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96-403: The relatively narrow trough trends east-northeast to west-southwest and has a maximum depth of 7,686 metres (25,217 ft). Within the trough is a slowly spreading north–south ridge which may be the result of an offset or gap of approximately 420 kilometres (260 mi) along the main fault trace. The Cayman spreading ridge shows a long-term opening rate of 11–12 mm/yr. The eastern section of

192-410: A halocline . If a zone undergoes a strong, vertical chemistry gradient with depth, it contains a chemocline . Temperature and salinity control ocean water density. Colder and saltier water is denser, and this density plays a crucial role in regulating the global water circulation within the ocean. The halocline often coincides with the thermocline, and the combination produces a pronounced pycnocline ,

288-493: A mid-ocean ridge , which creates a long mountain range beneath the ocean. Together they form the global mid-oceanic ridge system that features the longest mountain range in the world. The longest continuous mountain range is 65,000 km (40,000 mi). This underwater mountain range is several times longer than the longest continental mountain range – the Andes . Oceanographers state that less than 20% of

384-468: A common feature at oceanic spreading centers. A feature of the elevated ridges is their relatively high heat flow values, of about 1–10 μcal/cm s, or roughly 0.04–0.4 W/m . Most crust in the ocean basins is less than 200 million years old, which is much younger than the 4.54 billion year age of Earth . This fact reflects the process of lithosphere recycling into the Earth's mantle during subduction . As

480-434: A crustal thickness of 7 km (4.3 mi), this amounts to about 19 km (4.6 cu mi) of new ocean crust formed every year. Ocean The ocean is the body of salt water that covers approximately 70.8% of Earth . In English , the term ocean also refers to any of the large bodies of water into which the world ocean is conventionally divided. The following names describe five different areas of

576-595: A gentle breeze on a pond causes ripples to form. A stronger gust blowing over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they are travelling nearly matches the speed of the wind. In open water, when the wind blows continuously as happens in the Southern Hemisphere in the Roaring Forties , long, organized masses of water called swell roll across

672-403: A result, the photic zone is the most biodiverse and the source of the food supply which sustains most of the ocean ecosystem . Ocean photosynthesis also produces half of the oxygen in the Earth's atmosphere. 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). The continental shelf is where

768-496: A shallow area and this, coupled with a low pressure system, can raise the surface of the ocean dramatically above a typical high tide. The average depth of the oceans is about 4 km. More precisely the average depth is 3,688 meters (12,100 ft). Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep. "Deep ocean," which is anything below 200 meters (660 ft), covers about 66% of Earth's surface. This figure does not include seas not connected to

864-553: A ship of the Lamont–Doherty Earth Observatory of Columbia University , traversed the Atlantic Ocean, recording echo sounder data on the depth of the ocean floor. A team led by Marie Tharp and Bruce Heezen concluded that there was an enormous mountain chain with a rift valley at its crest, running up the middle of the Atlantic Ocean. Scientists named it the 'Mid-Atlantic Ridge'. Other research showed that

960-408: A subduction zone drags the rest of the plate along behind it. The slab pull mechanism is considered to be contributing more than the ridge push. A process previously proposed to contribute to plate motion and the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor" due to deep convection (see image). However, some studies have shown that the upper mantle ( asthenosphere )

1056-403: A wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion. Material worn from the margins of the land eventually ends up in the sea. Here it is subject to attrition as currents flowing parallel to the coast scour out channels and transport sand and pebbles away from their place of origin. Sediment carried to the sea by rivers settles on

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1152-406: A zone undergoes dramatic changes in temperature with depth, it contains a thermocline , a distinct boundary between warmer surface water and colder deep water. In tropical regions, the thermocline is typically deeper compared to higher latitudes. Unlike polar waters , where solar energy input is limited, temperature stratification is less pronounced, and a distinct thermocline is often absent. This

1248-439: Is a bay , a small bay with a narrow inlet is a cove and a large bay may be referred to as a gulf . Coastlines are influenced by several factors including the strength of the waves arriving on the shore, the gradient of the land margin, the composition and hardness of the coastal rock, the inclination of the off-shore slope and the changes of the level of the land due to local uplift or submergence. Normally, waves roll towards

