The following points highlight the ten main currents in the Pacific ocean. The currents are: 1. North Equatorial Current 2. South Equatorial Current 3. Counter Equatorial Current 4. Kuroshio System 5. Oyashio Current 6. California Current 7. Peru Current 8. El Nino or Counter Current 9. East Australia Current 10. West Wind Drift.
1. North Equatorial Current (Warm):
The north equatorial current originates off the western coast of Mexico and flows in westerly direction (fig. 29.2) and reaches the Philippines coast after covering a distance of 7500 nautical miles. This current is originated because of the Californian current and north-east monsoon. The volume of water continuously increases westward because numerous minor branches join this current from the north.
A few branches also come out of the main current and turn towards north and south. One branch emerges from the north equatorial current near Taiwan and flows northward to join Kuroshio current while the southern branch turns eastward to form counter equatorial current.
It is significant to note that north equatorial current flows as a continuous current in the north Pacific Ocean but there are seasonal variations in its northern and southern marginal areas. The velocity of the current ranges between 12 and 18 nautical miles per day. With the northward (northern summer) and southward (southern summer) migration of the sun this current moves northward and southward but it always remains to the north of equator.
2. South Equatorial Current (Warm):
The south equatorial current is originated due to the influence of south-east trade winds and flows from east to west. This current is stronger than the north equatorial current. The average velocity is 20 nautical miles per day while the maximum velocity becomes 100 nautical miles a day. Numerous minor currents join this current from the left and thus the volume of water continuously increases westward. The current is bifurcated into northern and southern branches near New Guinea. The northern branch turns eastward and flows as counter equatorial current while the southern branch moves towards the northern and north-eastern coasts of Australia.
3. Counter Equatorial Current (Warm):
The current flowing west to east between the north and south equatorial currents is termed counter equatorial current. Because of trade winds immense volume of water is piled up in the western marginal parts of the ocean, with the result there is general slope gradient of water surface from west to east.
This higher water level in the west and descending slope gradient of water surface from west to east make the oceanic water flow in easterly direction in the name of counter equatorial current which is the most developed counter current in the Pacific Ocean. This counter equatorial current is extended upto the Panama Bay. The average temperature and salinity are 27.50C and 34.50/00 respectively. The current transports oceanic water at the; rate of 25 million m3 per second.
4. Kuroshio System (Warm):
The Kuroshio system comprised of several currents and drifts is similar to the Gulf Stream system of the Atlantic Ocean. This system runs from Taiwan to the Bering Strait and consists of the Kuroshio Current, the Kuroshio extension, the north Pacific drift, the Tsushima current and the counter Kuroshio Current.
(i) Kuroshio Current:
The north equatorial current turns northward due to the obstruction of Philippines and thus gives birth to the Kuroshio Current which flows from Taiwan to Ryuku ridge at 30°N latitude. The Kuroshio, a warm current, is similar to the Florida current of the North Atlantic Ocean. The average temperature and salinity are 8°C and 35%o respectively. The depth of water involved in this current between Taiwan and South Ryuku is 700m while its average velocity is 89cm per second. The average discharge is 20 million m3 per second.
(ii) Kuroshio Extension:
The Kuroshio Current leaves Japanese coast and turns eastward near 35°N latitude under the influence of the westerlies and is bifurcated into two branches. One branch moves in easterly direction while the second branch flows in north-eastern direction upto 42°N latitude and thereafter it also turns eastward. The northern branch ultimately merges with the cold Oyashio current coming from the north.
(iii) North Pacific Drift:
The Kuroshio Current is extended further eastward under the influence of the westerlies and reaches the western coast of North America. Just before 150°W longitude the major part of this current turns southward while the remaining water moves eastward upto Hawaiin coast and the western coast of N. America.
The north Pacific drift is bifurcated into two branches. The northern branch becomes Aleutian current while the southern branch gives birth to the Californian cold current. The Aleutian current is further divided into two branches. One branch goes towards the Bering Strait while the second branch moves towards Gulf of Alaska.
Near 30°N latitude one branch separates from the Kuroshio Current and enters the Japan Sea and flows along the western coast of Japan in the name of Tsushima current. This warm current with relatively higher temperature and salinity modifies the weather condition of the Japanese coast.
(v) Counter Kuroshio Current:
The Kuroshio Current forms a gyral system between Hawaiian islands and the American coast and thus the oceanic water moves in westerly direction in the name of counter Kuroshio Current.
