RAPID: Investigating the incorporation of elements into ice in Lake St. Clair during extreme weather conditions: an analogy for chemical cycling in the Arctic Ocean

海冰在北冰洋元素和化合物的化学循环中起着重要作用。物质可以从水中、沉积物和大气中浓缩成冰，当它在海岸附近形成时，当它被洋流输送到开阔的海洋时。然而，人们对海冰形成过程中许多元素被纳入其中的过程知之甚少，部分原因是这需要在海冰形成时进行现场采样。美国中西部最近出现的非常寒冷的天气为研究大型湖泊的这些过程提供了一个机会，然后可以用来提高我们对海冰的理解。RAPID资助机制允许对这种独特的天气事件做出快速反应，其成本远低于对北极海冰进行类似研究所需的成本。这项研究将在休伦湖和伊利湖之间的底特律附近的圣克莱尔湖和周围的河流中进行。该项目将涉及几名本科生和一名研究生。为了研究颗粒反应物质进入冰中的机制，研究人员将收集和分析密歇根州东南部圣克莱尔湖和流入圣克莱尔湖的河流的一套湖冰样本（冰厚12英寸），以及210Pb， 210Po和7Be的降水（雪和雨）。目的是量化从不同地点收集的冰中捕获的不同沉积物粒度中这些同位素活动的时空变化。本研究的结果有望为回答两个基本问题提供见解：1)在冰（包括淡水和海水）中的沉积物中导致210Pb和7Be富集（在某些情况下是100倍）的机制是什么；ii)与含沙冰相比，贫沙冰的210Po/210Pb活度比如何变化？由于7Be完全来源于大气沉降，而浮冰沉积物高度富集7Be，那么载沙冰中的210Po（降水和气溶胶中的210Po/210Pb 0.1）有多少来源于大气沉降和地表水？此外，这项研究将包括在冬季剩余的时间里收集雪和大气气溶胶，以了解大气中同位素在冰和湖面上的沉积。该奖项反映了美国国家科学基金会的法定使命，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。

Sea ice plays an important role in the chemical cycling of elements and compounds in the Arctic Ocean. Material can be concentrated from the water, from sediments, and from the atmosphere into ice as it forms near shore, and as it is transported by currents into the open ocean. The processes by which many elements are incorporated into sea ice as it forms are poorly understood, however, in part because it requires being on site and sampling as the ice forms. The recent occurrence of very cold weather in the midwestern U.S. provided an opportunity to study these processes in large lakes, that can then be used to advance our understanding of sea ice. The RAPID funding mechanism allows a quick response to this unique weather event, at much lower cost than would be required to mount a similar study of Arctic sea ice. This study will take place in Lake St. Clair and surrounding rivers near Detroit, between Lakes Huron and Erie. The project will involve several undergraduate students and a graduate student. To investigate the mechanism of incorporation of particle-reactive species into ice, the investigators will collect and analyze a suite of lake ice samples (ice thickness 12 inches) from Lake St. Clair and rivers that discharge into Lake St. Clair as well as precipitation (both snow and rain) for 210Pb, 210Po and 7Be in southeast Michigan. The objective is to quantify the spatial and temporal variations of the activities of these isotopes in different sediment grain-sizes trapped in ice collected from different sites. The results from this study are anticipated to provide insights in answering two fundamental questions: i) what is the mechanism that leads to the enrichment (100 times in some cases) of 210Pb and 7Be in sediments incorporated in ice (both in fresh water and seawater); and ii) how does the 210Po/210Pb activity ratio vary in sediment-depleted ice compared to sediment-laden ice? Since 7Be is completely derived from atmospheric deposition and ice-rafted sediment is highly enriched in 7Be, how much of the 210Po (210Po/210Pb 0.1 in precipitation and in aerosol) in sediment- laden ice is derived from atmospheric deposition and from surface water? In addition, the study will involve collection of snow and atmospheric aerosols through the remainder of the winter, to understand atmospheric deposition of isotopes to ice and the lake surface.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.