Measuring 210Po in Seawater: A Comparison of Methods

天然放射性核素铅-210和它的孙女钋-210溶解在海水中，在了解海洋过程方面有多种应用，包括确定其他类似元素从海洋中消失的速度，以及作为颗粒有机碳从透光层下沉的指标。后一个过程是对大气中二氧化碳水平的重要控制，因此测量是重要的。值得注意的是，这两种放射性核素具有非常不同的地球化学行为-铅被吸附在颗粒表面，而钋可以结合到有机物质中并与之一起循环。从20世纪70年代到现在，这些放射性核素已经在许多海洋考察中被测量到。两种方法已被用来从海水中提取它们进行测量。一个涉及从水样中沉淀氢氧化铁;另一个涉及添加到样品中的胶体螯合剂的沉淀。历史和最近的结果表明，这两种方法对铅-210的结果相当，但后一种方法可以产生比前者更高浓度的钋-210。本研究假设，海水中的钋-210可以与溶解的有机物相关联，特别是在有机物循环高的上层水柱中，这可以防止通过氢氧化铁沉淀从海水样品中提取它。该研究项目的目的是确定在什么情况下这两种方法对海水中的钋-210浓度给出了可比的结果。这项研究将在地中海一个历史悠久的海洋学站点（DYFAMED）比较这两种方法，在那里可以获得这些放射性核素的先前结果。这项工作将涉及现场取样和一系列氢氧化铁方法的实验室实验。这将有助于就今后使用这些方法的最佳做法提出建议，即使在GEOTRACES和EXPORTS等不同的海洋学活动中使用不同的方法。该项目将资助一名研究生和纽约美国自然历史博物馆的外展活动。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The natural radionuclides lead-210 and its granddaughter polonium-210 are present dissolved in seawater and have multiple applications for understanding ocean processes, including determining how fast other similar elements are removed from the oceans and as indicators of the sinking of particulate organic carbon from the photic zone. The latter process is an important control on the level of carbon dioxide in the atmosphere and is thus important to measure. Significantly, the two radionuclides have very different geochemical behaviors- lead is taken up on particle surfaces while polonium can be incorporated into organic matter and recycled with it. From the 1970’s to the present, these radionuclides have been measured on many oceanographic cruises. Two methods have been used to extract them from seawater for measurement. One involves precipitating iron hydroxide from a water sample; the other involves precipitation of a colloidal chelating agent added to the samples. Historical and recent results suggest that both methods give comparable results for lead-210, but the latter method can produce higher concentrations of polonium-210 than the former. This research hypothesizes that polonium-210 in seawater can be associated with dissolved organic matter, especially in the upper water column where organic matter cycling is high, and this can prevent its extraction from a seawater sample by precipitation of iron hydroxide. The aim of this research project is to determine under what circumstances the two methods give comparable results for polonium-210 concentrations in seawater. This research will compare the two methods at a long-established oceanographic site (DYFAMED) in The Mediterranean Sea, where prior results are available for these radionuclides. The work will involve field sampling and a series of laboratory experiments with the iron hydroxide method. This will enable recommendations of best practices for utilization of the methods going forward, even if different methods are used on different oceanographic campaigns such as GEOTRACES and EXPORTS. The project will support one graduate student and outreach events at American Natural History Museum, New York.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.