Waves breaking on the shore
Coastal sea waves at Paracas National Reserve, Ica, Peru
Shipping at Singapore Harbour
Seas have always been essential for human development and trade, as at Singapore with its harbour (the world's busiest transshipment port) and the important shipping lanes through the Singapore Strait and the Strait of Malacca.

The sea, the world ocean or simply the ocean is the connected body of salty water that covers over 70 percent of the Earth's surface. It moderates the Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. It has been travelled and explored since ancient times, while the scientific study of the sea—oceanography—dates broadly from the voyages of Captain James Cook to explore the Pacific Ocean between 1768 and 1779. The word "sea" is also used to denote smaller, partly landlocked sections of the ocean.

The most abundant solid dissolved in sea water is sodium chloride. The water also contains salts of magnesium, calcium, and potassium, amongst many other elements, some in minute concentrations. Salinity varies widely, being lower near the surface and the mouths of large rivers and higher in the depths of the ocean; however the relative proportions of dissolved salts varies little across the oceans. Winds blowing over the surface of the sea produce waves, which break when they enter shallow water. Winds also create surface currents through friction, setting up slow but stable circulations of water throughout the oceans. The directions of the circulation are governed by factors including the shapes of the continents and the rotation of the earth (the Coriolis effect). Deep-sea currents, known as the global conveyor belt, carry cold water from near the poles to every ocean. Tides, the generally twice-daily rise and fall of sea levels, are caused by the rotation of the Earth and the gravitational effects of the orbiting Moon, and to a lesser extent of the Sun. Tides may have a very high range in bays or estuaries. Submarine earthquakes arising from tectonic plate movements under the oceans can lead to destructive tsunamis, as can volcanoes, huge landslides or the impact of large meteorites.

A wide variety of organisms, including bacteria, protists, algae, plants, fungi and animals, live in the sea, which offers a wide range of marine habitats and ecosystems, ranging vertically from the sunlit surface waters and the shoreline to the enormous depths and pressures of the cold, dark abyssal zone, and in latitude from the cold waters under the Arctic ice to the colourful diversity of coral reefs in tropical regions. Many of the major groups of organisms evolved in the sea and life may have started there.

The sea provides substantial supplies of food for humans, mainly fish, but also shellfish, mammals and seaweed, whether caught by fishermen or farmed underwater. Other human uses of the sea include trade, travel, mineral extraction, power generation, warfare, and leisure activities such as swimming, sailing and scuba diving. Many of these activities create marine pollution. The sea is important in human culture, with major appearances in literature at least since Homer's Odyssey, in marine art, in cinema, in theatre and in classical music. Symbolically, the sea appears as monsters such as Scylla in mythology and represents the unconscious mind in dream interpretation.


Cylindrical projection map of world's oceans
The interconnected system of the world's oceans

The sea is the interconnected system of all the Earth's oceanic waters, including the Atlantic, Pacific, Indian, Southern and Arctic Oceans.[1] However, the word "sea" can also be used for many specific, much smaller bodies of seawater, such as the North Sea or the Red Sea. There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as marginal seas) or wholly (as inland seas) bordered by land.[2] However, the Sargasso Sea has no coastline and lies within a circular current, the North Atlantic Gyre.[3](p90) Seas are generally larger than lakes and contain salt water, but the Sea of Galilee is a freshwater lake.[4][a] The United Nations Convention on the Law of the Sea states that all of the ocean is "sea".[8][9][b]

