Prouty Nancy G, Roark E Brendan, Mohon Leslye M, Chang Ching-Chih
US Geological Survey, 2885 Mission St., Santa Cruz, CA 95060, United States.
Department of Geography, Texas A&M University, College Station, TX 77843, United States.
J Environ Radioact. 2018 Jul;187:122-132. doi: 10.1016/j.jenvrad.2018.01.003. Epub 2018 Feb 13.
Understanding iodine concentration, transport, and bioavailability is essential in evaluating iodine's impact to the environment and its effectiveness as an environmental biogeotracer. While iodine and its radionuclides have proven to be important tracers in geologic and biologic studies, little is known about transport of this element to the deep sea and subsequent uptake in deep-sea coral habitats. Results presented here on deep-sea black coral iodine speciation and iodine isotope variability provides key information on iodine behavior in natural and anthropogenic environments, and its geochemical pathway in the Gulf of Mexico. Organo-iodine is the dominant iodine species in the black corals, demonstrating that binding of iodine to organic matter plays an important role in the transport and transfer of iodine to the deep-sea corals. The identification of growth bands captured in high-resolution scanning electron images (SEM) with synchronous peaks in iodine variability suggest that riverine delivery of terrestrial-derived organo-iodine is the most plausible explanation to account for annual periodicity in the deep-sea coral geochemistry. Whereas previous studies have suggested the presence of annual growth rings in deep-sea corals, this present study provides a mechanism to explain the formation of annual growth bands. Furthermore, deep-sea coral ages based on iodine peak counts agree well with those ages derived from radiocarbon (C) measurements. These results hold promise for developing chronologies independent of C dating, which is an essential component in constraining reservoir ages and using radiocarbon as a tracer of ocean circulation. Furthermore, the presence of enriched I/I ratios during the most recent period of skeleton growth is linked to nuclear weapons testing during the 1960s. The sensitivity of the coral skeleton to record changes in surface water I composition provides further evidence that iodine composition and isotope variability captured in proteinaceous deep-sea corals is a promising geochronometer as well as an emerging tracer for continental material flux.
了解碘的浓度、迁移和生物有效性对于评估碘对环境的影响及其作为环境生物地球化学示踪剂的有效性至关重要。虽然碘及其放射性核素已被证明是地质和生物学研究中的重要示踪剂，但对于该元素向深海的迁移以及随后在深海珊瑚栖息地的吸收情况却知之甚少。本文给出的关于深海黑珊瑚碘形态和碘同位素变异性的结果，提供了有关碘在自然和人为环境中的行为及其在墨西哥湾地球化学途径的关键信息。有机碘是黑珊瑚中主要的碘形态，这表明碘与有机物的结合在碘向深海珊瑚的迁移和转移中起着重要作用。在高分辨率扫描电子显微镜（SEM）图像中捕获的生长带与碘变异性的同步峰值表明，陆源有机碘通过河流输送是解释深海珊瑚地球化学年度周期性的最合理原因。尽管先前的研究表明深海珊瑚中存在年度生长环，但本研究提供了一种解释年度生长带形成的机制。此外，基于碘峰值计数的深海珊瑚年龄与通过放射性碳（C）测量得出的年龄非常吻合。这些结果有望用于建立独立于碳定年的年代学，这是限制储层年龄和使用放射性碳作为海洋环流示踪剂的重要组成部分。此外，在骨骼生长的最近时期富集的I/I比值的存在与20世纪60年代的核武器试验有关。珊瑚骨骼对记录地表水碘组成变化的敏感性进一步证明，在蛋白质类深海珊瑚中捕获的碘组成和同位素变异性是一种很有前景的地质年代计以及一种新兴的大陆物质通量示踪剂。
