Séminaire
Numerous observations show the presence of anomalously high biological activity in anticyclonic mesoscale eddies in the ocean. This high productivity suggests that upwelling of nutrient-rich water from the thermocline occurs inside anti-cyclonic eddies. However, this upwelling is not captured by existing climate models and so hinders efforts to close the carbon budget. The upwelling process is considered for the first time from the fundamental potential vorticity viewpoint. High resolution numerical simulations show intense upwelling of high potential vorticity filaments from the thermocline in anticyclonic eddies that can drive simulated phytoplankton blooms. The dynamical cause of this upwelling is investigated and found to be symmetric instability. As well as being an upwelling pathway, numerical and observational evidence is presented to show that symmetric instability in mesoscale eddies also leads to strong downwelling of fluid from the mixed layer to the thermocline. Finally, it will be shown that symmetric instability in eddies may lead to a strong cyclone-anticyclone asymmetry.