1344-587: Is a seafloor mountain system formed by plate tectonics . It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin . This feature is where seafloor spreading takes place along a divergent plate boundary . The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin. The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at

1440-420: Is a global scale ion-exchange system. Hydrothermal vents at spreading centers introduce various amounts of iron , sulfur , manganese , silicon , and other elements into the ocean, some of which are recycled into the ocean crust. Helium-3 , an isotope that accompanies volcanism from the mantle, is emitted by hydrothermal vents and can be detected in plumes within the ocean. Fast spreading rates will expand

1536-743: Is about −2 °C (28 °F). In all parts of the ocean, deep ocean temperatures range between −2 °C (28 °F) and 5 °C (41 °F). Constant circulation of water in the ocean creates ocean currents . Those currents are caused by forces operating on the water, such as temperature and salinity differences, atmospheric circulation (wind), and the Coriolis effect . Tides create tidal currents, while wind and waves cause surface currents. The Gulf Stream , Kuroshio Current , Agulhas Current and Antarctic Circumpolar Current are all major ocean currents. Such currents transport massive amounts of water, gases, pollutants and heat to different parts of

1632-444: Is an important reference point for oceanography and geography, particularly as mean sea level . The ocean surface has globally little, but measurable topography , depending on the ocean's volumes. The ocean surface is a crucial interface for oceanic and atmospheric processes. Allowing interchange of particles, enriching the air and water, as well as grounds by some particles becoming sediments . This interchange has fertilized life in

1728-411: Is customarily divided into five principal oceans – listed below in descending order of area and volume: The ocean fills Earth's oceanic basins . Earth's oceanic basins cover different geologic provinces of Earth's oceanic crust as well as continental crust . As such it covers mainly Earth's structural basins , but also continental shelfs . In mid-ocean, magma is constantly being thrust through

1824-399: Is due to the fact that surface waters in polar latitudes are nearly as cold as deeper waters. Below the thermocline, water everywhere in the ocean is very cold, ranging from −1 °C to 3 °C. Because this deep and cold layer contains the bulk of ocean water, the average temperature of the world ocean is 3.9 °C. If a zone undergoes dramatic changes in salinity with depth, it contains

1920-443: Is in a constant state of 'renewal' at the mid-ocean ridges by the processes of seafloor spreading and plate tectonics. New magma steadily emerges onto the ocean floor and intrudes into the existing ocean crust at and near rifts along the ridge axes. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis. New magma of basalt composition emerges at and near

2016-456: Is irregular, unevenly dominating the Earth's surface . This leads to the distinction of the Earth's surface into a water and land hemisphere , as well as the division of the ocean into different oceans. Seawater covers about 361,000,000 km (139,000,000 sq mi) and the ocean's furthest pole of inaccessibility , known as " Point Nemo ", in a region known as spacecraft cemetery of

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2112-454: Is produced and magma is forced up creating underwater mountains, some of which may form chains of volcanic islands near to deep trenches. Near some of the boundaries between the land and sea, the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed. As they grate together, the continental plates are deformed and buckle causing mountain building and seismic activity. Every ocean basin has

2208-407: Is pushed across the surface of the ocean by the wind, but this represents a transfer of energy and not horizontal movement of water. As waves approach land and move into shallow water , they change their behavior. If approaching at an angle, waves may bend ( refraction ) or wrap around rocks and headlands ( diffraction ). When the wave reaches a point where its deepest oscillations of the water contact

2304-423: Is reflected back out of the water. Red light is most easily absorbed and thus does not reach great depths, usually to less than 50 meters (164 ft). Blue light, in comparison, can penetrate up to 200 meters (656 ft). Second, water molecules and very tiny particles in ocean water preferentially scatter blue light more than light of other colors. Blue light scattering by water and tiny particles happens even in

