The Kuroshio Extension (KE) is a natural boundary region characterized by complex hydrodynamic processes in the western North Pacific Ocean that fuel spring phytoplankton blooms in high latitudes. This study looked at the spatial patterns and diversity of phytoplankton community and biomass associated with oceanographic profiles across the KE from the north to south in June 2011. Results showed that upper-ocean gradients were strongly correlated with observed spatial variability in phytoplankton communities (> 10 μm). Phytoplankton abundance, species richness, and Chl a biomass were generally higher in the Kuroshio–Oyashio transition region than in the KE axis and the southern KE. No bloom event was recorded in late spring. A total of 81 phytoplankton taxa belonging to 45 genera of four phyla were identified. Dominant taxa in both abundance and occurrence included the diatoms Chaetoceros radicans, C. curvisetus, C. convolutes, C. deblis, C. peruvianus, Pseudonitzchia delicatissima, Coscinodiscus asteromphalus, Thalassionema nitzschioides, T. frauenfeldii, Thalassiothrix longissima, the dinoflagellates Protoperidinium pyrifoprmus, and the Cyanobacterium Trichodesmium thiebautii. Depth-averaged abundance and Chl a were 2076 ± 3,615 cells L⁻¹ and 0.20 ± 0.10 mg m⁻³, respectively. Subsurface Chl a maxima (SCM) was mainly found at 50 m, while the abundance maximum differed regionally in the water column. A cluster analysis grouped phytoplankton communities into three assemblages related to geographic locations influenced by Oyashio and Kuroshio currents. Nutrient limitation rather than light led to low Chl a and abundance during late spring. Redundancy correspondence and spearman’s correlation further suggest that dissolved inorganic nitrogen was the major factor regulating phytoplankton distribution north of KE, while phosphate limitation was more prominent in the KE axis and the southern KE. The Oyashio and Kuroshio interaction caused evident variability in the hydrodynamic environment including the MLD and Z_eu of the region, and changes in chemical profiles such as nutrients, pH, and DO. The observed distributional shift in the spatial pattern of phytoplankton was attributed to upper-ocean environmental gradients within the KE axis and its northern and southern sections.

黑潮扩展区（KE）是一个自然边界区域，其特征是北太平洋西部的复杂水动力过程，使春季的浮游植物在高纬度地区开花。这项研究研究了2011年6月从南北向南穿过KE的浮游植物群落和生物量的空间格局和多样性，以及与海洋剖面相关的生物量。结果表明，上层海洋梯度与浮游植物群落的空间变异性密切相关（> 10微米）。浮游植物的丰度，物种丰富度和叶绿素a黑潮-大潮过渡区的生物量通常比KE轴和KE南部更高。春末没有记录到盛开的事件。共鉴定到浮游植物类群81个，属于4个门的45属。在这两种丰度和发生优势种类包括硅藻角毛藻radicans，C. curvisetus，C.盘旋，C. deblis，C。peruvianus，Pseudonitzchia delicatissima，Coscinodiscus asteromphalus，Thalessionema nitzschioides，T。frauenfeldii，Thalassiothrix longissima，鞭毛虫吡喃丙酸原卟啉菌和锡氏梭状芽胞杆菌（Cyanobacterium Trichodesmium thiebautii）。深度平均丰度和叶绿素一个分别为2076±3615传感器L ^-1 0.20±0.10毫克m和^-3分别。地下叶绿素一个最大值（SCM），主要发现在50米，而丰度最大的水柱区域不同。聚类分析将浮游植物群落分为与受潮潮和黑潮影响的地理位置有关的三个集合。营养限制而不是光导致低叶绿素一春末的丰盈。冗余度的对应关系和spearman的相关性进一步表明，溶解的无机氮是调节KE北部浮游植物分布的主要因素，而磷酸盐限制在KE轴和KE南部更为突出。Oyashio和Kuroshio的相互作用在该区域的MLD和Z _eu等流体动力学环境中引起了明显的变化，并改变了营养成分，pH和DO等化学特征。在浮游植物的空间格局中观察到的分布变化归因于KE轴及其北部和南部区域内的上层海洋环境梯度。