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A sea is a large body of salt water that is surrounded in whole or in part by land.[1][2][a] More broadly, "the sea" is the interconnected system of Earth's salty, oceanic waters—considered as one global ocean or as several principal oceanic divisions. The sea moderates Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. Although the sea has been traveled and explored since prehistory, the modern scientific study of the sea—oceanography—dates broadly to the British Challenger expedition of the 1870s.[3] The sea is conventionally divided into up to five large oceanic sections—including the International Hydrographic Organization's four named oceans[4] (the Atlantic, Pacific, Indian, and Arctic) and the Southern Ocean;[5] smaller, second-order sections, such as the Mediterranean, are known as seas. Owing to the present state of continental drift, the Northern Hemisphere is now fairly equally divided between land and sea (a ratio of about 2:3) but the South is overwhelmingly oceanic (1:4.7).[6] Salinity
Salinity
in the open ocean is generally in a narrow band around 3.5% by mass, although this can vary in more landlocked waters, near the mouths of large rivers, or at great depths. About 85% of the solids in the open sea are sodium chloride. Deep-sea currents are produced by differences in salinity and temperature. Surface currents are formed by the friction of waves produced by the wind and by tides, the changes in local sea level produced by the gravity of the Moon
Moon
and Sun. The direction of all of these is governed by surface and submarine land masses and by the rotation of the Earth
Earth
(the Coriolis effect). Former changes in sea levels have left continental shelves, shallow areas in the sea close to land. These nutrient-rich waters teem with life, which provide humans with substantial supplies of food—mainly fish, but also shellfish, mammals, and seaweed—which are both harvested in the wild and farmed. The most diverse areas surround great tropical coral reefs. Whaling
Whaling
in the deep sea was once common but whales' dwindling numbers prompted international conservation efforts and finally a moratorium on most commercial hunting. Oceanography
Oceanography
has established that not all life is restricted to the sunlit surface waters: even under enormous depths and pressures, nutrients streaming from hydrothermal vents support their own unique ecosystem. Life may have started there and aquatic microbial mats are generally credited with the oxygenation of Earth's atmosphere; both plants and animals first evolved in the sea. The sea is an essential aspect of human trade, travel, mineral extraction, and power generation. This has also made it essential to warfare and left major cities exposed to earthquakes and volcanoes from nearby faults; powerful tsunami waves; and hurricanes, typhoons, and cyclones produced in the tropics. This importance and duality has affected human culture, from early sea gods to the epic poetry of Homer
Homer
to the changes induced by the Columbian Exchange, from burial at sea to Basho's haikus to hyperrealist marine art, and inspiring music ranging from the shanties in The Complaynt of Scotland to Rimsky-Korsakov's "The Sea
Sea
and Sinbad's Ship" to A-mei's "Listen to the Sea". It is the scene of leisure activities including swimming, diving, surfing, and sailing. However, population growth, industrialization, and intensive farming have all contributed to present-day marine pollution. Atmospheric carbon dioxide is being absorbed in increasing amounts, lowering its pH in a process known as ocean acidification. The shared nature of the sea has made overfishing an increasing problem.

Contents

1 Definition 2 Physical science

2.1 Seawater 2.2 Waves 2.3 Tsunami 2.4 Tides 2.5 Currents 2.6 Basins 2.7 Coasts 2.8 Sea
Sea
level 2.9 Water
Water
cycle 2.10 Carbon cycle 2.11 Acidification

3 Marine life

3.1 Habitats 3.2 Algae
Algae
and plants 3.3 Animals and other life

4 Humans and the sea

4.1 Navigation
Navigation
and exploration 4.2 Trade 4.3 Fishing 4.4 Law 4.5 War 4.6 Travel 4.7 Leisure 4.8 Power generation 4.9 Extractive industries 4.10 Pollution 4.11 Indigenous sea peoples 4.12 In culture

5 See also 6 Notes 7 References 8 External links

Definition[edit]

The interconnected system of the world's oceans and their various divisions.

Further information: List of seas Both senses of sea date to Old English; the larger sense has required a definite article since Early Middle English.[5] As the term has been applied over time, there are no sharp distinctions between seas and oceans, although seas are smaller and are usually bounded by land masses (and ones smaller scale than continents),[7] the singular standard exception being the Sargasso Sea, which is created by the four currents bounding what is termed the North Atlantic Gyre.[8](p90) Seas are generally larger than lakes and contain salt water. While the defining elements of size and being bounded are generally used, there is no formally accepted technical definition of "sea" among oceanographers.[b] In international law, the United Nations
United Nations
Convention on the Law of the Sea states that all the ocean is "the sea".[11][c]

Physical science[edit] Main articles: Oceanography
Oceanography
and Physical oceanography

The "Blue Marble" in its original orientation, showing the junction of the Indian and Atlantic at the Cape of Good Hope.

Earth
Earth
is the only known planet with seas of liquid water on its surface,[8](p22) although Mars
Mars
possesses ice caps and similar planets in other solar systems may have oceans.[13] It is still unclear where Earth's water came from, but, seen from space, our planet appears as a "blue marble" of its various forms: oceans, ice caps, clouds.[14] Earth's 1,335,000,000 cubic kilometers (320,000,000 cu mi) of sea contain about 97.2 percent of its known water[15][d] and cover more than 70 percent of its surface.[8](p7) Another 2.15% of Earth's water is frozen, found in the sea ice covering the Arctic
Arctic
Ocean, the ice cap covering Antarctica
Antarctica
and its adjacent seas, and various glaciers and surface deposits around the world. The remainder (about 0.65% of the whole) form underground reservoirs or various stages of the water cycle, containing the freshwater encountered and used by most terrestrial life: vapor in the air, the clouds it slowly forms, the rain falling from them, and the lakes and rivers spontaneously formed as its waters flow again and again to the sea.[15] The sea's dominance of the planet is such that the British author Arthur C. Clarke once noted that "Earth" would have been better named "Ocean".[8](p7) The scientific study of water and Earth's water cycle is hydrology; hydrodynamics studies the physics of water in motion. The more recent study of the sea in particular is oceanography. This began as the study of the shape of the ocean's currents[20] but has since expanded into a large and multidisciplinary field:[21] it examines the properties of seawater; studies waves, tides, and currents; charts coastlines and maps the seabeds; and studies marine life.[22] The subfield dealing with the sea's motion, its forces, and the forces acting upon it is known as physical oceanography.[23] Marine biology (biological oceanography) studies the plants, animals, and other organisms inhabiting marine ecosystems. Both are informed by chemical oceanography, which studies the behavior of elements and molecules within the oceans: particularly, at the moment, the ocean's role in the carbon cycle and carbon dioxide's role in the increasing acidification of seawater. Marine and maritime geography charts the shape and shaping of the sea, while marine geology (geological oceanography) has provided evidence of continental drift and the composition and structure of the Earth, clarified the process of sedimentation, and assisted the study of volcanism and earthquakes.[21]

Seawater[edit]

Solutes in seawater at 35
salinity[24]

Solute
of water (by mass) % of total solutes

Chloride 19 .3 55 .0

Sodium 10 .8 30 .6

Sulfate 2 .7 7 .7

Magnesium 1 .3 3 .7

Calcium 0 .41 1 .2

Potassium 0 .40 1 .1

Bicarbonate 0 .10 0 .4

Bromides 0 .07 0 .2

Carbonate 0 .01 0 .05

Strontium 0 .01 0 .04

Borate 0 .01 0 .01

Fluoride 0 .001 < 0 .01

All others < 0 .001 < 0 .01

Main article: Seawater

The first global map of oceanic surface salinity, produced by the ESA's SMOS satellite (2011). The salinity varies from 32
(purple) to 38
(red).

Seawater
Seawater
is invariably salty and, although its degree of saltiness (salinity) can vary, about 90% of the water in the ocean has 34–35 g (1.2 oz.) of dissolved solids per liter, producing a salinity between 3.4 and 3.5%.[25] To easily describe small differences, however, oceanographers usually express salinity as a millage (‰) or part per thousand (ppt) instead of using percents. The surface salinity of waters in the Northern Hemisphere
Northern Hemisphere
are generally closer to the 34‰ mark, while those in the South are closer to 35‰.[6] The solutes in ocean water come both from inflowing river water and from the ocean floor.[26] The relative composition of the solutes is stable throughout the world's oceans:[24][27] sodium (Na) and chloride (Cl) make up about 85%. Other solutes include metal ions such as magnesium (Mg) and calcium (Ca) and negative ions such as sulfate (SO₄), carbonate (CO₃), and bromides. In the absence of other pollution, seawater would not be harmful to drink except that it is much too saline;[e] similarly, it cannot be used for irrigating most plants without being desalinated. For scientific and technical purposes, a standardized form of artificial seawater is often used. Variations in salinity are caused by many factors: currents flowing between the seas; incoming freshwater from rivers and glaciers; precipitation; the formation and melting of sea ice; and evaporation, which is in turn affected by temperature, winds, and waves. For example, the upper level of the Baltic Sea
Baltic Sea
has a very low salinity (5 to 8
– see Salinity) because the low temperatures of the surrounding climate produce minimal evaporation; it has many inflowing rivers; and its small connection to the North Sea
North Sea
tends to create a cold, dense under-layer that hardly mixes with the surface waters.[30] By contrast, the Red Sea
Red Sea
lies between the Sahara
Sahara
and Arabian Deserts; it has high evaporation but little precipitation; it has few (and mostly seasonal) inflowing rivers; and its connection to other seas—the Suez Canal
Suez Canal
in the north and the Bab-el-Mandeb
Bab-el-Mandeb
in the south—are both very narrow. Its salinity averages 40‰.[31] The Mediterranean is a little lower, at 37‰, while some landlocked lakes are much higher: the Dead Sea
Dead Sea
has 300 grams (11 oz) of dissolved solids per liter (300‰).

Mean surface temperature (2009), from −2 °C (light violet) to 30 °C (light red).

Sea
Sea
temperature chiefly depends on the amount of solar radiation it absorbs. In the tropics where sunlight falls more directly, the temperature of the surface layers can rise to over 30 °C (86 °F); near the poles, the temperature is in equilibrium with the sea ice at its freezing point. Its salinity makes this lower than freshwater's, usually about −1.8 °C (28.8 °F). These temperature differences contribute to the continuous circulation of water through the sea. Warm surface currents cool as they move away from the tropics; as the water becomes denser, it sinks. The cold water in the deep sea moves back towards the equator before welling up again to the surface. Deep seawater has a temperature between −2 and 5 °C (28 and 41 °F) in all parts of the globe.[32] In freezing seas, ice crystals begin to form on the surface. These break into small pieces and coalesce into flat discs that form a thick suspension known as frazil. In calm conditions, frazil will freeze into a thin, flat sheet called nilas, which thickens as new ice forms in the sea beneath it. In turbulent waters, frazil instead join together into larger flat discs known as "pancakes". These slide over and under one another to form floes. During these processes, salt water and air are trapped amid the ice. Nilas
Nilas
forms with a salinity around 12–15
and is greyish in color but grows fresher over time: after a year, it is bluish and closer to 4–6
saline.[28][33]

Mean surface oxygen levels (2009), from 0.15 (light violet) to 0.45 (light red) moles of O₂ per cubic meter.

The amount of light that penetrates the sea depends on the angle of the sun, the local weather, and the sea's turbidity. Of the light that reaches the surface of the sea, much of it is reflected at the surface and its red wavelengths are absorbed in the top few meters. Yellow and green reach greater depths, and the longer blue and violet wavelengths may penetrate as deep as 1,000 m (3,300 ft). The amount of oxygen present in seawater depends primarily upon its temperature and the photosynthetic organisms living in it, particularly algae, phytoplankton, and plants such as seagrass. During the day, their photosynthetic activity produces oxygen, which dissolves into the seawater and is used by marine animals. The water's oxygen saturation is lower during the night and much lower in the deep sea. Below a depth of about 200 m (660 ft), there is insufficient light for photosynthesis[34] and consequently little dissolved oxygen. Below this, anaerobic bacteria break down falling organic material, producing hydrogen sulfide (H₂S).[35] It is projected that global warming will reduce oxygen both in surface and deep waters, due to oxygen's decreased solubility as temperatures increase[36] and increased oceanic stratification.[37]

Waves[edit] Main article: Wind
Wind
wave

Mean wave height (1992), from 0 m (light violet) to 6 m (white). Note the large swells in the southern oceans.