2400-480: Is sometimes referred to as the World Ocean, global ocean or the great ocean . The concept of a continuous body of water with relatively unrestricted exchange between its components is critical in oceanography . The word ocean comes from the figure in classical antiquity , Oceanus ( / oʊ ˈ s iː ə n ə s / ; ‹See Tfd› Greek : Ὠκεανός Ōkeanós , pronounced [ɔːkeanós] ),

2496-552: Is the open ocean's water column from the surface to the ocean floor. The water column is further divided into zones based on depth and the amount of light present. 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" (approximately 200 m in the open ocean). This is the zone where photosynthesis can occur. In this process plants and microscopic algae (free floating phytoplankton ) use light, water, carbon dioxide, and nutrients to produce organic matter. As

2592-478: Is the result of changes in the volume of the ocean basins which are, in turn, affected by rates of seafloor spreading along the mid-ocean ridges. The 100 to 170 meters higher sea level of the Cretaceous Period (144–65 Ma) is partly attributed to plate tectonics because thermal expansion and the absence of ice sheets only account for some of the extra sea level. Seafloor spreading on mid-ocean ridges

2688-440: Is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and observations of the seismic discontinuity in the upper mantle at about 400 km (250 mi). On the other hand, some of the world's largest tectonic plates such as

2784-451: Is underlain by denser material and is deeper. Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. Rates can be computed by mapping marine magnetic anomalies that span mid-ocean ridges. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of

2880-797: The North American Plate is 11 mm/yr to the east and the motion relative to the Caribbean Plate is 8 mm/yr . The western section of the trough is bounded to its south by the Swan Islands Transform Fault . During the Eocene the trough was the site of a subduction zone which formed the volcanic arc of the Cayman Ridge and the Sierra Maestra volcanic terrain of Cuba to the north, as

2976-585: The North American plate and South American plate are in motion, yet only are being subducted in restricted locations such as the Lesser Antilles Arc and Scotia Arc , pointing to action by the ridge push body force on these plates. Computer modeling of the plates and mantle motions suggest that plate motion and mantle convection are not connected, and the main plate driving force is slab pull. Increased rates of seafloor spreading (i.e.

Cayman Trough - Misplaced Pages Continue

3072-691: The North Sea or the Red Sea . There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as marginal seas ) or wholly (as inland seas ) bordered by land. 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 Earth. The global, interconnected body of salt water

3168-481: The South Pacific Ocean , at 48°52.6′S 123°23.6′W  /  48.8767°S 123.3933°W  / -48.8767; -123.3933  ( Point Nemo ) . This point is roughly 2,688 km (1,670 mi) from the nearest land. There are different customs to subdivide the ocean and are adjourned by smaller bodies of water such as, seas , gulfs , bays , bights , and straits . The ocean

3264-473: The Southwest Indian Ridge ). The spreading center or axis commonly connects to a transform fault oriented at right angles to the axis. The flanks of mid-ocean ridges are in many places marked by the inactive scars of transform faults called fracture zones . At faster spreading rates the axes often display overlapping spreading centers that lack connecting transform faults. The depth of

3360-592: The Thames Barrier is designed to protect London from a storm surge, while the failure of the dykes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States. Most of the ocean is blue in color, but in some places the ocean is blue-green, green, or even yellow to brown. Blue ocean color is a result of several factors. First, water preferentially absorbs red light, which means that blue light remains and

3456-406: The coastline and structure of the world ocean. A global ocean has existed in one form or another on Earth for eons. Since its formation the ocean has taken many conditions and shapes with many past ocean divisions and potentially at times covering the whole globe. During colder climatic periods, more ice caps and glaciers form, and enough of the global water supply accumulates as ice to lessen

3552-414: The longest mountain range in the world. The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes , the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long. At the spreading center on a mid-ocean ridge, the depth of the seafloor is approximately 2,600 meters (8,500 ft). On

3648-591: The ocean floor , they begin to slow down. This pulls the crests closer together and increases the waves' height , which is called wave shoaling . When the ratio of the wave's height to the water depth increases above a certain limit, it " breaks ", toppling over in a mass of foaming water. This rushes in a sheet up the beach before retreating into the ocean under the influence of gravity. Earthquakes , volcanic eruptions or other major geological disturbances can set off waves that can lead to tsunamis in coastal areas which can be very dangerous. The ocean's surface

