s Oceans

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The World’s Oceans: 

The World’s Oceans 71% of the Earth’s surface is covered by ocean water. The oceans contain 97% of the earth’s water. All the oceans and seas are actually one continuous body of water.


Oceans The oceans are the Atlantic, Pacific, Indian. Arctic and Southern. The Pacific Ocean is the largest ocean. The area and volume of the Pacific Ocean are greater than the Atlantic and Indian combined.


Seas A sea is a part of an ocean that is nearly surrounded by water. The Mediterranean, Arctic and Black Sea are really part of the Atlantic Ocean.

Water Cycle: 

Water Cycle The sun’s rays heat the surface of the ocean. The heat causes the water to evaporate. The evaporating water (clean, fresh water) enters the atmosphere as water vapor. The salt remains behind.

Water Cycle: 

Water Cycle Winds carry water vapor over land. Some of the water vapor condenses to form clouds. The water in the clouds falls as precipitation.

Water Cycle: 

Water Cycle Some of this water runs into rivers and streams which flow back into the oceans. Some of the water seeps into the soil and rocks become part of the groundwater.

Properties of Ocean Water: 

Properties of Ocean Water Ocean water is a mixture of gases and solids dissolved in pure water. Oceanographers believe oceans contain all the natural elements on Earth. 85 of 90 have been found in the ocean.

Major Elements in the Ocean: 

Major Elements in the Ocean Ocean water is 96% pure water. Chlorine (1.9) and sodium (1.1) make up the next largest concentration of elements. Sodium chloride is table salt.


Salinity Salinity describes the amount of dissolved water in the ocean. Salinity is expressed in parts per thousand. The salinity level of the ocean is expressed in parts per thousand. The average salinity of ocean is 35 parts per thousand.

Sources of Salt in the Ocean: 

Sources of Salt in the Ocean When volcanoes erupt, rock materials and gases, such as chlorine, spew forth. As rivers, streams and glaciers move over rock and soil, they dissolve salts, such as magnesium, sodium and potassium, in them. As waves pound the shoreline, they dissolve salts from the rocks.

Salinity Levels: 

Salinity Levels The salinity is lower in areas where freshwater rivers run into the ocean. Salinity levels are also affected by animals such as clams and oysters that use calcium salts to build their shells. They remove salt from the water. In warm ocean areas where there is little rainfall and much evaporation, the amount of dissolved salts is much greater. In polar regions, the salinity levels are high because temperatures are cold enough for ocean water to freeze. Pure water is removed and salts are left behind.

Gases in Ocean Water: 

Gases in Ocean Water The most abundant gases in ocean water are nitrogen, carbon dioxide and oxygen. The amounts of these elements vary with depth. They are more abundant at the ocean’s surface where sunlight causes more plant life.

Temperature of Ocean Water: 

Temperature of Ocean Water Warm water holds less dissolved gas than cold water. When ocean water is cold, like in polar regions, it sinks and carries oxygen rich water to the ocean depths. As a result, fish and other animals can live in deep parts of the ocean.

Temperature of Ocean Water: 

Temperature of Ocean Water Sun is the major source of heat for the ocean. Motions of the ocean, such as waves and currents, mix the surface water and transfer the heat downward.

Surface Zone: 

Surface Zone The zone where the water is mixed by waves and currents is called the surface zone. The surface zone extends 100-400 meters downward. The temperature remains constant with depth. Temperature in a surface zone changes due to seasons and locations.


Thermocline The zone of rapid temperature change is called the thermocline. The thermocline does not occur at a certain depth. The season and flow of ocean currents alter the depth of the thermocline. The thermocline exists because warm, surface water does not mix easily with colder, denser water.

Deep Zone: 

Deep Zone The thermocline forms a transition between the surface zone and the deep zone. The deep zone is an area of extremely cold water that extends from the bottom of the thermocline to depths of 4000 meters or more.

Deep Zone: 

Deep Zone Within the deep zone, temperatures decrease only slightly. At depths greater than 1500 meters, the temperature is about 4 degrees C. The three ocean zones are not found in the polar (Arctic and Antarctica) regions since the surface waters are always cold.

