Ocean current has been defined as the persistent, dominantly horizontal flow of ocean water. It is the general movement of a mass of oceanic water in a definite direction which is more or less similar to water streams (rivers).
Ocean currents flow for great distances, and together, create the global conveyor belt which plays a dominant role in determining the climate of many of the Earth’s regions. Primarily, ocean currents influence the temperature of the regions through which they travel.
CAUSES OF OCEAN CURRENTS
1) Planetary Winds – The water beneath the wind forms surface water current. The pushing action of these winds makes the water flow in definite direction.
2) Rotation of Earth – The earth rotates from the west to the east. As a result of the Coriolis force, the permanent winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere; consequently the ocean currents are also deflected in similar manner. The Counter equatorial Currents are also result of the rotation of the earth.
3) Configuration of Coastline – The direction & shape of the coastline modify the ocean currents.
4) Ocean water temperature – The temperature of ocean water decreases from equator towards the poles. The density of water is low in the equatorial region due to high temperature. The lighter water of the equatorial region moves towards the colder and denser polar areas and vice versa.
5) Ocean water salinity – Ocean currents on the water surface are generated from the areas of low salinity to the areas of high salinity. For example, ocean currents flow from the Atlantic Ocean to the Mediterranean Sea and from the Arabian Sea to the Red sea. Water in the polar region is cold and heavy, so it sinks and flows towards the equator.
GENERAL CHARACTERISTICS OF OCEAN CURRENTS
1. The general movement of the currents in the northern hemisphere is clockwise and in the southern hemisphere, anti-clockwise except for those currents seen in the northern Indian Ocean. Here, the direction of the currents changes in response to the seasonal change in the direction of monsoon winds.
2. In the lower latitudes, the warm currents flow on the eastern shores and cold on the western shores. The situation is reversed in the higher latitudes—the warm currents move along the western shores and the cold currents along the eastern shores.
3. The warm currents move towards the cold seas and cool currents towards the warm seas.
4. The currents flow not only at the surface but also below the sea surface. Such currents are caused by the differences in salinity and temperature.
CURRENTS OF THE ATLANTIC OCEAN
CURRENTS OF THE PACIFIC OCEAN
CURRENTS IN THE INDIAN OCEAN
The oceanic current systems in the Indian Ocean are affected by the contour of the landmass and monsoon winds. The consistent system of ocean currents cannot be developed in Indian Ocean as it is surrounded by the Indian subcontinent, Africa and Australia on three sides. The characteristic feature of the currents in the northern Indian Ocean is that there occurs change in flow direction twice a year due to north-east and south-west monsoon winds.
|North-East Monsoon Current||Warm Current||Important for sea-trade, cultural interaction|
|South-West Monsoon Current||Warm Current|
• Tide is the regular rise and fall of water level in the world’s ocean, resulting from the gravitational attraction that is exerted upon the earth by the Moon and the Sun. The gravitational & centrifugal forces together play an important role in formation of tides.
• The tide-producing force of the Moon is slightly more than twice that of the Sun. The times and amplitude of tides at any given locale are influenced by the alignment of the Sun and Moon, by the pattern of tides in the deep ocean, by the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry.
• Most coastal areas, with some exceptions, experience two high tides and two low tides every lunar day. Unlike a solar day, a lunar day is 24 hours and 50 minutes. The lunar day is 50 minutes longer than a solar day because the moon revolves around the Earth in the same direction that the Earth rotates around its axis.
• Because the Earth rotates through two tidal “bulges” every lunar day, coastal areas experience two high and two low tides every 24 hours and 50 minutes. High tides occur 12 hours and 25 minutes apart. It takes six hours and 12.5 minutes for the water at the shore to go from high to low, or from low to high.
• There are 2 types of tides
1) Spring tide – Spring tides are produced when sun, moon and earth are in a straight line. They occur twice every month during full moon and new moon.
2) Neap Tides – Neap tides are produced when sun, moon and earth are in such a position so as to form a right angle. They too occur twice during a month.
• The difference in height between the high tide and the low tide is called the tidal range. A horizontal movement of water often accompanies the rising and falling of the tide. This is called the tidal current.
• According to the characteristics of the tidal pattern tides are classified as follows:
1) In the Diurnal Tide, only a single high and single low water occur each tidal day. Tides of the diurnal type occur along the northern shore of the Gulf of Mexico, in the Java Sea, the Gulf of Tonkin, and in a few other places.
2) In the Semidiurnal Tide, there are two high and two low waters each tidal day, with relatively small differences in the respective highs and lows. Tides on the Atlantic coast of the United States are of the semidiurnal type.
3) In the Mixed Tide, the diurnal and semidiurnal oscillations are both important factors and the tide is characterized by a large inequality in the high water heights, low water heights, or in both. There are usually two high and two low waters each day, but occasionally the tide may become diurnal. Such tides are prevalent along the Pacific coast of the United States and in many other parts of the world.
