Download OCR ASA Level Geography Exploring Oceans Learner Resource 1

Learner Resource 1 –
Features of the ocean basin
Resource for Continental shelf and slope
Definition
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Continental shelf = area of the continent (land mass) that extends into the ocean.
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Continental slope = marks the end of the shelf, a steep slope that descends to the abyssal
plain.
Key Features:
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Average water depth above the continental shelf is 60 m.
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During the last Ice Age some continental shelves were dry land, for example the British Isles
and mainland Europe were one land mass.
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The continental shelf gently slopes at approximately 2 m/km
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The continental slope is quite narrow, typically only 16 km.
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The slope descends steeply at an average rate of 70 m/km.
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The shelf makes up less than 10% of the world’s oceans.
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All of the ocean’s plants live on the continental shelf, including the symbiotic coral reefs.
http://nationalgeographic.org/encyclopedia/continental-shelf/
Resource for abyssal plain
Definition
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Abyssal plain = adjacent to the continental slope, this is an area of flat sea bed at depths
of 3 km-6 km.
Key Features:
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Abyssal plains are largest and most common in the Atlantic Ocean.
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Abyssal plains appear flat due to the accumulation of land-derived sediment, in areas up to 1
km thick.
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Abyssal plains are rare in the Pacific Ocean.
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It is thought the plains make up about half the Earth’s surface.
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In the North Atlantic, the Sohm Plain has an area of 900,000 km2.
http://www.britannica.com/science/abyssal-plain
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Resource for ocean ridges and rifts
Definitions
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Ridges = often found in the middle of oceans and are large underwater mountain ranges.
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Rifts = found in the middle of ridges, as steep sided notches. Here is where magma rises
at constructive plate margins.
Key Features:
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At the Mid-Atlantic Ridge, one side of the abyssal plain flows east, the other west at a rate of
2.5 cm/yr.
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Hydrothermal vents can be found on ocean ridges; these are commonly incorrectly referred to
as underwater volcanoes- these vents do not produce magma but heated water and minerals.
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At a constructive boundary, as the plates move apart new magma rises and hardens when it
reaches the cold sea. This occurs at the bottom of rift valleys.
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The Mid Atlantic Rift Valley is 15 km wide in places.
http://nationalgeographic.org/encyclopedia/rift-valley/
Resource for ocean trenches
Definition
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Ocean trench = Long narrow depressions on the sea floor, some of the deepest places on
earth.
Key Features:
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Vary in depth but can be 7-11 km deep.
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Formed by subduction at a destructive plate boundary, commonly where a denser oceanic
plate is being subducted below a continental plate.
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The deepest Ocean Trench is the Challenger Deep, part of the Mariana Trench in the South
Pacific. Mount Everest could fit in the Mariana Trench with more than 2 km to spare.
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Oceanic trenches are one of the most hostile environments on earth, with temperatures just
above freezing, no sunlight for photosynthesis and pressure more than 1000 times that on the
surface. Organisms do exist here and are highly adapted with no bones or lungs.
http://nationalgeographic.org/encyclopedia/ocean-trench/
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Resource for guyots
Definition
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Guyot = an undersea mountain with a flattened top, more than 200 m below the surface.
Key Features:
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Guyots were seamounts that extended above sea level, wave erosion flattened the ridge.
As the mount moved long the plate away from the ridge, through the process of sea floor
spreading, the mount subsided below the level of the sea.
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A seamount maintains a ‘volcanic’ shape as it never reaches the ocean surface.
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At the ‘peak’ of guyots, evidence of coral reefs can be found indicting their former shallow sea
existence.
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Guyots tend to have high levels of biodiversity and are therefore important for the fishing
industry.
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Guyots are most commonly found in the Pacific Ocean.
http://www.utdallas.edu/~pujana/oceans/guyot.html
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Oceanic basin
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