3744-442: The Earth's biosphere . Oceanic evaporation , as a phase of the water cycle, is the source of most rainfall (about 90%), causing a global cloud cover of 67% and a consistent oceanic cloud cover of 72%. Ocean temperatures affect climate and wind patterns that affect life on land. One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where

3840-769: The East Pacific Rise lack rift valleys. The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–145 mm/yr. The highest known rate is over 200 mm/yr in the Miocene on the East Pacific Rise. Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges (e.g., the Gakkel Ridge in the Arctic Ocean and

3936-680: The Mid-Atlantic Ridge have spread much less far (showing a steeper profile) than faster ridges such as the East Pacific Rise (gentle profile) for the same amount of time and cooling and consequent bathymetric deepening. Slow-spreading ridges (less than 40 mm/yr) generally have large rift valleys , sometimes as wide as 10–20 km (6.2–12.4 mi), and very rugged terrain at the ridge crest that can have relief of up to 1,000 m (3,300 ft). By contrast, fast-spreading ridges (greater than 90 mm/yr) such as

Cayman Trough - Misplaced Pages Continue

4032-456: The Moon are 20x stronger than the Moon's tidal forces on the Earth.) The primary effect of lunar tidal forces is to bulge Earth matter towards the near and far sides of the Earth, relative to the moon. The "perpendicular" sides, from which the Moon appears in line with the local horizon, experience "tidal troughs". Since it takes nearly 25 hours for the Earth to rotate under the Moon (accounting for

4128-403: The Moon's 28 day orbit around Earth), tides thus cycle over a course of 12.5 hours. However, the rocky continents pose obstacles for the tidal bulges, so the timing of tidal maxima may not actually align with the Moon in most localities on Earth, as the oceans are forced to "dodge" the continents. Timing and magnitude of tides vary widely across the Earth as a result of the continents. Thus, knowing

4224-471: The Moon's gravity, oceanic tides are also substantially modulated by the Sun's tidal forces, by the rotation of the Earth, and by the shape of the rocky continents blocking oceanic water flow. (Tidal forces vary more with distance than the "base" force of gravity: the Moon's tidal forces on Earth are more than double the Sun's, despite the latter's much stronger gravitational force on Earth. Earth's tidal forces upon

4320-400: The Moon's position does not allow a local to predict tide timings, instead requiring precomputed tide tables which account for the continents and the Sun, among others. During each tidal cycle, at any given place the tidal waters rise to maximum height, high tide, before ebbing away again to the minimum level, low tide. As the water recedes, it gradually reveals the foreshore , also known as

4416-648: The Okeanos is represented with a dragon-tail on some early Greek vases. Scientists believe that a sizable quantity of water would have been in the material that formed Earth. Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. This is called atmospheric escape . During planetary formation , Earth possibly had magma oceans . Subsequently, outgassing , volcanic activity and meteorite impacts , produced an early atmosphere of carbon dioxide , nitrogen and water vapor , according to current theories. The gases and

4512-741: The World Ocean, such as the Caspian Sea . The deepest region of the ocean is at the Mariana Trench , located in the Pacific Ocean near the Northern Mariana Islands . The maximum depth has been estimated to be 10,971 meters (35,994 ft). The British naval vessel Challenger II surveyed the trench in 1951 and named the deepest part of the trench the " Challenger Deep ". In 1960, the Trieste successfully reached

4608-421: The amounts in other parts of the water cycle. The reverse is true during warm periods. During the last ice age, glaciers covered almost one-third of Earth's land mass with the result being that the oceans were about 122 m (400 ft) lower than today. During the last global "warm spell," about 125,000 years ago, the seas were about 5.5 m (18 ft) higher than they are now. About three million years ago

