In an article published in the Nov. 29 issue of Nature Climate Change, researchers from Woods Hole Oceanographic Institution and Scripps Institution of Oceanography found the robust acceleration of Southern Ocean zonal flow based on the independent satellite altimeter and hydrographic data since 1993. This statistically significant acceleration of zonal flow is reproduced in a hierarchy of climate models, including an ocean-eddy-resolving model. Guided by the model ensemble, the observed, significant acceleration has just emerged from the background variability only during the recent decade.

Previous studies paid much attention to the wind change on the ocean circulation in a changing climate. The Southern Ocean, as the predominant anthropogenic heat absorber, has shown a differential warming pattern between the upwelling regime and the subtropical region to the north of the Antarctic Circumpolar Current. The article shows that this uneven buoyancy distribution is linked with the acceleration of zonal velocity in the upper layer due to the increase of meridional density gradient. Change in westerly winds, which was widely discussed in previous studies as the main driver of Southern Ocean climate change, is found to play a secondary role in the acceleration. It highlights the need to consider the subsurface temperature or density change as drivers of the Southern Ocean circulation or even global ocean circulation change.

It’s important to note that the Southern Ocean zonal flow acceleration is expected to continue and even increase in the future given the continuing role of the Southern Ocean anthropogenic heat uptake and equatorward heat transport. It again draws our attention to have a better understanding of the responses in the ocean interior by using Argo floats.

This study is supported by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. Here is a news release from Scripps Institution of Oceanography, https://scripps.ucsd.edu/news/climate-change-making-one-worlds-strongest-currents-flow-faster?auHash=3iEElCNzWlofLr3Q-uE_JrsPBd3Izo7Q7Y876BT25cA.