Biogeochemical and ecological consequences of the freeze-melt cycle of freshwater ice

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Half of the world's lakes freeze periodically, but the duration of freezing shortens each year. This pattern will have vast consequences at a local and global level. While the presence of ice, changes in its duration, and altered timing of its melt are known to affect many important biological activities in polar marine ecosystems, there is very little information regarding how lake ice influences the biogeochemistry and ecology of northern freshwaters. Most northern lakes are shallow with much of their water volume freezing in winter, concurrently trapping compounds, gases and organisms and providing an ice-water interface that sustains biological production. This project will address the emerging and pressing need for an understanding of carbon, nutrients and plankton food webs associated with lake ice in Arctic Canada. The research program has been planned as projects for the training of two PhD and two MSc students, who will graduate with broad skills in the aquatic sciences. Research will be carried out around Cambridge Bay, Nunavut, where >100 lakes of different size and depth are found within a 20-km radius. The project will address the overarching question: how do northern freshwater ecosystems respond to the freezing, presence, and melting of ice. Winter ice cover links two open water seasons, and thus another key question arises: is there a constant accumulation and production of material and gases in the ice during winter, or are there abrupt changes, for example when solar radiation increases after the polar winter? Given that these waters lie in catchments containing permafrost, there is a particular interest in the question: how will lake ice react with the increasing amount of organic and inorganic particles released from thawing permafrost? The project will therefore address the question: is the content of these particles trapped and transferred in the ice and made available to biological production, or is it transformed into greenhouse gases? By characterizing the organic and inorganic carbon and nutrient regimes, as well as algae and their partitioning between ice and water at each lake, and their consumption by planktonic consumers, this research will generate a new vision of Arctic freshwater ecosystems, which for the first times accounts for the effect of winter ice cover for the functioning of Arctic lakes. It will link with the multiple permafrost and lake studies taking place throughout the circumpolar North and produce information that will affect both policy and science.