"Ocean Currents and the Distribution of Life "
By Jose Reyes
Ocean Currents recycle our planet by maintaining the ocean water at a stable low temperature and by distributing food to all the ocean's inhabitants and also to the land inhabitants throughout all the continents. Ocean currents are generated by the thrust of the wind, the spin of the Earth and the pull of the Moon's gravity. Climate change and its relation to wind is very important to know also in order to understand ocean currents. There are also many more factors to learn about, to fully understand ocean currents. Overall, I will try to explain how Ocean currents work and with some detail, but simultaneously, I will try not to overwhelm the reader with too much confusing information. If you would like to go further on and learn some more, this is a good foundation. There are website links located throughout this page that will navigate the readers to more information.
There are a multitude of ocean currents in our planet and they vary from very warm to extremely cold. Within these currents there are 9 major currents that dominate the oceans and are the ones that I will concentrate on. The circulation of these major ocean currents influence global climate and benefit all living species by providing a transportation system. Ocean currents naturally transport plankton, fish, heat, and different types of chemicals like salt, oxygen, and carbon dioxide. Enlarge Picture
"The Ancient Voyager"
The major ocean currents have helped humans to benefit the most, as they were able to navigate away from the freezing climates near the North Pole in the early years of existence. Water vessels have been around for thousands of years. The Egyptians, the Greeks, the Romans had them, but the Polynesians were the foremost travelers of open Ocean. By 1500 B.C., ocean currents were aiding the Polynesians with their enormous double-hulled sailing canoes. They would study the rotation of the ocean currents very intensely and made themselves formidable astronomers as they followed the path of the stars year round so when they were out at sea they would be able to navigate successfully.
Informative Websites on Ocean Navigation and Ancient Voyagers:
Gallery on Ocean Navigation The History of Oceanography
Types of Water Currents
Our Oceans consist of 2 Types of Currents; Surface Currents and Deep Water Currents. The ocean currents that we plot on our maps and study are the surface currents, but if you are planning to go for a swim underwater, you better be prepared for very strong turbulent deep water currents. Powered by constant trade winds and westerly winds, the surface currents also create Gyres. In the North Pacific and North Atlantic Oceans there are small irregular gyres that have been formed from the interference of land masses, but overall gyres are formed in open water.
Surface Currents: These currents make up about 10% of all the water in our oceans and flow on the surface layer, taking up the upper 440 yards of the ocean.
Significant Surface Currents
Artic Ocean: 1.East Greenland Current 2.Norwegian Current
Atlantic Ocean: 1.Labrador Current 2.Gulf Stream 3.North Equatorial Current 4.South Equatorial Current 5.North Brazil Current 6.Guinea Current 7.Angola Current 8.Brazil Current 9.Benguela Current 10.South Atlantic Current
Pacific Ocean: 1.Aleutian Current 2.Humboldt (Peru) Current 3.Kuroshio (Japan) Current 4.North Equatorial Current 5.South Equatorial Current 6.Cromwell Current
Indian Ocean: 1.Aqulhas Current 2.East Madagascar Current 3.Somali Current 4.Mozambique Current 5.Leeuwin Current 6.Indonesian Throw-flow 7.North Equatorial Current 8.South Equatorial Current 9.Indian Monsoon
Southern Ocean: 1.Antarctic Circumpolar 2.Weddell Gyre
Deep Water Currents: These currents make up the other 90% of our oceans. They are powered by their high density and also by the pull of gravity. These currents are more dense (Heavier) because they have a higher salinity (Salt) level. These currents are colder than the surface currents because of the lack of heat from the Sun.
Thermohaline circulation refers to the deepwater circulation of the oceans and is primarily caused by differences in density between the waters of different regions. It is mainly a convection process where cold, dense water formed in the polar regions sinks and flows slowly toward the equator. Most of the deep water acquires its characteristics in the Antarctic region and in the Norwegian Sea. Antarctic bottom water is the densest and coldest water in the ocean depths. In general, heat flows toward the poles in the surface currents, while the displaced cold water flows toward the equator in deeper ocean layers.
