Three-Dimensional Structure of Mesoscale Eddies and Their Impact on Diapycnal Mixing in a Standing Meander of the Antarctic Circumpolar Current

Abstract

Mesoscale eddies are known to enhance diapycnal mixing in the ocean, yet direct observation of this effect remains a significant challenge, especially in the robust Antarctic Circumpolar Current (ACC). To quantify the diapycnal mixing induced by mesoscale eddies in the standing meander of the ACC, satellite altimeter and Argo profile data were combined to composite eddies, where the 1.6 m dynamic height contour was used for the first time instead of the climatological Northern Sub-Antarctic Front (SAFN) to define the northern boundary of the ACC to eliminate the influence of frontal shift. The 3D structures of the composite anticyclonic/cyclonic eddy (CAE/CCE) were obtained. Both the CAE and CCE were similar in shape to Taylor columns, from sea surface to the neutral surface of 28.085 (Formula presented.) (1689 ± 66 dbar) for the CAE, and from sea surface to 28.01 (Formula presented.) (1491 ± 202 dbar) for the CCE. On the same neutral surface, the diffusivity ((Formula presented.)) inside the CCE was one to two orders of magnitude higher than that inside the CAE. Vertically, the maximum influence depth of the CCE on (Formula presented.) reached 1200 dbar, while for the CAE, it reached 800 dbar, where (Formula presented.) exceeded (Formula presented.), and (Formula presented.) gradually decreased from these depths downwards.