Movement of fluid parcels as waves pass.

Ocean
Ocean
surface waves are propagating oscillations caused by the drag and friction from air moving across the surface of the water. This friction transfers energy and forms surface waves in the water more or less in the direction of the wind. The top of a wave is known as its crest and its foot as its trough; the distance between two crests is the wavelength. These waves are mechanical: as they approach, the water at a given point rise up and, as they pass, the water goes down, with parcels of water tracing a roughly circular path. The energy is passed along with the wave at a much greater speed than the motion of the water itself. The sea state of the ocean is determined by the size of these waves, which—on the open ocean—depends upon the wind speed and the fetch, the distance over which the wind blows upon the water. The smallest waves are called ripples, strongly affected by surface tension. As strong and prolonged winds push against ripples' raised crests, larger and more irregular waves form, which are known as seas. These waves reach their maximum height when the rate at which they are traveling nearly matches the speed of the wind. As the wind drops, the waves remain as swell and, over time, they naturally separate[f] into long, powerful waves with a common direction and wavelength. These swells can travel over large distances—even half the globe—and originate particularly often from the Roaring Forties
Roaring Forties
of the Southern Hemisphere where the wind blows continuously.[38][39] When the wind dies down, ripples easily disappear owing to water's internal friction (viscosity), but longer waves in seas and swells are only (very) slowly reduced by viscosity.[38] Constructive interference, however, can also cause individual (unexpected) rogue waves much higher than normal.[40] Most waves are less than 3 m (10 ft) high[40] and it is not unusual for strong storms to double or triple that height;[41] offshore construction such as wind farms and oil platforms use metocean statistics from measurements in computing the wave forces (due to for instance the hundred-year wave) they are designed against.[42] Rogue waves, however, have been documented at heights above 25 meters (82 ft).[43][44]

When waves enter shallow water, they slow down and their amplitude (height) increases.

As waves approach land and move into shallow water, they change their behavior. If approaching at an angle, waves may bend (refraction) or wrap rocks and headlands (diffraction). When the wave reaches a point where its deepest oscillations of the water contact the seabed, 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.[40] This rushes in a sheet up the beach before retreating into the sea under the influence of gravity.[38]

The 2004 tsunami crashing ashore in Thailand. An estimated 8,000 Thais were killed; 220,000 other people died around the Indian Ocean.[45]

Tsunami[edit] Main article: Tsunami A tsunami is an unusual form of wave caused by a sudden and powerful event such as an underwater earthquake or landslide, a meteorite impact, a volcanic eruption, or a collapse of land into the sea. These events can temporarily lift or lower the surface of the sea in the affected area, usually by a few feet. The potential energy of the displaced seawater is turned into kinetic energy, creating a shallow wave radiating outwards at a velocity proportional to the square root of the depth of the water. Tsunamis, therefore, travel much faster in the open ocean than on a continental shelf.[46] Despite traveling at speeds of over 600 mph (970 km/h),[47] tsunamis in deep seas have wavelengths from 80 to 300 miles (130 to 480 km) and an amplitude of less than three feet.[48] Standard surface waves in the same region may only have wavelengths of a few hundred feet and speeds up to 65 mph (105 km/h) but, when compared to their possible amplitudes of up to 45 ft (14 m), tsunamis at this stage are often able to pass unnoticed.[48] Tsunami
Tsunami
warning systems rely on the fact that seismic waves caused by earthquakes travel around the world at around 14,400 kilometers (8,900 mi) per hour, allowing threatened regions to be alerted to the possibility of a tsunami.[49] Measurements from a network of sea-level measuring stations make it possible to confirm or cancel a tsunami warning.[50] A trigger event on the continental shelf may cause a local tsunami on the land side and a distant tsunami that travels out across the ocean. The energy of the wave is dissipated only gradually but is spread out over the wave front. As the wave radiates away from the source, the front gets longer and the average energy reduces, so distant shores will generally be hit by weaker waves. However, as the speed of the wave is controlled by the water depth, it does not travel at the same speed in all directions and this affects the direction of the wave front. This effect, known as refraction, can focus the strength of an advancing tsunami on some areas while weakening it in others, according to the undersea topography along its path.[51][52] Just as with other waves, moving into shallow water causes the tsunami to slow but grow in height.[48] Either the trough or the crest of the tsunami can arrive at the coast first.[46] In the former case, the sea draws back and leaves subtidal areas unusually exposed.[53] When the crest arrives, it does not usually break but rushes inland, flooding all in its path. Much of the disaster's destruction can be produced by these flood waters, which drain back into the sea while pulling people and debris along. Several tsunamis can be caused by a single geological event. In such cases, it is common for the later waves to arrive between eight minutes and two hours after the first, which may not be the biggest or most destructive.[46] Occasionally, in a shallow bay or estuary, a tsunami may transform into a bore.[47]

Tides[edit] Main article: Tide

High tides (blue) at the nearest and furthest points of the Earth
Earth
from the Moon

Tides are the regular rise and fall in water level experienced by seas and oceans in response to the gravitational influences of the Moon
Moon
and the Sun, and the effects of the Earth's rotation. At any given place, the water rises over the course of the tidal cycle to a maximum height known as "high tide" before ebbing away again to a minimum "low tide" level. As the water recedes, it uncovers more and more of the foreshore or intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude.[54][55] Tidal bores can occur at the mouths of rivers, where the force of the incoming tide pushes waves of seawater upstream against the current. At Hangzhou
Hangzhou
in China, the bore can reach 9 meters (30 ft) high and travel up to 40 km (25 mi) per hour. Most places experience two high tides each day, occurring at intervals of about 12 hours and 25 minutes, half the period that it takes for the Earth
Earth
to make a complete revolution and return the Moon
Moon
to its previous position relative to an observer. The Moon's mass is some 27 million times smaller than the Sun, but it is 400 times closer to the Earth.[56] Tidal force
Tidal force
or tide-raising force decreases rapidly with distance, so the moon has more than twice as great an effect on tides as the Sun.[56] A bulge is formed in the ocean at the place where the Earth
Earth
is closest to the Moon, because it is also where the effect of the Moon's gravity is stronger. On the opposite side of the Earth, the lunar force is at its weakest and this causes another bulge to form. These bulges rotate around the Earth
Earth
as the moon does. The Sun's effect is less powerful but, when the Sun, Moon
Moon
and Earth
Earth
are all aligned at the full and new moons, the combined effect results in the high "spring tides". In contrast, when the Sun
Sun
is at 90° from the Moon
Moon
as viewed from Earth, the combined gravitational effect on tides is correspondingly reduced, causing the lower "neap tides".[54] Tidal flows of seawater are resisted by the water's inertia and can be affected by land masses. In places like the Gulf of Mexico
Gulf of Mexico
where land constrains the movement of the bulges, only one set of tides may occur each day. Inshore from an island, there may be a complex daily cycle with four high tides. The island straits at Chalkis on Euboea experience strong currents which abruptly switch direction, generally four times per day but up to 12 times per day when the moon and the sun are 90 degrees apart.[57][58] Where there is a funnel-shaped bay or estuary, the tidal range can be magnified. The Bay of Fundy
Bay of Fundy
in Canada can experience spring tides of 15 m (49 ft). Although tides are regular and predictable, the height of high tides can be lowered by offshore winds and raised by onshore winds. The high pressure at the center of an anticyclones pushes down on the water and is associated with abnormally low tides while low-pressure areas may cause extremely high tides.[54] A storm surge can occur when high winds pile water up against the coast in a shallow area and this, coupled with a low pressure system, can raise the surface of the sea at high tide dramatically. In 1900, Galveston, Texas, experienced a 15 ft (5 m) surge during a hurricane that overwhelmed the city, killing over 3,500 people and destroying 3,636 homes.[59]

Currents[edit]

Mean surface density, from 1020 (light violet) to 1028 (light pink) kilograms per cubic meter.

Main article: Ocean
Ocean
current Wind
Wind
blowing over the surface of the sea causes friction at the interface between air and sea. Not only does this cause waves to form but it also makes the surface seawater move in the same direction as the wind. Although winds are variable, in any one place they predominantly blow from a single direction and thus a surface current can be formed. Westerly winds are most frequent in the mid-latitudes while easterlies dominate the tropics.[60] When water moves in this way, other water flows in to fill the gap and a circular movement of surface currents known as a gyre is formed. There are five main gyres in the world's oceans: two in the Pacific, two in the Atlantic, and one in the Indian Ocean. The North Atlantic gyre that produces the Sargasso Sea
Sargasso Sea
accumulates salinity levels as high as 38‰.[6] Other smaller gyres are found in lesser seas and a single gyre flows around Antarctica. These gyres have followed the same routes for millennia, guided by the topography of the land, the wind direction, and the Coriolis effect. The surface currents flow in a clockwise direction in the Northern Hemisphere
Northern Hemisphere
and anticlockwise in the Southern Hemisphere. The water moving away from the equator is warm, while that flowing towards it has lost most of its heat. These currents tend to moderate the Earth's climate, cooling the equatorial region, and warming regions at higher latitudes.[61] Global climate and weather forecasts are powerfully affected by the world ocean, so global climate modelling makes use of ocean circulation models as well as models of other major components such as the atmosphere, land surfaces, aerosols, and sea ice.[62] Ocean
Ocean
models make use of a branch of physics, geophysical fluid dynamics, that describes the large-scale flow of fluids such as seawater.[63]

Surface currents: red–warm, blue–cold

Surface currents only affect the top few hundred meters (yards) of the sea, but there are also large-scale flows in the ocean depths caused by the movement of deep water masses. A main deep ocean current flows through all the world's oceans and is known as the thermohaline circulation or global conveyor belt. This movement is slow and is driven by differences in density of the water caused by variations in salinity and temperature.[64] At high latitudes, the water is chilled by the low atmospheric temperature and becomes saltier as sea ice crystallizes out. Both these factors make it denser and the water sinks. From the deep sea near Greenland, such water flows southwards between the continental landmasses on either side of the Atlantic. When it reaches the Antarctic, it is joined by further masses of cold, sinking water and flows eastwards. It then splits into two streams that move northwards into the Indian and Pacific Oceans. Here it is gradually warmed, becomes less dense, rises towards the surface, and loops back on itself. Some flows back into the Atlantic. It takes a thousand years for this circulation pattern to be completed.[61]

The global conveyor belt shown in blue with warmer surface currents in red

Besides gyres, there are temporary surface currents that occur under specific conditions. When waves meet a shore at an angle, a longshore current is created as water is pushed along parallel to the coastline. The water swirls up onto the beach at right angles to the approaching waves but drains away straight down the slope under the effect of gravity. The larger the breaking waves, the longer the beach, and the more oblique the wave's approach, the stronger the longshore current is.[65] These currents can shift great volumes of sand or pebbles, create spits, and make beaches disappear and water channels silt up.[61] A rip current can occur when water piles up near the shore from advancing waves and is funnelled out to sea through a channel in the seabed. It may occur at a gap in a sandbar or near a man-made structure such as a groyne. These strong currents can have a velocity of 1 m/s (3.3 ft/s), can form at different places at different stages of the tide, and can carry away unwary swimmers.[66] Temporary upwelling currents occur when the wind pushes water away from the land and deeper water rises to replace it. This cold water is often rich in nutrients and creates blooms of phytoplankton and a great increase in the productivity of the sea.[61]

Basins[edit] Main article: Ocean
Ocean
basin

Three types of plate boundary

Bathymetry
Bathymetry
is the mapping and study of the topography of the ocean floor. Methods used for measuring the depth of the sea include single or multibeam echosounders, laser airborne depth sounders and the calculation of depths from satellite remote sensing data. This information is used for determining the routes of undersea cables and pipelines, for choosing suitable locations for siting oil rigs and offshore wind turbines and for identifying possible new fisheries.[67] The Earth
Earth
is composed of a magnetic central core, a mostly liquid mantle, and a hard rigid outer shell (or lithosphere), which is composed of the Earth's rocky crust and the deeper and mostly solid outer layer of the mantle. The crust below land is known as continental while that under the abyssal sea is called oceanic. The latter is composed of relatively dense basalt and is some five to ten kilometers (three to six miles) thick. The relatively thin lithosphere floats on the weaker and hotter mantle below and is fractured into a number of tectonic plates.[68] In mid-ocean, magma is constantly being thrust through 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 is also produced and magma is forced up, creating underwater mountains, some of which grow into volcanic islands. Near some 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.[69][70] The Earth's deepest trench is the Mariana Trench
Mariana Trench
which extends for about 2,500 kilometers (1,600 mi) across the seabed. It is near the Mariana Islands, a volcanic archipelago in the West Pacific. Though it averages just 68 km (42 mi) wide, its deepest point is 10.994 kilometers (nearly 7 miles) below the surface of the sea.[71] An even longer trench runs alongside the coast of Peru and Chile, reaching a depth of 8,065 m (26,460 ft) and extending for approximately 5,900 km (3,700 mi). It occurs where the oceanic Nazca Plate
Nazca Plate
slides under the continental South American Plate and is associated with the upthrust and volcanic activity of the Andes.[72]

