Reshaping of New Nitrogen Regime by Anticyclonic Eddies in the Northern South China Sea

作者：Juan Tian, Yue Zhang, Hongmei Jing, Haojia Ren, Huabin Mao, Hantao Zhou, Minfang Zheng, Mengya Chen, Run Zhang, Min Chen · 发表于：Journal of Geophysical Research Oceans · 年份：2025 · DOI：10.1029/2024jc021684 · 被引用次数：4 · 研究领域：Marine and coastal ecosystems、Oceanographic and Atmospheric Processes

Abstract Mesoscale anticyclonic eddies (ACEs) act as an important physical disturbance for marine biogeochemical cycle, but our knowledge of the dynamics of critical new nitrogen (N) sources in such environments remains ambiguous. Here, we report concurrent data on two major sources of new N , that is, the N 2 fixation rate (via 15 N 2 bubble release method) and vertical diffusive nitrate flux ( F diff ‐), for the euphotic zone (EZ) in the northern South China Sea ACEs during summer 2020. Depth‐integrated N 2 fixation rates (INF) were moderately elevated (∼30%) in the center of the ACEs compared with those in the outside stations, suggesting that ACEs generally provide a more favorable environment for N 2 fixation. In contrast, the upward F diff ‐ into the EZ were greatly lowered by an order of magnitude in the ACE center (center: 26.0 ± 8.2 μmol N m −2 d −1 ; outside: 124.0 ± 127.6 μmol N m −2 d −1 ), thus making N 2 fixation a much more significant contributor to new production under ACE influence. Such contribution is further demonstrated in the nutrient depleted layer where substantial carbon export may be taking place. Interestingly, a significant positive correlation for the ratio of the INF to the upward F diff ‐ versus sea level anomaly was observed. ACE will likely leave an imprint on the isotopic composition of exported N, implying that there is possibly a need to take mesoscale forcings into account when interpreting isotopic signals from sinking particles. These f...