• People often use the term sea in reference to the ocean. To geographers, a sea is a division of the ocean that is enclosed or partly enclosed by land. For this reason, all seas are saline, or salty. Some seas are called bays (like the Bay of Bengal, between India, Bangladesh, Myanmar, and Indonesia), while some lakes are called seas (like the Caspian Sea, shared by Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan). There are more than 50 seas on Earth.

    There are three major types of seas: nearly enclosed seas, partly enclosed seas, and hypersaline lakes.

    Nearly enclosed seas reach deeply into continents and are connected with the open ocean by narrow waterways called straits. Seas of this type include the Mediterranean Sea and the Baltic Sea. Because such seas are almost landlocked, they have a small range of tides. Some have no tides at all. Since there is little exchange of water between an enclosed sea and the open ocean, the two may differ from each other physically, chemically, and biologically.

    The Red Sea, for instance, is much saltier than the Indian Ocean, to which it is connected by a narrow strait called Bab-el-Mandeb. The organisms, including coral reefs, that live in the Red Sea have adapted to life in salty water. About 10 percent of fish found in the Red Sea do not exist in any other habitat, including the Indian Ocean.

    Partly enclosed seas are more like the open ocean, especially in the circulation of their waters.

    Some, such as the Weddell Sea of Antarctica, are linked to the ocean by a wide opening. The tides and organisms of the Weddell Sea are virtually the same as the tides and organisms of the Atlantic Ocean.

    Other seas, such as the South China Sea, are connected with the ocean by passages between islands. (The islands that dot the South China Sea are controlled by China, Malaysia, the Philippines, and Vietnam.) The organisms of the South China Sea are familiar across the South Pacific Ocean. The large range of tides of the open ocean are slightly reduced in the South China Sea.

    Some bodies of salt water that are called seas are really lakes. These bodies of water were part of prehistoric oceans or seas. Tectonic shifts blocked their access to larger bodies of water, and they are now completely surrounded by land. Some of these seas are called hypersaline lakes, due to the extremely high salt content in their waters.

    Among these landlocked seas is the Caspian Sea, between Europe and Asia. The Volga River drains into this body of water in the north. As a result, the northern part of the sea, in Russia and Kazakhstan, is almost a freshwater lake. The southern part of the sea, in Iran and Turkmenistan, is much more saline.

    Another landlocked sea is the Dead Sea, a hypersaline lake between Jordan, Israel, and the West Bank, an area of land controlled by the Palestinian Authority. The Jordan River flows into the Dead Sea, but no rivers flow out. The Jordan River has been managed for the benefit of agriculture and industry. Because of canals and dams for irrigation and power, less water reaches the Dead Sea. As a result, the Dead Sea is shrinking at a rate of about a meter (3.3 feet) a year. (Due to the complex way evaporation works, the Dead Sea will probably never dry up completely.)

    The Dead Sea is a popular tourist destination, known for its spas and historic sites. The governments of Israel, Jordan, and the Palestinian Authority are considering a project called the Two Seas Canal that would divert water from the Red Sea to the Dead Sea to increase economic activity in the area. This canal would replenish water to the Dead Sea and create a series of dams through the desert of Arabah.

    Critics of the Two Seas Canal worry about the environmental impact of such a project. The delicate coral reef ecosystem of the Gulf of Aqaba would probably be destroyed by power plants. The aquifer of Arabah would probably be disturbed, limiting the freshwater available to the desert. Finally, the unique, salty ecosystem of the Dead Sea would be altered by exotic species and a different quality of water.

    The Mediterranean Sea brackets three continents: Europe, Asia, and Africa.

    Admiral of the Ocean Sea
    That would be Christopher Columbus, who earned the title after sailing back from the New World in 1493.

    Sea of Tranquility
    Lunar mares, or seas, appear as dark splotches on the moon's surface. Using their eyes and simple telescopes, early astronomers thought they looked like oceans or seas. They're actually dark because of a type of mineral (basalt) left over from ancient volcanic eruptions. There are about 11 lunar mares. The Sea of Tranquility (officially known by its Latin name, Mare Tranquillitatis) was the landing site for Apollo 11, the first manned spacecraft to land on the moon.

  • Term Part of Speech Definition Encyclopedic Entry
    agriculture Noun

    the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

    Encyclopedic Entry: agriculture
    aquifer Noun

    an underground layer of rock or earth which holds groundwater.

    Encyclopedic Entry: aquifer
    bay Noun

    body of water partially surrounded by land, usually with a wide mouth to a larger body of water.

    Encyclopedic Entry: bay
    canal Noun

    artificial waterway.

    circulation Noun

    moving in a circular motion.

    complex Adjective


    continent Noun

    one of the seven main land masses on Earth.

    Encyclopedic Entry: continent
    coral reef Noun

    rocky ocean features made up of millions of coral skeletons.

    dam Noun

    structure built across a river or other waterway to control the flow of water.

    delicate Adjective

    fragile or easily damaged.

    desert Noun

    area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.

    Encyclopedic Entry: desert
    destination Noun

    place where a person or thing is going.

    destroy Verb

    to ruin or make useless.

    disturb Verb

    to bother or interfere with.

    divert Verb

    to direct away from a familiar path.

    economic Adjective

    having to do with money.

    ecosystem Noun

    community and interactions of living and nonliving things in an area.

    Encyclopedic Entry: ecosystem
    environmental impact Noun

    incident or activity's total effect on the surrounding environment.

    evaporation Noun

    process by which liquid water becomes water vapor.

    Encyclopedic Entry: evaporation
    exotic species Noun

    non-native species.

    freshwater Noun

    water that is not salty.

    geographer Noun

    person who studies places and the relationships between people and their environments.

    government Noun

    system or order of a nation, state, or other political unit.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    hypersaline lake Noun

    type of lake with a very high salt content.

    industry Noun

    activity that produces goods and services.

    irrigation Noun

    watering land, usually for agriculture, by artificial means.

    Encyclopedic Entry: irrigation
    island Noun

    body of land surrounded by water.

    Encyclopedic Entry: island
    lake Noun

    body of water surrounded by land.

    Encyclopedic Entry: lake
    landlocked Adjective

    having no access to an ocean or sea.

    ocean Noun

    large body of salt water that covers most of the Earth.

    Encyclopedic Entry: ocean
    open ocean Noun

    area of the ocean that does not border land.

    power plant Noun

    industrial facility for the generation of electric energy.

    prehistoric Adjective

    period of time that occurred before the invention of written records.

    reduce Verb

    to lower or lessen.

    replenish Verb

    to supply or refill.

    saline Adjective


    sea Noun

    large part of the ocean enclosed or partly enclosed by land.

    Encyclopedic Entry: sea
    spa Noun

    facility, usually with mineral hot springs, offering health benefits.

    strait Noun

    narrow passage of water that connects two larger bodies of water.

    Encyclopedic Entry: strait
    tectonic Adjective

    having to do with the structure of the Earth's crust.

    tide Noun

    rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

    Encyclopedic Entry: tide
    tourist Noun

    person who travels for pleasure.

    Two Seas Canal Noun

    proposed project that would bring water from the Red Sea to the Dead Sea.

    unique Adjective

    one of a kind.

    virtually Adverb

    almost or nearly.