Most global carbon-budgeting efforts assume a direct “pipeline” transfer of carbon dioxide (CO₂) from river mouths to the open ocean. But that ignores the complex interplay between streams, rivers, lakes, groundwater, estuaries, mangroves and more.

Now, a study published in the current issue of Nature details how carbon is stored and transported through the intricate network of inland and coastal waterways.

The researchers, co-led by Laure Resplandy, an assistant professor of geosciences at Princeton, discovered that this network carries a substantial amount of carbon of anthropogenic (e.g., fossil-fuel) origin. Thus, the carbon removed from the atmosphere by terrestrial ecosystems is not all stored locally, as is commonly assumed.

The researchers also found that the land-to-ocean carbon transfer of natural origin was larger than previously thought, with far-reaching implications for the assessment of the anthropogenic CO₂ uptake by the ocean and the land.

The study demonstrates that anthropogenic carbon carried by rivers is either outgassed back to the atmosphere or eventually stored in aquatic sediments and the open ocean.

The work has significant implications for enforcing the carbon calculations that are part of international climate accords.