[Model Answer QP2022 GS1] What are the forces that influence ocean currents? Describe their role in the fishing industry of the world.

Ocean currents are continuous movements of water in the ocean that follow set paths, kind of like rivers in the ocean.
An ocean current flows for great distances and together they create the global conveyor belt, which plays a dominant role in determining the climate of many of Earth’s regions.
Ocean Currents play an important role in maintaining latitudinal heat balance and helps stabilize heat on earth. 

The primary forces that influence the currents are:

1. Planetary Winds: Winds blowing on the surface of the ocean push the water. Friction is the coupling between the wind and the water’s surface. Example: Trade winds push the Equatorial currents westwards. 
2. Coriolis force: Coriolis force acts to the right in the northern hemisphere and to the left in the southern hemisphere. Hence the circulation of ocean current (GYRE) in the northern hemisphere and southern hemisphere is clockwise and anti clockwise respectively. 
3. Solar Heating: Solar heating causes water to expand. Near the equator the water is about 8 centimeters higher than in middle latitudes. This causes a very slight slope and water wants to flow down the slope.
4. Temperature Difference: Cold water near the poles sink and thus pull the warm water from the equator towards the poles. 
5. Salinity Difference: Salinity influences density of water. Highly saline water is of higher density and tends to sink. Thus near the poles the high saline and hence high density water sinks and this pulls the water from the equator. (Note: Salinity is high at the poles because on freezing of ocean water, only water turn into ice leaving behind salts, thus increasing salinity).

Ocean currents and their role in fishing Industry: 

1. Mixing cold and warm ocean currents forms  the richest fishing grounds in the world. Because the mixing of warm and cold currents help to replenish the oxygen and favor the growth of planktons, the primary food for fish population. The best fishing grounds of the world exist mainly in these mixing zones.
Example: Grand Banks around Newfoundland, Canada and North-Eastern Coast of Japan.
2. Also the zones of cold upwellings bring enormous nutrients and hence attracts fishes along the western coast of the continents. Example: Anchovies along the coast of Peru or the Sardines off the coast of Benguela, Angola.

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