The western subarctic Pacific (WSP) is known as one of the most productive regions among the world's oceans in spring. However, its oceanic waters are also known as a high‐nutrient, low‐chlorophyll region during summer due to low iron (Fe) availability in seawater. Indeed, recent studies have demonstrated that the distribution of Fe in the WSP is complex and heterogeneous. This study thus investigated the effects of Fe availability on the community composition and photophysiology of surface phytoplankton from coastal to offshore waters in the WSP in the summer of 2014. Although relatively high concentrations (>2 mg/m³) of chlorophyll (chl) a were found in the Sea of Okhotsk and some coastal waters, low chl a concentrations (<1 mg/m³) were commonly observed in offshore waters. Based on dissolved Fe and macronutrient concentrations, we deduced that low Fe availability limited phytoplankton growth in offshore waters, whereas low silicate and/or nitrate levels limited growth in the shelf areas. Scanning electron microscopy also revealed that the centric diatom Chaetoceros exclusively dominated the diatom assemblages in the shelf and coexisted with pennate diatoms in offshore waters, respectively. Primary productivity in surface waters was negatively correlated with the bottom of the euphotic layer or the light saturation index of the photosynthesis‐irradiance curve, which indicates that the phytoplankton assemblages were well acclimated to in situ light conditions regardless of the water masses.

中文翻译：

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千岛群岛附近的西亚太平洋太平洋浮游植物的群落组成和光合生理，特别是铁的有效性

春季，西部北极太平洋（WSP）被誉为世界海洋中生产力最高的地区之一。但是，由于海水中铁（Fe）的利用率低，夏季的海水也被称为高营养，低叶绿素区域。实际上，最近的研究表明，WSP中Fe的分布是复杂且异质的。因此，本研究于2014年夏季调查了WSP中Fe的有效性对沿海到近海水域浮游植物群落组成和光生理的影响。尽管叶绿素（chl）a的浓度相对较高（> 2 mg / m ³）在鄂霍次克海和一些沿海水域发现了低浓度的chl a（<1 mg / m ³）通常在近海中观察到。根据溶解的铁和大量营养素的浓度，我们推论出低铁的可利用性限制了近海浮游植物的生长，而低硅酸盐和/或硝酸盐水平限制了架子地区的生长。扫描电子显微镜还显示，中心硅藻Chaetoceros独占了架子上的硅藻组合，并分别与近海的戊二烯硅藻共存。地表水中的初级生产力与富营养层的底部或光合作用-辐照度曲线的光饱和指数呈负相关，这表明无论水体如何，浮游植物都很好地适应了原位光照条件。