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

Abstract

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.