Defining Southern Ocean fronts and their influence on biological and physical processes in a changing climate

The Southern Ocean is a critical component of the global climate system and an important ecoregion that contains a diverse range of interdependent flora and fauna. It also hosts numerous fronts: sharp boundaries between waters with different characteristics. As they strongly influence exchanges between the ocean, atmosphere and cryosphere, fronts are of fundamental importance to the climate system. However, rapid advances in physical oceanography over the past 20 years have challenged previous definitions of fronts and their response to anthropogenic climate change. Here we review the implications of this recent research for the study of climate, ecology and biology in the Southern Ocean. We include a frontal definition 'user's guide' to clarify the current debate and aid in future research. Ocean fronts and other hydrographic features are important for climate and ecology. This Review discussed fronts in the Southern Ocean, their detection and response to climate change, alongside the implications for studying the biology of the region.