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、沉积物捕集效率（例如，Buesseler等人，1994年），表面沉积物混合，垂直和水平的颗粒迁移率都是通过测量天然存在的，颗粒反应性的234 Th和它的一般可溶性母体238 U之间的不平衡来计算的。虽然234 Th/238 U不平衡的测量已被证明是非常有用的，在了解粒子动力学在开放的海洋，使用这种无线电天文台的实用性和设施减少在近岸，河口和淡水系统。 有趣的是，90 Y与234 Th相似，因为它是粒子反应性的，而其母体通常是非反应性的，并且是水生系统中的保守成分。然而，90 Y的半衰期只有64小时，而234 Th的半衰期为24.1 days.In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的实用性，同时测量90 Y/90 Sr和234 Th/238 U的不平衡在近岸和离岸密歇根湖作为一种新的手段量化的短期时间动态的颗粒在水生系统。在稳态和非稳态条件下，将测量90 Y、90 Sr、234 Th和238 U的溶解（0.45 μ m）和颗粒结合核素活度。 在为期四年的项目中，这些核素将同时在浅水（20米）和深水（100米）站进行测量，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品。在该项目的第三和第四年，每日变化的90 Y/90 Sr和234 Th/238 U不平衡的水柱将结合每天测量的过量颗粒结合库存的90 Y和234 Th在湖底在一系列的5天巡航在不同的物理/季节制度。用于将234 Th/238 U不平衡与颗粒和颗粒反应性物种的物理动力学相关联的数学表达式也适用于90 Y/90 Sr对，以便分别估计颗粒清除率和去除率。

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.