World Facts

What is the Difference Between an Ocean and a Sea?

Seas are part of the ocean, but are partially enclosed by land.

An ocean is a body of salty water that makes up most of a planet’s combined water mass. Oceans found on Earth are divisions of the global ocean. The oceans present on Earth include the Pacific, Atlantic, Indian, Southern, and the Arctic Ocean. A sea is considered a salty water body which is partially or fully surrounded by land.

What Is an Ocean?

Oceans cover around 71% of the Earth’s surface, and they are part of the carbon cycle having a huge impact on the climate and weather. The oceans of the Earth are also home to a vast variety of animal species. The global ocean has a volume of approximately 320 million cubic miles and an average depth of 12,100 feet. The oceans are divided into zones according to biological and physical properties. The pelagic zone is made up of the open ocean, and it is divided further into areas based on their depth and amount of light present in the region. The pelagic zone is also divided into the oceanic and neritic zones. The oceanic zone encompasses the ocean’s open waters while the neritic zone includes water above the continental shelves. Waters from the ocean surface up to 656.17 feet deep make up the photic zone, while the aphotic zone are regions of depths exceeding 656.17 feet. Oceans can also be divided into three depth zones which include a surface zone which falls between 500 feet to 3,300 feet, a middle pycnocline zone, and the deep zone which occurs in depths below 3,300 feet. Mariana trench, located in the Pacific Ocean, is the deepest part of the ocean with a depth of about 35,994 feet.

What Is a Sea?

There are several seas present in the world, and they influence the Earth’s climate, carbon cycle, water cycle, and the nitrogen cycle. The salty water in the seas usually varies in the amount of salinity in different places. The difference in salinity of the water and temperature causes deep-sea currents while surface currents are as a result of the changes in the sea level and the friction of waves caused by winds. The sea levels have been decreasing over the years, and this has left behind continental shelves which are rich in nutrients and have plenty of marine life. The sea waters have been explored and navigated by man for purposes of trade, travel, mining, and electricity generation. Deep sea divers have also been able to explore most of the sea floors.

Differences Between a Sea and an Ocean

There is no significant difference between a sea and an ocean as the sea is considered the connected system of Earth’s oceans. Seas are smaller than oceans, and they tend to be located near land areas. The waters of the seas are shallower than those of the oceans; this, in turn, tends to have an effect on the number of plant life and animal life in the sea and ocean beds. The seabed makes a good habitat for plants and animals that are primarily dependent on the light while the ocean floors harbor those that thrive in dark areas.

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