Effect of mesoscale eddy on thermocline depth over the global ocean: deepen and uplift

Abstract. Existing studies on the vertical displacement of thermoclines driven by mesoscale eddies are insufficient and rare. Using 17-year Argo dataset in combination with satellite altimetry, the deepening and uplifting of the depth of thermocline (DTC) by anticyclonic (AE) or cyclonic eddies (CE), respectively, were estimated globally. DTC shifts exhibited multiple geographic and seasonal trends, with the largest magnitude shifts occurring in March and September in the Northern and Southern Hemispheres, respectively. The more pronounced DTC shifts were concentrated in the midlatitudes, and the largest DTC displacements appeared along the western boundaries of strong current systems, with peak shifts of more than 40 m. In general, eddy-induced DTC shifts were linearly correlated with eddy radius and amplitude, suggesting that high intensity eddies induced larger DTC displacements. Finally, a normalized analysis revealed a monopole (ring) structure of DTC ringing the eddy center inside the AE (CE). The forces of AE and CE on the DTC were different, seen in the stronger deepening at the center of the AE (~ 30 m) than the uplifting at the center of the CE (~ 20 m). One possible mechanism for this asymmetry could stem from differential current shears in the thermoclines in AE and CE.