4704-427: The asthenosphere at ocean trenches . Two processes, ridge-push and slab pull , are thought to be responsible for spreading at mid-ocean ridges. Ridge push refers to the gravitational sliding of the ocean plate that is raised above the hotter asthenosphere, thus creating a body force causing sliding of the plate downslope. In slab pull the weight of a tectonic plate being subducted (pulled) below an overlying plate at

4800-479: The atmosphere are thought to have accumulated over millions of years. After Earth's surface had significantly cooled, the water vapor over time would have condensed, forming Earth's first oceans. The early oceans might have been significantly hotter than today and appeared green due to high iron content. Geological evidence helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption)

4896-478: The axis because of decompression melting in the underlying Earth's mantle . The isentropic upwelling solid mantle material exceeds the solidus temperature and melts. The crystallized magma forms a new crust of basalt known as MORB for mid-ocean ridge basalt, and gabbro below it in the lower oceanic crust . Mid-ocean ridge basalt is a tholeiitic basalt and is low in incompatible elements . Hydrothermal vents fueled by magmatic and volcanic heat are

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4992-490: The axis changes in a systematic way with shallower depths between offsets such as transform faults and overlapping spreading centers dividing the axis into segments. One hypothesis for different along-axis depths is variations in magma supply to the spreading center. Ultra-slow spreading ridges form both magmatic and amagmatic (currently lack volcanic activity) ridge segments without transform faults. Mid-ocean ridges exhibit active volcanism and seismicity . The oceanic crust

5088-407: The bottom of the trench, manned by a crew of two men. Oceanographers classify the ocean into vertical and horizontal zones based on physical and biological conditions. The pelagic zone consists of the water column of the open ocean, and can be divided into further regions categorized by light abundance and by depth. The ocean zones can be grouped by light penetration into (from top to bottom):

5184-407: The discovery of the worldwide extent of the mid-ocean ridge in the 1950s, geologists faced a new task: explaining how such an enormous geological structure could have formed. In the 1960s, geologists discovered and began to propose mechanisms for seafloor spreading . The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegener's theory to be expanded so that it included

5280-509: The elder of the Titans in classical Greek mythology . Oceanus was believed by the ancient Greeks and Romans to be the divine personification of an enormous river encircling the world. The concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion,

5376-483: The field preserved in the oceanic crust comprise a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at known intervals throughout its history, the pattern of geomagnetic reversals in the ocean crust can be used as an indicator of age; given the crustal age and distance from the ridge axis, spreading rates can be calculated. Spreading rates range from approximately 10–200 mm/yr. Slow-spreading ridges such as

5472-474: The floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot sima [rising] from depth". However, Wegener did not pursue this observation in his later works and his theory was dismissed by geologists because there was no mechanism to explain how continents could plow through ocean crust , and the theory became largely forgotten. Following

5568-412: The formation of unusually high rogue waves . Most waves are less than 3 m (10 ft) high and it is not unusual for strong storms to double or triple that height. Rogue waves, however, have been documented at heights above 25 meters (82 ft). The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave

5664-484: The globe are linked by plate tectonic boundaries and the trace of the ridges across the ocean floor appears similar to the seam of a baseball . The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi). The mid-ocean ridges of the world are connected and form the Ocean Ridge, a single global mid-oceanic ridge system that is part of every ocean , making it

5760-421: The interface between water and air is called swell – a term used in sailing , surfing and navigation . These motions profoundly affect ships on the surface of the ocean and the well-being of people on those ships who might suffer from sea sickness . Wind blowing over the surface of a body of water forms waves that are perpendicular to the direction of the wind. The friction between air and water caused by

5856-482: The intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude. When the sun and moon are aligned (full moon or new moon), the combined effect results in the higher "spring tides", while the sun and moon misaligning (half moons) result in lesser tidal ranges. In the open ocean tidal ranges are less than 1 meter, but in coastal areas these tidal ranges increase to more than 10 meters in some areas. Some of

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5952-739: The largest tidal ranges in the world occur in the Bay of Fundy and Ungava Bay in Canada, reaching up to 16 meters. Other locations with record high tidal ranges include the Bristol Channel between England and Wales, Cook Inlet in Alaska, and the Río Gallegos in Argentina. Tides are not to be confused with storm surges , which can occur when high winds pile water up against the coast in

