Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctica: The Geographical Setting

The cold and stormy Southern Ocean surrounding the Antarctic Continent connects the southernmost parts of the 3 major oceans, the Pacific, Indian and Atlantic Oceans. This stretch of water has a crucial effect on the global climate system through its role in the circulation of the oceans of the Earth, the uptake of CO₂ from the atmosphere and, through its formation of annual sea ice, an important influence on climate elements that are important to the productivity of the ocean.

Formally, 60^oS is taken to be its northern limit, which corresponds roughly to the southern boundary of the Antarctic Circumpolar Current (ACC), and to the northern limit of the winter sea ice. It covers an area of 20.3 million km², and has a mean depth of 4,500 m, with a greatest depth of 7,235 m. To appreciate its role in the climate system, however, it needs to include the entire ACC which reaches as far as 40^oS. When its northern boundary is includes an area of 70 million km², which corresponds to 20% of the world’s oceans. Where Drake Passage separates Cape Horn, on the South American side, from the South Shetland Islands on the Antarctic side the Southern Ocean narrows to only 800 km wide, whereas the distance from South Africa (Cape Agulhas) to the Antarctic continent (coast of Dronning Maud Land) is 3,900 km. To the south the southern Ocean is limited by the coastline of Antarctica of 17,968 km which is largely covered by ice shelves.

The Weddell Abyssal Plain is east of the Antarctic Peninsula and is limited to the north by the South Scotia and Weddell Ridge and to the east of it, the Enderby Abyssal Plain is bounded to the north by the Southwest-Indian Ridge.  Further to the east, and beyond the Kerguelen Plateau, the Australian-Antarctic Basin is limited to the north by the Southeast Indian and Indian-Antarctic Ridges. To the east of the Macquarie Ridge the Ross and Amundsen Abyssal Plains and the Bellingshausen Plain lead into the Drake Passage, limited to the north by the Pacific-Antarctic Ridge and the Eltanin Fracture Zone. The locations of the major currents and fronts are influenced by these ridges.

During the breakup of Gondwana about 120 million years ago (120 Ma ) the Southern Ocean began forming as the Southern Hemisphere continents, South America, the African Plate and part of the of the Indo-Australian Plates  began drifting north. About 100 Ma the Pacific Plate broke from the Antarctic plate and the Australian part of the Indo-Australian plate about 60 Ma. After the Tasmania-Antarctica Passage had opened about 34 Ma and the Drake Passage about 31 Ma a circumpolar deep water flow existed for the first time and dramatically changed the climate and biology of the entire southern hemisphere. The formation of these circumpolar wind and current systems was a direct effect, and Antarctica cooled and the ice sheet began to grow that eventually covered the entire continent.

Fahrback, E., Walton, W.H., (ed.), 2013, Antarctica:  The Geographical Setting,