earth science: ch 14 review: ch 14 review the vast world ocean

Earth Science: Ch 14 Review:

Ch 14 Review

The Vast World Ocean

The Vast World Ocean: Review

The World’s Oceans: Nearly 71% of the Earth’s surface is

covered by ocean.

Oceanography, the study of the world’s oceans, is a science that draws on the methods and knowledge of geology, chemistry, physics, and biology to study all aspects of the world’s oceans.

The world’s oceans can be divided into 4 main ocean basins: The Pacific Ocean the Atlantic Ocean the Indian ocean the Arctic ocean.


The World’s Oceans: The Pacific Ocean is the largest of

Earth’s oceans. It is the single largest geographical feature on the Earth’s surface.

It covers more than half the ocean surface on Earth. It is also the world’s deepest ocean with an average depth of 3940 meters.

The Atlantic Ocean is about half the size of the Pacific Ocean. It is a relatively narrow ocean compared to the Pacific. Both the Atlantic and Pacific are bounded to the east and west by continents.


The World’s Oceans: The Indian Ocean is slightly smaller

than the Atlantic Ocean, but is about the same average depth.

The Arctic Ocean is about 7% of the size of the pacific ocean. It is only a little more than one quarter as deep as the rest of the oceans.


The World’s Oceans:

The topography of the ocean floor is as diverse as that of the continents.

Bathymetry is the measurement of ocean depths and the charting of the shape or topography of the ocean floor.

In the 1920’s, a technological breakthrough occurred with the invention of sonar, a type of depth sounding equipment. Sonar is an acronym for Sound Navigation And Ranging.


The World’s Oceans:

In the last few decades, more complex systems using multi-beam sonar systems have developed.

Measuring the shape of the ocean floor from space with satellites is another recent technological breakthrough that has led to a better understanding.

Another way scientists learn about the ocean floor is by direct contact; going there in small submersibles designed to handle the immense pressures of deep ocean waters.


Oceanographers studying the topography of the ocean floor have divided it into three major zones

Continental margins The ocean basin floor The mid ocean ridge

The zone of transition between a continent and the adjacent ocean basin floor is known as the continental margin. In the Atlantic, thick layers of undisturbed sediment cover the continental margin. This region has very little volcanic or earthquake activity.


In the Pacific Ocean, where plate boundaries converge, oceanic crust is plunging beneath continental crust in a subduction zone. This force results in a narrow continental margin that experiences both volcanic activity and earthquakes.

The continental shelf is the gently sloping submerged area extending from the shoreline. On average, the shelf is about 80 kilometers wide 130 meters deep at it’s seaward edge.

Continental shelves contain important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits.


Marking the seaward edge of the continental shelf is the continental slope. The slope is steeper than the shelf and it marks the transition from continental crust to oceanic crust. The average slope is 5 degrees.

Deep, steep sided valleys known as submarine canyons are cut into the continental slope. Submarine canyons are formed by erosion from underwater currents.


In regions where trenches do not exist, the steep continental slope merges into a more gradual incline known as the continental rise. Here the steepness of the slope drops to about 6 meters per kilometer. Where the width of the continental slope averages only about 20 kilometers wide, the continental rise may be hundreds of kilometers wide.

Deep ocean trenches are long, narrow creases in the ocean floor that form the deepest parts of the ocean. Most trenches are located along the margins of the Pacific Ocean, and many exceed 10,000 meters (almost 30,000 feet) in depth.

Continental rise


Between the continental margin and mid-ocean ridge, lies the oceanic basin floor. The size of this region is comparably equal to the percentage of land above sea level.

This region includes deep ocean trenches, very flat areas known as abyssal plains, and tall volcanic peaks called seamounts and guyots.

Abyssal plains have accumulations of thick accumulations of fine sediment that have buried an otherwise rugged sea floor.

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The submerged volcanic peaks that dot the ocean floor are called seamounts. They are volcanoes that have not reached the ocean surface.

Once underwater volcanoes reach the surface, they form islands. Over time, running water and wave action erode these islands to near sea-level. Over millions of years, these islands gradually sink below sea-level. These once active flat-topped but now submerged structures are called guyots.


