129I: A New Tracer for Carbon Cycling

129I：核时代(约1945年)以来碳循环的新示踪剂人类活动极大地提高了放射性碘(129I)的环境水平。大部分放射性物质都聚集在海洋表层，那里的放射性水平比核活动前的水平至少提高了200倍。碘在有机物质形成时被结合，因此这种增加的129I活度将伴随着新形成的有机物质，并将它们与核前物质区分开来。除了初级生产，生物群中的绝大多数碘是通过食物链获得的，而不是直接从海水中摄取。因此，正在进行的堆积的过去值应该记录在存档的生物标本中。如果在特定区域，我们能够记录表层海洋水域和表层海洋生物群中129I浓度的历史，这些生物群是下面几乎整个食物网的碳(和碘)的来源，那么我们可能能够确定该区域所有核弹后海洋有机质中存在的碘的年份，从而确定碘的年代。然后，这一方法可以推广到任何其他有适当档案的地区。这项工作将在墨西哥湾水域内建立过去和现在的129I值。这些水平低于所有常用测量技术的检测水平，但大约是采用加速器质谱仪(AMS)时灵敏度极限的100,000倍。罗切斯特大学的AMS小组将进行这些测量。

129I: A New Tracer For Carbon Cycling Since the beginning of the nuclear age (circa 1945) human activities have greatly increased the environmental levels of the radio-iosotope of iodine (129I). Much of this radioactivity has collected in the surface layers of the ocean, where levels have been raised by at least a factor of 200 above the pre-nuclear activity levels. Iodine is incorporated into organic matter as it forms, so this increased 129I activity will accompany freshly formed organics and distinguish them from pre-nuclear. Except during primary production, the great majority of iodine in the biota is derived through the food chain, and not by direct uptake from seawater. Therefore past values of the ongoing build-up should be recorded in archived biological specimens. If, in a particular region, we can document the history of 129I concentration in the surface ocean waters, and in surface ocean biota that are the source of carbon (and iodine) for almost the entire food web below, then we may be able to identify the year-class of iodine present in all post-bomb marine organic matter in that region, and thereby iodine date the organic matter. This approach could then be extended to any other region where suitable archives exist. This work will establish past and present 129I values within the waters of the Gulf of Mexico. These levels are below detection by all commonly employed measurement techniques but are approximately 100,000 times the sensitivity limits when Accelerator Mass Spectrometry (AMS) is employed. The AMS group of the University of Rochester will make these measurements.