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The Southern Ocean's eddy response to changing climate remains unclear, with observations suggesting non‐monotonic changes in eddy kinetic energy (EKE) across scales. Here simulations reappear that smaller‐mesoscale EKE is suppressed while larger‐mesoscale EKE increases with strengthened winds. This change was linked to scale‐wise changes in the kinetic energy cycle, where a sensitive balance between the dominant mesoscale energy sinks—inverse KE cascade, and source—baroclinic energization. Such balance induced a strong (weak) mesoscale suppression in the flat (ridge) channel. Mechanistically, this mesoscale suppression is attributed to stronger zonal jets weakening smaller mesoscale eddies and promoting larger‐scale waves. These EKE multiscale changes lead to multiscale changes in meridional and vertical eddy transport, which can be parameterized using a scale‐dependent diffusivity linked to the EKE spectrum. This multiscale eddy response may have significant implications for understanding and modeling the Southern Ocean eddy activity and transport under a changing climate.

Since the 1950s, observations and climate models show an amplification of sea surface temperature (SST) seasonal cycle in response to global warming over most of the global oceans except for the Southern Ocean (SO), however the cause remains poorly understood. In this study, we analyzed observations, ocean reanalysis, and a set of historical and abruptly quadrupled CO₂simulations from the Coupled Model Intercomparison Project Phase 6 archive and found that the weakened SST seasonal cycle over the SO could be mainly attributed to the intensification of summertime westerly winds. Under the historical warming, the intensification of summertime westerly winds over the SO effectively deepens ocean mixed layer and damps surface warming, but this effect is considerably weaker in winter, thus weakening the SST seasonal cycle. This wind‐driven mechanism is further supported by our targeted coupled model experiments with the wind intensification effects being removed.

Climate models show that the largest uncertainties in the 21st century dynamic sea level (DSL) projections are in the high latitudes of the North Atlantic and Southern Oceans. We conduct an intermodel singular value decomposition analysis and find that the DSL uncertainties in these two oceans are both intrinsically connected to the uncertainty in the change of the Atlantic meridional overturning circulation (AMOC). We further conduct a freshwater hosing experiment to show that the AMOC decline not only accounts for the dipole pattern in the DSL change in the North Atlantic but also remotely induces a poleward shift in the Southern Hemisphere westerlies that helps build a belted pattern of DSL change in the Southern Ocean. Our results suggest that reducing the intermodel spread in the change of the AMOC can greatly improve the consistency of DSL projection among models not only in individual basins but over the global ocean.