Dynamics of Eddies Generated by Sea Ice Leads

Abstract

Interaction between the atmosphere and ocean in sea ice-covered regions is largely concentrated in leads, which are long, narrow openings between sea ice floes. Refreezing and brine rejection in these leads injects salt that plays a key role in maintaining the polar halocline. The injected salt forms dense plumes that subsequently become baroclinically unstable, producing submesoscale eddies that facilitate horizontal spreading of the salt anomalies. However, it remains unclear which properties of the stratification and leads most strongly influence the vertical and horizontal spreading of lead-input salt anomalies. In this study, the spread of lead-injected buoyancy anomalies by mixed layer and eddy processes are investigated using a suite of idealized numerical simulations. The simulations are complemented by dynamical theories that predict the plume convection depth, horizontal eddy transfer coefficient and eddy kinetic energy as functions of the ambient stratification and lead properties. It is shown that vertical penetration of buoyancy anomalies is accurately predicted by a mixed layer temperature and salinity budget until the onset of baroclinic instability (~3 days). Subsequently, these buoyancy anomalies are spread horizontally by eddies. The horizontal eddy diffusivity is accurately predicted by a mixing length scaling, with a velocity scale set by the potential energy released by the sinking salt plume and a length scale set by the deformation radius of the ambient stratification. These findings indicate that the intermittent opening of leads can efficiently populate the polar halocline with submesoscale coherent vortices with diameters of around 10 km, and provide a step toward parameterizing their effect on the horizontal redistribution of salinity anomalies.

Driving Mechanisms of an Extreme Winter Sea Ice Breakup Event in the Beaufort Sea

“…At the ice‐ocean interface, the opening of leads can trigger eddy generation through increased buoyancy fluxes that in turn affect large‐scale sea ice dynamics and drift (Cohanim et al., 2021). The increase in drift speeds promotes a significant increase in ocean mixing and drives enhanced bottom melt by mixing up warmer water from below (J. Zhang et al., 2013; Graham et al., 2019).…”

“…When sea ice breaks up, it exposes the underlying warmer ocean within narrow, linear openings in the ice cover known as leads. This has important consequences for air‐sea exchange, ocean eddy generation and dynamics, sea ice production, and Arctic Ocean properties in general (Cohanim et al., 2021; Graham et al., 2019; Nguyen et al., 2009), especially during the winter months when heat fluxes over sea ice are generally small (Andreas & Cash, 1999). In addition, breakup in winter weakens the ice cover, potentially preconditioning the minimum ice extent in summer (Y. Zhang et al., 2018; Babb et al., 2019) and thus creating a positive feedback to Arctic amplification (Dai et al., 2019).…”

“…In the Beaufort Sea in particular, the loss of MYI may contribute to the earlier onset of the melt season in recent years (Johnson & Eicken, 2016).When sea ice breaks up, it exposes the underlying warmer ocean within narrow, linear openings in the ice cover known as leads. This has important consequences for air-sea exchange, ocean eddy generation and dynamics, sea ice production, and Arctic Ocean properties in general (Cohanim et al, 2021;Graham et al, 2019;Nguyen et al, 2009), especially during the winter months when heat fluxes over sea ice are generally small (Andreas & Cash, 1999). In addition, breakup in winter weakens the ice cover, potentially preconditioning the minimum ice extent in summer (Y.…”

Driving mechanisms of an extreme winter sea-ice breakup event in the Beaufort Sea

“…from enhanced ridging or reduced concentration, will influence the atmosphere-ice momentum transfer 44 , but this is not captured when using a constant atmospheric drag coefficient. At the ice-ocean interface the opening of leads can trigger eddy generation through increased buoyancy flux which in turn affects large-scale ice dynamics and drift 13 . The increase in drift speeds promotes significant increase in ocean mixing and drives enhanced bottom melt by mixing up warmer water from below 14,21 .…”

“…When sea ice breaks up it exposes the underlying warmer ocean within narrow, linear openings in the ice cover known as leads. This has important consequences for air-sea exchange, ocean eddies generation and dynamics, sea ice production and Arctic Ocean properties in general [13][14][15] , especially during the winter months when heat fluxes over sea ice are generally small 16 .…”