6048-612: The linear weakness between the separating plates, and emerges as lava , creating new oceanic crust and lithosphere upon cooling. The first discovered mid-ocean ridge was the Mid-Atlantic Ridge , which is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are traditionally called mid-ocean ridges. Mid-ocean ridges around

6144-417: The majority of Earth's surface. It includes the Pacific , Atlantic , Indian , Southern/Antarctic , and Arctic oceans. As a general term, "the ocean" and "the sea" are often interchangeable. Strictly speaking, a "sea" is a body of water (generally a division of the world ocean) partly or fully enclosed by land. The word "sea" can also be used for many specific, much smaller bodies of seawater, such as

6240-532: The mid-ocean ridge causing basalt reactions with seawater to happen more rapidly. The magnesium/calcium ratio will be lower because more magnesium ions are being removed from seawater and consumed by the rock, and more calcium ions are being removed from the rock and released into seawater. Hydrothermal activity at the ridge crest is efficient in removing magnesium. A lower Mg/Ca ratio favors the precipitation of low-Mg calcite polymorphs of calcium carbonate ( calcite seas ). Slow spreading at mid-ocean ridges has

6336-548: The mid-ocean ridge from the South Atlantic into the Indian Ocean early in the twentieth century. Although the first-discovered section of the ridge system runs down the middle of the Atlantic Ocean, it was found that most mid-ocean ridges are located away from the center of other ocean basins. Alfred Wegener proposed the theory of continental drift in 1912. He stated: "the Mid-Atlantic Ridge ... zone in which

6432-402: The movement of oceanic crust as well as the continents. Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a major paradigm shift in geological thinking. It is estimated that along Earth's mid-ocean ridges every year 2.7 km (1.0 sq mi) of new seafloor is formed by this process. With

6528-637: The northeastward-moving Caribbean Plate was subducted beneath the southwest-moving North American Plate , or as some researchers contend, beneath a plate fragment dubbed the East Cuban Microplate. In 2010 a UK team from the National Oceanography Centre in Southampton (NOCS), equipped with an autonomously controlled robot submarine, began mapping the full extent of the trench and discovered black smokers on

6624-408: The ocean faces many environmental threats, such as marine pollution , overfishing , and the effects of climate change . Those effects include ocean warming , ocean acidification and sea level rise . The continental shelf and coastal waters are most affected by human activity. The terms "the ocean" or "the sea" used without specification refer to the interconnected body of salt water covering

6720-540: The ocean floor at a depth of 5 km (16,000 ft), the deepest yet found. In January 2012, the researchers announced that water exits the vents at a temperature possibly exceeding 450 °C (842 °F), making them among the hottest known undersea vents. They also announced the discovery of new species, including an eyeless shrimp with a light-sensing organ on its back. 18°30′N 83°0′W  /  18.500°N 83.000°W  / 18.500; -83.000 Mid-ocean ridge A mid-ocean ridge ( MOR )

6816-423: The ocean meets dry land. It is more shallow, with a depth of a few hundred meters or less. Human activity often has negative impacts on marine life within the continental shelf. Ocean temperatures depend on the amount of solar radiation reaching the ocean surface. In the tropics, surface temperatures can rise to over 30 °C (86 °F). Near the poles where sea ice forms, the temperature in equilibrium

6912-508: The ocean, on land and air. All these processes and components together make up ocean surface ecosystems . Tides are the regular rise and fall in water level experienced by oceans, primarily driven by the Moon 's gravitational tidal forces upon the Earth. Tidal forces affect all matter on Earth, but only fluids like the ocean demonstrate the effects on human timescales. (For example, tidal forces acting on rock may produce tidal locking between two planetary bodies.) Though primarily driven by

7008-469: The ocean. If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. The size of the waves depends on the fetch , the distance that the wind has blown over the water and the strength and duration of that wind. When waves meet others coming from different directions, interference between the two can produce broken, irregular seas. Constructive interference can lead to

