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Ocean Currents and Tides

Prabhakar Pillai Mar 6, 2019
Oceans are nature's gift; they cover 71% of the earth's surface and contain 96.5% water. Currents and tides are the two major forces of the ocean. In layman terms, currents are those that move left to right, whereas tides are those that move up and down.

Did You Know?

In reality, there is only one ocean -- the Pacific, Atlantic, Indian, and Arctic oceans are all interlinked, forming a vast world ocean.
The ocean is defined as a large water body, limitless in quantity or volume, and comprising an important part of the hydrosphere.
Oceans are vast and majestic, covering nearly three-quarters of our planet, and contain many beautiful plants and animal species. Ocean currents and ocean tides are the two main forces of the sea.

Ocean Currents

The horizontal circulation of ocean waters are known as currents. The main causes of ocean currents include variation in water density, gravity, and wind friction.
Surface ocean currents are primarily caused by the wind. Ocean currents can flow for thousands of kilometers, and also play a significant role in preserving the climate of the various continents.
Currents act as a massive heat reservoir that stores heat during the summer and releases it in the winter. The winds that mainly affect the ocean currents are -
a)The Westerlies (40-50 degrees latitude) that blow from west to east.
b)The Trade Winds (20 degrees latitude) that blow from east to west.
These winds are both a consequence of warm air from the tropics moving to the poles, and also due to the Coriolis effect, where the water moves clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, because of the rotation of the Earth.
Since continents block these enormous circular currents, smaller ocean current circles termed gyres are created.
Differences in the water density level significantly affects the vertical ocean currents, i.e., the movement of surface ocean water to the bottom of the ocean, and the movement of deep ocean water to the surface gets affected.
Variations in water density are caused by a number of reasons like the prevailing temperature, wind, earth's rotation, the topography of the ocean bed, and the amount of salt in water. Saltier water is denser than less salty water; cold water is denser than warm water. Less dense water tends to rise while denser water tends to sink.
Cold water currents are created as the cold water at the poles sinks and slowly moves toward the equator. Warm water currents move from the equator along the surface, flowing toward the poles to replace the sinking cold water. As these currents mix the ocean's surface and deep waters, they help replenish the stock of oxygen in the water.
Other causes of currents include ocean-bottom topography tides, rain, and runoff. The seven major ocean currents are the Kuroshio Current, the Peru Current, the North and South Equatorial currents, East Wind Drift, the Gulf Stream, and the Antarctic Circumpolar Current.
The Gulf Stream is one of the strongest existing currents. The Stream moves along the Gulf of Mexico, passes through the east coast of the United States and on to Northern Europe. Without the warm Gulf Stream, England and other places in Europe would have been equally cold as Canada.
El Nino is a natural phenomenon in which an ocean current is reversed resulting in devastating climate changes from the west coast of South America all the way to Australia.

Ocean Tides

Tides are formed when the ocean surfaces rise and fall on account of:
a) the earth's rotation, and
b) the gravitational pull of the moon and sun.

Other factors that influence these tides are the weather, winds, sea floor topography, local water depth, and coastline configuration.
The moon has the maximum effect on the tides, as it is much closer to the earth than the sun. The sun's effect is about 46% of the moon.
• The oceans react to the moon's gravitational pull and ferociously rise up and down, producing high tides. A low tide is generated, when it goes in the opposite direction of the moon.
Maximum tides occur when the gravitational pull of the Sun, Earth and Moon are in a straight line. The high and low tides are not always in the same place at the same time -- they keep changing every 50-60 minutes.
Spring tides and neap tides are the two types of tide levels. Spring tides occur during the new moon and full moon, when the gravitational pull is stronger and the tides are very high. Neap tides occur during the first and third quarters of the moon, when the gravitational pull is weaker and the tides are very low.
The difference in height between the high tide and the low tide is defined as tidal range. Tides originate in the ocean and move toward the coastlines. Hence, tidal flows must be taken into account for accurate navigation of the ocean.
The incoming tide along the coast is termed as a flood current. The outgoing tide is termed an ebb current. The strongest flood and ebb currents generally take place before or near the time of the high and low tides. The weakest currents that take place between the flood and ebb currents are termed as slack tides.
Tidal energy is known to be a clean, renewable source of energy. Even though tidal mills have been used since the 11th century, today, only one sizable tidal power plant has been built.
The Rance Tidal Power Station in France is the 1st tidal power station in the world, that has a capacity of generating 2,40,000 kilowatts per day, whereas the Sihwa Tidal Power Station in South Korea is the world's largest tidal power plant, with a capacity of generating 2,54,000 kilowatts per day.
The world's highest tides can be found in Canada and Alaska. The Bay of Fundy in Nova Scotia, Canada is one of the most excellent places to watch this incredible natural phenomenon. The closest for the world's highest tides goes to Anchorage, in Alaska. It's a spectacular and sensational feeling to experience such dramatic increase in the water level.
Nowadays, currents and tides are studied and measured to keep a track of the change in water levels, to help in predicting a tsunami or any other cataclysm. It is also studied to decide a perfect fishing spot, and also measured when building bridges.