Gyres: Gyres are closed systems of circulating water and are located 30° latitude, both on the southern hemisphere and northern hemisphere. Winds come from the east between 0º and 30º and from the west between 30º and 60º, of course on both hemispheres. The winds blowing from the east are called the Trade Winds. The winds blowing from the west are called Westerly Winds. These opposing wind systems contribute to the formation of gyres. Gyres in the northern hemisphere rotate clockwise and gyres in the southern hemisphere rotate counterclockwise.
Movement of Water
With Solar Heating provided by our powerful Sun and the kick-start power of Wind , the magical movement of water begins. The thrusting forces of Gravity and The Coriolis force are major factors also. Land masses are significant contributors in great ways, by blocking, creating and splitting the major ocean currents so the water cycling system can continue over and over without any interruptions.
Solar Heating: The heat from the Sun is what generates wind.
Wind: Wind is created by the movement of heated masses of air in conjunction to cooling masses of air. Air heated by the sun becomes less dense and rises, creating an area of low pressure. The air from adjacent areas moves toward the low pressure, and that movement is wind. The air on land heats up faster than in the sea and that is why the wind blows in from the sea, but only during the day. At night, because land air cools off much faster than the sea, the wind will then blow out from the shore towards the sea.
(Simple Animated Look)
Waves: Waves are created by wind blowing over water, the stronger the wind the bigger the wave. There are 2 types of waves that occur in the Ocean, shallow waves and deep water waves. The difference is the depth of the water where it is occurring. A wave in deep water has more space to travel down towards the seabed, but in shallow water there is less space for it to tumble around in a circular motion. For that reason you can imagine how a wave can carry so much power and energy on its back and can travel quite a distance once it starts rolling, just ask a professional surfer. For More Information:
All you wanted to know about Waves Tidal Waves and Tsunamis
Killer Waves or Freak Waves Rogue Waves or Freak Waves
Types of Waves: Animated Views
Upwelling: This natural phenomenon occurs when the wind blows from land out to sea and also along the shore. The wind pushes the coastal surface water further out to the sea and the deeper water moves in to replace the missing surface water. Upwelling can change the temperature of both the surface ocean water and the adjacent land mass in a dramatic fashion, as well as increasing biological productivity of the ocean.
Downwelling: When surface waters are influenced by wind and the Coriolis effect they are driven toward the coastline where it piles up. The driven water is forced against the shore where it cannot go back horizontally, so it is forced. This vertical flow of water to a deeper level is called Downwelling. This process carries oxygen to deeper levels in the ocean system, replenishing its supply to oxygen dependent organisms.
Coriolis Force and the Ekman Spirals
Coriolis Force: Coriolis effect is an inertial force described by the 19th-century French engineer-mathematician Gustave-Gaspard Coriolis in 1835. Coriolis implemented Newton's law of motion of bodies to the rotation of the earth and its effect on currents.
Images courtesy of zebu.uoregon.edu
An inertial force, acting to the right of the direction of body motion for counterclockwise rotation of the reference frame or to the left for clockwise rotation must be included in the equations of motion. This force causes currents to deflect clockwise or counter-clockwise and develop Ekman spirals.
The Ekman Spiral: The wind pattern drives the ocean currents in the near surface water, but at ocean depths of 100 to 200 feet, the current behaves differently. Friction and other forces cause the deeper ocean water to move slower and turn to the right of the main surface current, this is known as the Ekman Spiral or drift.
Gravity and the Tide: The Moon and the Sun's gravity effect the tide of the ocean but the Moon, because it's so much closer has a much stronger pull. When the Moon's gravity pulls on the Earth it makes the ocean a little deeper and also because it is pulling the Earth from the ocean on the opposite side, the depth of the oceans on that side will also increase. Now since the Earth is rotating, then there are 2 high tides and 2 low tides on a daily basis.
