Distribution Characteristics of Nutrients in the Kuroshio Extension Region of the Northwest Pacific Ocean

This study investigated the distribution patterns of dissolved inorganic nitrogen (DIN; NO₃^-+NO₂+NH₃), phosphate (PO₄), and silicate (SiO₃) in the Kuroshio Extension (KE) region and their controlling factors, based on field data collected in May-June, 2021. The results indicate that the Kuroshio-Oyashio interaction dominates the spatial pattern of nutrients through physical biogeochemical coupling processes: the surface nutrient distribution has significant spatial differences, and the NO₃^- concentration in the northern part of the surveyed sea area affected by Oyashio Current is 3~4 times higher than that in the southern part. The vertical distribution of DIN shows a trend of "surface consumption middle enrichment deep gradual decline", and the changes in PO₄ and DIN are consistent; And dominated by siliceous biological pumps, SiO₃ continue to accumulate with depth. Under the synergistic regulation of water mass dynamics and biological cycles, NO₂ exhibits a bipolar distribution, with the bipolar layer corresponding to the nitrification equilibrium zone at the bottom of the euphotic layer and the microbial processes at the tidal front. E2 station′s subsurface anticyclone caused the sinking of the iso density surface, forming a warm core and low nutrient zone, while E4 station exhibited low temperature and high nutrient characteristics due to the invasion of the intertidal subsurface. These patterns were regulated by the Kuroshio-Oyashio interaction and biogeochemical processes. Our findings advance the understanding of nutrient dynamics in this ecologically critical region.