The Seafloor (69)

Contiental Shelf

• Ocean basins, which are low areas of Earth that are filled with water, have many different features.

• The continental shelf is the gradually sloping end of a continent that extends under the ocean as deep as 350 meters.

• Beyond the shelf, the ocean floor drops more steeply, forming the continental slope.

• The continental slope extends from the outer edge of the continental shelf down to the ocean floor.

• Beyond the continental slope lie the trenches, valleys, plains, mountains, and ridges of the ocean basin.

• In the deep ocean, sediment, derived mostly from land, settles constantly on the ocean floor.

• These deposits fill in valleys and create flat seafloor areas called abyssal plains.

• Some areas of abyssal plains have small hills and seamounts.

• Seamounts are underwater, inactive volcanic peaks.

Ridges and Trenches

• Mid-ocean ridges can be found at the bottom of all ocean basins. They form a continuous underwater ridge approximately 70,000 km long.

• A mid-ocean ridge is the area in an ocean basin where new ocean floor is formed

• As crustal plates move, the ocean floor changes.

• When ocean plates separate, hot magma from Earth’s interior forms new ocean crust.

• New ocean floor forms along mid-ocean ridges as lava erupts through cracks in Earth’s crust.

• When the lava hits the water, it cools quickly into solid rock, forming new seafloor.

Subduction Zone• On the ocean floor,

subduction zones are marked by deep ocean trenches.

• A trench is a long, narrow, steep-sided depression where one crustal plate sinks beneath another.

• http://www.youtube.com/watch?v=wP380-Iaoos

Life in the Ocean• Marine organisms such as plants and algae use

energy from the Sun to build their tissues and produce their own food.

• This process of making food is called photosynthesis.

• Chemosynthesis involves using sulfur or nitrogen compounds as an energy source, instead of light from the Sun, to produce food.

• Bacteria that perform chemosynthesis using sulfur compounds live along mid-ocean ridges near hydrothermal vents where no light is available.

http://www.youtube.com/watch?v=XotF9fzo4Vo

• Marine organisms that drift with the currents are called plankton.

• Plankton range from microscopic algae and animals to organisms as large as jellyfish.

• Most phytoplankton plankton that are producersare one-celled organisms that float in the upper layers of the ocean where light needed for photosynthesis is available.

Plankton

• One abundant form of phytoplankton is a once-celled organism called a diatom.

• Diatoms and other phytoplankton are the source of food for zooplankton, animals that drift with ocean currents.

Coral Reefs• Corals thrive in clear, warm water that receives a

lot of sunlight.• Each coral animal builds a hard capsule around

its body from the calcium it removes from seawater.

• Each capsule is cemented to others to form a large colony called a reef.

• A reef is a rigid, wave-resistant structure built by corals from skeletal material.

• https://www.youtube.com/watch?v=wbNeIn3vVKM

• What is the continental shelf?

• The continental shelf is the gradually sloping end of a continent that extends under the ocean.

• Which structure extends from the outer edge of the continental shelf to the ocean floor?– A. abyssal plain– B. continental slope– C. oceanic trench– D. seamount

• What is the area in an ocean basin where new ocean floor is forming?

• New seafloor forms at mid-ocean ridges as lava erupts through cracks in Earth’s crust.

• Which process involves using sulfur or

• nitrogen compounds as an energy source to produce food?– A. chemosynthesis– B. nitrosynthesis– C. photosynthesis– D. sulfurosynthesis