Featured Science Paper
Mixed layer lateral eddy fluxes mediated by air-sea interaction
The exchange of heat and carbon dioxide across the sea surface is an important element of the climate system since the ocean acts as a vast store of these tracers. We led a study, in collaboration with colleagues from the US and France, to quantify for the first time the modulation of air-sea fluxes by ocean eddies due to stirring at the sea surface.
The effect is especially pronounced in the eddy-rich Southern Ocean. The Southern Ocean has a strong north-south gradient in sea-surface temperature and is filled with coherent circulation anomalies with a typical size of a few tens of kilometres, known as eddies. These eddies sweep anomalously warm water poleward and anomalously cold water equatorward. The warm or cold anomalies will then be out of equilibrium with the overlying atmosphere and be damped. The eddies may then return to their original latitudes, taking the water with modified temperature with them and thus reducing the north-south temperature gradient, which is eventually restored by air-sea interactions on the large scale. We have found that in the frontal areas prevalent in the Antarctic Circumpolar Current this effect results in a significant air-sea heat flux, which would be absent in coarse-resolution models unless explicitly accounted for.
The effect of the eddies is not confined just to temperature, and the magnitude of the effect depends on how fast the ocean surface responds to the atmospheric state - and this is different for different tracer fields. This timescale is about 1-2 months for temperature and dissolved organic carbon, but just a few days for phytoplankton. This has important implications for model parameterisations as it suggests that, near the surface, different values of eddy diffusivity may be required for different tracers.
This work lays down some very significant challenges to the developers of climate and Earth System models, but also shows the way forward in improving model performance.
Shuckburgh, E., Maze, G., Ferreira, D., Marshall, J., Jones, H. and Hill, C., 2011
Journal of Physical Oceanography, 41, 130-144