Y-90/Sr-90 and Th-234/U-238 Disequilibria: The Utility of Dual fast Process Chronometers as Tracers of Particle Dynamics in Shallow Coastal, Estuarine and Freshwater Systems

在海洋环境中，颗粒反应性清除率、沉积物捕集器效率（例如，Buesseler等，1994）、表面沉积物混合以及垂直和水平颗粒输运率都是通过测量天然存在的颗粒反应性234与其可溶母体238U之间的不平衡来部分计算的。虽然234 /238U不平衡的测量已被证明在了解开阔海洋中的粒子动力学方面非常有用，但在近岸、河口和淡水系统中，使用这种无线电计时器的实用性和设备减少了。有趣的是，90Y与234相似，它是粒子反应性的，而它的母体在水生系统中通常是非反应性的，是一种保守的成分。然而，90Y的半衰期只有64小时，而234的半衰期为24.1天。在这项研究中，威斯康星大学密尔沃基分校的研究人员打算探索同时测量近岸和近岸密歇根湖90Y /90Sr和234 /238U不平衡的效用，作为量化水生系统中颗粒短期时间动态的新方法。在稳态和非稳态条件下，将测量90Y、90Sr、234和238U的溶解（0.45 um）和粒子结合核素活性。在为期四年的项目中，这些核素将同时在浅水站（20米）和深水站（100米）进行测量，并特别强调在平静、强烈的底部沉积物再悬浮、强烈的初级生产和白化事件期间收集样本。在该项目的第三年和第四年，将测量水柱中90Y /90Sr和234 /238U不平衡的日变化，同时在一系列为期5天的不同物理/季节制度的巡航中测量湖床上90Y和234的过量颗粒限制库存。用于将234 /238U不平衡与粒子和粒子反应物质的物理动力学联系起来的数学表达式也适用于90Y /90Sr对，因此可以对粒子清除率和去除率进行单独估计。

ABSTRACTOCE-0351824In marine environments, particle-reactive scavenging rates, sediment trap efficiencies (e.g., Buesseler et al., 1994), surface sediment mixing, and vertical and horizontal particle transport rates have all been calculated in part by measuring the disequilibrium between naturally occurring, particle-reactive 234Th and its generally soluble parent, 238U. While measurements of 234Th/238U disequilibria have proven very useful in understanding particle dynamics in the open ocean, the utility and facility of using this radio chronometer diminishes in nearshore, estuarine and freshwater systems. Interestingly, 90Y is similar to 234Th in that it is particle reactive while its parent is generally non-reactive and a conservative constituent in aquatic systems. However, 90Y has a half-life of only 64 hours while 234Th has a half-life of 24.1 days.In this study, researchers at the University of Wisconsin-Milwaukee intend to explore the utility of simultaneously measuring 90Y /90Sr and 234Th/238U disequilibria in both nearshore and offshore Lake Michigan as a novel means of quantifying short term temporal dynamics of particles in aquatic systems. Under steady state and non-steady state conditions both dissolved ( 0.45 um) and particle bound nuclide activities of 90Y, 90Sr, 234Th and 238U will be measured. Over the four-year project, these nuclides will be measured simultaneously in both shallow (20 m) and deep ( 100 m) water stations with special emphasis on collecting samples during periods of calm, intense bottom sediment resuspension, intense primary production, and a whiting event. During the third and fourth years of this project, daily variations in 90Y /90Sr and 234Th/238U disequilibria in the water column will be measured in conjunction with daily measurements of excess particle-bound inventories of 90Y and 234Th on the lakebed during a series of 5-day cruises over different physical/seasonal regimes. Mathematical expressions used to relate 234Th/238U disequilibria to the physical dynamics of particles and particle-reactive species also apply to the 90Y /90Sr pair so that separate estimates of both particle scavenging and removal rates will be made.