Interannual variability in the Mindanao Eddy and its impact on thermohaline structure pattern

The major feature, interannual variability and variation cause of the Mindanao Eddy and its impact on the thermohaline structure are analyzed based on the Argo profiling float data, the history observed data and the SODA data. The analysis results show that the Mindanao Eddy is a permanent cyclonic meso-scale eddy and spreads vertically from about 500 m depth upward do about 50 m depth. In addition to its strong seasonal variability, the Mindanao Eddy displays a remarkable interannual variability associated with ENSO. It strengthens and expands eastward during El Nino ? while it weakens and retreats westward during La Nina. ? The interannual variability in the Mindanao Eddy may be caused by the North Equatorial Counter Current, the North Equatorial Current, the Mindanao Current and the Indonesian Through Flow. The eddy variability can have a great influence on the thermohaline structure pattern in the local upper ocean. When the eddy is strong, the cold and low salinity water inside the eddy moves violently upward from deep layer, the thermocline depth greatly shoals, and the subsurface high salinity water largely decreases,with the upper mixed layer becoming thinner, and vice versa.