The Ocean Floor: 

The Ocean Floor The topography of the ocean floor is different from the topography of the continents

The Ocean Floor: 

The Ocean Floor The ocean floor has higher mountains, deeper canyons, and larger flatter plains. Earthquakes occur more often. The rocks are very different. The crust is thinner.

Edges of the Continents: 

Edges of the Continents The shoreline is a boundary between where the land and the ocean meet. The area where the underwater edge meets of a continent meets the ocean floor is called a continental margin.

Continental Margin: 

Continental Margin The area where the underwater edge of a continent meets the ocean floor is called a continental margin. A continental margin consists of a continental shelf, a continental slope and a continental rise.

Continental Shelf: 

Continental Shelf The flat part of a continental margin that is covered by shallow ocean water is called a continental shelf. A continental shelf slopes gently from the shoreline. The width of the continental shelf varies. Large mineral, oil and natural gas deposits are found here.

Continental Slope: 

Continental Slope At the edge of the continental shelf, the ocean floor plunges steeply 4 to 5 kilometers. A continental slope marks the boundary between the crust of the continent and the crust of the ocean floor.

Continental Rise: 

Continental Rise Separating a continental slope from the ocean floor is a continental rise. A continental rise is made of large amount of sediments, rocks, plants and animals. Sometimes the sediments are carried down the slope in masses of flowing water called turbidity currents, like an underwater avalanche.

Submarine Canyons: 

Submarine Canyons In many areas, submarine canyons cut through a continental shelf and slope. They are deep, V-shaped valleys that have been cut in the rock, possibly by turbidity currents. The Monterey Submarine Canyon(2000 meters) is deeper than the Grand Canyon.

Abyssal Plains: 

Abyssal Plains Large, flat areas on the ocean floor are called abyssal plains. The abyssal plains are larger in the Atlantic and Indian than in the Pacific due to the deposition of sediments by large rivers. The Pacific Ocean has large cracks that trap sediments and result in smaller abyssal plains.

Abyssal Plains: 

Abyssal Plains Abyssal plains close to the continent are made of mud, sand and silt. Farther out on the abyssal plains, some of them contain the remains of tiny organisms that form ooze. Where ocean life is not abundant, the floor of the ocean is covered with red clay

Seamounts and Guyots: 

Seamounts and Guyots Seamounts are underwater volcanic mountains that rise more than 100 meters above the ocean floor. Most have been found in the Pacific Ocean. Some seamounts reach above the surface of the water to form islands, like the Azores in the Atlantic and the Hawaiian islands in the Pacific. Guyots are flat-topped seamounts.


Trenches Trenches are the deepest parts of the ocean found along the edge of the ocean floor. The Mariana Trench in the Pacific Ocean contains the deepest spot (1100 meters) on Earth known as Challenger Deep.

Midocean Ridges: 

Midocean Ridges The midocean ridges form an almost continuous mountain belt that extends from the Arctic Ocean down through the middle of the Atlantic Ocean around Africa into the Indian Ocean and across the Pacific Ocean. In the Atlantic it is called the mid-Atlantic Ridge and in the Pacific, the Pacific-Antarctica Ridge.

Formation of Midocean Ridges: 

Formation of Midocean Ridges Mountain ranges on land are formed when the Earth’s crust folds and is squeezed together. Midocean ridges are areas where molten material from deep within the Earth flows up to the surface and cools and forms new crust.


Rifts Running along the middle of the midocean ridges between the rows of parallel mountains are deep crevices or rifts. Rifts are areas of great earthquake and volcanic activity.


Reefs Surrounding volcanic islands in tropical waters are large masses and ridges of limestone rock, known as coral reefs. The limestone structures contain the shells of animals. These animals cannot exist in water cooler than 18 degrees C and deeper than 55 meters.

Types of Coral Reefs: 

Types of Coral Reefs Fringing reefs Barrier reefs Atoll

Fringing Reefs: 

Fringing Reefs Fringing reefs are coral reefs that touch the shoreline of a volcanic island. Fringing reefs are usually less than 30 meters.

