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Topic

A Characterization of Trace Metal Distributions in Canada’s Pacific and Arctic Marine Waters

School of Earth and Ocean Sciences

Date & location

• Friday, February 14, 2025
• 8:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Jay Cullen, School of Earth and Ocean Sciences, University of Victoria (Supervisor)
• Dr. Roberta Hamme, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Diana Varela, School of Earth and Ocean Sciences, UVic (Member)
• Dr. Scott McIndoe, Department of Chemistry, UVic (Outside Member)

External Examiner

• Dr. Erin Bertrand, Department of Biology, Dalhousie University

Chair of Oral Examination

• Dr. Erin Kelly, Department of English, UVic

Abstract

Trace metals in the ocean, including iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb) and vanadium (V), may act as micronutrients or toxins to marine phytoplankton and thereby directly impact primary productivity. The efficiency of the biological carbon pump can be modulated by trace metal bioavailability in the upper ocean, controlling the biological transfer of carbon dioxide from the atmosphere to the oceans. Further, the health of marine life at higher trophic levels may be negatively impacted by the ocean’s trace metal content through bioaccumulation, with significant consequences for people dependent on marine foods (e.g. coastal Inuit communities).

The main objectives of this work are to address the distributions of trace metals in coastal regions of Canada’s marine waters and to assess the transport of these elements through and out of near-shore, shelf-dominated areas. We consider several trace metal sources and sinks, including biological uptake, remineralization, scavenging by particles, shelf sediment resuspension, fluvial runoff, sea-ice and glacial melt, and anthropogenic contamination.

Measurements of trace metal concentrations off the coast of British Columbia indicate some of the greatest surface water concentrations are found in the southern Vancouver Island region due to a combination of upwelling, eddies, and freshwater runoff. In the more northern regions of the BC Coast, atmospheric dust and meltwater runoff become more important for explaining trace metal distributions. The BC coast is the eastern border to the Northeast Subarctic Pacific Ocean – a High-Nutrient, Low-Chlorophyll (HNLC) region in which Fe limits primary productivity. Thus, the transport of Fe and other trace metals from the coast to the ocean interior is an area of key interest. We estimate the offshore flux of trace metals from the BC shelf to the open ocean by considering the transport by the Juan de Fuca Eddy, a separation of the Shelf Break Current, and the bottom-water Ekman transport via the California Undercurrent and Davidson Current. These fluxes are compared to previous estimates of transport by atmospheric dust, tidal currents, and mesoscale eddies, to evaluate the major sources of Fe to the region.

In the western Canadian Arctic, the chemical composition of Pacific- and Atlantic-derived waters are modified during transport over the Mackenzie shelf and through the Northwest Passage. Remineralization in sediments on the Chukchi shelf enriches the concentrations of dissolved Cd and Zn– a signature that can be detected in open waters of the Beaufort Sea as well as the Amundsen Gulf. Over the Mackenzie shelf, sediment resuspension acts as a source of Fe and Pb, and the Mackenzie River plume additionally provides high concentrations of most trace metals; however, this does not translate to effective trace metal transport to the Beaufort Sea’s interior. Through the Canadian Arctic Archipelago (CAA), other sources including small rivers, sea ice, and snow are found to supply trace metals to surface waters, further modifying trace metal concentrations as water is transported eastward.

Waters entering the eastern Canadian Arctic via Nares Strait and Parry Channel are found to retain the Chukchi shelf signature of Zn, Cd, and Ni, while these enhanced concentrations dissipate over shallow passages prior to entering Baffin Bay. Other trace metal sources in this eastern corridor include glacial meltwater, particularly in Nares Strait and the North Water Polynya immediately south of this passage, while sea ice melt and meteoric water runoff are found to have less significance relative to the western CAA. Estimates of trace metal flux indicate greatest transport of trace metals into Baffin Bay from Nares Strait, followed by the West Greenland Current in eastern Davis Strait, and finally Lancaster Sound. Flux estimates through Davis Strait indicate the Canadian Arctic is a source of Mn, Co, Ni, Cu, Zn, Cd, Pb, Ba and V to the Atlantic, while Fe export via the Baffin Current is equivalent to Fe import via the West Greenland Current.