Southern O, sometimes sidered aension of the Pacific, Atlantid Indian Os, whicircles Antarctica.
Arctic O, sometimes sidered a a of the Atlantic, which covers much of the Arctid washes upon northern North Amerid Eurasia.
The Pacifid Atlantic may be further subdivided by the equator into northern and southern portions. Smaller regions of the os are called as, gulfs, bays, straits and other names.
Geologically, an o is an area of oic crust covered by water. Oic crust is the thin layer of solidified volic basalt that covers the Earth’s mantle. tial crust is thicker but less den. From this perspective, the earth has three os: the World O, the Caspian Sea, and Black Sea. The latter two were formed by the collision of Cimmeria with Laurasia. The Mediterranean Sea is at times a discrete o, becau teic plate movement has repeatedly broken its e to the World O through the Strait of Gibraltar. The Black Sea is ected to the Mediterrahrough the Bosporus, but the Bosporus is a natural al cut through tial roe 7,000 years ago, rather than a piece of oic a floor like the Strait of Gibraltar.
Despite their names, smaller landlocked bodies of saltwater that are not ected with the World O, such as the Aral Sea, are actually salt lakes.
海洋災害（marine hazards）主要指風暴潮（storm tide）災害、巨浪（billow）災害，海冰（a ice）災害、海霧(a fog)災害、大風災害及地震海嘯(earthquake and tsunami)災害等突發性的自然災害(natural calamities)。
引發海洋災害的原因主要有大氣的強烈擾動，如熱帶氣旋(tropical cye)、溫帶氣旋(extra tropical cye)等；海洋水體本身的擾動或狀態驟變；海底地震（submarihquake）、火山爆發（volic explosion）及其伴生之海底滑坡（submarine landslide）、地裂縫（ground fissure）等。海洋自然災害不僅威脅海上及海岸，有些還危及自岸向陸廣大縱深地區的城鄉經濟和人民生命財產的安全。世界上經濟發達的海洋國家以及有關國際組織，都很重視海洋災害的預警和防禦。海洋災害（現象）發生、發展、移行和消失的監視監測，是預警和防禦體係最重要和最基本的內容。全球範圍的海洋災害監視監測是通過海洋監測（marine monit）或觀測網實現的。