Coasts[edit] Main article: Coast 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.[73] 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—is a bay; a small bay with a narrow inlet is a cove and a large bay or bay-shaped sea may be referred to as a gulf.[74] Coastlines are influenced by a number of 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 the shore at the rate of six to eight per minute. 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 their swash moves beach material seawards. Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide, 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. Along with other weathering processes such as frost, this tends to undercut the cliff. Gradually, a wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion.[73] Material worn from the margins of the land eventually ends up in the sea, where it is subject to attrition as currents flowing parallel to the coast scour out channels and transport material away from its place of origin. Sediment carried to the sea by rivers settles on the seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides, and currents.[73] Dredging
Dredging
removes material and deepens channels but may have unexpected effects elsewhere on the coastline. Governments make efforts to prevent flooding through building breakwaters, seawalls, and other defenses against the sea. In Britain, the Thames Barrier
Thames Barrier
protects London
London
from storm surges,[75] while the failure of the dykes and levees around New Orleans
New Orleans
during Hurricane
Hurricane
Katrina created a humanitarian crisis in the United States. Land
Land
reclamation in Hong Kong permitted the construction of Hong Kong International Airport through the leveling and expansion of two smaller islands.[76] Following the adoption of the present UNCLOS, the coastline under international law is a state's baseline, which is generally but not always equivalent to its low-water line.[77] Sea
Sea
level[edit]

Variations in sea level around the world (1992) from −1.4 m (light violet) to +1.0 m (light pink).

Main article: Sea
Sea
level Over most of geologic time, the sea level has been higher than it is today.[8](p74) The main factor affecting sea level over time is the result of changes in the oceanic crust, with a downward trend expected to continue in the very long term.[78] At the last glacial maximum some 20,000 years ago, the sea level was 120 meters (390 ft) below its present-day level. For at least the last 100 years, the sea level has been rising at an average rate of about 1.8 mm (0.071 in) per year.[79] Most of this rise can be attributed to an increase in the temperature of the sea and the resulting slight thermal expansion of the upper 500 m (1,600 ft) of water. Additional contributions, as much as one quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human needs.[80] The rising trend from global warming is expected to continue until at least the end of the 21st century.[81]

Water
Water
cycle[edit] Main article: Water
Water
cycle The sea plays a part in the water cycle, in which water evaporates from the ocean, travels through the atmosphere as vapor, condenses, falls (usually as rain or snow) again, and then largely returns to the sea.[82] Even in the Atacama Desert, where little rain ever falls, dense clouds of fog known as the camanchaca blow in from the sea and support plant life.[83] In large land masses, geologic features can block the access of some regions to the main sea. These endorheic basins, particularly in central Asia, sometimes build up permanent salt lakes as inflowing waters evaporate and their dissolved minerals accumulate over time. The largest of these is the Caspian Sea, although it is sometimes counted as a proper sea owing to its basin of (now-landlocked) oceanic crust. Other notable examples include the Aral Sea
Aral Sea
in central Asia
Asia
and the Great Salt
Salt
Lake
Lake
in the western United States.[84] The waters of these basins still eventually return to the sea through evaporation, the flow of ground water, and (over geologic time) the opening up of the basins by continental drift.

Carbon cycle[edit] Main article: Oceanic carbon cycle Oceans contain the greatest quantity of actively-cycled carbon in the world and are second only to the lithosphere in the amount of carbon they store.[85] The oceans' surface layer holds large amounts of dissolved organic carbon that is exchanged rapidly with the atmosphere. The deep layer's concentration of dissolved inorganic carbon is about 15 percent higher than that of the surface layer[86] and it remains there for much longer periods of time.[87] Thermohaline circulation exchanges carbon between these two layers.[85] Carbon enters the ocean as atmospheric carbon dioxide dissolves into the surface layers and is converted into carbonic acid, carbonate, and bicarbonate: CO2 (aq) + H2O ⇌ H2CO3 ⇌ HCO3− + H+ ⇌ CO32− + 2 H+. The process liberates hydrogen ions (H+), decreasing ocean pH and increasing its acidity. It can also enter as dissolved organic carbon through rivers and is converted by photosynthetic organisms into organic carbon. This can either be exchanged throughout the food chain or precipitated into the deeper, more carbon-rich layers as dead soft tissue or in shells and bones as calcium carbonate. It circulates in this layer for long periods of time before either being deposited as sediment or being returned to surface waters through thermohaline circulation.[87]

Acidification[edit] Main article: Ocean
Ocean
acidification Seawater
Seawater
is slightly alkaline and had a preindustrial pH of about 8.2. More recently, anthropogenic activities have steadily increased the carbon dioxide content of the atmosphere; about 30–40% of the added CO2 is absorbed by the oceans, forming carbonic acid and lowering the pH (now below 8.1[88]) through a process called ocean acidification.[89][90][91] The pH is expected to reach 7.7 (representing a 3-fold increase in hydrogen ion concentration) by the year 2100, which is a significant change in a century.[92][g] One important element for the formation of skeletal material in marine animals is calcium, but calcium carbonate becomes more soluble with pressure, so carbonate shells and skeletons dissolve below its compensation depth.[94] Calcium
Calcium
carbonate also becomes more soluble at lower pH, so ocean acidification is likely to have profound effects on marine organisms with calcareous shells, such as oysters, clams, sea urchins, and corals,[95] because their ability to form shells will be reduced,[96] and the carbonate compensation depth will rise closer to the sea surface. Affected planktonic organisms will include the snail-like molluscs known as pteropods, and single-celled algae called coccolithophorids and foraminifera. All of these are important parts of the food chain and a diminution in their numbers will have significant consequences. In tropical regions, corals are likely to be severely affected as it becomes more difficult to build their calcium carbonate skeletons,[97] in turn adversely impacting other reef dwellers.[92] The current rate of ocean chemistry change appears to be without precedent in Earth's geological history, making it unclear how well marine ecosystems will be able to adapt to the shifting conditions of the near future.[98] Of particular concern is the manner in which the combination of acidification with the expected additional stressors of higher temperatures and lower oxygen levels will impact the seas.[99]

Marine life[edit]

A map of mean surface chlorophyll a (1998–2006), from 0.03 (light violet) to 30 mg chl per m³ (dark red) on a logarithmic scale.

Main article: Marine life The oceans are home to a diverse collection of life forms that use it as a habitat. Since sunlight illuminates only the upper layers, the major part of the ocean exists in permanent darkness. As the different depth and temperature zones each provide habitat for a unique set of species, the marine environment as a whole encompasses an immense diversity of life.[100] Marine habitats
Marine habitats
range from surface water to the deepest oceanic trenches, including coral reefs, kelp forests, seagrass meadows, tidepools, muddy, sandy and rocky seabeds, and the open pelagic zone. The organisms living in the sea range from whales 30 meters (100 ft) long to microscopic phytoplankton and zooplankton, fungi, bacteria and viruses, including recently discovered marine bacteriophages which live parasitically inside bacteria.[101] Marine life
Marine life
plays an important part in the carbon cycle as photosynthetic organisms convert dissolved carbon dioxide into organic carbon and it is economically important to humans for providing fish for use as food.[102][103](pp204–29) Life may have originated in the sea and all the major groups of animals are represented there. Scientists differ as to precisely where in the sea life arose: the Miller-Urey
Miller-Urey
experiments suggested a dilute chemical "soup" in open water, but more recent suggestions include volcanic hot springs, fine-grained clay sediments, or deep-sea "black smoker" vents, all of which would have provided protection from damaging ultraviolet radiation which was not blocked by the early earth's atmosphere.[8](pp138–40) Habitats[edit] Main article: Marine habitats

Marine habitats

Littoral zone Intertidal zone Estuaries Kelp
Kelp
forests Coral
Coral
reefs Ocean
Ocean
banks Continental shelf Neritic zone Straits Pelagic
Pelagic
zone Oceanic zone Seamounts Hydrothermal vents Cold seeps Demersal zone Benthic zone

v t e

Marine habitats
Marine habitats
can be divided horizontally into coastal and open ocean habitats. Coastal habitats extend from the shoreline to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only 7 percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf. Alternatively, marine habitats can be divided vertically into pelagic (open water), demersal (just above the seabed), and benthic (sea bottom) habitats. A third division is by latitude: from tropical to temperate to polar waters.[8](pp150f) Coral
Coral
reefs, the so-called "rainforests of the sea", occupy less than 0.1 percent of the world's ocean surface, yet their ecosystems include 25 percent of all marine species.[104] The best-known are tropical coral reefs such as Australia's Great Barrier Reef, but cold water reefs harbor a wide array of species including corals (only six of which contribute to reef formation).[8](pp204–07)[105]

Algae
Algae
and plants[edit] Main article: Algae Marine primary producers—plants and microscopic organisms in the plankton—are widespread and very diverse. Microscopic photosynthetic algae, phytoplankton, contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined. About 45 percent of the sea's primary production of living material is contributed by diatoms.[106] Much larger algae, commonly known as seaweeds, are important locally; Sargassum forms floating drifts, while kelp form seabed forests.[103](pp246–55) Flowering plants in the form of seagrasses grow in "meadows" in sandy shallows,[107] mangroves line the coast in tropical and subtropical regions,[108] and salt-tolerant plants thrive in regularly inundated salt marshes.[109] All of these habitats are able to sequester large quantities of carbon and support a biodiverse range of larger and smaller animal life.[110] Light is only able to penetrate the top 200 m (660 ft) so this is the only part of the sea where plants can grow.[34] The surface layers are often deficient in biologically-active nitrogen compounds. The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen, its assimilation, nitrification, anammox, and denitrification.[111] Some of these processes take place in deep water so that where there is an upwelling of cold waters or near estuaries where land-sourced nutrients are present, plant growth is higher. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal.[8](pp160–63)

Animals and other life[edit] Further information: Marine zoology

Marine habitats
Marine habitats
such as coral reefs hold a diversity of species including starfish, corals and fish.

There is a broader spectrum of higher animal taxa in the sea than on land, many marine species have yet to be discovered, and the number known to science is expanding annually.[112] Some vertebrates such as seabirds, seals, and sea turtles return to the land to breed but fish, cetaceans, and sea snakes have a completely aquatic lifestyle and many invertebrate phyla are entirely marine. In fact, the oceans teem with life and provide many varying microhabitats.[112] One of these is the surface film which—despite being tossed about by the movement of waves—provides a rich environment and is home to bacteria, fungi, microalgae, protozoa, fish eggs, and various larvae.[113] The pelagic zone contains macro- and microfauna and myriad zooplankton which drift with the currents. Most of the smallest organisms are the larvae of fish and marine invertebrates which liberate eggs in vast numbers because the chance of any one embryo surviving to maturity is so minute.[114] The zooplankton feed on phytoplankton and on each other and form a basic part of the complex food chain that extends through variously-sized fish and other nektonic organisms, which are in turn eaten by larger squids, sharks, porpoises, dolphins, and whales.[115] Some marine creatures make large migrations, either to other regions of the ocean on a seasonal basis or up and down its vertical layers, often ascending to feed at night before descending to safety by day.[116] Ships can introduce or spread invasive species through the discharge of ballast water or through the transport of organisms that have accumulated as part of the fouling community on the hulls of vessels.[117] The demersal zone supports many animals that feed on benthic organisms or seek protection from predators. The seabed provides a range of habitats on or under the surface of the substrate which are used by creatures adapted to these conditions. The tidal zone with its periodic exposure to dehydrating air is home to barnacles, molluscs, and crustaceans. The neritic zone has many organisms that need light to flourish. Here, sponges, echinoderms, polychaete worms, sea anemones, and other invertebrates live among algal-encrusted rocks. Corals often contain photosynthetic symbionts and live in shallow waters where light penetrates. The extensive calcareous skeletons they extrude build up into coral reefs which are an important feature of the seabed. These provide a diverse habitat for reef dwelling organisms. There is less sea life on the floor of deeper seas but marine life also flourishes around seamounts that rise from the depths, where fish and other animals congregate to spawn and feed. Close to the seabed live demersal fish that largely feed on pelagic organisms or benthic invertebrates.[118] Exploration of the deep sea by submersibles revealed a new world of creatures living on the seabed that scientists had not previously expected. Some like the detritivores rely on organic material falling to the ocean floor. Others cluster round deep-sea hydrothermal vents where mineral-rich flows of water emerge, supporting communities whose primary producers are sulphide-oxidizing chemoautotrophic bacteria and whose consumers include specialized bivalves, sea anemones, barnacles, crabs, worms, and fish.[8](p212) A dead whale sinking to the bottom of the ocean provides food for an assembly of organisms which similarly rely largely on the actions of sulphur-reducing bacteria. Such places support unique biomes where many new microbes and other lifeforms have been discovered.[119]

Humans and the sea[edit]

A 19th-century illustration of Columbus's 'discovery' (to the western world) of the Americas
Americas
on 12 October 1492, displaying how even historical explorers could be mythologized both at home and abroad.

