The Atlantic Circumpolar Current encircles Antarctica with a constant eastward flow in the Southern Ocean. Researchers determined that it originated 30 million years ago, several million years after the tectonic opening of a deep-water channel in the Tasmanian gateway. The Tasmanian gateway was initially the conduit for westward current flow, but as the gateway migrated north tectonically, it eventually aligned with the mid-latitude westerly winds and effected the onset of the Antarctic Circumpolar Current.

Source: Ocean currents: Debut of the global mix-master