The Roles of Kuroshio-Origin New and Regenerated Nutrients Over the East China Sea Shelf

The Kuroshio brings a large amount of nutrients into the East China Sea, making it the largest source of external nutrients. However, significant unknowns remain regarding how they support primary production and how these Kuroshio-intruded nutrients are regenerated in the East China Sea. A physical-biological coupled module and a nutrient tracking module were used to classify Kuroshio nutrients (including dissolved inorganic phosphorus and dissolved inorganic nitrogen (DIN)) into two types: new nutrients and regenerated nutrients. The spatiotemporal distributions of new and regenerated nutrients in the East China Sea shelf were examined, and the contributions of Kuroshio nutrients to the new and regenerated production on the East China Sea shelf were assessed. New production supported by new nutrients is mainly located in the outer shelf, while the regenerated production supported by regenerated nutrients can extend into the inner shelf. The new (regenerated) DIN makes up 72.8% (27.2%) of the total inventory of DIN from the Kuroshio over the East China Sea and the new (regenerated) production accounts for 44.0% (56.0%) of primary production using DIN from Kuroshio. The new and export productions supported by Kuroshio nutrients are not balanced in the ECS shelf. The difference between them is attributed to the offshore transport of the regenerated nutrients, which induces a part of the regenerated nutrients not used for the export production in the ECS shelf. Therefore, lateral transport of regenerated nutrients away from shelf seas can serve as a new process for understanding the mismatch of new and export production there.