5. Oyashio Current (Cold):
The Oyashio cold current is also known as Kurile cold current. This cold current flows through the Bering Strait in southerly direction and thus transports cold water of the Arctic Sea into the Pacific Ocean. Near 50°N latitude this current is bifurcated into two branches. One branch turns eastward and merges with the Aleutian and Kuroshio currents.
The second branch moves up to the- Japanese coasts. This current is comparable to the cold Labrador Current of the North Atlantic Ocean. The convergence of cold Oyashio (Kurile) and warm Kuroshio Current causes dense fogs which become potential hazards for navigation.
6. California Current (Cold):
The California current, an example of cold current, is similar to the Canary cold current of the Atlantic Ocean in most of its characteristics. In fact, this current is the eastward extended portion of the North Pacific drift.
The cold California current is generated because of the movement of oceanic water along the Californian coast from north to south in order to compensate the loss of water which is caused due to large-scale transport of water off the coast of Mexico under the influence of trade winds in the form of the north equatorial current. This current after reaching the Mexican coast turns westward and merges with the north equatorial current.
7. Peru Current (Cold):
The cold current flowing along the western coast of South America from south to north is called Peru Current or Humboldt Current. This current is known as Peru coastal current near the coast while it is called Peru oceanic current off the coast. Mean annual temperature ranges between 14°C and 17°C and the average velocity of moving water is 15 nautical miles (27km) per day. The temperature of sea water increases from the coast towards the ocean.
8. El Nino or Counter Current (Warm):
A subsurface warm current, known as El Nino Current, flows from north to south between 3°S and 36°S latitudes at a distance of about 180 km from the Peruvian coast. The southward shifting of the counter equatorial warm current during southern winter gives birth to El Nino current.
The temperature at Peruvian coast does not fall considerably because of this current. Though the amount of rainfall increases along the coasts due to this current but fishes die due to disappearance of planktons and occurrence of guano disease and pests caused by El Nino. It may be pointed out that El Nino also affects monsoons in the Indian Ocean.
When El Nino is extended to the southern end of S. America warm water is pushed eastward to join the South Atlantic westerlies drift which brings warm water in the southern Indian Ocean during southern winters. Consequently, the high pressure in the Indian Ocean during southern winter is not intensified due to which the south-west summer monsoon is weakened.
Presently, El Nino is considered as a weather event or phenomenon. El Nino is considered as Christ child while La Nina as younger sister of El Nino. El Nino has been related to the increase of temperature of east Pacific Ocean off Peruvian coast while La Nina is related to the warming of the western Pacific Ocean. The strong El Nino brings heavy rainfall exceeding normal rainfall resulting into lush green otherwise dry coastal land of Peru.
The cold water mass near Peruvian coast becomes warm due to strong El Nino event resulting into heavy rainfall in the first half of the year (January to March). Earlier the people of Peru in the event of dry conditions while looking towards the sky prayed ‘Ye God, give us rain and keep drought away but when they came to know that copious heavy rainfall causing mass destruction of marine life (mainly death of fishes due to disappearance of planktons) was associated with strong El Nino event, they began to pray, ‘Ye God, give us rain and keep El Nino away.’
The heavy rainfall associated with strong El Nino even makes coastal Peruvial deserts green and there is rich harvest of cotton, coconuts and bananas but there is oceanic biological disaster. It may be maintained that in the event of strong El Nino the tropical eastern Pacific receives four to six times more rainfall than normal amount but dry condition prevails in the tropical western Pacific resulting into severe drought in Indonesia, Bangladesh, and India etc.
The widespread fire in the forest of Indonesia in 1997-98 was related to drought resulting from strong El Nino event. La Nina is a counter ocean current which becomes effective in the tropical western Pacific when El Nino becomes ineffective in the tropical eastern Pacific. The dry condition in the western Pacific is terminated and wet condition is introduced in the tropical western Pacific by La Nina.
9. East Australia Current (Warm):
South equatorial current is bifurcated near the Australian coast into northern and southern branches. The southern branch flows as east Australia current from north to south along the eastern coasts of Australia. New Zealand is surrounded by this current. It is deflected eastward near 40°S latitude due to deflective force of the earth and flows in easterly direction under the influence of the westerlies. This is a warm and more consistent current. It raises the temperature of east Australian coast for considerable distance southward.
10. West Wind Drift (Cold):
A strong ocean current, known as west wind drift, flows from west to east under the influence of the westerlies between Tasmania and South American coast in the zone of 40°-50°S latitudes. This current becomes much stronger because of immense volume of water mass and high velocity winds called as roaring forties and thus the current flows with great velocity. In the Far East the current is bifurcated into two branches. One branch enters the Atlantic Ocean through Cape Horn while the second branch turns northward and joins Peru Current.