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、沉积物和大气中浓缩成冰，因为它在近岸形成，并被洋流输送到开阔的海洋。然而，人们对海冰形成时许多元素被结合到海冰中的过程知之甚少，部分原因是它需要在现场进行，并在冰形成时进行采样。美国中西部最近发生的非常寒冷的天气为研究大型湖泊中的这些过程提供了机会，然后可以用来促进我们对海冰的理解。快速资助机制允许对这一独特的天气事件做出快速反应，成本远远低于对北冰洋海冰进行类似研究所需的成本。这项研究将在底特律附近的圣克莱尔湖和周围的河流中进行，位于休伦湖和伊利湖之间。该项目将涉及几名本科生和一名研究生。为了研究颗粒活性物质融入冰层的机制，研究人员将从圣克莱尔湖和流入圣克莱尔湖的河流收集并分析一套湖冰样本(冰厚12英寸)，以及密歇根州东南部210Pb、210Po和7Be的降雨量(雪和雨)。其目的是量化这些同位素在不同地点收集的冰中捕获的不同粒度的沉积物中的活动的时空变化。这项研究的结果预计将为回答两个基本问题提供见解：i)是什么机制导致冰中的沉积物(包括淡水和海水)中的210Pb和7Be的丰度(在某些情况下是100倍)；以及ii)与富含沉积物的冰相比，沉积物贫乏的冰中的210Po/210Pb活度比有什么变化？由于7Be完全来自大气沉积，冰筏沉积物高度富含7Be，那么含沉积物冰中的210Po(降水和气溶胶中的210Po/210Pb0.1)中有多少来自大气沉积和地表水？此外，这项研究将涉及在冬季剩余时间收集雪和大气气溶胶，以了解大气中同位素向冰和湖面的沉积。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.