7104-493: The ocean: Pacific , Atlantic , Indian , Antarctic/Southern , and Arctic . The ocean contains 97% of Earth's water and is the primary component of Earth's hydrosphere and is thereby essential to life on Earth. The ocean influences climate and weather patterns, the carbon cycle , and the water cycle by acting as a huge heat reservoir . Ocean scientists split the ocean into vertical and horizontal zones based on physical and biological conditions. The pelagic zone

7200-403: The oceanic crust and lithosphere moves away from the ridge axis, the peridotite in the underlying mantle lithosphere cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere , which sits above the less rigid and viscous asthenosphere . The oceanic lithosphere is formed at an oceanic ridge, while the lithosphere is subducted back into

7296-419: The oceans absorb CO 2 from the atmosphere , a higher concentration leads to ocean acidification (a drop in pH value ). The ocean provides many benefits to humans such as ecosystem services , access to seafood and other marine resources , and a means of transport . The ocean is known to be the habitat of over 230,000 species , but may hold considerably more – perhaps over two million species. Yet,

7392-425: The oceans could have been up to 50 m (165 ft) higher. The entire ocean, containing 97% of Earth's water, spans 70.8% of Earth 's surface, making it Earth's global ocean or world ocean . This makes Earth, along with its vibrant hydrosphere a "water world" or " ocean world ", particularly in Earth's early history when the ocean is thought to have possibly covered Earth completely. The ocean's shape

7488-434: The oceans have been mapped. The zone where land meets sea is known as the coast , and the part between the lowest spring tides and the upper limit reached by splashing waves is the shore . A beach is the accumulation of sand or shingle on the shore. A headland is a point of land jutting out into the sea and a larger promontory is known as a cape . The indentation of a coastline, especially between two headlands,

7584-537: The oceans may have always been on the Earth since the beginning of the planet's formation. In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity . The origin of Earth's oceans is unknown. Oceans are thought to have formed in the Hadean eon and may have been the cause for the emergence of life . Plate tectonics , post-glacial rebound , and sea level rise continually change

7680-455: The opposite effect and will result in a higher Mg/Ca ratio favoring the precipitation of aragonite and high-Mg calcite polymorphs of calcium carbonate ( aragonite seas ). Experiments show that most modern high-Mg calcite organisms would have been low-Mg calcite in past calcite seas, meaning that the Mg/Ca ratio in an organism's skeleton varies with the Mg/Ca ratio of the seawater in which it

7776-451: The photic zone, the mesopelagic zone and the aphotic deep ocean zone: The pelagic part of the aphotic zone can be further divided into vertical regions according to depth and temperature: Distinct boundaries between ocean surface waters and deep waters can be drawn based on the properties of the water. These boundaries are called thermoclines (temperature), haloclines (salinity), chemoclines (chemistry), and pycnoclines (density). If

7872-418: The power of a storm wave impacting on the foot of a cliff has a shattering effect as air in cracks and crevices is compressed and then expands rapidly with release of pressure. At the same time, sand and pebbles have an erosive effect as they are thrown against the rocks. This tends to undercut the cliff, and normal weathering processes such as the action of frost follows, causing further destruction. Gradually,

7968-574: The rate of expansion of the mid-ocean ridge) have caused the global ( eustatic ) sea level to rise over very long timescales (millions of years). Increased seafloor spreading means that the mid-ocean ridge will then expand and form a broader ridge with decreased average depth, taking up more space in the ocean basin. This displaces the overlying ocean and causes sea levels to rise. Sealevel change can be attributed to other factors ( thermal expansion , ice melting, and mantle convection creating dynamic topography ). Over very long timescales, however, it

8064-440: The ridge crest was seismically active and fresh lavas were found in the rift valley. Also, crustal heat flow was higher here than elsewhere in the Atlantic Ocean basin. At first, the ridge was thought to be a feature specific to the Atlantic Ocean. However, as surveys of the ocean floor continued around the world, it was discovered that every ocean contains parts of the mid-ocean ridge system. The German Meteor expedition traced

