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On the biogeochemical processes controlling trace metal distributions in the Canadian Arctic Ocean and Arctic rivers Colombo, Manuel


This PhD thesis describes some of the first distributions of lead, iron and manganese in the Canadian Arctic Ocean and other multiple trace metals in remote rivers in the Canadian Arctic Archipelago (CAA), unraveling the processes which modulate their distributions. A clear spatial variability in the distributions of dissolved aluminum, iron, manganese, nickel, copper, zinc, cadmium and lead was observed in small CAA rivers, which reflects differences in bedrock geology and South-North environmental gradients (e.g., solar radiation, precipitation, temperature) in the Archipelago. The concentrations of many trace metals from these small CAA rivers are considerably higher than those measured in Canada Basin waters, and therefore they have the potential to be a significant source of metals to transiting waters to adjacent coastal areas. Dissolved lead concentrations in the Canadian Arctic Ocean were among the lowest reported concentrations in ocean waters, attributed to the isolation of this region from anthropogenic inputs. Nonetheless, distinctive high and anthropogenically derived lead features, advected from the northeast Subarctic Pacific and the Labrador Sea, were observed in this study. The natural cycling of lead in the Canadian Arctic Ocean is primarily controlled by an interaction of glacial and sea ice melt water inputs, and scavenging throughout the water column and especially at the sediment water interface. Contrary to lead distributions, dissolved iron and manganese (DFe and DMn) concentrations measured in the Canadian Arctic Ocean were within the range of those reported for major basins. In our study the highest DFe and DMn concentrations were generally found in surface and subsurface waters. This is attributed to large riverine inputs present in this region and to continental shelf sediment fluxes. A dynamic interplay between removal processes and inputs of these trace metals largely control their vertical distribution below 300 m. Advective sources are predominant in the low productivity Canada Basin, contrasting with the important role of regenerated DFe and DMn in the productive Baffin Bay and Labrador Sea. The findings presented in this thesis shed light on important biogeochemical processes and water masses circulation taking place in this unique and underexplored environment.

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