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，颗粒反应性清除速率、沉积物捕集器效率(例如，Buesseler等人，1994)、表层沉积物混合以及垂直和水平颗粒输运率都部分地通过测量自然产生的颗粒反应性234与其通常可溶的母体238U之间的不平衡来计算。虽然对234U/238U不平衡的测量已被证明对理解公海中的粒子动力学非常有用，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便利性有所减弱。有趣的是，90Y与234Y的相似之处在于它是粒子反应性的，而它的母体通常是非反应性的，在水生体系中是保守的成分。然而，90Y的半衰期仅为小时，而234的半衰期为24.1d。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密歇根湖近岸和近海湖泊中90Y/90Sr和234/238U不平衡的实用性，作为一种新的方法来量化水生系统中粒子的短期时间动力学。在稳态和非稳态条件下，测量了90Y、90Sr、234和238U的溶解(0.45微米)和粒子结合核素活度。在为期四年的项目中，将在浅水站(20米)和深水站(100米)同时测量这些核素，特别强调在平静、强烈的海底沉积物再悬浮、密集的初级生产和捕鲸事件期间收集样本。在该项目的第三和第四年，将测量水柱中90Y/90SR和234U/238U不平衡的日变化，同时将在不同物理/季节区域的一系列5天巡航期间测量湖床上90Y和234U的超额颗粒结合清单。用于将234U/238U不平衡与粒子和粒子-反应物种的物理动力学联系起来的数学表达式也适用于90Y/90Sr对，因此将分别对粒子清除和去除率进行估计。

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.