Barrier Reefs: 

Barrier Reefs Barrier reefs are separated from the shore by an area of shallow water called a lagoon. Barrier reefs are usually larger than fringing reefs and surround islands that are more submerged. The largest barrier reef is the Great Barrier Reef of Australia. It is 23oo km long and 320 km wide.


Atoll An atoll is a ring of coral reefs that that surround an island that has sunk beneath the surface of the ocean.

Ocean Life Zones: 

Ocean Life Zones Intertidal Zone (Splash Zone) Neritic Zone (Continental Shelf) Open Sea Zone – Bathyal (Continental Slope) Abyssal (Ocean floor)

Ocean Life Zones: 

Ocean Life Zones The plant and animal life in the ocean is affected by several factors. One factor is the amount of sunlight that penetrates the ocean. Another factor is the temperature of the ocean water. Water pressure is also a factor.

Major Groups of Ocean Life: 

Major Groups of Ocean Life Plants and animals in the ocean are classified into three major groups based on their habits and the depth of the water in which they live. The three major groups are plankton, nekton and benthos.


Plankton Plankton float at or near the surface where sunlight can penetrate. Most of the plankton are very small, such as algae. These organisms drift with the currents or tides. Plankton are the main food for many larger organisms. They account for most of the organisms in the ocean.


Nekton Whales , seals , dolphins, squid octopuses, barracuda and other fish are all nekton. Nekton are free-swimming organisms that feed on other nekton as well as on plankton. Many have adaptations enabling them to function at depths that have great pressure and no light.


Benthos Organisms that live on the ocean floor are benthos. The forms of these animals include crustaceans and shell fish. The deep bottom environments are sparsely populated with benthos. Some benthos are plants that live on the ocean floor in shallow waters where sun can penetrate.

Ocean Life Zones: 

Ocean Life Zones The classification of the ocean into life zones is based on the conditions in the ocean. These conditions vary widely. The classification includes the intertidal zone, the neritic zone and open-ocean zones.

Intertidal (Splash) Zone: 

Intertidal (Splash) Zone This region is the most changeable in the ocean. Anemones, crabs, clams, mussels and plants such as seaweed live here. They must be able to exist without water for periods of time. They must be able to anchor to keep from being washed out to sea.

Neritic ( Shelf) Zone: 

Neritic ( Shelf) Zone This zone extends to a depth of 200 meters and receives plenty of sunlight. The water pressure is low and the temperature is constant. This zone can support plankton, nekton and benthos. Marine life is most abundant here.

Open Ocean Zones: 

Open Ocean Zones There are two open-ocean zones:bathyal and abyssal

Bathyal (Slope): 

Bathyal (Slope) The bathyal zone begins at the continental slope and extends down about 2000 meters. Sunlight cannot penetrate the bottom of this zone and plants do not grow at the bottom. Many forms of nekton, such as squid, octopus and large whales live in this zone.

Abyssal (Ocean Floor) Zone: 

Abyssal (Ocean Floor) Zone At a depth of about 2000 meters, the abyssal zone begins. The abyssal zone extends to a depth of 6000 meters. This zone covers the large flat plains of the ocean. No sunlight can penetrate and food is scarce. The water pressure is great. Most of the animals here are small. Some make their own light.

Studying the Ocean Floor: 

Studying the Ocean Floor In 1872, the first expedition to explore the ocean began when the Challenger sailed from England. Scientists used wire to measure the ocean depth. Scientists aboard used nets to collect animals and plants from the ocean floor. Special thermometers measured the temperature. Samples of water were collected.

Present Oceanographers: 

Present Oceanographers Today oceanographers have modern instruments. Underwater cameras provide pictures of the ocean floor. Corers bring up samples of med and sand from the ocean bottom. Bathyspheres, bathscaphs and other submersibles are able to dive deep under the surface to explore

Mapping the Ocean Floor: 

Mapping the Ocean Floor One of the most important goals is to map the ocean floor. This is done by indirect methods such as echo sounding, radar, sonar and seismographic surveys.

