Investigating the distributions of zinc and cadmium in the subarctic northeast Pacific Ocean

• Published in: Proceedings of the National Academy of Sciences
• Main Author: Janssen, David
• Other Authors: Cullen, Jay T.
• Format: Thesis
• Language: English
• Published: 2017
• Subjects: Zinc; Cadmium; Cadmium isotopes; northeast Pacific; GEOTRACES; biogeochemical cycles; Pacific; Pacific Point; North Atlantic; Subarctic
• Online Access: http://hdl.handle.net/1828/7851

Zinc (Zn) and cadmium (Cd) have nutrient-type vertical distributions reflecting control driven by biological uptake in surface waters and remineralization of sinking biogenic particles at depth. Both metals show strong correlations with major algal nutrients (Cd with phosphate (PO43-) and Zn with silicic acid (Si)) in the world ocean. Through their roles as micronutrients and toxins to marine phytoplankton, Zn and Cd can influence surface biological community composition. Preserved Zn and Cd records have been employed as proxies to gain insight into nutrient distributions, circulation, and organic carbon export in the paleocean. A thorough and mechanistic understanding of the biogeochemical cycling of Zn and Cd is necessary for accurate paleoceanographic reconstructions as well as predicting alterations in metal supply to the modern surface ocean and its impacts on primary productivity due to oceanic changes. My dissertation aims to further this understanding through an investigation of Zn and Cd distributions in the subarctic northeast Pacific through samples collected along the Line P transect. A major focus of this dissertation was identifying and characterizing depletions of metals in O2-depleted waters relative to global and basin scale metal:macronutrient correlations. Dissolved Cd profiles from the subarctic northeast Pacific and the eastern North Atlantic show a deficit of Cd relative to regional Cd:PO43- relationships. Particulate Cd and Cd stable isotopes (ε112/110Cd) from low-O2 North Atlantic waters and published sedimentary data from the subarctic northeast Pacific point to a previously undocumented water-column metal removal process acting in O2-depleted waters. Metal sulphide formation, likely in association with particulate microenvironments, can explain the observed deficits. Other metals with similar sulphide coordination chemistry should also form metal sulphides if this process is occurring. Dissolved Zn from Line P showed distributions and Zn:Si relationships that are consistent with the ...