To investigate the factors regulating the concentration of particulate iodine (PI) in seawater, it was measured in two Pacific coastal areas adjacent to Japan (offshore Aomori and offshore Fukushima) in two seasons (May and October) along with parameters such as particulate organic carbon (POC) and nitrogen (PON), dissolved iodine (DI), and phytoplankton pigments. The observed PI concentrations ranged from 0.0068 to 2.2 nmol L⁻¹, with uncertain seasonal and regional differences. The atomic ratio of PI to POC (I/C) ranged from 4.4 × 10⁻⁷ to 1.1 × 10⁻⁴, in line with previous studies on marine phytoplankton, although the lower part of the range of the I/C in this study was found to be somewhat lower compared to the previous studies. The dataset was divided in three groups namely, lower (Group A), average (Group B), and higher (Group C) I/C because the I/C is an indicator of the accumulation efficiency of PI in particles in seawater and POC is the main carrier of PI. Based on the observed POC concentrations, the atomic ratio of POC to PON (C/N), and the ratio of carbon derived from chlorophyll a to POC, the three groups were characterized by phytoplanktonic physiological states as highly productive, steady, and senescent states for Groups A, B, and C, respectively. Based on the finding that PI production is associated with the phytoplankton physiological state, the seasonal and regional differences in PI concentration and I/C in the observation areas were consistently explained. Finally, we suggest that the phytoplanktonic physiological state is one of the vital factors regulating the PI concentration in seawater.

中文翻译：

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近岸海水中颗粒碘浓度的调节因素

为了研究调节海水中颗粒碘（PI）浓度的因素，在两个季节（5月和10月）对日本邻近的两个太平洋沿海地区（青森近海和福岛近海）进行了测量，同时还测量了颗粒有机碳等参数(POC) 和氮 (PON)、溶解碘 (DI) 和浮游植物色素。观察到的PI浓度范围为0.0068至2.2 nmol L ^-1，季节和区域差异不确定。PI与POC的原子比（I/C）范围为4.4 × 10 ^-7至1.1 × 10 ^-4，与之前对海洋浮游植物的研究一致，尽管本研究中 I/C 范围的下半部分被发现比之前的研究略低。数据集分为三组，即较低（A 组）、平均（B 组）和较高（C 组）I/C，因为 I/C 是海水和 POC 中颗粒中 PI 积累效率的指标是PI的主要载体。基于观察到的 POC 浓度、POC 与 PON 的原子比 (C/N) 以及源自叶绿素a的碳的比例根据 POC，A、B 和 C 组的浮游植物生理状态分别为高产、稳定和衰老状态。基于PI产生与浮游植物生理状态相关的发现，一致地解释了观测区域PI浓度和I/C的季节和区域差异。最后，我们认为浮游植物的生理状态是调节海水中PI浓度的重要因素之一。