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Scientific Readings

Ocean Currents - Ocean Currents Drive The World's Climate

By Amanda Briney 

(Retrieved 13 September 2013)

Ocean currents are the vertical or horizontal movement of both surface and deep water

throughout the world’s oceans. Currents normally move in a specific direction and aid

significantly in the circulation of the Earth’s moisture, the resultant weather, and water

pollution.

Oceanic currents are found all over the globe and vary in size, importance, and strength.

Some of the more prominent currents include the California and Humboldt Currents in

the Pacific, the Gulf Stream and Labrador Current in the Atlantic, and the Indian Monsoon

Current in the Indian Ocean. These are just a sampling of the seventeen major surface currents

found in the world’s oceans. 

The Types and Causes of Ocean Currents

In addition to their varying size and strength, ocean currents differ in type. They can be

either surface or deep water.

Surface currents are those found in the upper 400 meters (1,300 feet) of the ocean and

make up about 10% of all the water in the ocean. Surface currents are mostly caused by

the wind because it creates friction as it moves over the water. This friction then forces the

water to move in a spiral pattern, creating gyres. In the northern hemisphere, gyres move

clockwise and in the southern they spin counterclockwise. The speed of surface currents isgreatest closer to the ocean’s surface and decreases at about 100 meters (328 ft) below the

surface.

Because surface currents travel over long distances, the Coriolis force also plays a role in

their movement and deflects them, further aiding in the creation of their circular pattern.

Finally, gravity plays a role in the movement of surface currents because the top of the ocean is

uneven. Mounds in the water form in areas where the water meets land, where water is

warmer, or where two currents converge. Gravity then pushes this water down slope on the

mounds and creates currents.

Deep water currents, also called thermohaline circulation, are found below 400 meters and

make up about 90% of the ocean. Like surface currents, gravity plays a role in the creation of 

deep water currents but these are mainly caused by density differences in the water.

Density differences are a function of temperature and salinity. Warm water holds less salt

than cold water so it is less dense and rises toward the surface while cold, salt laden water

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sinks. As the warm water rises though, the cold water is forced to rise through upwelling and fill

the void left by the warm. By contrast, when cold water rises, it too leaves a void and the rising

warm water is then forced, through downwelling, to descend and fill this empty space, creating

thermohaline circulation.

Thermohaline circulation is known as the Global Conveyor Belt because its circulation of 

warm and cold water acts as a submarine river and moves water throughout the ocean.

Finally, seafloor topography and the shape of the ocean’s basins impact both surface and

deep water currents as they restrict areas where water can move and "funnel" it into another.

The Importance of Ocean Currents

Because ocean currents circulate water worldwide, they have a significant impact on the

movement of energy and moisture between the oceans and the atmosphere. As a result, they

are important to the world’s weather. The Gulf Stream for example is a warm current that

originates in the Gulf of Mexico and moves north toward Europe. Since it is full of warm water,

the sea surface temperatures are warm, which keeps places like Europe warmer than other

areas at similar latitudes.

The Humboldt Current is another example of a current that affects weather. When this cold

current is normally present off the coast of Chile and Peru, it creates extremely productive

waters and keeps the coast cool and northern Chile arid. However, when it becomes disrupted,

Chile’s climate is altered and it is believed that El Niño plays a role in its disturbance.

Like the movement of energy and moisture, debris can also get trapped and moved aroundthe world via currents. This can be man-made which is significant to the formation of trash

islands or natural such as icebergs. The Labrador Current, which flows south out of the Arctic

Ocean along the coasts of Newfoundland and Nova Scotia, is famous for moving icebergs into

shipping lanes in the North Atlantic.

Currents plan an important role in navigation as well. In addition to being able to avoid

trash and icebergs, knowledge of currents is essential to the reduction of shipping costs and

fuel consumption. Today, shipping companies and even sailing races often use currents to

reduce time spent at sea.

Finally, ocean currents are important to the distribution of the world’s sea life. Many

species rely on currents to move them from one location to another whether it is for breeding

or just simple movement over large areas.

Ocean Currents as Alternative Energy

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Today, ocean currents are also gaining significance as a possible form of alternative energy.

Because water is dense, it carries an enormous amount of energy that could possibly be

captured and converted into a usable form through the use of water turbines. Currently this is

an experimental technology being tested by the United States, Japan, China, and some

European Union countries.

Whether ocean currents are used as alternative energy, to reduce shipping costs, or in their

natural to state to move species and weather worldwide, they are significant to geographers,

meteorologists, and other scientists because they have a tremendous impact on the globe and

earth-atmosphere relations.

Surface Ocean Currents

by Jennifer Bergman

(Retrieved 15 September 2013)

The water at the ocean surface is moved primarily by winds that blow in certain patterns

because of the Earth’s spin and the Coriolis Effect. Winds are able to move the top 400 meters

of the ocean creating surface ocean currents.

Surface ocean currents form large circular patterns called gyres. Gyres flow clockwise in

Northern Hemisphere oceans and counterclockwise in Southern Hemisphere oceans because of 

the Coriolis Effect creating surface ocean currents. Near the Earth’s poles, gyres tend to flow in

the opposite direction.

