Abstract

The Southern Ocean (>30°S) has taken up a large amount of anthropogenic heat north of the Subantarctic Front (SAF) of the Antarctic Circumpolar Current (ACC). Poor sampling prior to the 1990s and decadal variability have heretofore masked the ocean’s dynamic response to this warming. Here we use the lengthening satellite altimetry and Argo float records to show robust acceleration of zonally-averaged Southern Ocean zonal flow at 48˚S-58˚S. This acceleration is reproduced in a hierarchy of climate models, including an ocean-eddy-resolving model. Anthropogenic ocean warming is the dominant driver, as large (small) heat gain in the downwelling (upwelling) regime north (south) of the SAF causes zonal acceleration on the northern flank of the ACC and adjacent subtropics due to increased baroclinicity. In other words, the increase of latitudinal density gradient is causing the eastward flow to accelerate, while the strengthened wind stress is of secondary importance. Moreover, it is expected that the continued ocean warming could further accelerate Southern Ocean zonal flow in the future.