section_path: Geography
section_name: Geography
paragraph_text: Geography
  
  The Southern Ocean, geologically the youngest of the oceans, was formed when Antarctica and South America moved apart, opening the Drake Passage, roughly 30 million years ago. The separation of the continents allowed the formation of the Antarctic Circumpolar Current.
  
  With a northern limit at 60°S, the Southern Ocean differs from the other oceans in that its largest boundary, the northern boundary, does not abut a landmass (as it did with the first edition of Limits of Oceans and Seas). Instead, the northern limit is with the Atlantic, Indian and Pacific Oceans.
  
  One reason for considering it as a separate ocean stems from the fact that much of the water of the Southern Ocean differs from the water in the other oceans. Water gets transported around the Southern Ocean fairly rapidly because of the Antarctic Circumpolar Current which circulates around Antarctica. Water in the Southern Ocean south of, for example, New Zealand, resembles the water in the Southern Ocean south of South America more closely than it resembles the water in the Pacific Ocean.
  
  The Southern Ocean has typical depths of between 4,000 and 5,000 m (13,000 and 16,000 ft) over most of its extent with only limited areas of shallow water. The Southern Ocean's greatest depth of 7,236 m (23,740 ft) occurs at the southern end of the South Sandwich Trench, at 60°00'S, 024°W. The Antarctic continental shelf appears generally narrow and unusually deep, its edge lying at depths up to 800 m (2,600 ft), compared to a global mean of 133 m (436 ft).
  
  Equinox to equinox in line with the sun's seasonal influence, the Antarctic ice pack fluctuates from an average minimum of 2.6 million square kilometres (1.0 × 10 sq mi) in March to about 18.8 million square kilometres (7.3 × 10 sq mi) in September, more than a sevenfold increase in area.