The Role of Phytoplankton in the Biogeochemical Cycling of Iodine

浮游植物是世界海洋主要的初级生产者，是许多元素生物地球化学循环的重要组成部分。但是，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、代谢和储库大小方面，还缺乏资料。本项目旨在通过在实验中使用重要的海洋浮游植物（硅藻、鞭毛藻、球石藻、蓝藻）来解决这一缺陷，以确定：1)碘化物和碘酸盐的吸收率（使用放射性125I）；2)利用碘选择电极、提取技术和125I标记培养物研究细胞碘的浓度和化学形态；3)挥发性（主要是甲基碘，使用气相色谱和电子捕获检测器）和非挥发性细胞碘碳（125I标记培养物）的释放率，以及4)浮游植物中卤素过氧化物酶的存在（分光光度法和放射性同位素法）。从这些调查中获得的数据将使我们能够明确地评估浮游植物参与地表水中碘的化学形态的程度，以及它们参与碘从地表水向大气和更深的水的运输的程度。本研究适用于海洋和大气碘循环，基于过去和潜在的人为碘放射性核素释放，这一研究具有更大的重要性。

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.