The surface of the ocean floor is as varied as the land. 11.1 Ocean Basins The surface of the ocean floor is as varied as the land. The five major oceans, from largest to smallest, are the Pacific the Atlantic the Indian the Southern the Arctic The low points in the oceans are called basins. Oceans are vital to life, as they control temperature, create weather patterns and provide water for water cycles. See page 402 (c) McGraw Hill Ryerson 2007

The Origin of Ocean Water Oceans have filled over hundreds of millions of years. Scientists believe the oceans are more than 3 billion years old. Water may have originally been released from volcanic eruptions, or arrived on Earth via icy comets. See page 404 (c) McGraw Hill Ryerson 2007

Features of the Ocean Floor Although the word “basin” makes it sound flat, many features found on land, including mountain ranges, valleys, flat plains, canyons, and volcanoes also exist on the ocean floor. The basin is the large, flat middle part, while the continental margins are the edges rising up to the land. The ocean topography of the Caribbean See pages 404 - 405 (c) McGraw Hill Ryerson 2007

the dense oceanic plates run into, and slide under, Ocean Basins The largest changes to the ocean basin occur through the movement of tectonic plates, although there is also erosion via storms, earthquakes and icebergs. Mid-ocean ridges occur where new rock is forced up, and ocean floor spreads outward. The Mid-Atlantic Ridge is the largest example on Earth The Juan de Fuca plate lies 200 km off Vancouver Island A trench forms when the dense oceanic plates run into, and slide under, the continental plates. See pages 406 - 407 (c) McGraw Hill Ryerson 2007

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Ocean Basins (continued) Abyssal plains are the pieces of oceanic crust between a spreading mid-ocean ridge and the trench it disappears into. These make up 30% of the Atlantic sea floor, and 65% of the Pacific seafloor. Abyssal plains can be covered in 1 km of sediments Seamounts are old volcanic mountains found on abyssal plains. The Hawaiian Islands are an example. See page 407 (c) McGraw Hill Ryerson 2007

Continental margins are part of continental plates. Continental margins are made up of a continental shelf (averaging 80 km wide) and a continental slope down to the oceanic plate. Continental shelves were above water during the last ice age. Turbidity currents are slides on the slopes, and can create large submarine canyons in the shelf. See pages 407 - 409 Take the Section 11.1 Quiz (c) McGraw Hill Ryerson 2007