What Is the Ocean?

Ocean is the vast body of salt water that covers 70% of Earth’s surface and contains most of our planet’s water. It forms the primary component of the Earth’s hydrosphere and influences global climate and weather patterns. It also houses a variety of marine ecosystems, absorbs carbon dioxide and other greenhouse gases, and provides a means for humans to travel and trade.

Oceans are the largest and deepest of Earth’s aquatic systems. They differ from freshwater ecosystems in that they are surrounded by salt and have a higher concentration of dissolved minerals than most terrestrial waters. Marine ecosystems are incredibly complex and support more than 230,000 species of plants and animals.

The ocean’s surface can be disturbed by wind, currents and waves that produce mechanical undulations, known as swell. The surface of the ocean is also covered with biological communities of microscopic organisms such as plankton and algae. These communities are referred to as the photic zone and provide most of the food for ocean creatures.

Ocean surface water is warm in the tropics and cool in the polar regions. These characteristics result in a distinct thermocline, a vertical layer of water that stratifies by temperature with depth. The layer of colder water is typically at or near the surface in the polar regions, and at a lower depth in the tropics. The presence of the thermocline and pycnocline creates an essential boundary for oxygen exchange, and regulates the circulation of surface and deep ocean water.

Distinct boundaries can also be drawn based on the properties of the water, such as haloclines (salinity), chemoclines (chemistry) and pycnoclines (density). Generally, cooler water is denser than warmer water. Temperature and salinity control the density of ocean water, which in turn determines global water circulation.

There are five ocean zones in total. The first is the pelagic zone which encompasses the open ocean’s water column from the surface down to 1% of the light penetration depth. This is the layer of the ocean where most ocean creatures live, as it allows them to receive sunlight for photosynthesis.

The next is the bathypelagic zone which covers the continental slope down to 4,000 meters (13,000 ft). The bathypelagic zone is followed by the abyssal plains and the hadal zone located in the oceanic trenches. The Mariana Trench is the deepest part of the ocean and reaches a staggering depth of 11,000 meters (36,000 ft). This is so far down that many ocean organisms are unable to see, but incredible creatures still manage to survive in this dark, cold and dangerous environment! The oceans are also important carbon sinks and provide a large percentage of the world’s protein supply. In addition, they help control the Earth’s temperature.

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