When ocean water moves in a fixed direction within a fixed limit (of area) with very high velocity, it is called current. The velocity of a current is more than that of drift. | Ocean currents can be divided into two type warm currents and cold currents. The currents flowing from the equator to the poles are warm and those flowing from poles to the equator are cold.
Due to Coriolis force, the Ocean currents in the Northern Hemisphere deflect towards their right and those in the Southern Hemisphere, towards their left. The only exception of this rule of the flow of ocean is found in the Indian Ocean, where the direction of current flow changes with the change in the direction monsoon wind flow.
Ocean currents influence the climate of bordering coastal regions. They affect temperature, humidity and precipitation.
Coral reefs are the regions of very high bio-diversity. These are formed due to accumulation and solidification of skeletons of lime secreting organism known as coral polyps. They are dominating rocks. Coral reefs are of three types :
- Fringing Reef: Coral reefs developed along
the coasts are called fringing reefs. Examples: Gulf of Mannar (india), Southern Florida (USA) etc.
- Barrier Reef : The coral reefs qf the coastal platforms are called "barrier reefs". There is extensive but shallow lagoon between the coastal land and the reef. Great Barrier Reef, located parallel to the east coast of Australia, is the largest of all the barrier reefs of the world.
- Coral Ring or Atoll : A ring of narrow growing corals of horse-shoe shape is called atoll. It is generally found around an island or in elliptical form on a submarine platform. Examples : Fiji Atoll, Funfutti Atoll etc.
Rise and fall of the ocean water level due to the gravitational forces of the Sun and the Moon are referred to as Tides. The waves generated by tide-are called Tidal Waves. The hight of the tides at different places varies a lot due to several factors such as - depth of water, the coastal features and openness or closeness of the sea. Though the Sun is far bigger than the moon yet, the gravitational force of the Moon is double than that of the sun. This is due to the fact that the Sun is at a greater distance than the Moon, from the Earth.
Every place, along the coast, experiences tide and ebbs twice in 24 hours. When the Sun, the Earth and the Moon are aligned in a straight line this position is referred to as SYZYGY. The combined forces of the Sun and the Moon result into High or Spring Tides. High tides are experienced on the full moon and the new moon.
Unlike this, when the Sun, the Earth and the Moon are aligned in a right angle position, the gravitational forces of the Sun and the Moon work against each other, when Neap or Low Tides are experienced. The part of the Earth facing the Moon , experiences a tide due to the gravitational pull of the Moon, but, at the same time the part of the Earth on the Opposite side also experidences a tide. This is due to the strong centrifugal force to balance the rotation of the earth.