The Role of Phytoplankton in the Biogeochemical Cycling of Iodine

浮游植物作为世界海洋的主要初级生产者，是许多元素生物地球化学循环的重要组成部分。然而，关于浮游植物在碘的生物地球化学循环中的作用，特别是在通量、新陈代谢和水库大小方面，缺乏信息。这个项目试图通过在实验中使用重要的海洋浮游植物(硅藻、甲藻、球藻、蓝藻)来解决这一缺陷，以确定：1)碘和碘酸盐的摄取率(使用放射性125I)；2)通过使用碘选择电极、提取技术和125I标记的培养物来测定细胞碘的浓度和化学形态；3)挥发性(主要是甲基碘，使用带有电子捕获检测器的气相色谱)和非挥发性细胞碘碳(125I标记培养物)的释放速率，以及4)浮游植物中存在卤代过氧化物酶(分光光度和放射性同位素方法)。从这些调查中获得的数据将使人们能够毫不含糊地评估浮游植物在多大程度上参与了地表水中碘的化学形态，以及它们参与了碘从地表水向大气和更深水域的运输。这项研究适用于海洋和大气的碘循环，根据过去和可能释放的人为放射性碘核素，这一循环具有额外的重要性。

Phytoplankton, as dominant primary producers of the world's oceans, are important components in the biogeochemical cycling of many elements. There is a lack of information, however, as to the role of phytoplankton in the biogeochemical cycling of iodine specifically in terms of fluxes, metabolism and reservoir size. This project seeks to address this deficiency by using important marine phytoplankton (diatoms, dinoflagellates, coccolithophores, cyanobacteria) in experiments to determine: 1) iodide and iodate uptake rates (using radioactive 125I); 2) the concentration and chemical speciation of cellular iodine by using iodide selective electrodes, extraction techniques, and 125I labeled cultures; 3) release rates of both volatile (primarily methyl iodide, using gas chromatography with an electron capture detector) and non-volatile cellular iodocarbons (125I labeled cultures), and 4) the presence of haloperoxidases in phytoplankton (spectrophotometric and radioisotopic methods). The data obtained from these investigations will allow for the unambiguous assessment of the degree in which phytoplankton are involved in the chemical speciation of iodine in surface waters and their participation in the transport of iodine from the surface waters to the atmosphere and to deeper waters. This research has application to the marine and atmospheric iodine cycles, which takes on added importance based on past and potential releases of anthropogenic radionuclides of iodine.