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Faculty of Graduate Studies

Simin Kheradmand

  • M.Sc. (Karazmi University, 2018)
  • B.Sc. (Jondi-Shapour University of Technology, 2014)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Low subsurface oxygen utilization rates from BGC-Argo float data in the subarctic Northeast Pacific

School of Earth and Ocean Sciences

Date & location

  • Friday, July 24, 2026
  • 10:00 A.M.
  • Clearihue Building, Room B017

Examining Committee

Supervisory Committee

  • Dr. Roberta Hamme, School of Earth and Ocean Sciences, University of Victoria (Supervisor)
  • Dr. Tetjana Ross, School of Earth and Ocean Sciences, UVic (Member)
  • Dr. Kohen Bauer, Senior Manager of Research and Technology, Carbon to Sea Initiative (Outside Member)

External Examiner

  • Dr. Mathilde Jutras, Institut des sciences de la mer, Université du Québec à Rimouski

Chair of Oral Examination

  • Prof. Malcolm Gaston, School of Public Administration, UVic

Abstract

Subsurface oxygen utilization reflects carbon export from the surface ocean and is a key component of the biological carbon pump. However, estimating oxygen utilization rates (OUR) from in situ observations remains challenging because observed oxygen changes arise from both biological respiration and physical variability associated with water-mass exchange. Here, we use multi-year Biogeochemical-Argo (BGC-Argo) float observations in the subarctic Northeast Pacific to quantify summertime OUR while accounting for the influence of changing water masses on these estimates. We implement two complementary salinity-based approaches to isolate biologically driven oxygen consumption: (1) removing float observations that exhibit rapid changes in salinity and (2) using robust regression between OUR and salinity rate of change to estimate respiration at zero salinity change. Both approaches yield consistent vertical patterns, with OUR highest in the upper part of the analyzed depth range and decreasing toward near-zero values by approximately 120–200 m. Integrated summertime OUR values range from 1–3 mmol-O2m−2d−1 offshore to 4.5–5.5 mmol-O2m−2d−1 in the coastal zone. These values are low compared to other ocean basins, reflecting the high-nutrient, low-chlorophyll character of the Northeast Pacific, where iron limitation suppresses productivity and export. Coastal waters exhibit higher integrated OUR than offshore waters, primarily because shallower mixed layers allow respiration to be resolved at shallower depths where OUR is highest.

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