Energetics of the Upper‐Ocean Under Sea Ice
Frictional Dissipation Versus Baroclinic Production
Mukund Gupta (TU Delft - Physical and Space Geodesy)
Andrew F. Thompson (California Institute of Technology)
Patrice Klein (PSL Research University, California Institute of Technology)
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Abstract
In polar regions, the presence of sea ice is known to reduce the ocean's eddy kinetic energy (EKE) by enhancing frictional dissipation at the surface. Here, using a coupled ocean—sea ice model, we discuss a mechanism that can instead increase EKE generation under sea ice and, in our simulations, compensates surface dissipation by 69% to 30% for sea ice concentrations varying between 30% and 100%. Mesoscale Ekman pumping and suction due to the sea ice cover give rise to vertical buoyancy fluxes in the core of mesoscale eddies, leading to rectified baroclinic energy production below the mixed layer. Additionally, in the shallow surface layer (~5 m), heterogeneous sea ice melt generates mixed layer eddies that enhance baroclinic production for conditions typical of the summer marginal ice zone (MIZ). EKE dissipation and production are both affected by the dynamics of the individual ice floes resolved in our model, which result in distinct patterns of sea ice aggregation around ocean eddies, a preference for anticyclonic floe rotation in the MIZ, and size-dependent melt. These results emphasize the tightly coupled nature of ocean—sea ice interactions, and the challenge in capturing them within coarse and continuum-based models.
Plain Language Summary
Eddies are swirling features of various sizes that are ubiquitous in the ocean. At the poles, these features may be damped by the presence of sea ice, which is a layer of frozen sea water that can form on the ocean surface and provide frictional damping to the underlying currents. This work uses numerical simulations representing a patch of the polar ocean to explore how pieces of ice influence ocean eddies, particularly when the sea ice cover is not fully compacted. The simulations show that sea ice indeed damps surface eddies, but also enhances their production rate by generating fine-scale circulation patterns in the upper ocean. These physics are likely not well represented by traditional climate models, which may bias sea ice melt rates and other critical polar ocean processes. This motivates the development of better numerical schemes that can help coarse models capture the detailed mechanisms noted in the high-resolution simulations used in this work.
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