The Southern Ocean with the largest uptake of anthropogenic nitrogen into the ocean interior.

The oceanic external nitrogen (N) deposition to the global ocean is expected to rise significantly owing to human activities. The Southern Ocean (SO) is an important pathway, which brings external influences into the ocean interior. It touches the borders of several developing countries that emit a large amount of anthropogenic nitrogen. To comprehend the dynamics of N in the SO, we developed a new method to assess the change in the oceanic uptake of N (ΔN) in the entire SO. We obtained the spatiotemporal distribution of ΔN in the SO by applying this method to a high-resolution grid data constructed using ship-based observations. During the 1990s to the 2010s, N increased significantly by 67 ± 1 Tg-N year in the SO. By comparing this value with the rate of N deposition to the ocean, the SO has received ~70% of N deposition to the global ocean, indicating that it is the largest uptake region of anthropogenic nitrogen into the ocean interior.