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Stuckberry Valley lakes: Sentinels of environmental changes in the High Arctic

Among high latitude ecosystems, lakes are particularly sensitive to environmental variations. By studying their current and past conditions through their sediments, this project aims to provide a better understanding of the functioning of these high Arctic ecosystems and their roles in the global climate. The series of four lakes in Stuckberry Valley is one of the most northern terrestrial ecosystems in the world. These lakes are diversified and atypical in their limnological conditions. The functioning of these unusual ecosystems is poorly understood and a better characterization is needed to better interpret past changes in sedimentary records.

The first objective of this project is to model the annual dynamics of the physicochemical limnology of the Stuckberry Valley lakes. The valley was unexplored before a first expedition in 2017. Four lakes were sampled in spring 2017, 2018 and 2019. The analyzes carried out so far are limited to that period of the year when the lakes are covered by ice and snow. Limnological conditions are following annual cycles and it is critical to study this cycle to better understand these lakes, their susceptibility to change, and their value as sentinels and integrators of environmental change.

The second objective is to reconstruct long-term changes from the core taken in the adjacent ocean, thereby contributing to a better understanding of the links between coastal terrestrial ecosystems and the Arctic Ocean.

In the Quttinirpaaq National Park, Ellesmere Island, Nunavut, the Stuckberry Valley rises from the ocean to encompass a series of four lakes (SV1, SV2, SV3 and SV4) that had not been explored before our first sampling. SV1 is at the head of the altitudinal transect, while SV4 is closest to the sea. The marine limit in this area was 124 m, which means that these lakes were sea floor depressions when glaciomarine environments appeared after the retreat of glaciers ~11.4 cal ka BP. The isostatic uprising then separated the lakes from the ocean sequentially. The two lakes closest to the coast are small, less than 1 0m deep and were anoxic at the bottom during our spring samplings. The two other lakes are larger, deeper (27 and 49 m) and had well oxygenated water columns.

In the spring 2019, probes on moorings were installed in the water column of the lakes in order to measure water temperature, conductivity and dissolved oxygen at different depths. The data will be measured every hour for a full year, and then the moorings will be retrieved in the summer 2020 to collect the data. A marine sediment core was also taken from the Arctic Ocean in the bay adjacent to the valley. The changes in the geochemistry of this core will be analyzed as well as biolipid markers from ice algae.

With the data from the probes, the brewing dynamics, changes in lake ice conditions, and oxygen consumption by bacteria will be modeled. Very few studies have examined the predominant conditions of lakes under ice in the extreme Arctic because of logistical challenges. Yet, understanding the functioning of aquatic ecosystems in their annual cycle is crucial for the interpretation of palaeoenvironmental reconstructions. Lipid biomarker analyzes of ice algae will allow palaeoenvironmental reconstruction of sea ice. The detected variations of sea ice will then be compared to reconstructions made from lake sediments of already completed studies. These results will fill a gap in knowledge about the interconnection of terrestrial coastal environments and Arctic sea ice.