Critical Role of Continental Slopes in Halocline and Eddy Dynamics of the Ekman‐Driven Beaufort Gyre

• Published in: Journal of geophysical research. Oceans 2019-04, Vol.124 (4), p.2679-2696
• Main Authors: Manucharyan, G. E., Isachsen, P. E.
• Format: Article
• Language: English
• Subjects: Activation; Anticyclonic circulation; Balancing; Baroclinic flow; Baroclinic instability; Beaufort Gyre; Climate models; Continental slope; continental slopes; Diffusion coefficients; Diffusivity; Dynamics; Eddy diffusion; Eddy diffusivity; eddy‐mean flow interactions; Ekman pumping; Freshwater; freshwater content; Geophysics; Halocline; Inland water environment; Instability; mesoscale eddies; Momentum; Observational studies; Ocean circulation; Ocean currents; Reduction; Salt advection; Slope; Slope stability; Slopes; Thickness; Transport; Vortices
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014624

The Beaufort Gyre (BG) is a large‐scale bathymetrically constrained circulation driven by a surface Ekman convergence that creates a bowl‐shaped halocline and stores a significant portion of the Arctic Ocean's freshwater. Theoretical studies suggest that in the gyre interior, the halocline is equilibrated by a balance between Ekman pumping and counteracting mesoscale eddy transport energized by baroclinic instability. However, the strongest anticyclonic flows occur over steep continental slopes, and, despite bathymetric slopes being known to influence baroclinic instability, their large‐scale impacts on BG halocline remain unexplored. Here we use an idealized eddy‐resolving BG model to demonstrate that the existence of continental slopes dramatically affects key gyre characteristics leading to deeper halocline, stronger anticyclonic circulation, and prolonged equilibration. Over continental slopes, the magnitude of the Eulerian mean circulation is dramatically reduced due to the Ekman overturning being compensated by the eddy momentum‐driven overturning. The eddy thickness flux overturning associated with lateral salt transport is also weakened over the slopes, indicating a reduction of eddy thickness diffusivity despite the isopycnal slopes being largest there. Using a theoretical halocline model, we demonstrate that it is the localized reduction in eddy diffusivity over continental slopes that is critical in explaining the halocline deepening and prolonged equilibration time. Our results emphasize the need for observational studies of eddy overturning dynamics over continental slopes and the development of slope‐aware mesoscale eddy parameterizations for low‐resolution climate models. Key Points Beaufort Gyre halocline and eddy dynamics are affected by continental slopes Eddy momentum fluxes over the slopes counteract the Ekman component of the overturning and reduce eddy diffusivity As a consequence of reduced eddy diffusivity over slopes, the halocline deepens and has a prolonged equilibration timescale