Polarity and direction dependence of energetic cross-frontal eddy transport in the Southern Ocean’s Pacific sector

Abstract. Cross-frontal mesoscale eddies mediate meridional heat and mass transport across the Antarctic Circumpolar Current fronts. Yet their spatiotemporal characteristics and dynamical impacts in the Southern Ocean’s Pacific sector remain inadequately quantified. Utilizing 23 years (2000–2022) of satellite altimetry and Argo float data, we reveal, for the first time, a pronounced polarity and direction dependence in cross-frontal eddy (CFE) abundance, energetics, and interactions with jets. Equatorward-propagating cyclonic eddies (CEs) dominate CFE activity (36 % of total), exhibiting higher eddy kinetic energy (EKE, in terms of total EKE in eddy interiors, EKE_T), longer propagation distances, and stronger nonlinearity than other types, followed by poleward-moving anticyclonic eddies (AEs, 28 %). These two dominant directional groups primarily drive the significant increase in the overall CFEs’ EKE_T: CEs at (1.98 ± 1.53) × 10⁶ m⁴ s⁻² yr⁻¹ (excluding the anomalously low 2017 value) and AEs at (1.58 ± 0.74) × 10⁶ m⁴ s⁻² yr⁻¹. Specifically, complete CFEs (experience pre-crossing, crossing, and post-crossing phases) are responsible for these trends, distinct from non-CFEs, partial or transient CFEs, which show no trend. During frontal crossing, EKE_T enhances in equatorward CEs and poleward AEs but diminishes in poleward CEs and equatorward AEs, explaining the two former types’ capacity for long-distance propagation and energetic behaviors. The intensified CEs carry cold, fresh southern waters equatorward, while AEs transport warm, salty northern waters poleward. These cross-frontal exchanges mitigate thermohaline gradients between interfrontal zones while enhancing local mesoscale available potential energy. We conclude that CFEs serve dual climatic roles, in mediating meridional energy transport while dynamically stabilizing the ACC against strengthening winds.