![]() The concept of Ōkeanós has an Indo-European connection. Oceanus was believed by the ancient Greeks and Romans to be the divine personification of an enormous river encircling the world. The word ocean comes from the figure in classical antiquity, Oceanus ( / oʊ ˈ s iː ə n ə s/ Greek: Ὠκεανός Ōkeanós, pronounced ), the elder of the Titans in classical Greek mythology. The concept of a continuous body of water with relatively unrestricted exchange between its components is critical in oceanography. The global, interconnected body of salt water is sometimes referred to as the World Ocean, global ocean or the great ocean. The contemporary concept of the World Ocean was coined in the early 20th century by the Russian oceanographer Yuly Shokalsky to refer to the continuous ocean that covers and encircles most of the Earth. The continental shelf and coastal waters that are most affected by human activity are particularly vulnerable. However, the ocean faces numerous human-caused environmental threats, such as marine pollution, overfishing, and effects of climate change on oceans such as ocean warming, ocean acidification and sea level rise. It is known to be the habitat of over 230,000 species, but may hold considerably more – perhaps over two million species. It also provides a means of trade and transport as well as access to food and other resources. The ocean provides crucial environmental services to humankind, such as climate regulation. Carbon dioxide concentration in the atmosphere rises due to fossil fuel combustion, which causes higher levels in ocean water, resulting in ocean acidification. This gas exchange occurs at the ocean's surface and solubility depends on the temperature and salinity of the water. Ocean water contains a high concentration of dissolved gases, including oxygen, carbon dioxide and nitrogen. By transporting these pollutants from the surface into the deep ocean, this circulation impacts global climate and the uptake and redistribution of pollutants such as carbon dioxide. Currents transport massive amounts of water and heat around the world. The Gulf Stream, Kuroshio Current, Agulhas Current and Antarctic Circumpolar Current are all major ocean currents. Tides create tidal currents, while wind and waves cause surface currents. ![]() These directed movements of seawater are caused by forces operating on the water, such as temperature variations, atmospheric circulation (wind), the Coriolis effect and salinity changes. Constant circulation of water in the ocean creates ocean currents. In all parts of the ocean, deep ocean temperatures range between −2 ☌ (28 ☏) and 5 ☌ (41 ☏). Near the poles where sea ice forms, the temperature in equilibrium is about −2 ☌ (28 ☏). In the tropics, surface temperatures can rise to over 30 ☌ (86 ☏). Ocean temperatures depend on the amount of solar radiation reaching the ocean surface. Human activity often has negative impacts on the ecosystems within the continental shelf. It is more shallow, with a depth of a few hundred meters or less. The continental shelf is where the ocean meets dry land. Light can only penetrate a few hundred more meters the rest of the deeper ocean is cold and dark (these zones are called mesopelagic and aphotic zones). Ocean photosynthesis also produces half of the oxygen in the Earth's atmosphere. As a result, the photic zone is the most biodiverse and the source of the food supply which sustains most of the ocean ecosystem. In this process plants and microscopic algae (free floating phytoplankton) use light, water, carbon dioxide, and nutrients to produce organic matter. This is the zone where photosynthesis can occur. The photic zone starts at the surface and is defined to be "the depth at which light intensity is only 1% of the surface value" : 36 (approximately 200 m in the open ocean). The water column is further divided into zones based on depth and the amount of light present. The pelagic zone is the open ocean's water column from the surface to the ocean floor. Oceanographers split the ocean into vertical and horizontal zones based on physical and biological conditions. ![]() The ocean influences climate and weather patterns, the carbon cycle, and the water cycle by acting as a huge heat reservoir. The ocean contains 97% of Earth's water and is the primary component of the Earth's hydrosphere, thus the ocean essential to life on Earth. Distinct names are used to identify five different areas of the ocean: Pacific, Atlantic, Indian, Antarctic/Southern, and Arctic. In English, the term ocean also refers to any of the large bodies of water into which the world ocean is conventionally divided. The world ocean ( sea) is the body of salt water that covers ~70.8% of the Earth. ![]() 1 Shore length is not a well-defined measure.
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