The mid-ocean ridge is located near the center of most ocean basins. The mid-ocean ridge system is an interconnected system of underwater mountains that have developed on newly formed ocean crust. This system is the longest topographic feature on Earth running 70,000 kilometers around the world’s oceans.

A high amount of volcanic activity takes place along mid-ocean ridges. This activity is associated with sea-floor spreading. Sea-floor spreading occurs where divergent plate boundaries are moving apart from each other. New ocean is formed at mid-ocean ridges as magma rises between diverging plates and cools.


Except for steep areas of the continental slope and the crest of the mid-ocean ridge, most of the sea floor is covered with sediment. Some of this sediment has been deposited by turbidity currents. The rest has slowly settled to the seafloor from above.

The thickness of ocean seafloor sediments varies. Some trenches act as traps of sediment originating on the continental margin. The accumulation of sediment may approach as much as 10 kilometers in thickness. In general accumulations of sediment are much less, about 500 to 1000 meters.


Ocean floor sediments can be classified, according to their origin, into three broad categories: Terrigenous sediments Biogenous sediments Hydrogenous sediments

Terrigenous sediment is sediment that originates on land.

Biogenous sediment is sediment that is biological in origin. Biogenous sediments consist of shells and skeletons of small marine animals and algae.

Hydrogenous sediment consists of minerals that crystallize directly from the ocean water through various chemical reactions.

Ocean bottom sediment map. Lithogenous areas are mauve, biogenous areas are purple and brown (purple = siliceous ooze, brown = calcareous ooze), and hydrogenous areas are blue.


The ocean floor is rich in mineral and energy resources. Recovering them however often involves technological challenges and high costs. Most of the value of nonliving resources in the ocean comes from energy products; oil and natural gas.

The ancient remains of microscopic organisms are the source of today’s deposits of oil and natural gas. These organisms were buried in marine sediments before they could decompose. After millions of years of exposure to heat and pressure, the remains have transformed into oil and natural gas.


Gas hydrates are compact chemical structures made of water and natural gas. The most common type of natural gas is methane, which produces methane hydrate. Gas hydrates occur beneath permafrost areas on land and under the ocean floor at depths below 525 meters.

Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean-floor sediments. Gas hydrates resemble chunks of ice but ignite when lit by a flame. The hydrates burn because methane and other flammable gases are released as the gas hydrates evaporate.


The offshore sand and gravel industry is second in economic value only to the petroleum industry.

Sand and gravel, which include rock fragments that are washed out to sea and shells of marine organisms, are mined by offshore barges using suction devices.

Sand and gravel are used for landfill, to fill in recreational beaches, and to make concrete.


As described earlier, manganese nodules are hard lumps of manganese and other metals that precipitate around a small object. They are found in fields in deep ocean areas. They contain high concentrations of manganese, iron, and smaller concentrations of copper, nickel, and cobalt.

These alloys are used in high-speed cutting tools, powerful permanent magnets, and jet engine parts. With current technology, mining of the deep-ocean floor for deposits of manganese nodules is possible but not economically profitable.


Evaporative salts:

When seawater evaporates, the salts increase in concentration until they can no longer remain dissolved.

When the concentration becomes high enough, the salts precipitate out of solution and form halite (salt) deposits.

These halite deposits can than be harvested. At right is the process from the website of a commercial sea-salt greenhouse system in Marshfield Maine.

How We Extract Natural Sea Salt from Ocean Water1. Our solar greenhouses, known as "salt

houses" are filled with fresh sea water from the Gulf of Maine.

2. The sea water evaporates naturally, from the heat of the sun and the drying effects of the wind blowing through the greenhouses.

3. Over a period of time, fleur de sel floats on the pool surface, then grows and sinks to the floor to form the salt bed.

4. When all of the water has evaporated, the sea salt is ready to be packaged as natural Maine Sea Salt™, seasoned with our natural ingredients, or smoked over a wood fire.

earth science: ch 14 review: ch 14 review the vast world ocean

Documents

pacific ocean

ocean floor

atlantic ocean

ocean surface

indian ocean

narrow ocean

arctic ocean

worlds deepest ocean