Heat transport towards sea ice by transient processes and coherent mesoscale eddies in an idealized Southern Ocean

Abstract

Oceanic mesoscale variability contributes significantly to meridional heat transport (HT), especially in regions with high eddy kinetic energy such as the Southern Ocean (SO). However, there are gaps in our understanding of mesoscale contributions towards and within sea-ice covered regions due to the lack of observations and resolution in ocean and climate models. Using output from an idealized configuration of a coupled ocean-sea ice model simulating the SO at 10 km horizontal resolution, the contribution of the full spectrum of resolved transient mesoscale variability to the total meridional HT towards and under sea ice is investigated. The total HT is poleward, dominated by the transient HT which is primarily along isopycnals and closely follows the residual overturning circulation. The HT induced by coherent mesoscale eddies is extracted using an eddy detection and tracking algorithm. Coherent eddies contribute up to 20-30% to the meridional transient HT, depending on latitude, with equal contributions from cyclones and anticyclones. The meridional HT by coherent eddies is predominantly accomplished by stirring with only 30% contributed by heat trapped inside these eddies. The majority of the transient HT across the ice edge occurs below the mixed layer, and this heat is then upwelled towards the surface with coherent eddies contributing between 20-30%. Within the mixed layer, 15-25% of the upwelled heat is transferred to the pack ice. Albeit significant, coherent mesoscale eddies play a secondary role in the SO's poleward HT that is primarily achieved by other transient mesoscale processes.

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