The World of Ocean Currents

People often say that our planet is a ‘blue’ planet. This is probably because oceansoceans cover 71 percent of the Earth’s surface and contain 97 percent of the planet’s water. Earth’s oceans are home to Marine ecosystemsMarine ecosystems, such as coral reefs and the abysses. These are among the largest of Earth’s aquatic ecosystems. They are also home to the largest animal on the planet, the blue whaleblue whale.

Did you know?

The blue whale’s heart is the size of a small car!

It may seem like we know a lot about oceans, but we really don’t. We know more about the Moon than we know about our oceans! More than 80% of our oceans have yet to be explored. So let’s dive deep into the characteristics of our ocean planet, from moving water at the surface to the depths of the ocean.

The World Ocean

All water on Earth is part of the hydrospherehydrosphere The hydrosphere is the total amount of water found on, under, and over the surface of a planet. Oceans are an important part of the hydrosphere.

The oceans on Earth may have different names, but they are really all one ocean. The boundaries only exist on our maps! We will use the term “Ocean” to mean the World Ocean’s body of salinesalinewater. Saline water is water that contains a large amount of dissolved salts.

Misconception Alert

People often use the word “sea” interchangeably with the word “ocean”. The word sea refers to a large body of saline water partly or fully surrounded by land.

Geography

Oceans cover a total area of 360 million square kilometres (km2). 36 countries the size of Canada could fit in it! While the Ocean is geographically one body of water, people refer to five large oceanic areas. From largest to smallest these are:

1. Pacific Ocean
2. Atlantic Ocean
3. Indian Ocean
4. Antarctic Ocean
5. Arctic Ocean

The oceans are not equally distributed over the Earth. Oceans cover about 80 percent of the areas south of the EquatorEquator, but only 61 percent of the areas north of the Equator.

Did you know?

The study of all the physics, chemistry, geology, and biology of oceans and seas is called oceanographyoceanography.

Chemistry

Oceans contain seawater. SeawaterSeawater is water that includes a variety of dissolved solids and gases. The total amount of dissolved material is a measure of the water’s salinitysalinity. For every kilogram of seawater, there is about 35 grams of dissolved material. 

Different parts of the Ocean have different levels of salinity. Differences in salinity can happen because of differences in evaporationevaporation and precipitation. Higher levels of salinity are found closer to the Equator, where evaporation is greater. Lower levels of salinity are found closer to the North and South poles where there is less evaporation.

Did You Know?

The Dead Sea is actually a salt lake. The water there has 9.6 times the amount of salt in regular ocean water.

Ocean Currents

Water in the Ocean is constantly moving. On a global scale, this water has a great influence on our weather and climate. We use the word ocean currentocean current to describe the motion of this water. Ocean currents occur for several reasons. 

Wind

A second cause of currents is wind. Winds act on the water at the ocean’s surface. Winds can affect currents both on a small scale, such as near coastal areas as well as on a large scale, such as out in the open ocean.

Image - Text Version

Shown is a colour photograph of a lighthouse on a rocky shore. Large waves are seen crashing in. The wind is also blowing water at the peaks of the waves towards the shore.

 

Surface Ocean Currents

Surface ocean currentsSurface ocean currents are caused by winds blowing across the surface of the ocean. If the Earth did not rotate, the winds would simply circulate cold, dense air near the poles with warm, less dense air near the Equator. In that case, the ocean surface currents would follow the same path. However, the Earth does rotate which leads to something called the Coriolis Effect. So, instead of following a straight path between the poles and the equator, the circulating air appears to curve to the right in the Northern Hemisphere, in which is North America. And in the Southern Hemisphere, the ocean currents curve to the left. The ocean surface currents in both hemispheres flow in roughly circular patterns called gyresgyres. Watch the video below and pay close attention to 1:47-2:45 min. It explains these big loops or gyres.

Oceans receive the most of their heat from the Sun in areas near the Equator. This heat is distributed by ocean currents. As surface currents move towards the poles, they carry warm, salty water to the colder polar regions. By the time the water reaches the poles, it has lost this heat. This very cold water becomes denser, causing it to sink. This connects it with deep ocean currents, which we will explore later on.

Deep Ocean Currents

Deep ocean currentsDeep ocean currents are driven by thermohaline circulation. This constant moving up, down and around is also called the Global Ocean Conveyor Belt. Deep ocean currents are caused by changes in the densitydensity of seawater. The density of seawater can change depending on the temperature and salinity. There is evidence to show that climate change is impacting deep ocean currents.

• Rising sea temperatures are slowing down the conveyor belt. Without the large change in temperature, the current cannot not flow.
• Melting freshwater glaciers and polar ice caps add more freshwater to the ocean. This would result in a drop in the density of the sea water. If the North Atlantic current is not heavy enough to sink as per usual, then the Gulf Stream would not be able to pump warm water.

Already, changes to deep ocean currents are affecting weather patterns on both sides of the Atlantic Ocean.

1. Deep ocean current circulation begins in the North Atlantic where cold, dense, salty water sinks and flows southward at great depths.
2. Next it moves into the South Atlantic.
3. Here it mixes with cold and dense water flowing northward from the Weddell Sea, which is a sea in the Antarctic
4. This cold, deep water then flows into the Pacific Ocean
5. As the deep ocean currents move through the Pacific Ocean, the water is slowly warmed, becoming less dense, and rising to the surface
6. The shallower, warmer current moves south across the Pacific Ocean and then westward into the South Atlantic.
7. The water then moves north into the North Atlantic where the cycle starts all over again. 

Did you know?

The circulation of both the surface and deep currents within the oceans is a main controller of the world’s climate. 

Rising Oceans

Not only can global warming lead to changes in deep ocean currents, it also leads to rising ocean levels. Coastal areas risk being flooded and disappearing by rising sea water. As coastal land is no longer above water, people will be forced to move inland. This affects the living space of humans, coastal biodiversity and ecological balance.

Waves and Erosion

Waves have a powerful impact on coastlines. This makes coastal erosionerosion very common worldwide. About 70% of the world’s sandy coast experiences some form of erosion. This process is being made worse by climate change and sea level rise.

The warming of the oceans has made storms more frequent and intense. This means that stronger waves are crashing and breaking up shorelines. For example, in Canada, an ice footice foot that would normally protect shorelines against erosion has been melting with the rising temperatures. In fact, some receding glaciers in the Canadian arctic have exposed land that has been covered by ice for more than 40 000 years! 

Did you know?

70% of Canadian coastlines are in the Canadian Arctic. 

Both humans and other living things are affected every day by ocean currents. You can read more here about other ocean topics such as Ocean Zones, Waves, Tides and Tsunamis, and ocean warming.