Control of the ACC system by eddies, topography and localised forcing

Strong winds blow from west to east in the Southern Hemisphere. These winds drive a major ocean current around Antarctica, known as the Antarctic Circumpolar Current. The Antarctic Circumpolar Current is the largest and strongest current on the surface of the Earth, squeezing more than 130 billion kilograms of water between the southern tip of South America and Antarctica every second. This current links the Pacific, Indian and Atlantic Ocean basins, and permits a truly global ocean circulation. Perpendicular to the Antarctic Circumpolar Current's intense, West-East flow is a more subtle yet critical North-South circulation, known as the Meridional Overturning, or 'Global Conveyor'. Although weaker, constituting an exchange of 10-30 billion kilograms distributed across the entire Southern Ocean, the Meridional Overturning is critical to the Earth's climate. The Meridional Overturning transports heat from the equator towards the poles. The Overturning upwells water from the deep ocean around Antarctica, exposing carbon and nutrient rich water to the surface, feeding biological production, and influencing the amount of greenhouse gases absorbed by the Ocean. The intense East-West Antarctic Circumpolar Current is intimately linked to the North-South Meridional Overturning. As the current is forced by the winds it can accelerate. This accelerated current often becomes turbulent and collides with islands, seamounts and continents. As it does so, it forms swirling vortices of water, like cyclones or storms in the atmosphere. It is these swirling vortices that move heat, salt and CO2 from North to South. The winds, the current and turbulent processes all contribute to the fate of the Meridional Overturning. Understanding how this interplay works is the subject of our research. To do this we will make use of state of the art computer models, observations of the ocean from satellites, and go to sea, to measure the dynamics of the Ocean Circulation in-situ. Understanding the Antarctic Circumpolar Current and the Meridional Overturning, how they interact and may change, is critical. Decade to decade, the evolution of the Meridional Overturning will strongly affect the evolution and impact of climate change, including greenhouse gas concentrations (hence global temperatures), Antarctic Glacial Melt (hence global sea levels), and marine ecosystems (hence fisheries and biodiversity).