1. 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
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2. 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
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3. 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
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4. 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
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5. Ocean Basins A trench forms when the dense oceanic plates
run into, and slide under,
the continental plates.
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6. Ocean Basins
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
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7. Continental Margins
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.
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Take the Section 11.1 Quiz
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