The sea, linked as the arena ocean or honestly the ocean, is the frame of salty water that covers about seventy one percentage of the Earth's surface. The phrase sea is likewise used to indicate second-order sections of the sea, together with the Mediterranean Sea, in addition to sure large, completely landlocked, saltwater lakes, together with the Caspian Sea.

The sea moderates Earth's weather and has essential roles with inside the water cycle, carbon cycle, and nitrogen cycle. Humans harnessing and analyzing the ocean had been recorded considering the fact that historic times, and evidenced nicely into prehistory, at the same times as its cutting-edge clinical look at is known as oceanography. The maximum considerable stable dissolved in seawater is sodium chloride. The water additionally carries salts of magnesium, calcium, potassium, and mercury, among many different elements, a few in minute concentrations. Salinity varies widely, being decrease close to the floor and the mouths of huge rivers and better with inside the depths of the ocean; however, the relative proportions of dissolved salts range little throughout the oceans. Winds blowing over the floor of the ocean produce waves, which destroy once they input the shallow water. Winds additionally create floor currents thru friction, putting in place sluggish however solid circulations of water for the duration of the stream are ruled with the aid of using factors, which include the shapes of the continents and Earth's rotation. Deep-sea currents, referred to as the worldwide conveyor belt, convey bloodless water from close to the poles to each ocean. Tides, the usually twice-every day upward thrust and fall of sea levels, are due to Earth's rotation and the gravitational results of the Sun. Tides may also have a totally excessive variety in bays or estuaries. Submarine earthquakes bobbing up from tectonic plate actions tsunamis, as can volcanoes, large landslides, or the effect of huge meteorites. A huge type of organisms, which include bacteria, protists, algae, plants, fungi, and animals, stay within side the sea, which gives a huge variety of marine habitats and ecosystems, ranging vertically from the colorful range of coral reefs in tropical regions. Many of the important organizations of organisms advanced with inside the sea and lifestyles may also have began out there. 

The sea offers sizeable elements of meals for people, especially fish, however additionally shellfish, mammals and seaweed, whether or not stuck with the aid of using fishermen or farmed underwater.