Intoduction: Ocean Currents

Oceans are the lifeline of the Earth and humankind because it plays an important role in the Earth’s climate and in global warming.

It produces over half of the world’s oxygen and absorbs 50 times more carbon dioxide than our atmosphere.

What is Ocean Currents?

The Ocean Currents consists of horizontal and vertical components of the circulation system of ocean waters that is produced by gravity, wind friction, and water density variation in different parts of the ocean.

They are classified into three part i.e. Drift, Current and Stream on the basis of the direction of flow, speed and shape. It may be cold, warm and hot.

Warm ocean currents originate near the equator and move towards the poles or higher latitudes while cold currents originate near the poles or higher latitudes and move towards the tropics or lower latitude.

The current’s direction and speed depend on the shoreline and the ocean floor. They can flow for thousands of miles and are found in all the major oceans of the world.

The list of Ocean Currents of the world is given below along with their nature.

There are two type of Ocean Currents:

1. Surface Currents—Surface Circulation:

• These waters make up about 10% of all the water in the ocean.
  
  
• These waters are the upper 400 meters of the ocean.

2. Deep Water Currents—Thermohaline Circulation

• These waters make up the other 90% of the ocean
  
  
• These waters move around the ocean basins by density driven forces and gravity.

The density difference is a function of different temperatures and salinity.

These deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.

Ocean Currents are influenced by two types of forces:

1. Primary Forces–start the water moving

• The primary forces are:

1. Solar Heating
2. Winds
3. Gravity
4. Coriolis

2. Secondary Forces–influence where the currents flow

• Surface Circulation:

Solar heating cause water to expand. Near the equator the water is about 8 centimeters high than in middle latitudes. This cause a very slight slope and water wants to flow down the slope.

Winds blowing on the surface of the ocean push the water. Friction is the coupling between the wind and the water’s Surface.

A wind blowing for 10 hours across the ocean will cause the surface waters to flow at about 2% of the wind speed.

Water will pile up in the direction the wind is blowing.

Gravity will tend to pull the water down the “hill” or pile of water against the pressure gradient.

But the Coriolis Force intervenes and cause the water to move to the right (in the northern hemisphere) around the mound of water.

These large mounds of water and the flow around them are called Gyres. The produce large circular currents in all the ocean basins.

North Atlantic Gyre is separated into four distinct Currents

• The North Equatorial Current
• The Gulf Stream
• The North Atlantic Current
• The Canary Current.

But why doesn’t the water spin towards the center of the ocean? Why does it flow around the hill in this circular motion.

Remember the hill of water- This hill is formed by the inward push of water through a process call Ekman Transport

Wind blowing on the surface of the ocean has the greatest effect on the surface. However, for the lower layers of the ocean to move they must be pushed by the friction between the layers of water above.

Consequently, the lower layer moves slower than the layer above. With each successive layer down in the water column the speed is reduce. This leads to the spiral affect seen in the above diagram.

When the water is pushed to the right it forms the hill we described above. So, when water is pushed along by the wind it wants to be turned to the right by the Coriolis force (in the northern hemisphere) but it must fight against gravity (trying to move up the hill of water formed by Ekman transport).

A balance is met between the Coriolis and the gravity (pressure gradient force). This balance produces a balanced flow called a Geostrophic current.

List of Important Ocean Currents of the World:

The Ocean Currents in the northern hemisphere deflects towards their right and in the southern hemisphere deflect towards their left due to the Coriolis force.

The only exception to this rule of the flow of ocean water is found in the Indian Ocean, where the direction of current flow changes with the change in the direction of monsoon wind flow.

It is noteworthy that the cold currents are lesser in number as compared to the warm or hot current.

What’s the difference between a tide and a current?

Tides go up and down; currents move left and right.

Tides are driven by the gravitational force of the moon and sun. Tides are characterized by water moving up and down over a long period of time.

When used in association with water, the term “current” describes the motion of the water. Oceanic currents are driven by several factors. One is the rise and fall of the tides.

Tides create a current in the oceans, near the shore, and in bays and estuaries along the coast. These are called “tidal currents.”

Tidal currents are the only type of currents that change in a very regular pattern and can be predicted for future dates.

TYPES OF TIDES

We will use two classifications to define the tide types. The first of them is the value awarded to the height of the tide and is the one reflected in the tide tables.

The second is the lunar phase and is directly related to the average activity of fish in the solunar charts.

According to the height of the tide

High tide: when the sea water reaches its greatest height within the tide cycle.

Low tide: when the sea water reaches its lowest height within the tide cycle.

Normally there are two high tides and two low tides for every lunar day as, at the same time as the Moon lifts the water over the Earth on the side facing it, it also separates the Earth from the water on the opposite side.

According to the lunar phase

In accordance with the lunar phase, we can distinguish two types of tides:

Spring tides

During the full moon and new moon phases, the Moon and the Sun are aligned and their effects combined, producing the spring tides.

There is a proven increase in the activity of fish during spring tides, above all if these coincide with sunrise or sunset, and these are the most propitious days for fishing.

Neap tides

During waxing and waning moons, on the contrary, the effects are detracted, thereby obtaining tides of less amplitude (lower tidal coefficient), called neap tides.

The movement on the seabed tends to be less and this normally results in days that are less propitious for fishing than days with spring tides.

Jet streams are narrow and meandered strip of fast blowing air currents found in the upper altitude (i.e. upper troposphere or lower stratosphere).

El Niño, also known as El Niño Southern Oscillation (or ENSO), refers to the cycle of warm and cold temperatures, as measured by sea surface temperature, of the tropical central and eastern Pacific Ocean.

However, the cool phase of ENSO is known as “La Niña.”

El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific.

Cyclone is a large-scale air mass that keeps rotating around a strong center of low pressure. It rotates counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

In the northeastern Pacific oceans and the Atlantic Ocean, the tropical cyclone is known as “Hurricane.”

In the Indian and south Pacific Oceans, the tropical cyclone is called as “Cyclone,” and in the northwestern Pacific Ocean it is known as “Typhoon.”


In the South Indian Ocean (specifically South-west of Australia), a tropical cyclone is known as “Willy-Willy.”

Anticyclone is a large-scale wind system that circulates around a central region of high atmospheric pressure.

It rotates clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere (the following image illustrates the comparative structure of cyclone and anti-cyclone).