# Forces that influence ocean currents
Ocean currents are like rivers of water flowing in the ocean. They are influenced by a combination of primary and secondary forces.
## Primary forces
Primary forces are the ones that initiate the movement of water. They include:
Heating by solar energy:
The sun heats up the water near the equator more than the water near the poles. This creates a difference in water density and pressure, which causes water to flow from high to low pressure areas. The flow is usually from east to west along the equator.
Wind:
The wind blows over the surface of the ocean and pushes the water along with it. The wind also creates waves and upwelling, which are vertical movements of water. Upwelling brings cold, nutrient-rich water from the deep ocean to the surface, which supports marine life.
Gravity: Gravity pulls the water towards the center of the earth, creating a bulge of water around the equator. This bulge also creates a slight slope of water from the equator to the poles, which drives water flow.
Coriolis force:
The Coriolis force is an apparent force caused by the rotation of the earth. It deflects moving objects to the right in the northern hemisphere and to the left in the southern hemisphere. This affects the direction of ocean currents, making them curve into circular patterns called gyres.
## Secondary forces
Secondary forces are the ones that modify or influence the existing currents. They include:
Temperature difference: Temperature affects the density of water, with warm water being less dense than cold water. Warm water tends to rise to the surface and flow away from the equator, while cold water tends to sink and flow towards the equator. This creates a circulation of water called thermohaline circulation, which affects deep ocean currents.
Salinity difference: Salinity is the amount of salt dissolved in water. Salinity also affects the density of water, with salty water being denser than fresh water. Salty water tends to sink and flow along the bottom of the ocean, while fresh water tends to rise and flow along the surface. This creates a circulation of water called haline circulation, which also affects deep ocean currents.
# Role of ocean currents in fishing industry
Ocean currents play a crucial role in the fishing industry, as they affect the distribution of nutrients and marine life across the ocean. Some of the ways that ocean currents impact fishing are:
Mixing of warm and cold currents:
When warm and cold currents meet, they create zones of high productivity and biodiversity. This is because they bring together different types of plankton, which are microscopic organisms that form the base of the food chain for fish and other animals. Mixing of warm and cold currents also helps to replenish oxygen and carbon dioxide levels in the water, which are essential for life.
Upwelling zones:
Upwelling zones are areas where cold, nutrient-rich water rises from the deep ocean to the surface. These zones are usually found along the western coasts of continents, where wind-driven currents push surface water away from the shore. Upwelling zones support large populations of fish and other marine life, as they provide abundant food and oxygen.
Migration routes:
Ocean currents can also act as migration routes for fish and other marine animals. Many fish species follow seasonal changes in ocean currents to find food, mates, or spawning grounds. For example, tuna fish migrate across the Pacific Ocean following warm currents, while salmon fish migrate up rivers following cold currents.
Temperature and salinity preferences:
Ocean currents can also affect fishing by creating different temperature and salinity conditions in different regions. Some fish species prefer warmer or colder waters, while others prefer saltier or fresher waters. For example, cod fish prefer cold and salty waters, while herring fish prefer warm and fresh waters.
# Summary
Ocean currents are influenced by primary forces such as solar heating, wind, gravity, and Coriolis force, and secondary forces such as temperature and salinity differences. Ocean currents affect fishing by creating zones of high productivity and biodiversity, upwelling zones, migration routes, and temperature and salinity preferences for different fish species.