers that display the higher values, and very low variations of the DIC isotopic signature. These results indicate important exchanges with the atmospheric CO₂, due to the presence of lakes and dams on theses rivers. A similar pattern could be observed for the St. Lawrence River. On the other hand the Deseado, Coyle Chico and Gallegos Rivers show lower values and higher variation of the signal. No relationship with seasonality can be determined because of too few available discharge data. Spatially, an increasing trend of the δ¹³C_DIC between the source and the mouth can be observed as a result of progressive equilibrium with atmospheric CO₂ for all the rivers, excepted for the Coyle river. For this river, the decrease exhibits the role of organic carbon oxidation in the river. Indeed, the plot of the DIC isotopic signature versus DOC content shows that the less negative values of δ¹³C_DIC correspond to the highest DOC concentrations. This relationship shows that, in the river, organic carbon oxidation or respiration contributes to increase the pool of DIC (eq.1: CH₂O + O₂ ↔ CO₂ + H₂O) and to lower the isotopic signal. In terms of DIC budget exported by the Patagonian Rivers to the South Atlantic Ocean, one can estimate a flux of 603.10³ T/year of inorganic carbon with a mean δ¹³C value of -4,9 per mille. (author)