Biogeochemical cycles associated with mesoscale eddies in the South China Sea (SCS) were investigated. The study was based on a coupled physical-biogeochemical Pacific Ocean model (Regional Ocean Model SystemCarbon, Silicate, and Nitrogen Ecosystem, ROMS-CoSiNE) simulation for the period from 1991 to 2008. A total of 568 mesoscale eddies with lifetime longer than 30 days were used in the analysis. Composite analysis revealed that the cyclonic eddies were associated with abundance of nutrients, phytoplankton, and zooplankton while the anticyclonic eddies depressed biogeochemical cycles, which are generally controlled by the eddy pumping mechanism. In addition, diatoms were dominant in phytoplankton species due to the abundance of silicate. Dipole structures of vertical fluxes with net upward motion in cyclonic eddies and net downward motion in anticyclonic eddies were revealed. During the lifetime of an eddy, the evolutions of physical, biological, and chemical structures were not linearly coupled at the eddy core where plankton grew, and composition of the community depended not only on the physical and chemical processes but also on the adjustments by the predator-prey relationship.
Mesoscale eddies in the oceans are known to modify the nutrient supply, stimulate phytoplankton growth, and significantly affect carbon fixation. Submesoscale processes associated with mesoscale eddies have been suggested to induce even stronger variability in phytoplankton dynamics; however, their large‐scale impact has not been quantitatively evaluated in the global ocean. By combining multiple satellite products to resolve both mesoscale and submesoscale dynamic regimes, we evaluated their contributions to high sea surface chlorophyll. Our results reveal that the dominant dynamics associated with high chlorophyll in different gyres are not the same and can vary from the mesoscale to the submesoscale. In subtropical gyres worldwide, the contribution of submesoscale structures around mesoscale eddies to high chlorophyll is comparable to that of mesoscale eddies (34.1% versus 30.8%). These results extend our current understanding of the impacts of eddies on biogeochemical processes and may have important implications for the global carbon cycle.
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