An Overview of Oceans

Biblical Reference

God called the dry ground “land,” and the gathered waters he called “seas.” And God saw that it was good.

Genesis 1:10

The Oceans• In the late 1800s, the British Challenger

expedition became the first research ship to use relatively sophisticated measuring devices to study the oceans.

– Oceanography is the scientific study of Earth’s oceans, which is usually considered to have started with the Challenger expedition.

Modern Oceanography• In the 1920s, the German ship, Meteor, used

sonar for the first time to map the seafloor features of the South Atlantic Ocean.

• Sonar, which stands for sound navigation and ranging, uses the return time of an echo and the known velocity of sound in water to determine water depth.– The velocity of sound in water is 1500 m/s. – To calculate the distance to the ocean floor,

multiply the time by 1500 m/s, then divide by 2.

Mapping the Seafloor - Sonar

Sonar = Sound Navigation and Ranging

Advanced Technology• Satellites like the Topex/Poseidon continually

monitor the ocean’s surface temperatures, currents, and wave conditions.

• Submersibles (underwater vessels) investigate the deepest ocean trenches.

• Large portions of the seafloor have been mapped using side-scan sonar.– Side-scan sonar is a technique that directs sound

waves to the seafloor at an angle, so that the sides of underwater hills and other topographic features can be mapped.

Origin of the Oceans• Studies of radioactive isotopes indicate that

Earth is about 4.6 billion years old.

– Radioactive studies and lava flows offer evidence that there has been abundant water throughout Earth’s geologic history.

• Scientists hypothesize that Earth’s water could have originated from two sources:

– Comets

– Volcanoes

Comets• Comets occasionally collide with Earth and

release water on impact - possibly enough to fill the ocean basins over geologic time.

•

– Studies of meteorites indicate that they may contain up to 0.5% water.

– If the early Earth contained the same percentage of water, it would have been more than sufficient to form the early oceans.

Volcanoes• Shortly after the Earth

formed, violent volcanism released huge amounts of water vapor, CO2, and other gases, which combined to form Earth’s early atmosphere.

– As Earth’s crust cooled, the water vapor gradually condensed into oceans.

Volcanoes• Volcanism still adds water to the hydrosphere,

but the process is balanced by the continuous destruction of some water molecules by ultraviolet radiation from the Sun.– As a result, the volume of water in the oceans has

remained fairly constant.

Distribution of Earth’s Water• The oceans contain 97% of the water found

on Earth.

– The remaining 3% is freshwater located in the frozen ice caps of Greenland and Antarctica and in rivers, lakes, and underground sources.

– The percentage of ice has ranged from near zero to as much as 10% of the hydrosphere over geologic time.

The Blue Planet• Approximately 71% of Earth’s

surface is covered by oceans that have an average depth of 3800 m.

– Because most landmasses are in the northern hemisphere, oceans only cover 61% of the northern hemisphere.

– Water covers 81% of the southern hemisphere.

• All oceans are connected.

• Separated into 6 Main Bodies:

– Atlantic Ocean– Pacific Ocean– Indian Ocean– Southern Ocean– Arctic Ocean

Earth’s Oceans

Earth’s Oceans

Pacific Ocean: Largest & Deepest

Atlantic Ocean: Occupies about 20% of Earth’s Surface

Indian Ocean: Between Africa, India and Indonesia

Southern Ocean: Surrounds Antarctica and has ice year-round

Arctic Ocean: Smallest & Shallowest. Covers the North Pole

Earth’s Oceans

Major Oceans• The largest ocean, the Pacific, contains about

half of Earth’s seawater and is larger than all of Earth’s landmasses combined.

• The second-largest ocean, the Atlantic, extends from Antarctica to the Arctic Circle.

• North of the Arctic Circle is often referred to as the Arctic Ocean.

• The third-largest ocean, the Indian, is located mainly in the southern hemisphere.

• The water surrounding Antarctica, south of 50° south latitude, is known as the Antarctic (or Southern) Ocean.

Major Oceans

Jacques Cousteau

Sea Ice• The Arctic and Antarctic Oceans are covered

by vast expanses of sea ice, particularly during the winter.

– An ice-crystal slush develops at the surface of the water and eventually solidifies into individual round pieces called pancake ice.

– The pieces of pancake ice thicken and freeze into a continuous ice cover called pack ice.

– Pack ice is generally several meters thick and may cover an area more than 1000 km wide.

Sea Ice

Pancake Ice

Pack Ice

Seas• Seas are smaller than oceans and are partly

or mostly landlocked. – The Mediterranean Sea is located between

Africa and Europe and was the first sea to be explored and mapped by ancient peoples.

– Notable seas in the northern hemisphere include the Gulf of Mexico, the Caribbean Sea, and the Bering Sea, which is located between Alaska and Siberia.

– All seas and oceans belong to one global ocean whose waters are thoroughly mixed.

Major World Seas

Sea Level• Global sea level is the level of the oceans’

surfaces.

– Sea level has risen and fallen by hundreds of meters in response to melting ice during warm periods and expanding glaciers during ice ages.

– Tectonic forces that lift or lower portions of the seafloor has also affected sea level.

Sea Level

Bruce Heezen

Identify whether the following statements are true or false.

Pop Quiz

______ Oceans contain 97% of the water found on Earth.

______ Oceans cover 71% of Earth’s surface.

______The Earth’s major oceans are isolated from each other by landmasses.

______Presently, average global sea level is rising 1 to 2 cm per year.

true

true

false

false

According to one hypothesis, how did volcanism play a part in forming Earth’s early oceans?

Pop Quiz

During a period of massive volcanism that occurred shortly after the formation of Earth, huge quantities of water vapor, carbon dioxide, and other gases were released. These gases formed Earth’s early atmosphere. As Earth’s crust cooled, the water vapor gradually condensed into oceans.

What is side-scan sonar?

Pop Quiz

Side-scan sonar is a technique that directs sound waves to the seafloor at an angle, so that the sides of underwater hills and other topographic features can be mapped.