Importance of Tides
1. Tidal flows are of great importance in navigation. Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour.
2. Fish may concentrate during ebb tides. Commercial fishermen follow the tides and learn to fish during levels of highest concentration to improve their economic investment and to make more efficient use of their time.
3. Tides and tidal currents affect the weather by stirring the ocean waters. The tides and tidal currents mix arctic water that can’t absorb lots of sunlight with warmer topic water that does. The stirring produces more predictable and habitable climate conditions and balances temperatures on the planet.
4. Tidal energy is non-polluting, reliable and predictable. Tidal barrages, undersea tidal turbines – like wind turbines but driven by the sea – and a variety of machines harnessing undersea currents are under operation world over. Unlike wind and waves, tidal currents are entirely predictable.
The ocean is one of Earth’s most valuable natural resources. In its broadest sense marine resources are the things that plants, animals and humans need for life that originates in the ocean. Different organisms derive different resources from the marine biome.
A) Physical Resources: They are the result of the deposition, precipitation or accumulation of useful substances in the ocean or sea-bed e.g. minerals, petroleum, natural gas, sand & gravel etc.
B) Biological Resources: It consists of living animals (fish, crabs etc) and plants collected for human use.
C) Non-extractive services: (i) Marine tourism & recreation , (ii) Waste disposal, absorption & detoxification, (iii) Carbon capture & storage, (iv) nutrient cycling, Transportation of people and commodities by sea
Resources such as oil, natural gas, and solid mineral deposits are present in the ocean in fixed amounts and cannot be replenished during human life times.
• Petroleum and Natural Gas: The oceans make a significant contribution to the present world needs of petroleum and natural gas. Gulf of Persia, Gulf of Oman, North Sea, Seas of South East Asia have huge reserves of oil & natural gas.
• Sand and gravel: Although not very glamorous marine resources, they are second in dollar value only to oil and natural gas.
Supporting and regulating services
1) Marine tourism – Humans use the sea for leisure in many different ways, from scuba diving to whale watching, surfing to sailing, jet-skiing to fishing.
2) Waste disposal, absorption and detoxification – Since 2006, disposal of waste at sea has been regulated under the Global London Dumping Convention. Now, only certain types of wastes may be dumped at sea, including dredged material, sewage sludge, fish wastes, natural organic material, and carbon dioxide streams from carbon dioxide sequestration programmes. Marine organisms store, bury and transform many waste materials through assimilation and chemical transformation, either directly or indirectly.
3) CO2 capture and storage – Scientists are trying to mitigate climate change by capture and storage of carbon dioxide from the atmosphere.
4) Habitats – Marine habitats, such as coral reefs, support biodiversity, which we rely on for food (fish), medicines (from certain marine species we get painkillers and cancer drugs), tourism (e.g. fishing and scuba diving).
5) Nutrient cycling – Nutrient cycling is the storage, cycling and maintenance of nutrients by living organisms. Marine microbial nutrient cycling is essential for primary production in the sea (for phytoplankton and algae); without it the marine primary production ecosystem, which is the basis for most life on Earth, would collapse.
6) Water circulation and exchange – Water circulation is essential for life in the oceans, as it enables transport of nutrients and oxygenated water around the oceans. Water that comes up from the deep ocean through upwelling is nutrient and oxygen-rich, and these upwelling zones are associated with high productivity of fisheries.
7) Gas and climate regulation – Gas and climate regulation include in particular the maintenance of the chemical composition of the atmosphere and oceans. An important mechanism in this regard is the biological pump, a series of biologically-mediated processes that transport organic material from the ocean surface to deeper layers. The biological pump recycles nutrients and provides food for deep-sea species. It also plays an important role in the Earth’s carbon cycle, carrying carbon away from the atmosphere and upper ocean layers.
Marine organisms act as a reserve or sink for carbon in living tissue and by facilitating burial of carbon in seabed sediments. Through this natural carbon sequestration and storage process, it provides a climate regulation service.
Polymetallic nodules (also known as manganese nodules) are potato-shaped, largely porous nodules found in abundance carpeting the sea floor of world oceans in deep sea. Besides manganese and iron, they contain nickel, copper, cobalt, lead, molybdenum, cadmium, vanadium, titanium, of which nickel, cobalt and copper are considered to be of economic and strategic importance.
India signed a 15 year contract for exploration of Polymetallic Nodules (PMN) in Central Indian Ocean Basin with the International Seabed Authority (ISA) (an Institution set up under the Convention on Law of the Sea to which India is a Party)
It will enhance India’s presence in the Indian Ocean where other players like China, Korea and Germany are active. The program will be implemented by the Ministry of Earth Sciences with the participation from various national institutes and research laboratories/ organisations.
All the material that accumulates on the ocean floor is known as ‘Ocean Deposits’.