Meghan Zee
- BSc Hons. (Queen’s University, 2020)
Topic
A Chemical Characterization of the Endeavour Neutrally Buoyant Plume, Juan de Fuca Ridge
School of Earth and Ocean Sciences
Date & location
- Thursday, June 20, 2024
- 10:00 A.M.
- Clearihue Building, Room B017
Examining Committee
Supervisory Committee
- Dr. Jay Cullen, School of Earth and Ocean Sciences, University of Victoria (Supervisor)
- Dr. Laurence Coogan, School of Earth and Ocean Sciences, UVic (Member)
- Dr. Roberta Hamme, School of Earth and Ocean Sciences, UVic (Member)
- Dr. Damian Grundle, Bermuda Institute of Ocean Sciences, Arizona State University (Outside Member)
External Examiner
- Dr. Kristen Buck, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University
Chair of Oral Examination
- Dr. Tara Troy, Department of Civil Engineering, UVic
Abstract
This study aims to provide a quantitative chemical characterization of the Endeavour Neutrally buoyant plume and examine the processes that impact trace metal transport from vent sites to the ocean interior. The chemistry of the Endeavour neutrally buoyant plume was analyzed using filtered and unfiltered seawater samples collected at 5 stations, starting on-axis at the Main Endeavour Vent field and extending ~45 km southwest of the axial valley. The spatial distribution of these trace metals is likely controlled by a number of processes, including metal sulfide precipitation, oxidation, sedimentation, and plume mixing.
Iron (Fe) and manganese (Mn) are limiting or co-limiting nutrients for primary productivity, nitrogen fixation and other biogeochemically important processes in the ocean. The transport of metals associated with hydrothermal plumes and the processes that impact their fate are poorly understood. High concentrations of dFe (24.11-68.20 nmol kg-1) and dMn (45.77-98.43 nmol kg-1), relative to ambient seawater concentrations at similar depths in the region, were observed proximal to the vent field, followed by a sharp decrease to 1.23-2.98 nmol kg-1 dFe and 0.76-1.36 nmol kg-1 dMn 45 km southwest of the axial valley at END5. Roughly 66% of the Fe present in the neutrally buoyant plume proximal to the vent field is in the particulate phase (defined as the difference between total dissolvable and dissolved). The particulate phase decreases to ~45% at the most distal station. Particulate Mn increases with distance from the vent field with 25% proximal to the vent field and 56% 45 km off-axis. This study shows that the spatial distribution and size partitioning of Fe and Mn can be explained by a combination of sulfide precipitation near-field, oxidation and oxide formation, and plume mixing with surrounding seawater.
Chalcophile elements including cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lead (Pb) and cadmium (Cd), are trace metals often associated with hydrothermal systems. Due to precipitation processes, these trace metals are not typically found in neutrally buoyant plumes far from vent fields. Correlations between these chalcophile elements with particulate Fe at END1 indicate similar removal pathways and highlight the importance near-field processes (precipitation, oxidation, mixing) play in controlling their net-input to the ocean. When compared to the geochemistry of sediments at the Main Endeavour Vent field, neutrally buoyant plume chemistry shows similar spatial trends. Furthermore, high mass accumulations of Fe, Zn and Cu on-axis along with the presence of chalcopyrite, pyrite, and sphalerite help explain the higher proportion of the particulate phase of these elements.