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<p>Rivers are a major source of nutrients, carbon and alkalinity to the global ocean. In this study, we firstly estimate pre-industrial riverine loads of nutrients, carbon and alkalinity based on a hierarchy of weathering and terrestrial organic matter export models, while identifying regional hotspots of the riverine exports. Secondly, we implement the riverine loads into a global ocean biogeochemical model to describe their implications for oceanic nutrient concentrations, net primary production (NPP) and air–sea <span class="inline-formula">CO₂</span> fluxes globally, as well as in an analysis of coastal regions. Thirdly, we quantitatively assess the terrestrial origins and the long-term fate of riverine carbon in the ocean. We quantify annual bioavailable pre-industrial riverine loads of 3.7&thinsp;Tg P, 27&thinsp;Tg N, 158&thinsp;Tg Si and 603&thinsp;Tg C delivered to the ocean globally. We thereby identify the tropical Atlantic catchments (20&thinsp;% of global C), Arctic rivers (9&thinsp;% of global C) and Southeast Asian rivers (15&thinsp;% of global C) as dominant suppliers of carbon for the ocean. The riverine exports lead to a simulated net global oceanic <span class="inline-formula">CO₂</span> source of 231&thinsp;Tg C&thinsp;yr<span class="inline-formula">⁻¹</span> to the atmosphere, which is mainly caused by inorganic carbon (source of 183&thinsp;Tg C&thinsp;yr<span class="inline-formula">⁻¹</span>) and by organic carbon (source of 128&thinsp;Tg C&thinsp;yr<span class="inline-formula">⁻¹</span>) riverine loads. Additionally, a sink of 80&thinsp;Tg C&thinsp;yr<span class="inline-formula">⁻¹</span> is caused by the enhancement of the biological carbon uptake from dissolved inorganic nutrient inputs from rivers and the resulting alkalinity production. While large outgassing fluxes are simulated mostly in proximity to major river mouths, substantial outgassing fluxes can be found further offshore, most prominently in the tropical Atlantic. Furthermore, we find evidence for the interhemispheric transfer of carbon in the model; we detect a larger relative outgassing flux (49&thinsp;% of global riverine-induced outgassing) in the Southern Hemisphere in comparison to the hemisphere's relative riverine inputs (33&thinsp;% of global C inputs), as well as an outgassing flux of 17&thinsp;Tg C&thinsp;yr<span class="inline-formula">⁻¹</span> in the Southern Ocean. The addition of riverine loads in the model leads to a strong NPP increase in the tropical west Atlantic, Bay of Bengal and the East China Sea (<span class="inline-formula">+</span>166&thinsp;%, <span class="inline-formula">+</span>377&thinsp;% and <span class="inline-formula">+</span>71&thinsp;%, respectively). On the light-limited Arctic shelves, the NPP is not strongly sensitive to riverine loads, but the <span class="inline-formula">CO₂</span> flux is strongly altered regionally due to substantial dissolved inorganic and organic carbon supplies to the region. While our study confirms that the ocean circulation remains the main driver for biogeochemical distributions in the open ocean, it reveals the necessity to consider riverine inputs for the representation of heterogeneous features in the coastal ocean and to represent riverine-induced pre-industrial carbon outgassing in the ocean. It also underlines the need to consider long-term <span class="inline-formula">CO₂</span> sources from volcanic and shale oxidation fluxes in order to close the framework's atmospheric carbon budget.</p>