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

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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.