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 (HNLC) 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 m^–3) of chlorophyll (chl) a were found in the Sea of Okhotsk and some coastal waters, low chl a concentrations (<1 mg m^–3) were commonly observed. 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.

This data was collected from surface waters in the western subarctic Pacific near the Kuril Islands and the eastern Kamchatka Peninsula.
The dataset includes (1)geographical information, (2)physicochemical properties of surface seawater, (3)light conditions at the surface and (4) community composition of surface phytoplankton identified using a scanning electron microscopy . 

The first speadsheet includes dissolved iron concentrations in surface waters (~5m). The dissolved iron data is cited from Nishioka et al. (submitted).
Please cite and refer to Nishioka et al. (submitted) if you would use the dissolved iron data in this study.
We will update the status of Nishoka et al. (submitted) if there is any progress (e.g., DOI).