Sea
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. Although the sea has been travelled and explored since ancient times, the scientific study of the sea—oceanography—dates broadly from the voyages of Captain James Cook who explored the Pacific Ocean between 1768 and 1779. In geography, "sea" is used in the names of smaller, partly landlocked sections of the ocean, for example the Irish Sea, while "ocean" is used in the names of the five largest sections, such as the Pacific Ocean.
The most abundant ions in sea water are chloride and sodium. The water also contains magnesium, sulfate, calcium, potassium, and many other components, 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 vary little across the oceans. Carbon dioxide from the air is currently being absorbed by the sea in increasing amounts, lowering seawater pH in a process known as ocean acidification, which is likely to damage marine ecosystems in the near future.
Text source: Wikipedia
Image source: Jon Sullivan