Echo Soundings: 

Echo Soundings All of these methods are based on the same principles. Energy waves are sent down to the floor are reflected and return to the surface, where they are recorded. Knowing the speed of sound, 1500 m per second, oceanographers can determine the depth. The most complete picture was gathered from information from a satellite, the Seasat, launched in 1978

Motions of the Oceans: 

Motions of the Oceans Ocean water never stops moving. The three basic motions of the ocean are : the up and down movement of the waves. The steady movement of ocean currents and the rise and fall of the ocean tides.


Waves Waves are pulses of energy that move through the ocean. Waves are set in motion by winds, earthquakes and the gravitational pull of the moon. The most common source of wave movement is the wind blowing across the surface.

Movement of Waves: 

Movement of Waves The water in a wave is not moving forward at all. Only the energy moves forward through the water producing one wave after another. The energy is passed from particle to particle. It is also passed downward. With increasing depth, the motion of the particles decrease. At a certain depth the motion stops. In deep water, there are no waves except those caused by tides and earthquakes.

Height of the Waves: 

Height of the Waves Three factors affect the height of waves: wind speed, the length of time the wind blows and the distance the wind blows over the water. As each of these factors increases, the height of the wave increases.

Wave Characteristics: 

Wave Characteristics The point of the wave is called the crest. The lowest point of the wave is called the trough. The horizontal distance between two consecutive crests or troughs is the wavelength. The vertical distance between a crest and a trough is called the wave height.

Wave Period and Frequency: 

Wave Period and Frequency The amount of time it takes consecutive crests or troughs to pass is called the wave period. The number of crests or troughs passing a given point in a certain wave period is called the wave frequency. As wave frequency increases, wave length decreases.


Swells Waves stay the same distant apart out in the open ocean. The wavelength is constant. These waves are called swells.


Surf Waves change as they near the shore. They slow down and get closer together. Their wavelength decreases and their increase until they crash forward as breakers. This is called the surf.


Undertow The water then flows back toward the ocean carrying bits of seaweeed, sand and pebbles. The retreating water is called an undertow.


Tsunamis Some ocean waves are caused by earthquakes. Tsunamis have very long wavelengths and are very deep. They carry a huge amount of energy Which is concentrated in much less water as it nears the shore. Tsunamis reach heights of 35 meters (an average 10-story building).


Currents Water below the surface moves in streams called currents. Currents are caused by two factors: wind patterns and differences in water density.

Surface Currents: 

Surface Currents Currents caused mainly by wind patterns are called surface currents. These currents have a depth of several hundred meters. The temperature of a current depends on where it originated, making it either warm or cold.

Long-Distance Currents: 

Long-Distance Currents Surface currents that travel thousands of kilometers are called long-distance currents, such as the Gulf Steam. The Gulf Stream carries warm water from the southern tip of Florida north along the eastern coast of the United States moving at speeds of 1.5 meters per second.

Continuous Currents: 

Continuous Currents All currents form a continuous worldwide pattern of water circulation. The water in each ocean moves in a large, almost circular pattern. In the Northern Hemisphere, the currents move clockwise. In the Southern hemisphere, the currents move counterclockwise.

Short- Distance Currents: 

Short- Distance Currents Short distance currents are usually found near a shoreline where the waves hit at an angle. When the waves hit the shoreline, the water turns and produces currents that move parallel to the shoreline called longshore currents. Longshore currents move large quantities of sand which deposit in sand bars.

Rip Current: 

Rip Current If the longshore current cuts an opening in the sandbar the water will return to ocean in a powerful narrow flow called a rip current. A rip current is a type of undertow.

Deep Currents: 

Deep Currents Deep currents are caused mainly by differences in water density. The cold, salty water, that is more dense, flowing from the polar regions moves under the less dense water away from the polar regions. Most deep currents flow in the opposite direction from surface currents.


Upwellings The densest water on Earth lies off the coast of Antarctica. This water sinks to the ocean floor and flows north. As the Antarctic currents come close to land, the ocean floor rises, forcing these cold currents upward. These risings, called upwellings, carry rich food from the ocean floor that results in rich fishing grounds near PSpring and Neap Tides Spring Tides, higher than normal high tides, are produced when the sun, Earth and moon line up or new and full moon phases. Neap tides, lower than normal high tides, are produced when the sun, Earth and moon are at right angles or first and last quarter moon phases.

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