Dr Stephen Rintoul has become the pre-eminent authority on the circulation of the Southern Ocean and its pivotal role in the global climate system. He has caused a paradigm shift in oceanography by demonstrating that the ocean’s vertical overturning circulation is closed by water mass transformations in the Southern Ocean, in contrast to the long-standing view that the overturning is driven by wide-spread interior mixing. His pioneering work on the transport and dynamics of the Antarctic Circumpolar Current, the formation of water masses, and his inspirational scientific leadership have had a profound impact on the field and earned him an outstanding international reputation.