The oceans cover greater than 70% of the earth’s surface and give Earth its blue appearance when seen from outer space. Oceans play an important role in our everyday life. Without the oceans, life on earth will be very different.

What is the Difference between the Sea and the Ocean?
The Oceans on Earth are all connected to one another. There are five oceans. They are: the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean. Seas are smaller branches of an ocean. Seas are often partly enclosed by land. All the seas and oceans on Earth join to form the World Ocean. The Black Sea is an inland sea which is almost completely cut off from other seas and oceans. Apart from this difference, oceans and seas are just the same thing.

The above globe map shows the location of the Pacific, Atlantic, Indian, Southern and Arctic Oceans.

Why is the Sea so Salty?

If you have been to the beach, you know that seawater is salty. Well, why is the seawater salty? The explanation is simple – because it contains salt. If someone removes all the salt in the sea and spreads it on the Earth’s surface, he would be able

to build a huge layer of salt which is more that 500 feet thick, that is similar to the height of a 40-storey apartment building! At this point, you might be wondering where the salt in the oceans came from. Ocean salt comes from very old rocks from the Earth’s crust (known as igneous rocks) that have been broken down to small bits through various processes such as erosion and the dissolving action of rain and streams. These processes which release salt into the oceans and seas have been taking place for millions of years.

Why is the sea salty even if fresh water flows out to the sea?
You must be pondering why the seas remain salty even though fresh water from river and streams run into them everyday. The saltiness of the sea is caused by a few natural processes and the volume of freshwater from streams and rivers alone will not be able to reduce the saltiness of seas. The correct term to describe the saltiness of seas is ‘salinity’. Salinity is the total salt content in sea water; it’s described in parts per thousand (ppt) and the symbol is o/oo. Salinity of 35ppt means translates into 35 pounds of salt per 1000 pounds of seawater. The salinity for sea water is about 35ppt and for freshwater is 0ppt.

Why is the Sea Blue?

When we collect sea water in a cup, it looks clear. But when we look at the sea, it looks blue. To understand why this happens, you first need to know that sunlight comprises the colours of rainbow, which are: red, orange, yellow, green, blue and violet. When a portion of the sunlight shines

on seawater, it is reflected off the surface of water and reflects the colour of the sky. When some of the sunlight penetrates the seawater, the currents and particles in water scatter the sunlight. In areas where the water is deep, the oxygen in water scatters more of the blue light from the overall sunlight. This is why the seas and oceans look blue.

Sometimes, you might notice that the sea look green. The abundance of plant life or sediment from rivers that flow into the ocean and sea may cause the sea to look green. Apart from that, the blue light from sunlight mixes with the yellow pigments from plants to produce the colour green.

Parts of the ocean may look milky brown. This usually happens after a storm. Winds and currents from the storm cause the sand and sediment from the rivers and along the coastline to stir up, thus resulting in a milky brown colour effect.

There are also some very oddly coloured seas. The Red Sea looks red because it has a lot of red algae in that sea. There’s also a sea called The Black Sea and it looks almost black. This is because the sea contains a high concentration of hydrogen sulphide, which is black in colour. But don’t worry; you will not turn pink or grey if you happen to go swimming in these seas.

Why is the Sea Important to Us?
The sea is important to us in many aspects. People depend on the sea for food, transportation, recreation, inspiration, medicinal sources, and to sustain modern living necessities.

Biodiversity

The oceans and seas comprise different ecosystem environments such as: corals reefs, salt marshes, estuaries, mangroves, and seagrass beds. These environments support a

large number of different species. Biodiversity relates to variance and abundance of species in any community - in this case an aquatic community. Estuaries and mangroves act as nurseries for baby fish, better known as juveniles. Coral reefs act as shelters where fish can find food and protect themselves from predators. Mangroves and coral reefs provide protection against shoreline erosion and inundation from the ocean. The sand on beach is not only useful to make sand castles, but is also the home to many tiny beach creatures such as fiddler crabs and burrowing worms. Without these environments, oceans will lose many important organisms which would result in a loss of biodiversity (abundance of species). Although these environments support and sustain their own inhabitants and serve a specific purpose, each of them are inextricably

Tsunami!!!!! No one can forget the tsunami which happened in 2004 that took thousands of lives. But do you know that mangroves can actually help to reduce the impact of tsunami? That’s right, studies done by scientists say that 30 trees per 100 square meters may reduce the maximum flow of a tsunami by more than 90%!

linked to each other and form the physical sea or ocean that we can see. For example, when the baby fish that has sought shelter in the mangrove grows to be an adult fish, it will leave its nursery ground for the ‘bluer’ sea mainly to eat other fish or creatures!

Transportation

Oceans are not only important to sustain life on Earth, but also for moving objects from one place to another. Commercial ships and barges often carry large, heavy goods from place to place and country to country. Of course, nowadays we can transport goods by air, but air freight paid to transport goods by aeroplane can be very expensive. Some goods are also too big to be put on an aeroplane.

Natural Resources

The ocean floor and continental shelves (gently-sloping seabed closest to a coast) contain many important minerals including oil and natural gas. These minerals are very important in fulfilling the energy needs of the modern living style of humans today. One of the most important energy sources of today is the fossil fuel. Oil and natural gas are fossil fuels from the ocean. Oil can be turned into gasoline,

diesel fuel, jet fuel and petrol to run vehicles and other machinery. It’s also used in producing topical medicines such as petroleum jelly that you sometimes apply on dry skins. Natural gas is used for household cooking, heating homes and buildings during cold weather, and often for factories and businesses to make electricity.


Food

The oceans have been an important source of food for humans for a long time. As much as 10% of human protein intake (in the form of seafood) is said to come from the oceans. Without the oceans, we would not have seafood. If you’re a seafood lover,

can you imagine life without those delicious fish, prawns, mussels, squids, cockles, etc that mommy cooks for you?


Economy

The sea is very important to many countries. Many people have jobs that require them to live by the sea or even at sea for a period of time. Sea-based or marine-based jobs include those related to fishing, aquaculture, ports, tourism, maritime defence, marine research, mining and shipping.

Other important things about the sea

Lots more important things can be said about the sea. For example, scientists are trying to utilise more elements from the sea to invent medicines that fight certain diseases. Other biological products from the sea such as, shells and pearls are widely used for jewellery. People also like to have fun at sea: having picnics or playing volleyball on the beach, surfing, yachting, going fishing and

enjoying holiday cruises across the oceans are some of the activities people have been enjoying for many decades. With these uses in mind, we should all strive to respect, conserve and protect the oceans from pollution, which can potentially destroy all the benefits that we enjoying from this environment.


References
http://www.enchantedlearning.com/subjects/ocean/Blue.shtml http://www.palomar.edu/oceanography/salty_ocean.htm http://www.kidzworld.com/article/1423-fossil-fuel-energy