The Arctic Ocean receives freshwater from rivers, glacier melt, sea ice melt, as well as waters originating from the Pacific and Atlantic Oceans. As these different water masses pass through the Beaufort Sea and the Canadian Arctic Archipelago, they mix together, resulting in changed chemical properties. They also carry small amounts of trace metals, including zinc, nickel, copper, manganese, iron, and cadmium. At low concentrations, many of these metals are essential for the functioning of marine ecosystems, while others can become toxic when present in excessive amounts. Scientists can use these trace metals as natural tracers to better understand the movement and transformation of water masses in the Arctic.
During the 2021 expedition aboard the CCGS Amundsen, a research team collected seawater samples over the Mackenzie Shelf and the western Canadian Arctic Archipelago. The objective was to measure trace metal concentrations and gain a better understanding of the transformations experienced by waters entering the Canadian Arctic. Measurements of trace metals, combined with observations of temperature, salinity, nutrients, and other chemical tracers, made it possible to identify the different water masses in these regions and assess the influence of river runoff, sea ice melt, and continental shelf sediments on their chemical composition.
Pacific waters entering the western Arctic are naturally enriched in zinc, cadmium, and nickel through interactions with sediments on the Chukchi Shelf. This study showed that as these waters travel eastward through the Arctic, their chemical composition is further modified. Sea ice melt supplies iron, manganese, cobalt, and copper, while waters from the Mackenzie River increase the concentrations of several metals in coastal areas. However, most of these river-derived metals are removed before reaching the offshore Beaufort Sea. The analyses also revealed that shallow coastal regions and seafloor sediments strongly influence the distribution of trace metals and micronutrients as Pacific waters pass into and through the Northwest Passage.
These findings improve our understanding of the circulation and transformation of Arctic water masses. They also advance current knowledge of the processes shaping the chemical composition of Arctic waters, including sea ice melt, river inputs, and interactions with marine sediments. Finally, this study provides an important baseline for tracking future changes in these processes under a warming climate and for assessing their potential impacts on primary production, the foundation of the marine food web.
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