Navigation
Navigation
and exploration[edit] Main: Ancient maritime and maritime history, the history of navigation and cartography, and list of first human settlements. Humans have travelled the sea since prehistoric times, originally on rafts and in dugout, reed, and bark canoes. Most of the early human migrations occurred over land: even areas now separated by open sea such as the Americas, Japan, and Britain were accessible by land bridges or fast ice during the last ice age. However, the dwarf Flores man probably needed to cross a 19-kilometer (12 mi) wide strait from Sundaland
Sundaland
to reach Komodo[120] and, although the exact details remain uncertain, the ancestors of Australia's Aborigines must have crossed the broader deep-sea Wallace Line
Wallace Line
to Near Oceania tens of thousands of years ago.[h] Despite earlier theories, modern bathymetric soundings now suggest that even the earliest settlement of the Philippines required crossing deep water at the Mindoro Strait
Strait
or the Sibutu Passage. The hunter-gatherer Ortoiroid people began spreading through the Caribbean from Venezuela's Orinoco valley by at least the 6th millennium BC. Around the same time, Mesopotamians were using bitumen to caulk their reed boats and, a little later, masted sails.[124] Lothal
Lothal
in India boasted the earliest known dock around 2400 BC.[125] By c. 2000 BC, Austronesians
Austronesians
on Taiwan had begun spreading into maritime Southeast Asia.[126][127][128] From 1300 to 900 BC, the Austronesian "Lapita" peoples displayed great feats of navigation, reaching out from the Bismarck Archipelago
Archipelago
to as far away as Fiji, Tonga, and Samoa.[129] Their descendants continued to travel thousands of miles between tiny islands on outrigger canoes:[130] the Austronesians
Austronesians
of the Sunda Islands
Sunda Islands
settled Madagascar
Madagascar
off southeast Africa
Africa
before AD 500 and the Polynesians
Polynesians
settled the Hawaiian islands before 800,[131] Easter Island
Easter Island
before 1200,[132] and New Zealand shortly after.[133] The Egyptian pharaoh Necho II
Necho II
initiated construction on a canal which eventually linked the Mediterranean and Red
Red
Seas around 600 BC. Herodotus
Herodotus
records Egyptian claims that he also commissioned a 3-year-long expedition which circumnavigated Africa from the Red Sea
Red Sea
to the Nile delta.[134][i] Around 500 BC, the Carthaginian navigator Hanno left a detailed periplus of an Atlantic journey that reached at least Senegal
Senegal
and possibly Mount Cameroon;[136][137] and the Greek Pytheas
Pytheas
left another exploring the seas around Great Britain
Great Britain
around 325 BC. The massive 3rd-century BC Lighthouse of Alexandria
Lighthouse of Alexandria
was considered one of the Seven Wonders of the World.[138] In the 2nd century, the Alexandrian Ptolemy
Ptolemy
mapped the known world, using the "Fortunate Isles" as his prime meridian and including details as distant as the Gulf of Thailand. A modified form was used by Columbus for his voyages.[139] In the Mediaeval era, the Vikings
Vikings
used clinker-built ships to colonize Iceland, Greenland, Canada, and Russia.[8](pp12f) A compass showing magnetic north is first attested—in the form of a "south-pointing spoon"—in the 1st-century Chinese Lunheng. The first evidence of its use in Chinese maritime navigation, however, dates to Zhu Yu's c. 1115 Pingzhou Table Talks. Alexander of Neckham's De naturis rerum, the first European mention of a magnetized needle, dates to 1190 and immediately notes its use among sailors. Latitude
Latitude
(the ship's position ranging from 0° at the equator to 90° north and south) could be determined by inclinometers—including the astrolabe, sextant, and Jacob's staff—measuring the angle between the horizon and heavenly bodies like the sun or moon. Accurately determining longitude (the ship's position east or west of some fixed point) proved much harder.[140]

Gerardus Mercator's world map of 1569. The coastline of the Old World is quite accurately depicted, despite the great distortions of this projection in the polar regions and the uncertain information about the Americas.

In the 15th century, West European mariners—beginning with Portugal—started making still longer voyages of exploration, using improvements on translated Islamic star charts and a variation on African fishing boats called the caravel. In 1473, Lopes Gonçalves crossed the equator and disproved the Aristotelian notion that a ring of fire would bar exploration of the southern hemisphere. Bartolomeu Dias rounded the Cape of Good Hope
Cape of Good Hope
in 1487; in 1498, Vasco da Gama reached Malindi, where a local pilot showed him how to follow the monsoon to India. In 1492, relying on incorrect estimates of the circumference of the Earth, the Genovese Christopher Columbus
Christopher Columbus
sailed from Cadiz
Cadiz
to the Canaries and thence into the open Atlantic in a Spanish attempt to reach the Orient. Instead, he made landfall on an island in the Caribbean Sea. The resulting Columbian Exchange introduced potatoes, corn, and chili peppers to the Old World
Old World
while smallpox epidemics devastated the indigenous peoples of the Americas. This disruption and depopulation permitted rapid Spanish conquests and led to the widespread adoption of African slavery to man lucrative tobacco, sugar, indigo, and cotton plantations. In 1519, Juan Sebastián Elcano completed Magellan's Spanish expedition to sail around the world.[8](pp12f) These and other voyages permitted European maps to attain a previously impossible degree of accuracy. In 1538, Gerardus Mercator
Gerardus Mercator
devised a map projection conveniently making constant bearings (rhumb lines) straight.[8](pp12f) In the Arctic, in 1594, the Dutch captain Willem Barentsz
Willem Barentsz
reached Svalbard
Svalbard
and the Barents Sea
Barents Sea
while, in the south, Anthony de la Roché
Anthony de la Roché
crossed the Antarctic Convergence
Antarctic Convergence
in 1675 and three separate expeditions—one British, one American, and one Russian—all claimed to have discovered Antarctica
Antarctica
in 1820.[141][142][143] Not all voyages of discovery originated in Western Europe. Although accurate charting of the coasts of Russia only began in the 18th century and the archipelago of Severnaya Zemlya
Severnaya Zemlya
was not discovered until 1910,[144] Novgorodians had been sailing the White Sea
White Sea
since at least the 13th century.[145] Despite a long-standing preference for autarky, China briefly opened up under the Song and Mongol Yuan dynasties. In the early 15th century, Zheng He's fleet of treasure ships repeatedly sailed from Ming China with 37,000 men aboard 317 ships, reaching as far as the African coast.[8](pp12f) Chinese exploration, however, was soon curtailed again and finally outlawed. The peoples of East Asia were introduced to the true shape of the other continents from the maps of Matteo Ricci. Meanwhile, the determination of longitude continued to involve approximations and guesswork: its true calculation required an accurate clock which permitted comparison between noon aboard ship and the exact time at a fixed point, such as the Royal Observatory at Greenwich. Great Britain's Longitude prize
Longitude prize
was effectively awarded in 1773 to the self-educated John Harrison
John Harrison
for his sea watch of 1761. James Cook
James Cook
used a copy of this on his second and third voyages, which studied the Pacific[146] and inspired studies from Russia, France, the Netherlands, and the United States.[8](p15) The completion of a submarine telegraphic cable across the English Channel
English Channel
in 1850 and subsequent links of the All Red
Red
Line led to greater interest in the deep sea. Earlier ideas that no life could exist below 300 fathoms (550 meters or 1,800 feet) were disproved in 1860 when a Mediterranean line failed and was pulled up from depths four times lower, completely encrusted with marine life.[147] Michael Sars's discovery of "living fossils" deep in Norway's fjords helped spur British efforts including HMS Challenger’s expedition during the 1870s[148] that effectively created modern oceanography.[8](p15) From 1878 to 1880, the SS Vega successfully completed the Northeast Passage
Northeast Passage
and went on to circumnavigate Eurasia
Eurasia
for the first time. During the mid-1890s, Fridtjof Nansen
Fridtjof Nansen
used a specially-designed ship to drift through the northern pack ice, establishing that the Arctic
Arctic
was an open sea. In 1898 and 1899, Carl Chun
Carl Chun
raised and studied many new life forms from over 4,000 m (13,000 ft) below the surface of the South Atlantic. In the 20th century, the Gjøa
Gjøa
was the first vessel to accomplish the Northwest Passage
Northwest Passage
in 1906. From 1921, the International Hydrographic Organization in Monaco
Monaco
has standardized surveying and charting of the sea[149] and, from 1924, the Discovery Investigations
Discovery Investigations
studied whales and mapped the seas around Antarctica.[21] The spherical Bathysphere was able to descend to 434 meters (1,424 ft) in 1930 on a cable[150] and, in the 1940s, Jacques Cousteau
Jacques Cousteau
helped develop the first successful scuba gear and popularize underwater diving. The Cold War and oil exploration funded further deep sea research: by 1960, the self-powered Trieste could take her crew 10,915 m (35,810 ft) into the Mariana Trench[151] and a US Navy
US Navy
diver in an atmospheric diving suit reached 2,000 feet (610 m) below sea level in 2006.[152] Today, the American Global Positioning System
Global Positioning System
(GPS) enables accurate navigation worldwide using over thirty satellites and message timing so exact as to involve general relativity.[146] Ongoing oceanographic research includes marine lifeforms, conservation, the marine environment, the chemistry of the ocean, the studying and modelling of climate dynamics, the air-sea boundary, weather patterns, ocean resources, renewable energy, waves and currents, and the design and development of new tools and technologies for investigating the deep.[153] Researchers make use of satellite-based remote sensing for surface waters, with research ships, moored observatories and autonomous underwater vehicles to study and monitor all parts of the sea.[154]

Trade[edit] Main articles: Shipping
Shipping
and Trade

Shipping
Shipping
routes, showing relative density of commercial shipping around the world

