December 19, 2022: online Ocean Circulation and Climate Dynamics Colloquium

When?  Monday, December 19, 2022 at 11 am
Where?    ZOOM: https://geomar-de.zoom.us/j/82581586274?pwd=OUJtL0VQTXdoT2FzRmtySys0MWt0QT09

meeting room: 825 8158 6274
Code: 320488

The crucial role of mesoscale eddies for the global ocean circulation has long been recognized and the heat transport (HT) by eddies can be an important contributor to the total HT in regions with high eddy kinetic energy such as the Southern Ocean (SO). However, there are large gaps in our understanding of the processes that transport heat southward in the SO due to lack of observations and resolution in ocean and climate models. These gaps are particularly large in seasonally sea ice-covered regions where any HT could have strong effects on the melting of ice and trigger associated feedbacks on hydrography and circulation.
We expand our knowledge of the eddy HT towards and under the sea ice in the SO with the help of a coupled ocean-sea ice model. Using an idealized configuration of the Southern Ocean at 10 km horizontal resolution and eddy detection and tracking, we distinguish between HT by all transient mesoscale processes, often referred to as eddy HT, and HT only by coherent mesoscale eddies (CME) as a specific category of transient processes. We find that the southward total HT is mainly driven by the transient HT, especially near the ice edge where the mean HT is negligible. CME contribute 40-50% to this meridional transient HT depending on the latitude and thus contribute 40-50% of the total HT near the ice edge. The transient HT can almost entirely be attributed to advective (as opposed to diffusive) processes. Stirring induced by the CME accounts for the majority of meridional HT by CME, while HT associated with trapping of heat within the core of CME has a negligible contribution.
The majority of the HT by transient processes, including CME, across the ice edge occurs below the mixed layer and about two thirds of this heat is then upwelled across the base of the winter mixed layer and could potentially come in contact with the sea ice. Again, between 40-50% (an equivalent of 2-4 W/m²) of this vertical HT is by CME.

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