A model tracer study tracking global riverine freshwater in the world ocean

The distributions and effects of river water in the global ocean are studied by tagging riverine freshwater sources with passive tracers in the Community Earth System Model. Waters input by precipitation and sea-ice melt are also tagged with passive tracers to assess the influences of river runoff relative to these sources. Long-term tracer results show high concentrations of riverine source tracers near major river mouths as well as in the coastal ocean. For offshore waters, the Arctic and North Atlantic Oceans have overall higher river tracer concentrations than other oceans. The Arctic and North Atlantic Oceans are also characterized by higher ratios of river water to total freshwater from all sources than the ratio of global river discharge to combined global inputs from rivers, precipitation, and sea-ice melt. River waters contribute over half of the global coastal salinity stratification and as much as 80% of the stratification close to river mouths and on the Eurasian Arctic continental shelf. The river water on the Arctic continental shelf has the longest residence time, followed by the Indian, Pacific, Atlantic and Southern Ocean continental shelves. On the eastern margins of the Pacific and Indian Oceans, the river water has shorter residence times than on their western margins. Over time, river waters also reach the ocean interior driven by North Atlantic Deep Water (NADW) formation. It takes about 40 years for river water to reach 30 S within the NADW. River water accounts for about 13% of the total freshwater carried by the NADW.