Published by Australian Academy of Science
The Southern Ocean and global climate Box 1 | The Antarctic Circumpolar Current

The Circumpolar Current (so named because it circles around the pole, or more exactly around the continent of Antarctica) flows eastward or clockwise (looking from above the south pole) and it carries 150 times more water than all the world's rivers combined. It is also the home of the 'roaring forties', the 'furious fifties' and the 'screaming sixties' – all named by sailors who battled the dreadful storms in these regions as they passed through the latitudes of 40, 50 and 60 degrees south.

The Circumpolar Current mixes the oceans

The Circumpolar Current is not a single mass of water flowing around and around Antarctica, but a series of linked flows which follow the uneven shape of the sea bed. And just like water flowing along a creek, there are ups and downs and twists and turns. In some places it is shallower, and because more water has to get through a smaller space it flows faster – but where the sea is deep it tends to move more slowly.

Because the Circumpolar Current flows around the bottom of three of the world's great oceans – the Atlantic, Pacific and Indian - it mixes the waters. This means that water from, say, the Atlantic may get dragged into the Circumpolar Current and then flow out into the Pacific. The Circumpolar Current has a major effect on the way the world's oceans behave.

Antarctic Bottom Water

Cold water (which is denser) tends to flow under the warmer water at the surface of the ocean. In the ocean around Antarctica there is a great deal of heavy and cold water which sinks to the bottom of the sea and is called Antarctic Bottom Water. Antarctic Bottom Water flows downwards and outwards until it spills off the edge of the shallower continental shelf and 'falls' into the deep ocean and moves towards the equator. Scientists have estimated that this cold heavy water flows north at the rate of more than 10 million cubic metres per second. This huge amount of water pushes the warmer water out of the way, usually by flowing underneath it – and this causes new flows and currents in other directions. In fact the masses of cold water flowing from Antarctica literally have a flow-on right around the planet. The Antarctic Bottom Water flowing along the bottom of the oceans and away from Antarctica has to be replaced by other water, so the warmer waters in the north tend to flow southward to fill in the gap. Then they cool down and the cycle keeps going.

Related sites

• Antarctic circumpolar current (Tasmanian Parks and Wildlife Service, Australia)

• Antarctic surface water (Rice University, Texas, USA)

Other boxes

Box 2. Observing the Southern Ocean