[A-OS26] Global ocean observing systems, their recent status, research results and future directions

[AOS26-P04] Spatiotemporal distribution of anthropogenic nitrogen and internal nitrogen dynamics in the Southern Ocean

*Xianliang Pan¹, Bofeng Li¹, Zhigang Chen¹, Yutaka Watanabe¹ (1.Hokkaido University)

Keywords:Southern Ocean, Anthropogenic nitrogen, Decadal variation, Nitrogen budget

The oceanic external nitrogen (N_ex) 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. It touches the borders of several developing countries that emit a large amount of anthropogenic nitrogen. To comprehend the dynamics of N_ex in the SO, We developed a new method to assess the change in the oceanic uptake of N_ex (ΔN_ex) in the entire SO. We obtained the spatiotemporal distribution of ΔN_ex 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_ex increased significantly by 67±1 Tg-N year^-1 in the SO. By comparing this with the rate of N_ex deposition to the ocean, the SO has received ~ 70% of N_ex deposition to the global ocean, indicating that it is the largest uptake region of anthropogenic nitrogen into the ocean interior. Additionally, in order to comprehensively understand the impact of natural nitrogen dynamics on N_ex transportation in the ocean interior, We have also quantified the nitrogen budget over the 110°E line using the chemical tracer N₂^*. The natural nitrogen balance of SO was found to be controlled primarily by physical processes, rather than being consumed by living organisms. As a result, N_ex is also possibly spreading from the SO to the global ocean through transportation of water mass.