Waves:

Wind pushes the water body. Then gravity pushes the crest downwards and falling water pulls the troughs upwards. The actual motion of water below the surface is circular.

Ocean Currents:

They are shallow and narrow streams of water circulating along the ocean margins. They circumnavigate the world.

The currents are created due to

1. Winds – Most currents follow the winds.
2. Coriolis force– the earth’s rotation deflects the ocean currents to the east north and south.
3. Insolation – water at the equator is heated and rises. The water at the poles cools and sinks, this water flows towards the equator at the subsurface level to maintain the loss.
4. Also, insolation increases salinity and the high saline water sinks and less saline water rises to the surface. The equator water is less saline [heavy rainfall] and moves to polar high saline water [icebergs].
5. Gravity and coastlines.
   

The best fishing grounds in the world are places where hot and cold currents meet like Japan and the east coast of America but are foggy areas making it tough for fishing.

The cold currents are also responsible for desiccating effect on the deserts.

The winter current in the Arabian Sea caused the movement of water towards Arabia and in summer caused movement of water towards India, Thus facilitating trade.

Upwelling:

• When the wind blows in the north direction it creates a flow of water in the western direction. This west-flowing water then leads to the divergence at the coast and draws water from below the surface to the top. This is “Upwelling”.
• The cool and nutrient-rich water from below comes to the surface. This causes the reproduction of phytoplankton and zooplankton.
• When the wind moves southward it causes the flow of water towards the coast and this creates downwelling.

Tides:

1. The gravitational pull of the sun and the moon causes tides.
2. The tides depend on the depth of the ocean, the configuration of the coastline, and the openness and closeness of the sea.
3. The perigee tides [moon is closer] are higher than apogee tides.
4. When the sun, moon, and earth are in a line either during the full moon or new moon we get spring tide which is the highest high tide and the neap tide is when the sun, moon, and earth are at right angles and this is the lowest high tide.
5. In spring tide low tide is lower than usual and in the neap tide, the low tide is higher than usual.
6. Tides help large ships enter and leave ports. E.g. Kandla and diamond harbor are tidal ports.

Vishakapatnam is the deepest landlocked port, Chennai is the oldest artificial port, and Kolkata is the oldest port.

Estuary: mouth of a river is submerged or low lying under sea water. The river deposit creates a long narrow delta-like Narmada and Tapti.

The temperature of ocean water

The process of insolation is responsible for ocean temperature. The average temperature of the ocean is 3-5°. But the average temperature of the surface of the ocean is 25°.

It is highest in the tropics, not the equator as the equator has high cloud cover and rainfall. It decreases towards the poles. For the same reason, the diurnal temperature range of the tropics is higher than the equator.

Due to the large landmass in the northern hemisphere, the temperature of the water is higher than in the south.

The enclosed seas of the tropics are warmer than open oceans. The enclosed seas of temperate are cooler than the Open Ocean.

Upwelling brings cold water on top but downwelling piles warm water on top.

Bigger the size of the ocean better the mixing of water and so less annual range of temperature.

Temperature decreases with depth. The decrease rate is higher at the equator than at the poles.

Salinity of oceans

Sodium chloride is the highest percentage present in the ocean. Both sodium and chlorine have high residual time and hence remain in the highest proportion.

The proportion of salt remains the same in all parts of the ocean.

Salinity decreases from the equator to the poles but the highest salinity is in tropics as equator gets high rainfall and low evaporation due to cloud cover.

Variations in salinity:

1. Salinity increases with a high evaporation rate, windy conditions, no freshwater source, and downwelling.
2. Salinity decreases due to high rainfall, low evaporation rate, upwelling, and melting of glaciers.