Articles | Volume 21, issue 5
https://doi.org/10.5194/os-21-2179-2025
https://doi.org/10.5194/os-21-2179-2025
Research article
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02 Oct 2025
Research article | Highlight paper |  | 02 Oct 2025

The coupled oxygen and carbon dynamics in the subsurface waters of the Gulf and Lower St. Lawrence Estuary and implications for artificial oxygenation

William A. Nesbitt, Samuel W. Stevens, Alfonso O. Mucci, Lennart Gerke, Toste Tanhua, Gwénaëlle Chaillou, and Douglas W. R. Wallace

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This preprint is open for discussion and under review for Ocean Science (OS).
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Cited articles

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Audet, T., de Vernal, A., Mucci, A., Seidenkrantz, M.-S., Hillaire-Marcel, C., Carnero-Bravo, V., and Gélinas, Y.: Benthic Foraminiferal Assemblages from the Laurentian Channel in the Lower Estuary and Gulf of ST. Lawrence, Eastern Canada: Tracers of Bottom-Water Hypoxia, Journal of Foraminiferal Research, 53, 57–77, https://doi.org/10.2113/gsjfr.53.1.57, 2023. 
Benoit, P., Gratton, Y., and Mucci, A.: Modeling of dissolved oxygen levels in the bottom waters of the Lower St. Lawrence Estuary: Coupling of benthic and pelagic processes, Marine Chemistry, 102, 13–32, https://doi.org/10.1016/j.marchem.2005.09.015, 2006. 
Blais, M., Galbraith, P. S., Plourde, S., and Lehoux, C.: Chemical and Biological Oceanographic Conditions in the Estuary and Gulf of St. Lawrence during 2022, Fisheries and Oceans Canada, Québec Region, Maurice Lamontagne Institute, Mont-Joli, QC, https://publications.gc.ca/site/eng/9.924924/publication.html, 2023. 
Bluteau, C. E., Galbraith, P. S., Bourgault, D., Villeneuve, V., and Tremblay, J.-É.: Winter observations alter the seasonal perspectives of the nutrient transport pathways into the lower St. Lawrence Estuary, Ocean Sci., 17, 1509–1525, https://doi.org/10.5194/os-17-1509-2021, 2021. 
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Co-editor-in-chief
The reoxygenation of the traditional hypoxic deep water of Gulf of St. Lawrence is a novel topic; this has not been addressed in the past. If reoxygenation would be implemented, it would represent an encouraging effort in the midst of reports on the dire consequences of climate change and ocean deoxygenation.
Short summary
We combine two decades of oxygen data with new carbon observations and a tracer-informed model to quantify oxygen loss and carbon buildup in the deep waters of the Gulf and Lower St. Lawrence Estuary. We then test a novel idea: reoxygenating these waters with the oxygen produced as a by-product from green-hydrogen production. Our results suggest this could significantly reduce hypoxia, though full recovery would require larger inputs.
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