Water-borne trade has been practiced since at least the dawn of civilization, when Sumeria was connected to Harappan India.[155] Around 2000 BC, the Minoans of Crete
Crete
established the earliest thalassocracy, a maritime empire heavily dependent upon its trade and naval power.[156] The city-states of the Phoenicians
Phoenicians
and Greeks then replaced them in the centuries after 1200 BC, ultimately establishing far-flung colonial empires which spread from the Sea of Azov
Sea of Azov
to the Atlantic coast of Morocco.[157] Under the Romans, commerce continued to thrive. In the first centuries BC, steppe nomads' interruption of India's access to Siberian gold caused them to open up maritime routes to Malaysia
Malaysia
and Indonesia,[158] exposing them first to Hindu
Hindu
and then Muslim
Muslim
traders. With the collapse of the Roman Empire, European trade dwindled but it continued to flourish elsewhere.[159] The Tamil Chola dynasty thrived on trade between Tang China, the Javanese Srivijaya Empire, and the Abbasid Caliphate
Abbasid Caliphate
in the west. Following further conquests, Arabians came to dominate maritime trade in the Indian Ocean, spreading Islam
Islam
along the East African coast and, eventually, Southeast Asia.[160] A major effect of the Age of Discovery
Age of Discovery
was the unification of the world's regional trade networks into a single world market, largely run by and for the European monarchs and the merchants of Amsterdam, London, and other Atlantic ports. From the 16th to the 19th centuries, about 13 million people were shipped across the Atlantic to be sold as slaves in the Americas.[161] The Hales Trophy was an award for the fastest commercial crossing of the Atlantic and was won by the SS United States
SS United States
in 1952 for a crossing that took three days, ten hours, and forty minutes.[162] Nowadays, large quantities of goods are transported by sea, especially across the Atlantic and around the Pacific Rim. A major trade route passes through the Pillars of Hercules, across the Mediterranean and the Suez Canal
Suez Canal
to the Indian Ocean
Ocean
and through the Straits of Malacca; much trade also passes through the English Channel.[163] Shipping lanes are the routes on the open sea used by cargo vessels, traditionally making use of trade winds and currents. Over 60 percent of the world's container traffic is conveyed on the top twenty trade routes.[164] Increased melting of Arctic
Arctic
ice since 2007 enables ships to travel the Northwest Passage
Northwest Passage
for some weeks in summer, avoiding the longer routes via the Suez Canal
Suez Canal
or the Panama Canal.[165] Shipping
Shipping
is supplemented by air freight, a more expensive process mostly used for particularly valuable or perishable cargoes. Seaborne trade carries more than US $4 trillion worth of goods each year.[166] There are two main kinds of freight, bulk cargo and break bulk or general cargo, most of which is now transported in containers. Commodities in the form of liquids, powder or particles are carried loose in the holds of bulk carriers and include oil, grain, coal, ore, scrap metal, sand and gravel. Break bulk cargo
Break bulk cargo
is usually manufactured goods and is transported in packages, often stacked on pallets. Before the arrival of containerization in the 1950s, these goods were loaded, transported and unloaded piecemeal.[167] The use of containers has greatly increased the efficiency and decreased the cost of moving them[168] with most freight now traveling in standard sized, lockable containers loaded on purpose-built container ships at dedicated terminals.[169][169] Freight forwarding firms book cargo, arrange pickup and delivery, and manage documentation.[170] The safety of shipping is regulated by the International Maritime Organization, based in London
London
and first convened in 1959. Its objectives include developing and maintaining a regulatory framework for shipping, maritime safety, environmental concerns, legal matters, technical co-operation and maritime security.[171]

Fishing[edit] Main articles: Seafood, Fishing, Aquaculture, and Whaling

19th-century Brixham trawlers at work.

Spearfishing
Spearfishing
with barbed harpoons along the sea coast was widespread by the Palaeolithic.[172] Fish
Fish
ponds surrounded Sumerian temples by 2500 BC and a Chinese classical text credited to the 5th-century BC businessman Fan Li[173] is the earliest known work on fish farming.[174] A surviving fragment of Isidore of Charax's 1st-century Parthian itinerary describes locals freediving for pearls in the Persian Gulf,[175] and Oppian's 2nd-century Halieutics relates the four main Greek and Roman fishing methods as hook-and-line, netting, passive traps, and trident.[176] Traditional fishing boats operate in near-shore waters but, during the late Middle Ages
Middle Ages
and early Modern period, fishing on the open sea—particularly cod—became important to the economic and naval development of Northern Europe, New England, and Canada.[177] Overfishing
Overfishing
along the coasts of the North Sea
North Sea
spurred the development of deep-sea fishers such as the Brixham[178] and otter trawlers, which might serve as motherships for longlining dories;[179] in the 19th century, advances such as rail transport, canning, and refrigeration allowed fishing to become a full-fledged industry. Improvements in sonar during the world wars were adapted as fishfinders and, during the 1950s, great factory ships caught and processed as many fish in an hour as earlier trawlers had in a season.[179] By the 1960s, the North Atlantic and North Pacific fisheries were close to maximal exploitation. After the catch from wild marine fisheries grew from 18 million metric tons (20 million tons) in 1950 to around 85 million metric tons (​93 1⁄2 million tons) by the late 1980s, it has remained essentially constant since.[180][j] Chinese economic reform
Chinese economic reform
led to massive growth of its fishing production, from 7% of the world total in 1961 to 35% by 2010.[180] Scientific studies of population dynamics and nationalization of formerly shared waters are both helping to cope with overexploitation but the success of modern commercial fishing has required major corrective actions: the collapse of the Grand Banks cod fishery to less than 1% of its historic levels required a complete moratorium by Canada in 1992[181] and China has enforced a zero-growth policy in its wild catch since 2000, redirecting its industry towards aquaculture;[182] its annual months-long bans on fishing in disputed areas of the South China Sea
South China Sea
is enforced over the protest of neighboring states.[183]

The whale factory vessel Tonan Maru №2 was torpedoed four times but repaired or raised each time.[184] Built to Norwegian design, the Japanese whaling fleet provided half of the country's meat supply during its American occupation and remains the world's most active. Similar whalers in Europe
Europe
inspired present-day fish processing ships.[179]

As of 2006, there were an estimated 43.5 million people involved in capturing or raising seafood, 85.5% of whom lived in Asia. About ​ 3⁄4 were fishers and the remainder fish farmers.[185] In 2012, total global production of fish, crustaceans, molluscs, and other aquatic animals was a record 158 million metric tons (174 million tons), of which 91.3 million metric tons (100 million tons) were caught in the wild.[186] This is also a record if ignoring the Peruvian anchovy,[186] whose population can vary dramatically with the El Niño
El Niño
cycle.[187][188] The overall trend remains increasing, but due to expanding aquaculture in inland waters and mariculture in the sea rather than higher catches in the wild. The exclusive economic zones around coastal countries under the UNCLOS regime have permitted states to institute quota and other management systems[189] over the most productive regions of the sea, accounting for around 87% of the annual harvest.[190] The results are sometimes dramatic—the lull in fishing over the course of the First World War
First World War
saw the North Sea's 1919 catch double 1913's[179]—and sometimes much less so: two decades on, the levels of cod in the Grand Banks remain only 10% of their peak. At present, the species most frequently landed are herring, cod, anchovy, tuna, flounder, mullet, squid, and salmon. A number of these, as well as large predatory fish,[191] remain well below historical levels.[192]

A purse seiner hauling in around 360 metric tons (400 tons) of mackerel off Peru.

Over 3 million vessels are employed in sea fishing.[190] Modern fishing vessels include fishing trawlers with a small crew, stern trawlers, purse seiners, long-line factory vessels, and large factory ships which are designed to stay at sea for weeks, processing and freezing great quantities of fish. The equipment used to capture the fish may be purse seines, other seine, trawls, dredges, gillnets, and long-lines. The Food and Agriculture Organization
Food and Agriculture Organization
of the United Nations is encouraging the development of local fisheries to provide food security to coastal communities and help alleviate poverty.[193]

Salmon
Salmon
pens off Vestmanna
Vestmanna
in the Faroes.

As well as the wild stock, about 79 million metric tons (87 million tons) of food and non-food products were produced by sea farming in 2010, an all-time high. About six hundred species of plants and animals were cultured, some for use in seeding wild populations. The animals raised included finfish, aquatic reptiles, crustaceans, molluscs, sea cucumbers, sea urchins, sea squirts, and jellyfish.[194] Integrated mariculture has the advantage that there is a readily-available supply of planktonic food and waste is removed naturally;[195] in cases where the waste would otherwise be harmful, multi-species techniques can used to, e.g., feed farmed shellfish from the waste being produced by farmed salmon. Various methods are employed. Mesh enclosures for finfish can be suspended in the open seas, cages can be used in more sheltered waters, or ponds can be refreshed with water at each high tide. Shrimps can be reared in shallow ponds connected to the open sea.[196] Ropes can be hung in water to grow algae, oysters, and mussels. Oysters can be reared on trays or in mesh tubes. Sea
Sea
cucumbers can be ranched on the seabed.[197] Captive breeding programmes have raised lobster larvae for release of juveniles into the wild resulting in an increased lobster harvest in Maine.[198] At least 145 species of seaweed—red, green, and brown algae—are eaten worldwide, some long farmed in Japan and other Asian countries; there is great potential for additional algaculture.[199] Few maritime flowering plants are widely used for food but one example is marsh samphire, which is eaten both raw and cooked.[200] A major difficulty for aquaculture is the tendency towards monoculture and the associated risk of widespread disease. In the 1990s, disease wiped out China's farmed Farrer's scallop and white shrimp and required their replacement by other species.[201] Shrimp farming has also caused the destruction of important mangrove forests throughout southeast Asia.[202]

Law[edit] Main articles: Admiralty law and Law
Law
of the Sea Admiralty law is the particular body of national laws applied to maritime questions and offenses, as the uncertainty of sea voyages has caused the sea to be viewed as a unique jurisdiction since antiquity. Rhodian, Roman, Byzantine, Trani, and Amalfian laws were important influences on the French, Genovese, and Hanseatic codes which established the first English courts of admiralty. Unlike the usual English common law system, the courts of admiralty hewed closer to Continental practice, leaving it open for abuse that contributed to the American Revolution.[204] The adoption of its present constitution reintroduced admiralty law to the United States, but with a relatively larger sphere for trials by jury. The Law of the Sea is the particular body international law applied to maritime questions and offenses. Empires such as Rome and China long claimed universal jurisdiction; during the Middle Ages, Italian maritime republics such as Venice and Genoa recognized the existence of rival states but claimed the right to close the seas to their traffic. Portuguese and Spanish pursuit of similar rights over new seas and lands during the Age of Discovery
Age of Discovery
and papal support of their claims was a factor in the Wars of Religion; in 1609, a jurist hired to defend a lucrative act of piracy by the Dutch East India Company penned Mare Liberum,[205] an argument in favor of freedom of the seas that ultimately produced the compromise[206] that territory extended as far as land-based cannonshot could reach, standardized to 3 nautical miles (5,556 m or 18,228 ft), and that everything beyond was international waters.[207] President Woodrow Wilson
Woodrow Wilson
argued this principle as part of United States's entrance into World War I and as one of his Fourteen Points
Fourteen Points
afterwards; nonetheless, President Harry S. Truman's unilateral claim of jurisdiction over the oil reserves of America's continental shelf in 1945[208] directly led to the end of the regime.[207] The three rounds of the United Nations' conferences on the Law of the Sea eventually reshaped international maritime law but the United States has not ratified the present treaty but instead adopted its policies piecemeal via presidential proclamations. The present Convention on the Law of the Sea (UNCLOS) was drafted in 1982 and came into force in 1994.[77] It states that "the high seas are open to all states, whether coastal or land-locked" and provides a non-exhaustive list of freedoms including navigation, overflight, the laying of submarine cables, the building of artificial islands, fishing, and scientific research.[209] It extended territorial waters up to 12 nautical miles (22.2 km or 13.8 mi) from a baseline generally (but not always) equivalent to the low-water line; this area is subject to national laws but free to both innocent and transit passage. (The "internal waters" landward of the baseline are solely under national control.) A "contiguous zone" of a further 12 nmi are permitted for hot pursuit of vessels charged with violating customs, taxation, immigration, or pollution laws in the territorial waters. An "exclusive economic zone" or EEZ places all exploitation of marine life and minerals within 200 nmi (370 km or 230 mi) of the baseline under national supervision. For legal purposes, the "continental shelf" is considered to be the actual continental shelf (to a depth of 200 m or 660 ft) contiguous to the baseline or 200 nmi, whichever is greater; the marine life and minerals "attached to" (or below) the seabed within this area also fall under national supervision.[207] Ships may cross numerous time zones on a voyage, so nautical time, introduced in the 1920s, is used in international waters. Each such zone is uniformly 15 degrees of longitude wide, the ship's clock going forward one hour per zone when travelling eastwards.[210]

War[edit]

A Byzantine galley using Greek fire
Greek fire
against rebel ships in the 9th century.

