Abstract
Mesoscale eddies play a critical role in mediating meridional transport across the Antarctic Circumpolar Current (ACC), yet the dynamics of cross-frontal eddies (CFEs) and their energy exchanges with frontal jets remain inadequately quantified. This study presents a systematic analysis of CFE characteristics, kinetic energy evolution, and thermohaline transport effects in the Pacific sector of the Southern Ocean, utilizing 23 years (2000–2022) of satellite altimetry and Argo float data. Our results reveal a fundamental polarity- and direction-dependent asymmetry in CFE dynamics. Equatorward-propagating cyclonic eddies (CEs) dominate CFE activity, followed by poleward-moving anticyclonic eddies (AEs). These dominant CFE types exhibit superior energetic characteristics, including significantly higher eddy kinetic energy (EKE) and stronger nonlinearity compared to their counterparts. Complete CFEs experience polarity- and direction-selective energy gains during frontal crossing, with equatorward CEs and poleward AEs extracting energy from eastward frontal jets, while their counterparts lose energy. This energization mechanism has intensified over the past two decades, with both polarity CFEs showing substantial EKE increases that substantially exceed previous basin-scale estimates. Hydrographic analysis demonstrates that CEs and AEs transport distinct water masses across frontal boundaries, creating sharp thermohaline contrasts within interfrontal zones. Our findings establish CFEs as crucial regulators that buffer wind- and warming-induced baroclinicity increases through compensatory heat transport, thereby maintaining the Southern Ocean's thermal equilibrium and modulating the ACC's response to external forcing in a changing climate.