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Chapter 16: The Marine Environment

Ch. 16.1 Shoreline Features

 

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Ch. 16.2 Seafloor Features

The ocean floor contains features similar to those on land and is covered with sediments of several origins.

The Continental Margin

Modern oceanographic techniques, including sonar and satellite data, reveal that the topography of the ocean bottom is as varied as that of the continents.

The seafloor has high mountains and deep depressions.

Continental margin- the area where edges of continents meet the ocean.
Consists of continental crust covered with sediment that meets ocean crust.
Includes: continental shelf, continental slope, and continental rise.

Continental Shelf

Continental shelf- the shallowest part of continental margin extending seaward from the shore.
Vary greatly in width: Pacific coast of U.S. the shelf is only a few km wide, Atlantic coast shelf is hundreds of kms wide.

During last ice age portions of the world's continental shelves were above sea level. Todays coastlines are very different from the way they were during the last ice age.
Land bridge existed between Siberia and North America; Great Britain was attached to Europe.

As ice sheets melted, the sea gradually covered up the continental shelves.
Shelves important for commercial fish, the sediment deposits are important for oil and natural gas.

Continental Slope

Continental slope- beyond the continental shelves, the sea floor drops away quickly to depths of several kms.
Continental slope is the true edge of a continent, marking the edge of the continental crust.
Submarine canyons cut into the continental slope.

Submarine canyons are cut by turbidity currents.
Turbidity currents- rapidly flowing water currents along the bottom of the sea that carry heavy loads of sediments.

Continental Rise

Continental rise- gently sloping accumulation of deposits from turbidity currents at the base of the continental slope.
The rise gradually becomes thinner and eventually merges with the sediments of the seafloor beyond the continental margin.

In some places the continental slope ends in deep-sea trenches. In these places, there is no continental rise at the foot of the continental margin (around Pacific Ocean).

Deep-Ocean Basins

Ocean basins makeup about 60% of Earth's surface.

Abyssal Plains: flattest parts of the ocean floor 5 or 6km below sea level. Covered with hundreds of meters of fine grained muddy sediment.

Deep-Sea Trenches: the deepest parts of the ocean basins; elongated, sometimes arc-shaped depressions in the seafloor. Trenches often lie next to chains of volcanic islands, such as the Aleutian Islands.

Mid-Ocean Ridges: the most prominent features of the ocean basins, runs through all the ocean basins. Sites of frequent volcanic eruptions and earthquake activity.
Mid-ocean ridges are broken into a series of shorter, stepped sections, which run at right angles across each ridge. This is called fracture zones.

Hydrothermal Vents

A hole in the seafloor through which fluid heated by magma erupts. Most are found at the bottom of the rifts. Black smoker occurs when metal oxides and sulfides precipitate out. White smokers are cooler than black smokers but also formed by minerals precipitating out.

Seamounts and Guyots

Seamount- submerged basaltic volcanoes more than 1km high.
Guyots- large, extinct, basaltic volcanoes with flat, submerged tops.

Marine Sediments

The sediments that cover the ocean floor come from a variety of sources, but most come from the continents.

Terrigenous Sediments

Ocean currents disperse fine silt, clay, and volcanic ash from land. Closer to land, the sediments become mixed with courser materials such as sand.

Biogenous Sediments

Deep-sea sediments that come from biological activity. These sediments are called oozes and consist of either calcium carbonate or silica.

Hydrogenous Sediments

Form from elements in seawater. Manganese nodules consist of oxides of manganese, iron, copper, and other valuable metals that have precipitated.

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