Main articles: Naval warfare, maritime geography, and list of naval battles Since the development of coordinated fleets of ships capable of landing an invasion force, naval warfare has been an important aspect in the defense (or conquest) of maritime states. The first naval battle in recorded history saw Suppiluliuma II
Suppiluliuma II
of the Hittites
Hittites
burn a Cypriot fleet at sea in 1210 BC.[211] Shortly after, the fleets of the Sea Peoples
Sea Peoples
disrupted the entire Eastern Mediterranean: over a period of about 50 years, raids and invasions violently destroyed nearly every coastal city between Pylos
Pylos
and Gaza.[212] As empires grew and their armies became too large to live off the lands through which they passed, disruption of their supply fleets also became a powerful tactic. The 480 BC Battle of Salamis
Battle of Salamis
largely determined the course of the Persian Wars[213] not because of its inherent damage (however considerable) but because Themistocles's deception and superior strategy left the Athenians capable of disrupting sea-borne supplies at will and potentially striking at the pontoon bridges across the Hellespont, cutting off the Persians' line of retreat.[214] During the age of wooden ships, however, great fleets were burdensome to maintain and always liable to destruction by contrary weather, most famously in the case of the two kamikaze typhoons that destroyed the Mongol invasions of Japan in AD 1274 and 1281. Piracy—both illicit in ancient Cilicia
Cilicia
and China and state-supported among the Cretans, Vikings, Japanese, English, and Berbers[215]—has remained a problem into the present day, given the expense involved in securely protecting every merchant vessel or in policing extensive coastlines.[216]

Naval warfare
Naval warfare
in the Age of Sail: contemporary painting of the 1588 Battle of Gravelines, which helped to disperse the Spanish Armada

In the ancient world, in addition to Salamis, major naval engagements included the Battle of Actium, which permitted the establishment of Augustus's empire. In the modern era, important naval battles include the English victories against the Armada in 1588 and at Trafalgar in 1805,[217] which broke the threats of invasion by the superior land forces of the Spanish and French empires.

Modern naval warfare: a torpedo strikes the USS West Virginia during the Japanese attack on Pearl Harbor.

With steam, mass-produced steel plate, and exploding shells, European gunships permitted the New Imperialism
New Imperialism
of the 19th century, forcing open access to Africa, China, Korea, and Japan for their merchants on favorable terms. Although internal politics hampered Chinese modernization, American naval power produced a major reform in Japan which bore fruit during the 1905 Battle of Tsushima
Battle of Tsushima
when the Japanese were able to decisively defeat Russia.[219] The great navies initially focused their efforts on constructing great dreadnoughts and battleships, but these fought inconclusively in the First World War.[220] By contrast, the much cheaper German U-boats showed that submarines could cripple shipping even in waters nominally controlled by the enemy.[221] Convoys, intelligence, and airborne anti-submarine warfare (ASW) won a hard-fought victory in the Second World War's Battle of the Atlantic,[222] but developments in applied physics meant that by the 1960s nuclear-powered ballistic missile submarines were being maintained on constant patrol as a second-strike force[223] along with a second set of hunters intended to counter them. Meanwhile, the battles of the Mediterranean[224] and Pacific[225][226] theaters of the war had shown that air power was capable of overcoming the strongest warships.

Travel[edit] Further information: Ship transport Although the use of small private vessels for personal transport undoubtably extends back into prehistory, large ships capable of braving the open ocean were typically dedicated to trade or fishing for most of human history. Even military campaigns would often simply hire or commandeer these private fleets to serve as troop transports, as did the traders, pilgrims, and wealthy tourists of antiquity and the Middle Ages. The voyages of exploration and colonization were often provided for by the crown out of naval funds; where they were not, they were usually chartered or else purchased and then used for shipping supplies after the initial settlement. Dedicated and scheduled local passenger services came to be offered in the 16th and 17th centuries, but the 1817 Black Ball was the first trans-Atlantic passenger line. In the Age of Sail, the duration of such passages depended much on the prevailing winds and the weather. The 18th-century coastal Margate hoys
Margate hoys
began the popularization of leisure travel in Britain and Ireland[227] that later gathered steam with Thomas Cook's package tours in the next century.[228] During the 19th century, steam-powered ocean liners connected the railroad networks of the world. By 1900, the Atlantic crossing took about five days and the passenger lines competed to win the Blue Riband, an unofficial accolade accorded to the fastest liner in regular service. For twenty years from 1909, the prize went to the RMS Mauretania for its average speed of 26.06 knots (48.26 km/h).[229] This era waned as cheaper and faster intercontinental flights became available, most importantly the 1958 New York City– Paris
Paris
route.[230] The sea still remains a venue for recreational boating and large cruise ships. It is also a route for refugees and economic migrants, some traveling in small unseaworthy craft and others smuggled into shipping vessels. Some flee persecution while many are economic migrants attempting to reach countries where they believe their prospects are brighter.[231] Leisure[edit] Main articles: Cruising (maritime), Sailing, and Recreational boat fishing Use of the sea for leisure developed in the nineteenth century and became a significant industry in the twentieth century.[232] Maritime leisure activities are varied and include self-organized trips cruising, yachting, powerboat racing[233] and fishing;[234] commercially organized voyages on cruise ships;[235] and trips on smaller vessels for ecotourism such as whale watching and coastal birdwatching.[236]

Scuba diver with face mask, fins, and underwater breathing apparatus

Many humans enjoy venturing into the sea: children paddle and splash in the shallows, while others swim or relax on the beach. This was not always the case, with sea bathing becoming the vogue in Europe
Europe
in the 18th century after Dr. William Buchan advocated the practice for health reasons.[237] Surfing
Surfing
is a sport in which a wave is ridden by a surfer, with or without a surfboard. Other water sports include kite surfing, where a power kite propels a manned board across the water;[238] windsurfing, where the power is provided by a fixed, maneuverable sail;[239] and water skiing, where a powerboat is used to pull a skier.[240] Beneath the surface, freediving is necessarily restricted to shallow descents. Pearl divers have traditionally greased their skins, put cotton in their ears and clips on their noses, and dived to 40 ft (12 m) with baskets in order to collect pearl oysters.[241] Human eyes are not adapted for use underwater, but vision can be improved by wearing a diving mask. Other useful equipment includes fins and snorkels. Scuba equipment allows underwater breathing, permitting hours of time beneath the surface.[242] The depths that can be reached by divers and the length of time they can stay underwater is limited by the increase of pressure they experience as they descend and the need to prevent decompression sickness as they return to the surface. Recreational divers are advised to restrict themselves to depths of under 100 feet (30 m) beyond which the danger of nitrogen narcosis increases. Deeper dives can be made with specialized equipment and training.[242] Power generation[edit] Main articles: Marine energy
Marine energy
and Offshore wind power

The first tidal power station in the world: the kilometer-long Rance Tidal Power Station, which produces around 540 GWh
GWh
per year, around 3% of Brittany's total electrical consumption (2011).[243]

The sea offers a very large supply of energy carried by ocean waves, tides, salinity differences, and ocean temperature differences which can be harnessed to generate electricity.[244] Forms of 'green' marine energy include tidal power, marine current power, osmotic power, ocean thermal energy and wave power.[244][245] Tidal power
Tidal power
uses generators to produce electricity from tidal flows, sometimes by using a dam to store and then release seawater. The Rance barrage, 1 kilometer (0.62 mi) long, near St Malo
St Malo
in Brittany opened in 1967; it generates about 0.5 GW, but it has been followed by few similar schemes.[8](pp111f) The large and highly variable energy of waves gives them enormous destructive capability, making affordable and reliable wave machines problematic to develop. A small 2 MW commercial wave power plant, "Osprey", was built in Northern Scotland in 1995 about 300 meters (1000 ft) offshore. It was soon damaged by waves, then destroyed by a storm.[8](p112) Marine current power
Marine current power
could provide populated areas close to the sea with a significant part of their energy needs.[246] In principle, it could be harnessed by open-flow turbines; sea bed systems are available, but limited to a depth of about 40 m (130 ft).[247] Offshore wind power
Offshore wind power
is captured by wind turbines placed out at sea; it has the advantage that wind speeds are higher than on land, though wind farms are more costly to construct offshore.[248] The first offshore wind farm was installed in Denmark in 1991,[249] and the installed capacity of European offshore wind farms reached 3 GW in 2010.[250] Electricity power stations are often located on the coast or beside an estuary so that the sea can be used as a heat sink. A colder heat sink enables more efficient power generation, which is important for expensive nuclear power plants in particular.[251] Extractive industries[edit] Main articles: Offshore drilling
Offshore drilling
and Deep sea
Deep sea
mining

A reverse osmosis desalination plant

There are large deposits of petroleum (as oil and natural gas) in rocks beneath the seabed. Offshore platforms and drilling rigs extract the oil or gas and store it for transport to land. Offshore oil and gas production can be difficult due to the remote, harsh environment.[252] Drilling for oil in the sea has environmental impacts. Animals may be disorientated by seismic waves used to locate deposits, probably causing the beaching of whales.[253] Toxic substances such as mercury, lead, and arsenic may be released. The infrastructure may cause damage and oil may be spilt.[254]

A black smoker releasing dissolved sulfides and other minerals amid its superheated jets of water.

The sea holds enormous quantities of valuable dissolved minerals.[255] The most important, salt for table and industrial use has been harvested by solar evaporation from shallow ponds since prehistoric times. Bromine, accumulated after being leached from the land, is economically recovered from the Dead Sea, where it occurs at 55,000 parts per million (ppm).[256] Other minerals on or within the seabed can be exploited by dredging. This has advantages over land-based mining in that equipment can be built at specialized shipyards and infrastructure costs are lower. Disadvantages include problems caused by waves and tides, the tendency for excavations to silt up, and the washing away of spoil heaps. There is a risk of coastal erosion and environmental damage.[257] Sulphide deposits are potential sources of silver, gold, copper, lead, zinc, and trace metals which were only discovered in the 1960s. They form when geothermally superheated water is emitted from deep sea hydrothermal vents known as "black smokers": in contact with the cold waters of the deep ocean, the minerals precipitate and settle around the vent. The ores are of high quality but currently very costly to extract.[258] Small scale mining of the deep sea floor is being developed off the coast of Papua New Guinea using robotic techniques, but the obstacles are formidable.[259] Desalination
Desalination
is the technique of removing salts from seawater to leave fresh water suitable for drinking or irrigation. The two main processing methods, vacuum distillation and reverse osmosis, use large quantities of energy. Desalination
Desalination
is normally only undertaken where fresh water from other sources is in short supply or energy is plentiful, as in the excess heat generated by power stations. The brine produced as a by-product contains some toxic materials and is returned to the sea.[260] Large quantities of methane clathrate exist on the seabed and in ocean sediment at a temperature of around 2 °C (36 °F) and these are of interest as a potential energy source. Some estimates put the amount available at between one and 5 million cubic kilometers (0.24 to 1.2 million cubic miles).[261] Also on the seabed are manganese nodules formed of layers of iron, manganese, and other hydroxides around a core. In the Pacific these may cover up to 30 percent of the deep ocean floor. The minerals precipitate from seawater and grow very slowly. Their commercial extraction for nickel was investigated in the 1970s but abandoned in favour of more convenient sources.[262] In suitable locations, diamonds are gathered from the seafloor using suction hoses to bring gravel ashore. In deeper waters, mobile seafloor crawlers are used and the deposits are pumped to a vessel above. In Namibia, more diamonds are now collected from marine sources than by conventional methods on land.[263]

