Key Points

Ocean water moves both horizontally and vertically. Horizontal motions include ocean currents and waves, while vertical motions include tides, upwelling, and sinking of water.

Waves are energy moving across the ocean surface, not the water itself. Water particles move in a small circular motion as the wave energy passes through them.

Wind provides the energy for waves. A wave breaks when it approaches the shore and the depth of the water is less than half of its wavelength, due to friction with the sea floor.

Key terms include crest (highest point), trough (lowest point), wave height (vertical distance between crest and trough), and wavelength (horizontal distance between two crests).

Tides are the periodical rise and fall of the sea level, which occurs once or twice a day. They are primarily caused by the gravitational attraction of the moon and the sun.

Tides are caused by the moon's and sun's gravitational pull combined with the Earth's centrifugal force. These forces together create two major tidal bulges on opposite sides of the Earth.

Spring tides occur when the sun, the moon, and the Earth are in a straight line (during full moon and new moon). This alignment results in higher high tides and lower low tides, creating a large tidal range.

Neap tides occur when the sun and moon are at right angles to each other relative to the Earth. Their gravitational forces counteract, resulting in a smaller tidal range with lower high tides.

When the moon is closest to Earth (perigee), tidal ranges are greater. When the moon is farthest from Earth (apogee), tidal ranges are less than average.

The time between high tide and low tide, when the water level is falling, is called the ebb. The time between low tide and high tide, when the water level is rising, is called the flow or flood.

Tides are crucial for navigation, helping ships enter harbors. They also help in desilting estuaries and are used to generate tidal energy.

Ocean currents are like rivers in the ocean, representing a regular flow of water in a definite path and direction. They are influenced by primary and secondary forces.

The primary forces that initiate currents are heating by solar energy, wind, gravity, and the Coriolis force, which deflects moving water.

Currents are classified by depth into surface currents (upper 400m, 10% of ocean water) and deep water currents (90% of ocean water), which move due to density differences.

Currents are classified as cold currents, which bring cold water to warm areas, and warm currents, which bring warm water to cold areas, significantly impacting coastal climates.

Warm currents create warm and rainy climates on the east coasts of continents in tropical latitudes. Cold currents create arid conditions with fog on the west coasts.

The mixing of warm and cold currents replenishes oxygen and nutrients, promoting the growth of plankton. This makes these zones the best fishing grounds in the world.