The Ocean Basins

Chapter 23, Section 1 - The Water Planet                                                                                                                                            

Global Ocean – The body of salt water that covers nearly three-fourths of the Earth’s surface.

Sea – A large, commonly saline body of water that is smaller than an ocean and that may be partially or completely surrounded by land.

The Global Ocean…

…contains 97% of Earth’s surface water.

…is divided into five major oceans:

  • Atlantic
  • Pacific
  • Indian
  • Arctic
  • Southern

Oceanography – the study of the ocean, including the properties and movements of ocean water, the characteristics of the ocean floor, and the organisms that live in the oceans.

SONAR SOund Navigation And Ranging.  A system that uses acoustic signals and returned echoes to determine the location of objects or to communicate.

  • A transmitter sends out a continuous series of sound waves.
  • The waves bounce off the ocean floor and return to a receiver.
  • Depth is calculated based on the time it takes the waves to return.

Info from sonar is used to make maps of the ocean floor.

Sound waves travel at about 1500 m/s through sea water.

Bathyspheres remain attached to the research ship for communications & life support.

Bathyscaphs are self-propelled, free-moving submarines.

Robotic submarines can take photos, collect mineral samples, and remain at depth for long periods of time.

Chapter 23, Section 2 - Features of the Ocean Floor                                                                                                                        

Continental Margin – Shallow parts of the ocean, made of continental crust and a thick wedge of sediment.

Continental Shelf

• A zone of shallow water where ocean covers the edge of the continent.
• Averages 60m deep.
• Slopes gently away from the shoreline.
• During glacial periods, water level drops and the shelf may be exposed.

Continental Slope

  • A steep slope at the edge of the continental shelf.
  • Averages 20km deep.
  • The base of the slope marks the boundary between continental and oceanic crust.

Continental Rise

• A wedge of sediments at the base of the continental slope.

Submarine Canyons

• Deep V-shaped valleys that cut through the continental shelf & slope.
• Formed at the mouths of major rivers or by turbidity currents from underwater earthquakes/landslides.

Deep-Ocean Basin – Deep part of the ocean, beyond the continental margin, made of oceanic crust and a thin layer of sediment.

Abyssal Plain

• A large, flat, almost level area of the deep-ocean basin.
• More than 4km deep.
• Cover half of the deep-ocean basin.
• Flattest area on Earth.
• Covered with fine sediment…
• Carried from continents by ocean currents and wind.
• Organisms die and settle to the bottom.
• Thickness of sediment determined by…
• Age of oceanic crust
• (older crust = thicker sediment)
• Distance from continental margin
• (farther = less brought there)
• Presence of trenches
• (thinner where bordered by trenches)

Mid-Ocean Ridge

• A chain of underwater mountains with a narrow depression in the center.
• A zone of sea-floor spreading.
• Magma rises, cools, and forms new crust, pushing away the old crust.
• Blocks that run parallel to the rift form abyssal hills.
• Segments that form from faults that run perpendicular to the ridge are fracture zones.


  • A long, narrow, steep depression that forms on the ocean floor as a result of subduction.
  • Runs parallel to a chain of volcanic islands or the coast of a continent.
  • May be as deep as 11km below sea level.

Seamount – Submerged volcanic mountain, taller than 1km.  Formed by hot spots in the mantle.

Guyot – A seamount that has sunk and eroded. /GEE-oh/

Chapter 23, Section 3 - Ocean-Floor Sediments                                                                                                                                

Sediments are…

   …carried in by rivers.

   …blown in by wind.

   …eroded from shore by waves.

   …formed from dead organisms that

      settle to the bottom.

Core Sample – A cylindrical piece of sediment, rock, soil, snow or ice that is collected by drilling.

Heavier sediments tend to be closer to land; lighter sediments can be transported farther.

Inorganic Sediments

• Rock particles carried from land by rivers.
• Undersea landslides move large amounts of sediment down the continental slope.
• Causes turbidity currents that spread sediments over continental rise and abyssal plains.
• Fine dust particles blown out to sea by wind.
• Includes volcanic dust.

• Rock/sediments picked up by glaciers are transported out to sea when icebergs are calved. 

• Dust from meteorites falls into the ocean, contributing to sediment layers on the ocean floor.

Biogenic Sediments

• Sediments formed from the remains of living things.
• Most common compounds in biogenic sediments are…
• silica (SiO2) - from diatoms and radiolarians
• calcium carbonate (CaCO3) - from foraminifera

Chemical Deposits

• Mineral deposits that form when dissolved substances crystalize on the ocean floor.
• May form nodules.
• Lumps of minerals found scattered on the ocean floor.
• Oxides of iron, copper, nickel or manganese.

Classification of Deep Ocean-Floor Sediments


• Very fine silt- and clay-sized particles of rock.
• Red clay (very common)
• 40% clay particles, mixed with silt, sand and biogenic material.
• Can be red, grey, blue, green, yellow-brown.


• Soft, fine sediment.
• About 40% of ocean floor covered in ooze.
• 30% of ooze is biogenic materials; the rest is fine mud.
• Two types…
• Calcareous Ooze
• Mainly CaCo3.
• Never found below 5km, because CaCO3 dissolves at that depth.
• Siliceous Ooze
• Mainly SiO2.
• Found at any depth.
• Most is found near Antarctica because of the abundance of diatoms and radiolarians there.

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