III.

Geologic Formation and Structural Features

Geologically the Southern Ocean is the youngest of the world’s oceans. It formed around 30 million years ago as Antarctica and South America moved apart. This process is known as continental drift or the theory of plate tectonics. The separation of South America and Antarctica created Drake Passage, the narrowest point in the Southern Ocean located between South America at Cape Horn and the Antarctic Peninsula.

The Southern Ocean is unique in not having a basin defined by land masses at its northern boundary. Its southern boundary is formed by the submerged border of Antarctica, a border narrow and deep due to the massive weight of the Antarctic Ice Sheet depressing the crust. The Kerguelen Plateau—an underwater volcanic ridge that erupted roughly 97 million years ago—is a significant structural feature situated between the Indian and Southern oceans. This area of thick ocean crust is one of the largest undersea plateaus, extending more than 2,200 km (more than 1,350 mi).

The Southern Ocean contains many ice shelves, floating platforms of ice that attach to the coast. The two largest are the Filchner-Ronne Ice Shelf and the Ross Ice Shelf. The Ross Ice Shelf is the world’s largest, extending up to 450 km (280 mi) from the Antarctic shore.