8160-416: The ridge flanks, the depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is correlated with its age (age of the lithosphere where depth is measured). The depth-age relation can be modeled by the cooling of a lithosphere plate or mantle half-space. A good approximation is that the depth of the seafloor at a location on a spreading mid-ocean ridge is proportional to

8256-455: The seabed between adjoining plates to form mid-oceanic ridges and here convection currents within the mantle tend to drive the two plates apart. Parallel to these ridges and nearer the coasts, one oceanic plate may slide beneath another oceanic plate in a process known as subduction . Deep trenches are formed here and the process is accompanied by friction as the plates grind together. The movement proceeds in jerks which cause earthquakes, heat

8352-407: The seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides and currents. Dredging removes material and deepens channels but may have unexpected effects elsewhere on the coastline. Governments make efforts to prevent flooding of the land by the building of breakwaters , seawalls , dykes and levees and other sea defences. For instance,

8448-431: The seafloor were analyzed by oceanographers Matthew Fontaine Maury and Charles Wyville Thomson and revealed a prominent rise in the seafloor that ran down the Atlantic basin from north to south. Sonar echo sounders confirmed this in the early twentieth century. It was not until after World War II , when the ocean floor was surveyed in more detail, that the full extent of mid-ocean ridges became known. The Vema ,

8544-401: The shore at the rate of six to eight per minute and these are known as constructive waves as they tend to move material up the beach and have little erosive effect. Storm waves arrive on shore in rapid succession and are known as destructive waves as the swash moves beach material seawards. Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide,

8640-439: The square root of the age of the seafloor. The overall shape of ridges results from Pratt isostasy : close to the ridge axis, there is a hot, low-density mantle supporting the oceanic crust. As the oceanic plate cools, away from the ridge axis, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens, and the density increases. Thus older seafloor

8736-456: The system forms). As the world's ocean is the principal component of Earth's hydrosphere , it is integral to life on Earth, forms part of the carbon cycle and water cycle , and – as a huge heat reservoir – influences climate and weather patterns. The motions of the ocean surface, known as undulations or wind waves , are the partial and alternate rising and falling of the ocean surface. The series of mechanical waves that propagate along

8832-796: The trough has been named the Gonâve Microplate . The Gonâve plate extends from the spreading ridge east to the island of Hispaniola . It is bounded on the north by the Oriente and Septentrional fault zones. On the south the Gonâve is bounded by the Walton fault zone , the Jamaica restraining bend and the Enriquillo-Plantain Garden fault zone . The two bounding strike slip fault zones are left lateral. The motion relative to

8928-434: The very clearest ocean water, and is similar to blue light scattering in the sky . Ocean water represents the largest body of water within the global water cycle (oceans contain 97% of Earth's water ). Evaporation from the ocean moves water into the atmosphere to later rain back down onto land and the ocean. Oceans have a significant effect on the biosphere . The ocean as a whole is thought to cover approximately 90% of

9024-476: The world, and from the surface into the deep ocean. All this has impacts on the global climate system . Ocean water contains dissolved gases, including oxygen , carbon dioxide and nitrogen . An exchange of these gases occurs at the ocean's surface. The solubility of these gases depends on the temperature and salinity of the water. The carbon dioxide concentration in the atmosphere is rising due to CO 2 emissions , mainly from fossil fuel combustion. As

9120-549: Was grown. The mineralogy of reef-building and sediment-producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by the rate of sea-floor spreading. The first indications that a ridge bisects the Atlantic Ocean basin came from the results of the British Challenger expedition in the nineteenth century. Soundings from lines dropped to

9216-775: Was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago. In the Nuvvuagittuq Greenstone Belt , Quebec , Canada, rocks dated at 3.8 billion years old by one study and 4.28 billion years old by another show evidence of the presence of water at these ages. If oceans existed earlier than this, any geological evidence either has yet to be discovered, or has since been destroyed by geological processes like crustal recycling . However, in August 2020, researchers reported that sufficient water to fill

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