The Spring Tide, The Neap Tide and the Proxigean Spring Tide
-When the sun and the moon are lined up to both pull in the same direction or opposite directions the tides are especially strong, this is called "Spring Tide".
-"Neap Tides" are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another, with respect to the Earth. Neap tides occur during quarter moon.
-The "Proxigean Spring Tide" is a rare occasion when the tide is unusually high. This very high tide occurs when the moon is both unusually close to the Earth and in the New Moon phase, when the Moon is between the Sun and the Earth. The Proxigean spring tide occurs once every 1.5 years.
The 9 Major Ocean Currents
This exceptional map shows the 10 major ocean currents and all the land masses on our planet, but most interesting it shows the smaller currents and their significance in supplying the major currents with water power. Checkout these Maps on: Encarta.Msn.Com/WorldAtlas , here you can type in anything, for example; "Labrador Current", then you can look at the map in all different "Styles" and you can then zoom in and out as much as you want.
(Courtesy of Windows.UCAR.Edu)
The Labrador current travels southwards from the Artic circle and along the Labrador coast. This current Originates at the Davis Strait and is a combination of the West Greenland Current, The Baffin Island Current and inflow from Hudson Bay. As the current travels down the coast, it runs into the Gulf of St. Lawrence, where some of the water enters, but the majority of its cold, freezing water continues around, as you can see here on the left, to move in a southwest fashion. Afterwards it branches out eastward and joins up with the warmer waters of the Gulf Stream current.
The Labrador current can be observed with no difficultness from practically anywhere, because it transfers high quantities of ice (Checkout picture from airplane window on right).
Checkout the USCG (United States Coast Guard) Website and the International Ice Patrol
These currents also known as the Equatorial Counter currents, run very close or on the equator itself, from West to East. These currents run from 4° from the north of the equator to 4° south of the equator and is 300 miles wide.
6. The Kuroshio Current
The Kuroshio Current also known as the Japan current is a warm ocean current that runs up northward from the North Equatorial Current and sweeps by the eastern section of Taiwan and Japan. As It then meets with a smaller current, the Tsushima Current which separates from the main current and flows into the Sea of Japan. At about latitude 35°N it divides to form an eastern branch flowing nearly to the Hawaiian Islands and a northern branch that skirts the coast of Asia and merges with the waters of the cold Oyashio Current to form the North Pacific Current. Dense fogs develop along the boundary between the Japan and Oyashio currents.
The Southbound current off the West Coast, known as the California current, is a cold current that carries polar water to the waters off of Central America. This current moves cold water from the Gulf of Alaska along the California coast and is partially responsible for the relatively cold water experienced when going to the beach. The California current is driven by the westerlies as it twists around Baja California and to Mexico. The colder water rises to replace warm surface water blown out to sea by strong offshore winds (Upwelling).
This Alaskan current loops northward along the coast of Alaska and flows west along the Aleutian Islands. The "West Wind Drift" ultimately forms a counterclockwise gyre in the Gulf of Alaska. The Alaska Current water is characterized by temperatures above 39° F (4° C) and surface salinities below 32.6 parts per thousand. Circulation and water mass structure in the Arctic and More
Doldrums: These events are also known as the equatorial belt of calms, area around the earth centered slightly north of the equator between the two belts of trade winds. The large amount of solar radiation that arrives at the earth in this area causes intense heating of the land and ocean. This heating results in the rising of warm, moist air; low air pressure; cloudiness; high humidity; light, variable winds; and various forms of severe weather, such as thunderstorms and squalls. Hurricanes originate in this region. The doldrums are also noted for calms, periods when the winds disappear, trapping sailing vessels for days or weeks.
Other informative websites on Ocean Currents:
Reed's Nautical Almanac Great Article: Floating Objects & Ocean Currents