Alexis Chaigneau (LEGOS - IRD, France); Rosemary Morrow (LEGOS, France)

The California Upwelling System is populated by numerous mesoscale eddies. As these eddies are preferentially generated in near-coastal upwelling regions and propagate offshore, they are able to advect coastal waters toward the open ocean. Investigating the spatio-temporal evolution of their vertical structure along the eddy life-cycles is thus important to better understand the impact of mesoscale eddies on the cross-shore redistribution of tracers. Mesoscale eddies also impact the water column locally, displacing the ispycnals up or down. These movements can generate significant thermohaline anomalies with respect to the eddy environment, especially when the temperature and salinity gradients are strong.
Merging 10 years of daily satellite altimetry maps and Argo floats data, we investigate the respective roles of vertical displacement (heaving) versus the lateral transport of coastal waters into the open ocean (isopycnal advection) contributing to the thermohaline anomalies of the main eddy types generated in the coastal region, i.e. surface- and subsurface-intensified anticyclones or cyclones.
The surface-intensified anticyclonic anomalies are mainly due to a small heaving both in temperature and salinity. For the subsurface-intensified anticyclones, the temperature anomalies are reinforced by both the heaving and the isopycnal advection, whereas the two terms compensate for the salinity anomalies. The strongly surface-intensified cyclones exhibit strong thermohaline anomalies due to a 30 m heaving, whereas the weaker surface-intensified cyclones show compensating heaving and isopycnal advection, especially for the salinity anomalies.
During their generation period close to the coast, the eddy structure is mainly impacted by heaving, whereas the isopycnal advection has more influence on the anomalies when the eddy is further from its generation area.