Western boundary currents (WBCs) of the Southern Hemisphere transport heat poleward and are regions of rapid ocean warming. However, the mechanisms responsible for the enhanced warming over the Southern Hemisphere WBC extensions are still debated. Here we show that enhanced eddy generation in the WBC extensions through changes in barotropic and baroclinic instabilities results in enhanced ocean warming as the eddies propagate. This results from a poleward shift of the WBCs, associated with changes in the mid-latitude easterly winds. Consequently, the WBCs have penetrated poleward but not strengthened and are now transporting more heat into their extensions. Our study clearly elucidates the dynamic processes driving increased eddying and warming in the Southern Hemisphere WBC extensions and has implications for understanding and predicting ocean warming, marine heatwaves and the impact on the marine ecosystem in the WBC extensions under climate change.

南半球的西部边界流 (WBC) 向极地输送热量，是海洋快速变暖的区域。然而，导致南半球 WBC 延伸区域变暖的机制仍然存在争议。在这里，我们表明通过正压和斜压不稳定性的变化在 WBC 扩展中增强的涡流产生导致随着涡流传播而增强的海洋变暖。这是由于与中纬度东风变化相关的 WBC 向极地移动造成的。因此，WBCs 已经向极地穿透但没有得到加强，现在正在将更多的热量输送到它们的延伸部分。