Ocean is the world’s largest water reservoir, covering 70% of Earth’s surface and supporting a wide variety of marine life. It is a source of food, energy and minerals. It is also a natural climate regulator and provides essential habitat for many organisms.
Marine species range in size from microscopic plankton to enormous cetaceans. The biological processes that occur in the ocean are the subject of the scientific fields of marine biology and physical oceanography.
The oceans are primarily salty but they also contain freshwater. Salty water can be found at the surface as well as deep down, depending on the location and conditions. The temperature of the ocean varies widely from region to region as does the salinity (salt content).
Seawater is continually moving around the globe, driven by forces such as temperature variations, atmospheric circulation, the Coriolis effect and wind. This movement of seawater creates the ocean currents that influence global climate.
Oceans are divided into zones based on physical and biological characteristics. The photic zone, where light is abundant, is home to most of the living marine organisms that form the core of the ocean ecosystem. It is also where most of the photosynthesis that produces oxygen takes place.
Beyond this, the ocean depths are dark and cold. This region, called the mesopelagic and aphotic zones, is less biodiverse than the photic zone. It is nevertheless vitally important because it absorbs and stores a large proportion of the carbon dioxide emitted into the atmosphere by human activities.
The aphotic zone is also important for its ability to store and transport heat. It is a major route for the circulation of heat from the tropics to the poles.
Ocean acidification is the result of the accumulation of carbon dioxide in the atmosphere by human activity. Atmospheric carbon dioxide levels are currently higher than they have been in hundreds of millions of years. This process is known as ocean acidification because the increased concentration of carbon dioxide reduces the pH of the surface waters, making them more acidic.
In the long term, this may threaten marine life and damage coastal infrastructure and economies. The oceans are an integral part of the Earth’s ecosystem and are critical to sustaining human life.
The movement of the Earth’s continental and oceanic plates causes the formation of our planet’s oceans. As the plates collide, the older and denser oceanic plate tends to sink beneath the continental plate forming deep ocean trenches and volcanic island arcs. The plates can also slide past each other horizontally along the transform boundaries, where they sometimes cause earthquakes.