Unlike the calm waters of ponds and lakes, ocean water keeps moving continuously. It is never still. The movements that occur in oceans can be broadly categorized as waves, tides and currents.
When the water on the surface of the ocean rises and falls alternately, they are called waves.
The action of wind on the surface of the oceans causes water particles to move over circular or near-circular orbits in a vertical plane parallel to the direction of the wind. There is almost no forward motion. The visible movement of the waves is only the result of changing form and does not involve the movement of the water masses themselves.
The tide is the periodic rise and fall of the sea caused by the attraction of the moon and the Sun. When the sea rises to the highest level, this is known as high tide. When the sea falls to the lowest level, this is called low tide.
The Earth's 24-hour rotation, together with the moon's daily movement along its path around the Earth, mean that theoretically coastlines will experience two high tides and two low tides approximately every 24 hours, 50 minutes (the length of a lunar day).
The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides. The water of the earth closer to the moon gets pulled under the influence of the moon’s gravitational force and causes high tide.
During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides. But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides.
Tsunamis are a train of waves caused by undersea seismic activity such as earthquakes and volcanic eruptions. They are extremely dangerous, rising as high as 100 feet as they meet the land, engulfing and devastating entire coastal settlements and often causing great losses of life and property.
Storm Tide is the name given to the high seas that occur during storms and to the waves driven onshore by the exceptional winds accompanying hurricanes or typhoons. These high seas, like Tsunamis, may be enormously destructive.
Rip Tides or Rip Currents are strong, sea-ward moving currents found near the shore and are caused by the channeled return of water from large waves that have broken against the land. These can be dangerous to swimmers, for the backwash can pull them out to sea.
Ocean currents are the primary means by which both water and heat are transported horizontally and vertically in the ocean. The surface currents of the oceans are related to the wind and pressure systems of the atmosphere.
The ocean currents may be warm or cold. Generally, the warm ocean currents originate near the equator and move towards the poles. The cold currents carry water from polar or higher latitudes to tropical or lower latitudes. The Labrador Ocean current is cold current while the Gulf Stream is a warm current.