Pollution[edit] Main article: Marine pollution Many substances enter the sea as a result of human activities. Combustion products are transported in the air and deposited through precipitation. Agricultural, industrial, and sewage outflows contribute heavy metals, pesticides, PCBs, disinfectants, cleaning products, and other synthetic chemicals. These become concentrated in the surface film and in marine sediment, especially estuarine mud. The result of all this contamination is largely unknown because of the large number of substances involved and the lack of information on their biological effects.[264] The heavy metals of greatest concern are copper, lead, mercury, cadmium, and zinc which may be accumulated by marine invertebrates. They are then passed up the food chain.[265] Run-off of fertilizers from agricultural land is a major source of pollution in some areas and the discharge of raw sewage has a similar effect. The extra nutrients provided by these sources can cause excessive plant growth. Nitrogen is often the limiting factor in marine systems and the addition of nitrogen sparks algal blooms and red tides, which then may lower the oxygen level of the water to the point where it kills marine animals. Such events have created dead zones in the Baltic Sea
Baltic Sea
and the Gulf of Mexico.[266] Some algal blooms are caused by cyanobacteria that make shellfish that filter feed on them toxic, harming animals like sea otters.[267] Nuclear facilities too can pollute. The Irish Sea
Irish Sea
was contaminated by radioactive caesium-137 from the former Sellafield
Sellafield
nuclear fuel processing plant[268] and nuclear accidents sometimes cause radioactive material to seep into the sea, as at Fukushima in 2011.[269] The dumping of waste (including oil, noxious liquids, sewage, and garbage) at sea is governed by international law. The London Convention (1972) is a United Nations
United Nations
agreement to control ocean dumping which had been ratified by 89 countries by 8 June 2012.[270] MARPOL 73/78
MARPOL 73/78
is a convention to minimize pollution of the seas by ships. By May 2013, 152 maritime nations had ratified MARPOL.[271] Much floating plastic trash does not biodegrade, instead disintegrating over time and eventually breaking down to the molecular level. Rigid plastics may float for years.[272] In the center of the Pacific gyre, there is a permanent floating accumulation of mostly plastic waste[273] and there is a similar garbage patch in the Atlantic.[274] Foraging sea birds such as the albatross and petrel may mistake debris for food and accumulate indigestible plastic in their digestive systems. Turtles and whales have been found with plastic bags and fishing line in their stomachs. Microplastics
Microplastics
may sink, threatening filter feeders on the seabed.[275] Most oil pollution in the sea comes from cities and industry.[266] Oil is dangerous for marine animals. It can clog the feathers of sea birds, reducing their insulating effect and the birds' buoyancy, or be ingested when they preen themselves in an attempt to remove the contaminant. Marine mammals
Marine mammals
are less seriously affected but may be chilled through the removal of their insulation, blinded, dehydrated, or poisoned. Benthic invertebrates are swamped when the oil sinks, fish are poisoned, and the food chain is disrupted. In the short term, oil spills result in wildlife populations being decreased and unbalanced, leisure activities being affected, and the livelihoods of people dependent on the sea being devastated.[276] The marine environment has self-cleansing properties and naturally occurring bacteria will act over time to remove oil from the sea. In the Gulf of Mexico, where oil-eating bacteria are already present, they take only a few days to consume spilt oil.[277] Indigenous sea peoples[edit] Several nomadic indigenous groups in Maritime Southeast Asia
Maritime Southeast Asia
live in boats and derive nearly all they need from the sea. The Moken people live on the coasts of Thailand
Thailand
and Burma and islands in the Andaman Sea.[278] The Bajau people
Bajau people
are originally from the Sulu Archipelago, Mindanao, and northern Borneo.[279] Some Sea
Sea
Gypsies are accomplished free-divers, able to descend to depths of 30 m (98 ft), though many are adopting a more settled, land-based way of life.[280][281] The indigenous peoples of the Arctic
Arctic
such as the Chukchi, Inuit, Inuvialuit, and Yupik hunt marine mammals including seals and whales[282] and the Torres Strait
Strait
Islanders claim ownership of the Great Barrier Reef. They live a traditional life on the islands involving hunting, fishing, gardening, and trading with neighboring peoples in Papua New Guinea
Papua New Guinea
and Australia.[283] In culture[edit] Main articles: Sea in culture
Sea in culture
and Nautical fiction

An Assyrian relief from c. 700 BC showing fish and a crab swimming around a bireme.

The sea appears in human culture in contradictory ways, as both powerful but serene and as beautiful but dangerous.[8](p10) It has its place in mythology and religion, literature, art, poetry, film, theater, and music.[284] The Ancients personified it, believing it to be under the control of a being who needed to be appeased. It has been populated by fantastic creatures: the Leviathan
Leviathan
of the Bible,[285] Scylla
Scylla
in Greek mythology,[286] Isonade
Isonade
in Japanese mythology,[287] and the kraken of late Norse mythology.[288][289](pp206–08) The sea is especially common in Christian imagery, where several of Jesus's disciples were said to have been fishermen on the Sea
Sea
of Galilee.

Hokusai's c. 1829 The Great Wave off Kanagawa, the first of the Thirty-six Views of Mount Fuji.

The sea, its life, and its ships have been depicted in art ranging from the simple drawings on the walls of caves outside Les Eyzies, France, to the early Christian ichthys to the Dutch Hendrik Vroom to Hokusai's ukiyo-e to seascapes by Winslow Homer. During the Golden Age of the Netherlands, artists such as Jan Porcellis, Hendrick Dubbels, Willem van de Velde the Elder
Willem van de Velde the Elder
and his son, and Ludolf Bakhuizen celebrated the sea and the Dutch navy
Dutch navy
at the peak of its military prowess.[290][291] Music too has been inspired by the ocean. Sea
Sea
shanties were chanted by mariners to help coordinate arduous tasks and impressions in music have been created of calm waters, crashing waves, and storms at sea.[292] Classical sea-related music includes Richard Wagner's The Flying Dutchman,[293] Claude Debussy's La mer (1903–05),[294] Charles Villiers Stanford's Songs of the Sea
Sea
(1904) and Songs of the Fleet (1910), Edward Elgar's Sea Pictures (1899), and Ralph Vaughan Williams's A Sea Symphony (1903–1909).[295]

The Gulf Stream
Gulf Stream
(1899) by Winslow Homer.

As a symbol, the sea has for centuries played a role in literature and poetry. Sometimes, it is there just as a gentle background but often it introduces such themes as storm, shipwreck, battle, hardship, disaster, the dashing of hopes, or death.[296] In his epic poem the Odyssey, written in the 8th century BC,[297] Homer
Homer
describes the ten-year voyage of the Greek hero Odysseus
Odysseus
who struggles to return home across the sea's many hazards after the war described in the Iliad.[298] The sea is a recurring theme in the Haiku
Haiku
poems of the Japanese poet Matsuo Bashō (1644–1694).[299] In modern literature, sea-inspired novels have been written by the sailors Herman Melville,[300] Joseph Conrad,[301] and Herman Wouk.[302] The psychiatrist Carl Jung
Carl Jung
argued that, in dream interpretation, the sea symbolizes the personal and the collective unconscious.[303] Although the origin of life on Earth
Earth
is still a matter of debate,[304] naturalist Rachel Carson
Rachel Carson
wrote in The Sea Around Us
The Sea Around Us
that "it is a curious situation that the sea, from which life first arose, should now be threatened by the activities of one form of that life. But the sea, though changed in a sinister way, will continue to exist: the threat is rather to life itself."[305] See also[edit]

Nautical portal Water
Water
portal

Seas – book

Notes[edit]

^ Note, this is a general definition that conceptually spans sources from technical to pedagogical to dictionary (the latter giving standard usage by laypersons). See the main body and the Notes, for the full range of understandings and definitions of the term. ^ One definition is that a sea is a sub-division of an ocean, although presently the IHO defines the boundaries of the world's oceans by reference to waters not otherwise included in seas,[4] which are taken as customary and essentially arbitrary.[9] Definitions for undergraduate and younger students, taking into account technical meaning and standard usage, often state that "sea" is a term for a largely "land-locked" body of salt water, for which exception must then be made for the ocean current-bounded (i.e., dynamically bounded) but commonly recognised Sargasso Sea.[1][2] A third requires that seas possess a floor formed of oceanic crust, which would accept the Caspian since it was once part of an ancient ocean.[10] ^ Accordingly, the Convention does not apply to the Caspian, which is instead an "international lake" for most legal purposes.[12] ^ Hydrous ringwoodite recovered from volcanic eruptions suggests that the transition zone between the lower and upper mantle holds between one[16] and three[17] times as much water as all of the world's surface oceans combined. Experiments to recreate the conditions of the lower mantle suggest it may contain still more water as well, as much as five times the mass of water present in the world's oceans.[18][19] ^ Human
Human
kidneys excrete urine that is around 2% saline,[28] so that drinking one liter of most forms of seawater will require drinking at least another liter of freshwater to prevent harmful excesses of sodium. Without this additional water, increased urination to remove the salt produces dehydration.[29] ^ "As the waves leave the region where they were generated, the longer ones outpace the shorter because their velocity is greater. Gradually, they fall in with other waves travelling at similar speed—where different waves are in phase they reinforce each other, and where out of phase they are reduced. Eventually, a regular pattern of high and low waves (or swell) is developed that remains constant as it travels out across the ocean."[8](pp83f) ^ To help put a change of this magnitude into perspective, when the pH of human blood plasma is raised from its normal 7.4 to a value above 7.8, or lowered to a value below 6.8, death ensues.[93] ^ Given that the most likely landfall regions have been under 50 meters (160 ft) of water since the end of the last ice age, it is unlikely that the timing will ever be established with certainty.[121] Two common theories are a crossing from Timor
Timor
to the northwest Australian mainland around 70,000 years ago and a crossing from Sulawesi
Sulawesi
to New Guinea
New Guinea
around 50,000 years ago,[121][122] possibly assisted by a tsunami.[123] ^ The Greek navigator Eudoxus was later reported by Strabo
Strabo
to have accidentally discovered a wrecked ship from Gades on the northeast coast of Africa
Africa
and to have then attempted two (failed) circumnavigations of Africa
Africa
around 116 BC.[135] ^ Capture of seafood from inland waters has grown constantly, from less than 3 million metric tons per year in 1950 to more than 11 million by 2010, but remains less than 10% of the total capture.[180]

References[edit]

^ a b NGS Staff (27 September 2011). "Sea". National Geographic (online). Washington, DC: The National Geographic Society (NGS). Retrieved 7 January 2017. [Quote:] ...a sea is a division of the ocean that is enclosed or partly enclosed by land...  ^ a b Karleskint, George (2009). Introduction to Marine Biology. Boston, MA: Cengage Learning. p. 47. ISBN 9780495561972. Retrieved January 7, 2017.  ^ National Oceanic and Atmospheric Administration. "Then and Now: The HMS Challenger Expedition and the 'Mountains in the Sea' Expedition". Ocean
Ocean
Explorer. ^ a b International Hydrographic Organization. "Limits of Oceans and Seas ( Special
Special
Publication №28)", 3rd ed. Imp. Monégasque (Monte Carlo), 1953. Retrieved 7 February 2010. ^ a b Oxford English Dictionary, 1st ed. "sea, n." Oxford University Press (Oxford), 1911. ^ a b c Reddy, M.P.M. (2001) Descriptive Physical Oceanography. p. 112. A.A. Balkema, Leiden. ISBN 90-5410-706-5. ^ NOS Staff (March 25, 2014). "What's the Difference between an Ocean and a Sea?". Ocean
Ocean
Facts. Silver
Silver
Spring, MD: National Ocean
Ocean
Service (NOS), National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
(NOAA). Retrieved January 7, 2017 – via OceanService.NOAA.gov.  ^ a b c d e f g h i j k l m n o p q r s t Stow, Dorrik A.V. (2004). Encyclopedia of the Oceans. Oxford, UK: Oxford University Press. ISBN 0198606877. Retrieved January 7, 2017.  ^ American Society of Civil Engineers (1994). The Glossary of the Mapping Sciences. p. 365. ASCE Publications. ISBN 0-7844-7570-9. ^ Conforti, B. (2005). The Italian Yearbook of International Law. Vol. 14, p. 237. Martinus Nijhoff. ISBN 978-90-04-15027-0. ^ Vukas, B. (2004) The Law
Law
of the Sea: Selected Writings. p. 271. Martinus Nijhoff. ISBN 978-90-04-13863-6. ^ Gokay, Bulent (2001). "The Politics of Caspian Oil". Palgrave Macmillan: 74. ISBN 978-0-333-73973-0.  ^ Ravilious, Kate (21 Apr 2009). "Most Earthlike Planet
Planet
Yet Found May Have Liquid Oceans" in National Geographic. ^ Platnick, Steven. "Visible Earth". NASA. ^ a b NOAA. "Lesson 7: The Water
Water
Cycle" in Ocean
Ocean
Explorer. ^ Oskin, Becky (12 Mar 2014). "Rare Diamond
Diamond
Confirms that Earth's Mantle Holds an Ocean's Worth of Water" in Scientific American. ^ Schmandt, B.; Jacobsen, S. D.; Becker, T. W.; Liu, Z.; Dueker, K. G. (2014). " Dehydration
Dehydration
melting at the top of the lower mantle". Science. 344 (6189): 1265–68. Bibcode:2014Sci...344.1265S. doi:10.1126/science.1253358.  ^ Harder, Ben (7 Mar 2002). "Inner Earth
Earth
May Hold More Water
Water
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Regions of North America

Northern

Eastern Canada Western Canada Canadian Prairies Central Canada Northern Canada Atlantic Canada The Maritimes French Canada English Canada Acadia

