2025 Volume 81 Issue 17 Article ID: 25-17171
To elucidate the mechanisms underlying wintertime phytoplankton primary production that modulates the intensity of the subsequent spring bloom in the offshore region of Enshu-nada Sea, a six-year numerical reanalysis was conducted using a three-dimensional physical–biogeochemical coupled model (ROMS-NPZD). Primary productivity exhibited pronouced contrasts between the northern and southern flanks of the Kuroshio path, with wintertime spatial variability strongly influenced by variations in the Kuroshio path. The wintertime carbon-based primary production was estimated at approximately 4.0 × 106 tons during meandering phases and 3.6 × 106 tons during non-meandering phases of the Kuroshio, indicating an enhanced carbon uptake of about 0.4 × 106 tons due to the meandering state. Furthermore, empirical orthogonal function (EOF) analysis was conducted to assess the contributions of seasonal wind-induced coastal upwelling and localized upwelling induced by anticloclwise cold-core eddies and bathymetric features such as submarine ridges. The results suggest that wintertime primary production in the offshore Enshu-nada region is regulated by the synergistic interplay of Kuroshio path variability, seasonal wind forcing, and topographic modulation.
