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9.1: Importance of the Oceans

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    What does this whale know about the oceans?

    People divide up the seas into five oceans, but they are really all interconnected. Even so, they are all very different. This ocean is near a shore and is obviously in a cold region. It appears to be a good habitat for whales! No matter what, the oceans have a huge influence on the planet, locally and as a whole.

    The Ocean Influence

    Oceans cover more than 70% of Earth's surface. Oceans hold 97% of the planet's surface water. It’s no surprise that the oceans have a big influence on the planet. The oceans affect the atmosphere, climate, and living things.

    Oceans and the Atmosphere

    Oceans are the major source of water vapor in the atmosphere. Sunlight heats water near the sea surface (Figure below). As the water warms, some of it evaporates. The water vapor rises into the air, where it may form clouds and precipitation. Precipitation provides the freshwater needed by plants and other living things.

    Gas exchange between the oceans and the atmosphere

    The oceans and atmosphere exchange gases. Why does water vapor enter the atmosphere from the water?

    Ocean water also absorbs gases from the atmosphere. The most important are oxygen and carbon dioxide. Oxygen is needed by living things in the oceans. Much of the carbon dioxide sinks to the bottom of the seas. Carbon dioxide is a major cause of global warming. By absorbing carbon dioxide, the oceans help control global warming, at least as long as the carbon dioxide stays in the seas.

    Oceans and Climate

    Coastal areas have a milder climate than inland areas. They are warmer in the winter and cooler in the summer. That’s because land near an ocean is influenced by the temperature of the oceans. The temperature of ocean water is moderate and stable. Why? There are two major reasons:

    1. Water warms up and cools down much more slowly than land. As a result, oceans never get as hot or as cold as land.
    2. Water flows through all the world’s oceans. Warm water from the Equator mixes with cold water from the poles. The mixing of warm and cold water makes the water temperature moderate.

    Even inland temperatures are milder because of oceans. Without oceans, there would be much bigger temperature swings all over Earth. Temperatures might plunge hundreds of degrees below freezing in the winter. In the summer, lakes and seas might boil! Life as we know it could not exist on Earth without the oceans.

    Oceans and Living Things

    The oceans provide a home to many living things. In fact, a greater number of organisms lives in the oceans than on land. Coral reefs (Figure below) have more diversity of life forms than almost anywhere else on Earth. Biological diversity is shortened to biodiversity. Oceans contain the majority of biomass on Earth.

    Coral reefs in the ocean teem with life

    Coral reefs teem with life.

    Further Reading

    Ocean Zones

    Surface Currents

    Ocean Currents and Climate

    Deep Currents


    • Oceans are an important part of the water cycle. They absorb gases from the atmosphere. They evaporate and supply water vapor to the atmosphere.
    • Oceans moderate Earth's temperature by not changing temperature rapidly. Oceans also distribute heat around the planet.
    • Oceans have tremendous biodiversity. They also contain the majority of all biomass on Earth.


    1. How do the oceans moderate Earth's temperature?
    2. What role do oceans play in the water cycle?
    3. Why do oceans have so much biomass?

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