Acadian Peninsula

Quebec City–Windsor Corridor Peace River
River
Country Cypress Hills Palliser's Triangle Canadian Shield Interior Alaska- Yukon
Yukon
lowland taiga Newfoundland (island) Vancouver Island Gulf Islands Strait
Strait
of Georgia Canadian Arctic
Arctic
Archipelago Labrador Peninsula Gaspé Peninsula Avalon Peninsula

Bay
Bay
de Verde Peninsula

Brodeur Peninsula Melville Peninsula Bruce Peninsula Banks Peninsula (Nunavut) Cook Peninsula Gulf of Boothia Georgian Bay Hudson Bay James Bay Greenland Pacific Northwest Inland Northwest Northeast

New England Mid-Atlantic Commonwealth

West

Midwest Upper Midwest Mountain States Intermountain West Basin and Range Province

Oregon Trail Mormon Corridor Calumet Region Southwest

Old Southwest

Llano Estacado Central United States

Tallgrass prairie

South

South Central Deep South Upland South

Four Corners East Coast West Coast Gulf Coast Third Coast Coastal states Eastern United States

Appalachia

Trans-Mississippi Great North Woods Great Plains Interior Plains Great Lakes Great Basin

Great Basin
Great Basin
Desert

Acadia Ozarks Ark-La-Tex Waxhaws Siouxland Twin Tiers Driftless Area Palouse Piedmont Atlantic coastal plain Outer Lands Black Dirt Region Blackstone Valley Piney Woods Rocky Mountains Mojave Desert The Dakotas The Carolinas Shawnee Hills San Fernando Valley Tornado Alley North Coast Lost Coast Emerald Triangle San Francisco Bay
Bay
Area

San Francisco Bay North Bay
Bay
(San Francisco Bay
Bay
Area) East Bay
Bay
(San Francisco Bay
Bay
Area) Silicon Valley

Interior Alaska- Yukon
Yukon
lowland taiga Gulf of Mexico Lower Colorado River
River
Valley Sacramento–San Joaquin River
River
Delta Yukon–Kuskokwim Delta Colville Delta Arkansas Delta Mobile–Tensaw River
River
Delta Mississippi Delta Mississippi River
River
Delta Columbia River
River
Estuary Great Basin High Desert Monterey Peninsula Upper Peninsula of Michigan Lower Peninsula of Michigan Virginia Peninsula Keweenaw Peninsula Middle Peninsula Delmarva Peninsula Alaska Peninsula Kenai Peninsula Niagara Peninsula Beringia Belt regions

Bible
Bible
Belt Black Belt Corn Belt Cotton Belt Frost Belt Rice Belt Rust Belt Sun
Sun
Belt Snow
Snow
Belt

Latin

Northern Mexico Baja California Peninsula Gulf of California

Colorado River
River
Delta

Gulf of Mexico Soconusco Tierra Caliente La Mixteca La Huasteca Bajío Valley of Mexico Mezquital Valley Sierra Madre de Oaxaca Yucatán Peninsula Basin and Range Province Western Caribbean Zone Isthmus of Panama Gulf of Panama

Pearl Islands

Azuero Peninsula Mosquito Coast West Indies Antilles

Greater Antilles Lesser Antilles

Leeward Leeward Antilles Windward

Lucayan Archipelago Southern Caribbean

Aridoamerica Mesoamerica Oasisamerica Northern Middle Anglo Latin

French Hispanic

American Cordillera Ring of Fire LAC

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Regions of Oceania

Australasia

Gulf of Carpentaria New Guinea

Bonis Peninsula Papuan Peninsula Huon Peninsula Huon Gulf Bird's Head Peninsula Gazelle Peninsula

New Zealand

South Island North Island

Coromandel Peninsula

Zealandia New Caledonia Solomon Islands (archipelago) Vanuatu

Kula Gulf

Australia Capital Country Eastern Australia Lake
Lake
Eyre basin Murray–Darling basin Northern Australia Nullarbor Plain Outback Southern Australia

Maralinga

Sunraysia Great Victoria Desert Gulf of Carpentaria Gulf St Vincent Lefevre Peninsula Fleurieu Peninsula Yorke Peninsula Eyre Peninsula Mornington Peninsula Bellarine Peninsula Mount Henry Peninsula

Melanesia

Islands Region

Bismarck Archipelago Solomon Islands Archipelago

Fiji New Caledonia Papua New Guinea Vanuatu

Micronesia

Caroline Islands

Federated States of Micronesia Palau

Guam Kiribati Marshall Islands Nauru Northern Mariana Islands Wake Island

Polynesia

Easter Island Hawaiian Islands Cook Islands French Polynesia

Austral Islands Gambier Islands Marquesas Islands Society Islands Tuamotu

Kermadec Islands Mangareva Islands Samoa Tokelau Tonga Tuvalu

Ring of Fire

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Regions of South America

East

Amazon basin Atlantic Forest Caatinga Cerrado

North

Caribbean South America West Indies Los Llanos The Guianas Amazon basin

Amazon rainforest

Gulf of Paria Paria Peninsula Paraguaná Peninsula Orinoco Delta

South

Tierra del Fuego Patagonia Pampas Pantanal Gran Chaco Chiquitano dry forests Valdes Peninsula

West

Andes

Tropical
Tropical
Andes Wet Andes Dry Andes Pariacaca mountain range

Altiplano Atacama Desert

Latin Hispanic American Cordillera Ring of Fire LAC

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Polar regions

Antarctic

Antarctic
Antarctic
Peninsula East Antarctica West Antarctica Eklund Islands Ecozone Extreme points Islands

Arctic

Arctic
Arctic
Alaska British Arctic
Arctic
Territories Canadian Arctic
Arctic
Archipelago Finnmark Greenland Northern Canada Northwest Territories Nunavik Nunavut Russian Arctic Sakha Sápmi Yukon North American Arctic

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Earth's oceans and seas

Arctic
Arctic
Ocean

Amundsen Gulf Barents Sea Beaufort Sea Chukchi Sea East Siberian Sea Greenland
Greenland
Sea Gulf of Boothia Kara Sea Laptev Sea Lincoln Sea Prince Gustav Adolf Sea Pechora Sea Queen Victoria Sea Wandel Sea White Sea

Atlantic Ocean

Adriatic Sea Aegean Sea Alboran Sea Archipelago
Archipelago
Sea Argentine Sea Baffin Bay Balearic Sea Baltic Sea Bay
Bay
of Biscay Bay
Bay
of Bothnia Bay
Bay
of Campeche Bay
Bay
of Fundy Black Sea Bothnian Sea Caribbean Sea Celtic Sea English Channel Foxe Basin Greenland
Greenland
Sea Gulf of Bothnia Gulf of Finland Gulf of Lion Gulf of Guinea Gulf of Maine Gulf of Mexico Gulf of Saint Lawrence Gulf of Sidra Gulf of Venezuela Hudson Bay Ionian Sea Irish Sea Irminger Sea James Bay Labrador Sea Levantine Sea Libyan Sea Ligurian Sea Marmara Sea Mediterranean Sea Myrtoan Sea North Sea Norwegian Sea Sargasso Sea Sea
Sea
of Åland Sea
Sea
of Azov Sea
Sea
of Crete Sea
Sea
of the Hebrides Thracian Sea Tyrrhenian Sea Wadden Sea

Indian Ocean

Andaman Sea Arabian Sea Bali Sea Bay
Bay
of Bengal Flores Sea Great Australian Bight Gulf of Aden Gulf of Aqaba Gulf of Khambhat Gulf of Kutch Gulf of Oman Gulf of Suez Java Sea Laccadive Sea Mozambique Channel Persian Gulf Red
Red
Sea Timor
Timor
Sea

Pacific Ocean

Arafura Sea Banda Sea Bering Sea Bismarck Sea Bohai Sea Bohol Sea Camotes Sea Celebes Sea Ceram Sea Chilean Sea Coral
Coral
Sea East China Sea Gulf of Alaska Gulf of Anadyr Gulf of California Gulf of Carpentaria Gulf of Fonseca Gulf of Panama Gulf of Thailand Gulf of Tonkin Halmahera Sea Koro Sea Mar de Grau Molucca Sea Moro Gulf Philippine Sea Salish Sea Savu Sea Sea
Sea
of Japan Sea
Sea
of Okhotsk Seto Inland Sea Shantar Sea Sibuyan Sea Solomon Sea South China Sea Sulu Sea Tasman Sea Visayan Sea Yellow Sea

Southern Ocean

Amundsen Sea Bellingshausen Sea Cooperation Sea Cosmonauts Sea Davis Sea D'Urville Sea King Haakon VII Sea Lazarev Sea Mawson Sea Riiser-Larsen Sea Ross Sea Scotia Sea Somov Sea Weddell Sea

Landlocked seas

Aral Sea Caspian Sea Dead Sea Salton Sea

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Physical oceanography

Waves

Airy wave theory Ballantine scale Benjamin–Feir instability Boussinesq approximation Breaking wave Clapotis Cnoidal wave Cross sea Dispersion Edge wave Equatorial waves Fetch Gravity
Gravity
wave Green's law Infragravity wave Internal wave Iribarren number Kelvin wave Kinematic wave Longshore drift Luke's variational principle Mild-slope equation Radiation stress Rogue wave Rossby wave Rossby-gravity waves Sea
Sea
state Seiche Significant wave height Soliton Stokes boundary layer Stokes drift Stokes wave Swell Trochoidal wave Tsunami

megatsunami

Undertow Ursell number Wave action Wave base Wave height Wave power Wave radar Wave setup Wave shoaling Wave turbulence Wave–current interaction Waves and shallow water

one-dimensional Saint-Venant equations shallow water equations

Wind
Wind
wave

model

Circulation

Atmospheric circulation Baroclinity Boundary current Coriolis force Coriolis–Stokes force Craik–Leibovich vortex force Downwelling Eddy Ekman layer Ekman spiral Ekman transport El Niño–Southern Oscillation General circulation model Geostrophic current Global Ocean
Ocean
Data Analysis Project Gulf Stream Halothermal circulation Humboldt Current Hydrothermal circulation Langmuir circulation Longshore drift Loop Current Modular Ocean
Ocean
Model Ocean
Ocean
dynamics Ocean
Ocean
gyre Princeton ocean model Rip current Subsurface currents Sverdrup balance Thermohaline circulation

shutdown

Upwelling Whirlpool World Ocean
Ocean
Circulation Experiment

Tides

Amphidromic point Earth
Earth
tide Head of tide Internal tide Lunitidal interval Perigean spring tide Rip tide Rule of twelfths Slack water Tidal bore Tidal force Tidal power Tidal race Tidal range Tidal resonance Tide
Tide
gauge Tideline

Landforms

Abyssal fan Abyssal plain Atoll Bathymetric chart Coastal geography Cold seep Continental margin Continental rise Continental shelf Contourite Guyot Hydrography Oceanic basin Oceanic plateau Oceanic trench Passive margin Seabed Seamount Submarine
Submarine
canyon Submarine
Submarine
volcano

Plate tectonics

Convergent boundary Divergent boundary Fracture zone Hydrothermal vent Marine geology Mid-ocean ridge Mohorovičić discontinuity Vine–Matthews–Morley hypothesis Oceanic crust Outer trench swell Ridge push Seafloor spreading Slab pull Slab suction Slab window Subduction Transform fault Volcanic arc

Ocean
Ocean
zones

Benthic Deep ocean water Deep sea Littoral Mesopelagic Oceanic Pelagic Photic Surf Swash

Sea
Sea
level

Deep-ocean Assessment and Reporting of Tsunamis Future sea level Global Sea
Sea
Level Observing System North West Shelf Operational Oceanographic System Sea-level curve Sea level
Sea level
rise World Geodetic System

Acoustics

Deep scattering layer Hydroacoustics Ocean
Ocean
acoustic tomography Sofar bomb SOFAR channel Underwater acoustics

Satellites

Jason-1 Jason-2 ( Ocean
Ocean
Surface Topography
Topography
Mission) Jason-3

Related

Argo Benthic lander Color of water DSV Alvin Marginal sea Marine energy Marine pollution Mooring National Oceanographic Data Center Ocean Ocean
Ocean
exploration Ocean
Ocean
observations Ocean
Ocean
reanalysis Ocean
Ocean
surface topography Ocean
Ocean
thermal energy conversion Oceanography Pelagic
Pelagic
sediment Sea
Sea
surface microlayer Sea
Sea
surface temperature Seawater Science
Science
On a Sphere Thermocline Underwater glider Water
Water
column World Ocean
Ocean
Atlas

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