Other Languages
Адыгэбзэ: Хы
Afrikaans: See
Alemannisch: Meer
አማርኛ: ባህር
العربية: بحر
aragonés: Mar
ܐܪܡܝܐ: ܝܡܐ
armãneashti: Amari
asturianu: Mar
Avañe'ẽ: Para
авар: Ралъад
Aymar aru: Lamara
azərbaycanca: Dəniz
تۆرکجه: دنیز
বাংলা: সাগর
Bân-lâm-gú: Hái
Basa Banyumasan: Segara
башҡортса: Диңгеҙ
беларуская: Мора
беларуская (тарашкевіца)‎: Мора
भोजपुरी: समुंद्र
Bikol Central: Dagat
български: Море
Boarisch: Meea
bosanski: More
brezhoneg: Mor
буряад: Тэнгис
català: Mar
čeština: Moře
corsu: Mare
Cymraeg: Môr
dansk: Hav
Deutsch: Meer
dolnoserbski: Mórjo
डोटेली: सागर
eesti: Meri
Ελληνικά: Θάλασσα
emiliàn e rumagnòl: Mèr
español: Mar
Esperanto: Maro
estremeñu: Mari
euskara: Itsaso
فارسی: دریا
Fiji Hindi: Samundar
føroyskt: Sjógvur
français: Mer
Frysk: See
furlan: Mâr
Gaeilge: Farraige
Gaelg: Mooir
Gàidhlig: Muir
galego: Mar
ГӀалгӀай: Форд
한국어: 바다
Hausa: Teku
հայերեն: Ծով
hornjoserbsce: Morjo
hrvatski: More
Ido: Maro
Ilokano: Baybay
Bahasa Indonesia: Laut
interlingua: Mar
Ирон: Денджыз
isiXhosa: Ulwandle
isiZulu: Ulwandle
íslenska: Sjór
italiano: Mare
עברית: ים
Basa Jawa: Segara
Kabɩyɛ: Teŋgu
ಕನ್ನಡ: ಸಮುದ್ರ
къарачай-малкъар: Тенгиз
ქართული: ზღვა
қазақша: Теңіз
kernowek: Mor
Kiswahili: Bahari
коми: Саридз
Kongo: Kalunga
Kreyòl ayisyen: Lanmè
kurdî: Derya
Кыргызча: Деңиз
кырык мары: Тангыж
Ladino: Mar
лакку: Хьхьири
ລາວ: ທະເລ
Latina: Mare
latviešu: Jūra
Lëtzebuergesch: Mier
лезги: Гьуьл
lietuvių: Jūra
Limburgs: Zieë
lingála: Lombú
la .lojban.: xamsi
lumbaart: Mar
magyar: Tenger
मैथिली: समुन्द्र
македонски: Море
മലയാളം: കടൽ
मराठी: समुद्र
მარგალური: ზუღა
مصرى: بحر
مازِرونی: دریو
Bahasa Melayu: Laut
Baso Minangkabau: Lauik
Mìng-dĕ̤ng-ngṳ̄: Hāi
Mirandés: Mar
монгол: Тэнгис
မြန်မာဘာသာ: ပင်လယ်
Nāhuatl: Huēyātl
Nederlands: Zee
Nedersaksies: Zee
नेपाली: समुन्द्र
नेपाल भाषा: समुद्र
Napulitano: Mare
нохчийн: ХӀорд
norsk: Hav
norsk nynorsk: Hav
occitan: Mar
олык марий: Теҥыз
ଓଡ଼ିଆ: ସମୁଦ୍ର
oʻzbekcha/ўзбекча: Dengiz
ਪੰਜਾਬੀ: ਸਮੁੰਦਰ
پنجابی: سمندر
Papiamentu: Laman
ភាសាខ្មែរ: សមុទ្រ
Picard: Mers
Plattdüütsch: Solten See
polski: Morze
português: Mar
Qaraqalpaqsha: Ten'iz
Ripoarisch: Meer
română: Mare
Romani: Derya
Runa Simi: Hatun qucha
русиньскый: Море
русский: Море
саха тыла: Байҕал
ᱥᱟᱱᱛᱟᱲᱤ: ᱫᱚᱨᱭᱟ
Scots: Sea
Seeltersk: See
shqip: Deti
sicilianu: Mari
Simple English: Sea
سنڌي: سمنڊ
slovenčina: More
slovenščina: Morje
Soomaaliga: Bad
کوردی: دەریا
српски / srpski: Море
srpskohrvatski / српскохрватски: More
Basa Sunda: Sagara
suomi: Meri
svenska: Hav
Tagalog: Dagat
தமிழ்: கடல்
tarandíne: Mare
татарча/tatarça: Диңгез
తెలుగు: సముద్రం
ไทย: ทะเล
тоҷикӣ: Баҳр
ತುಳು: ಕಡಲ್‍
Türkçe: Deniz
Türkmençe: Deňiz
українська: Море
اردو: بحیرہ
Vahcuengh: Haij
vèneto: Mar
vepsän kel’: Meri
Tiếng Việt: Biển
Võro: Meri
walon: Mer
West-Vlams: Zêe
Winaray: Dagat
Wolof: Géej
ייִדיש: ים
Zeêuws: Zeê
žemaitėška: Jūra