Quantifying Drivers of Seasonal and Interannual Variability of Dissolved Oxygen in the Canada Basin Mixed Layer

• Published in: Journal of geophysical research. Oceans 2024-07, Vol.129 (7), p.n/a
• Main Authors: Arroyo, Ashley, Timmermans, Mary‐Louise, DeGrandpre, Mike
• Format: Article
• Language: English
• Subjects: Air; air‐sea exchange; Annual cycles; Annual variations; Arctic Ocean; Atmosphere; Biological activity; Biological properties; Brines; Climate change; Dissolved oxygen; Entrainment; Gas exchange; Global warming; Ice cover; Ice melting; Interannual variability; Mixed layer; Ocean mixed layer; Ocean mixing; Oceans; Oxygen; Profilers; Satellite observation; Sea ice; Sea ice effects; Sea ice growth; seasonal; Seasonal variability; Seasonal variation; Seasonal variations; Solubility; Summer; Water masses; Winter
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2024JC020903

Analysis of dissolved oxygen (O2) in the Arctic's surface ocean provides insights into gas transfer between the atmosphere‐ice‐ocean system, water mass dynamics, and biogeochemical processes. In the Arctic Ocean's Canada Basin mixed layer, higher O2 concentrations are generally observed under sea ice compared to open water regions. Annual cycles of O2 and O2 saturation, increasing from summer through spring and then sharply declining to late summer, are tightly linked to sea ice cover. The primary fluxes that influence seasonal variability of O2 are modeled and compared to Ice‐Tethered Profiler O2 observations to understand the relative role of each flux in the annual cycle. Findings suggest that sea ice melt/growth dominates seasonal variations in mixed layer O2, with minor contributions from vertical entrainment and atmospheric exchange. While the influence of biological activity on O2 variability cannot be directly assessed, indirect evidence suggests relatively minor contributions, although with significant uncertainty. Past studies show that O2 molecules are expelled from sea ice during brine rejection; sea ice cover can then inhibit air‐sea gas exchange resulting in winter mixed layers that are super‐saturated. Decreasing mixed layer O2 concentrations and saturation levels are observed during winter months between 2007 and 2019 in the Canada Basin. Only a minor portion of the decreasing trend in wintertime O2 can be attributed to decreased solubility. This suggests the O2 decline may be linked to more efficient air‐sea exchange associated with increased open water areas in the winter sea ice pack that are not necessarily detectable via satellite observations. Plain Language Summary Dissolved oxygen (O2) is a valuable ocean property that allows us to better understand the exchange of gases between the different ocean layers, sea ice, and atmosphere, and the physical and biological processes that control its variability. Understanding how and why O2 concentrations in the Arctic Ocean mixed layer vary spatially and seasonally is crucial for interpreting its evolution over timescales of years to decades that are influenced by global warming. We use physical and thermodynamical relationships to model the main factors that influence O2 concentrations in the mixed layer of the Arctic Ocean's Canada Basin, which we compare to observations made by Ice‐Tethered Profilers. Model results indicate that seasonal variations in O2 concentrations are dominated by the