Collaborative Research: GEOTRACES Atlantic Section: Trace Element Sources and Sinks Elucidated by Short-Lived Radium and Thorium Isotopes

在这个项目中，伍兹霍尔海洋研究所和南卡罗来纳大学的研究人员将在美国首次在北大西洋进行的GEOTRACES巡航中测量一套铀/钍系列放射性核素。GEOTRACES的目标是确定控制海洋中微量元素和同位素(TEI)分布的过程和通量，并确定这些分布对不断变化的环境条件的敏感性。为了解释北大西洋盆地TEI的横向和垂直分布，钍和镭的放射性同位素非常适合在时间和空间尺度上研究TEI的源和汇。因此，该项目将使用四重镭？(224Ra、223Ra、228Ra和226Ra)来量化溶解的TEI的水平和垂直迁移，以及用来量化生物活性和/或粒子反应性TEI的颗粒清除、垂直通量和再矿化率的寿命较短的钍同位素234和228Th。在拟议的GEOTRACES北大西洋段将遇到一系列广泛的过程，这里提出的短暂的U-Th系列同位素将在解释观测到的TEI分布方面发挥关键作用。Th和Ra示踪剂的使用可用于解决两个主要关键过程：TEI的边界输入和TEI粒子循环，包括清除、垂直输出和再矿化。为此，采样计划包括：(1)在西部和东部边缘对短期Ra同位素(224Ra、223Ra)进行详细采样，以量化陆地输入和场外TEI运输；(2)上层海洋(0-1000米)第234和228层剖面，以捕捉出口和再矿化模式；(3)全水柱228Ra和226Ra剖面，以得出(A)海底地下水排放，(B)陆架-斜坡-盆地相互作用引起的海底热影响物的中水输送，(C)温跃层和海底边界层的昼夜混合速率，以及(4)近海底取样，以确定与深海平原沉积物和热液系统有关的热影响物源和汇。更广泛的影响：PIs积极地让本科生和高中生参与他们之前由NSF资助的项目，这项活动将通过本科生实习生的参与在这个项目中继续进行。GEOTRACES生产线的预期时间非常适合S学生参加邮轮，以及几周后回到实验室分析样品。

In this project, researchers at the Woods Hole Oceanographic Institution and the University of South Carolina will measure a suite of uranium/thorium series radionuclides on the first U.S.GEOTRACES cruise in the North Atlantic. The goal of GEOTRACES is to identify processes and quantify fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions. Thorium and radium radioisotopes are well suited to study the sources and sinks of TEIs on time and space scales that are required to interpret lateral and vertical TEI distributions in the NOrth Atlantic basin. Accordingly, this project will employ the radium ?quartet? (224Ra, 223Ra, 228Ra and 226Ra) to quantify horizontal and vertical transport of dissolved TEIs, as well as the shorter lived thorium isotopes, 234Th and 228Th, used to quantify particle scavenging, vertical fluxes and remineralization rates of bioactive and/or particle reactive TEIs. A wide range of processes will be encountered along the proposed GEOTRACES N. Atlantic leg, and the short-lived U-Th series isotopes proposed herein will play a key role in the interpretation of observed TEI distributions. The utility of the Th and Ra tracers can be used to address two main key processes: boundary inputs of TEIs and TEI particle cycling including scavenging, vertical export and remineralization. To this end, the sampling plan includes: (1) detailed underway sampling of short-lived Ra isotopes (224Ra, 223Ra) at the western and eastern margins to quantify terrestrial inputs and off-shelf TEI transport; (2) upper ocean (0-1000 m) 234Th and 228Th profiling to capture export and remineralization patterns, (3) full water column 228Ra and 226Ra profiles to derive (a) submarine groundwater discharge, (b) midwater transport of TEIs from shelf/slope-basin interactions and (c) diapycnal mixing rates across the thermocline and benthic boundary layer, and (4) near bottom sampling to ascertain TEI sources and sinks associated with abyssal plain sediments and hydrothermal systems. Broader Impacts: The PIs have actively involved undergraduate and high school students in their prior NSF-funded projects, and this activity will continue in this project through the participation of an undergraduate intern. The anticipated timing of the GEOTRACES line is ideal for the student?s participation in the cruise as well as for several weeks back in the laboratory analyzing samples.