Surface ocean currents flow in a regular pattern, but they are not all the same. Some

currents are deep and narrow. Other currents are shallow and wide. Currents are often affected

by the shape of the ocean floor. Some move quickly while others move more slowly. A current

can also change somewhat in depth and speed over time.

Surface ocean currents can be very large. The Gulf Stream, a surface current in the North

Atlantic, carries 4500 times more water than the Mississippi River. Each second, ninety million

cubic meters of water is carried past Chesapeake Bay (US) in the Gulf Stream.

Surface ocean currents carry heat from place to place in the Earth system. This affects

regional climates. The Sun warms water at the equator more than it does at the high

latitude polar regions. The heat travels in surface currents to higher latitudes. A current that

brings warmth into a high latitude region will make that region’s climate less chilly. 

Surface Ocean currents can create eddies, swirling loops of water, as they flow. Surface

ocean currents can also affect upwelling in many places. They are important for sailors planning

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routes through the ocean. Currents are also important for marine life because they transport

creatures around the world and affect the water temperature in ecosystems.

Ocean Gyres

By Jennifer Bergman.

(Retrieved 15 September 2013)

A gyre is another name for a swirling vortex. Ocean gyres are large swirling bodies of water

that are often on the scale of a whole ocean basin or 1000’s of kilometers across (hundreds to

thousands of miles across). Ocean gyres dominate the open ocean and represent the long-term

average pattern of ocean surface currents. Ocean gyres in the Northern hemisphere rotate

clockwise and gyres in the Southern hemisphere rotate counter-clockwise due to the Coriolis

effect. 

The major gyres of the ocean include: North Atlantic, South Atlantic, North Pacific, South

Pacific and Indian Ocean gyres. A simplistic drawing of those can be seen on this page. Many

other smaller gyres exist in the ocean too.

One such smaller gyre is the Beaufort gyre found in the Arctic Ocean. The Beaufort gyre is a

huge vortex of water being driven by strong winds that force currents in a clockwise direction.

This gyre is full of relatively fresh water as Siberian and Canadian rivers drain into the Beaufort

gyre. Scientists have been keeping a close eye on the Beaufort gyre because of the relatively

fresh water it holds. When winds slack off and the gyre weakens, fresh water leaks out of the

gyre and into the North Atlantic Ocean. The addition of fresh water from the Beaufort gyre

along with fresh water from melting sea ice could be contributing to the disruption of the globalocean current system known as the ocean conveyor. This slowing or halting of the ocean

conveyor system will have impacts on the climate in the North Atlantic and surrounding areas.

One of the largest ocean gyres, the North Pacific gyre, is home to an area called the Great

Pacific Garbage Patch. This area contains a lot of litter! It is estimated to cover an area roughly

twice the size of Texas and contains approximately 3 million tons of plastic litter, though much

of this plastic is broken up into pieces too small to see with the naked eye.

Surface ocean currents, ocean gyres, deep ocean circulation and the atmosphere are all parts

of the Earth system. Understanding ocean-atmosphere interactions is a key part of understanding global climate change as well as how different things like water, energy, 

nutrients or pollutants move through (or get trapped within!) different parts of the Earth

system.

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Ocean salinity reveals human climate impact

Thursday, 20 December 2012 Larry O'Hanlon

Discovery News

(Retrieved 30 September 2013)

When you read about human-induced climate change it's often about melting glaciers and

sea ice, increasing frequency of heat waves and powerful storms. Occasionally you'll hear about

the acidification of the oceans too.

What you don't often hear about is the saltiness of the seas. But according to a new piece of 

research just published in Geophysical Research Letters that is changing too.

The saltiness, or salinity, of the oceans is controlled by how much water is entering the

oceans from rivers and rain versus how much is evaporating, known as 'The Water Cycle'.

The more sunshine and heat there is, the more water can evaporate, leaving the salts

behind in higher concentrations in some places. Over time, those changes spread out as water

moves, changing the salinity profiles of the oceans.

Oceanographers from Scripps Institution of Oceanography and Lawrence Livermore

National Laboratory fingerprinted salinity changes from 1955 to 2004 from 60 degrees south

latitude to 60 degrees north latitude and down to the depth of 700 meters in the Atlantic,

Pacific and Indian oceans.

They found salinity changes that matched what they expected from such natural changes as

El Niño or volcanic eruptions (the latter can lower evaporation by shading and cooling the

atmosphere).

Next the ocean data was compared to 11,000 years of ocean data generated by simulations

from 20 of the latest global climate models.

When they did that they found that the changes seen in the oceans matched those that

would be expected from human forcing of the climate. When they combined temperature

changes with the salinity, the human imprint is even clearer, they reported.

"These results add to the evidence that human forcing of the climate is already taking place,

and already changing the climate in ways that will have a profound impact on people

throughout the world in coming decades," the oceanographers conclude.

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 Restless

Oceans

Lubag, Blesilda Anne B.

III – BSITE

Prof. Arlyne Marasigan