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Sea | Wikipedia audio article


The seat the world ocean or simply the ocean as the connected body of salty water that covers over 70% of the Earth’s surface it moderates the Earth’s climate and has important roles in the water cycle carbon cycle and nitrogen cycle it has been travelled and explored since ancient times while the scientific study of the sea oceanography dates broadly from the voyages of Captain James Cook to explore the Pacific Ocean between 1768 and 1779 the word sea is also used to denote smaller partly landlocked sections of the ocean the most abundant solid dissolved in seawater as sodium chloride the water also contains salts of magnesium calcium and potassium amongst many other elements some in minute concentrations salinity varies widely being lower near the surface and the mouths of large rivers and higher in the depths of the ocean however the relative proportions of dissolved salts varies little across the oceans winds blowing over the surface of the sea produce waves which break when they enter shallow water winds also create surface currents through friction setting up slow but stable circulations of water throughout the oceans the directions of the circulation are governed by factors including the shapes of the continents and the rotation of the earth the Coriolis effect deep sea currents known as the global conveyor belt carry cold water from near the poles to every ocean tides the generally twice daily rise and fall of sea levels are caused by the rotation of the earth and the gravitational effects of the orbiting moon and to a lesser extent of the Sun tides may have a very high range in Bay’s or estuaries submarine earthquakes arising from tectonic plate movements under the oceans can lead to destructive tsunamis as can volcanoes huge landslides or the impact of large meteorites a wide variety of organisms including bacteria protists algae plants fungi and animals live in the sea which offers a wide range of marine habitats and ecosystems ranging vertically from the sunlit surface waters in the shoreline to the enormous depths and pressures of the cold dark abyssal zone and in latitude from the cold waters under the Arctic ice to the colorful diversity of coral reefs in tropical regions many of the major groups of organisms evolved in the sea and life may have started there the sea provides substantial supplies of food for humans mainly fish but also shellfish mammals and seaweed whether caught by fishermen are farmed underwater other human uses of the sea include trade travel mineral extraction power generation warfare and leisure activities such as swimming sailing and scuba diving many of these activities create marine pollution the sea is important in human culture with major appearances in literature at least since Homer’s Odyssey in marine art in cinema in theatre and in classical music symbolically the sea appears as monsters such as Scylla in mythology and represents the unconscious mind in dream interpretation topic definition the sea is the interconnected system of all the Earth’s oceanic waters including the Atlantic Pacific Indian Southern and Arctic oceans however the word sea can also be used for many specific much smaller bodies of seawater such as the North Sea or the Red Sea there is no sharp distinction between seas and oceans though generally seas are smaller and are often partly as marginal seas or wholly as inland seas bordered by land however the Sargasso Sea has no coastline and lies within a circular current the North Atlantic gyre seas are generally larger than lakes and contains salt water but the Sea of Galilee is a freshwater lake the United Nations Convention on the law of the sea states that all of the ocean eyes see you topic physical science earth is the only known planet with seas of liquid water on its surface although Mars possesses ice caps and similar planets and other solar systems may have oceans it is still unclear where Earth’s water came from but seem from space our planet appears as a blue marble of its various forms oceans ice caps clouds first 1 billion 335 million cubic kilometres 320 million cu me of sea contain about 97.2% of its known water and cover more than 70% of its surface another two point one five percent of Earth’s water as frozen found in the sea ice covering the Arctic Ocean the ice cap covering Antarctica and it’s adjacent seas and various glaciers and surface deposits around the world the remainder about 0.65 percent of the whole form underground reservoirs are various stages of the water cycle containing the freshwater encountered and used by most terrestrial life vapour 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 the Seas dominance of the planet is such that the british author arthur c clarke once noted that earth would have been better named ocean the scientific study of water and Earth’s water cycle as 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 oceans currents but has since expanded into a large and multidisciplinary field it examines the properties of seawater studies waves tides and currents charts coastlines and maps the sea beds and studies marine life the subfield dealing with the Seas motion its forces and the forces acting upon it is known as physical oceanography 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 oceans role in the carbon cycle and carbon dioxides role in the increasing acidification of seawater marine and maritime geography charts the shape and shaping of the sea 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 topic see water the water in the sea was thought to come from the Earth’s volcanoes starting four billion years ago released by degassing from molten rock more recent work suggests much of the Earth’s water may come from comets a characteristic of seawater is that it is salty salinity is usually measured in parts per thousand per mil or per mil and the open ocean has about 35 grams one point two ounces solids per liter a salinity of the Mediterranean Sea is slightly higher at while the salinity in northern Red Sea could reach the constituents of table salt sodium and chloride make up about 85% of the solids in solution there are also other metal ions such as magnesium and calcium and negative ions including sulfate carbonate and bromide despite variations in the levels of salinity in different seas the relative composition of the dissolved salts is stable throughout the world’s oceans seawater is too saline for humans to drink safely as the kidneys cannot excrete urine as salty as seawater in contrast some landlocked hypersaline lakes have a much higher salinity for example the Dead Sea has 300 grams 11 ounces dissolved solids per liter although the amount of salt in the ocean remains relatively constant within the scale of millions of years various factors affect the salinity of a body of water evaporation and by-product of ice formation known as Brian rejection increased salinity whereas precipitation sea ice melt and runoff from land reduce it the Baltic Sea for example has many rivers flowing into it and thus the sea could be considered as brackish meanwhile the red sea is very salty due to its high evaporation rate sea temperature depends on the amount of solar radiation falling on its surface in the tropics with the Sun nearly overhead the temperature of the surface layers can rise to over 30 degrees Celsius 86 degrees Fahrenheit while near the poles the temperature in equilibrium with the sea ice is about minus 2 degrees Celsius 28 degrees Fahrenheit there is a continuous circulation of water in the oceans warm surface currents cool as they move away from the tropics and the water becomes denser and sinks the cold water moves back towards the equator as a deep-sea current driven by changes in the temperature and density of the water before eventually welling up again towards the surface deep sea water has a temperature between minus 2 degrees Celsius 28 degrees Fahrenheit and 5 degrees Celsius 41 degrees Fahrenheit in all parts of the globe sea water with a typical salinity of has a freezing point of about minus 1.8 degrees Celsius 28.8 degrees Fahrenheit when it’s temperature becomes low enough ice crystals form on the surface these break into small pieces and coalesce into flat disks that form a thick suspension known as fazil in calm conditions this freezes into a thin flat sheet known as Melies which thickens as new ice forms on its underside in more turbulent seas Brazil crystals joined together into flat disks known as pancakes these slide under each other and coalesced to form floes in the process of freezing salt water and air are trapped between the ice crystals Neela’s may have a salinity of 12 – but by the time the sea ice is one year old this falls to 4 – the amount of oxygen found in seawater depends primarily on the plants growing in it these are mainly algae including phytoplankton with some skilar plants such as sea grasses in daylight the photosynthetic activity of these plants produces oxygen which dissolves in the seawater and is used by marine animals at night photosynthesis stops and the amount of dissolved oxygen declines in the deep-sea where insufficient light penetrates for plants to grow there is very little dissolved oxygen in its absence organic material is broken down by anaerobic bacteria producing hydrogen sulfide global warming is likely to reduce levels of oxygen in surface waters since the solubility of oxygen and water falls at higher temperatures the amount of light that penetrates the sea depends on the angle of the Sun the weather conditions and the turbidity of the water much light gets reflected at the surface and red light gets absorbed in the top few meters yellow and green light reach greater depths and blue and violet light may penetrate as deep as 1000 meters 3,300 feet there is insufficient light for photosynthesis and plant growth beyond a depth of about 200 meters 660 feet topic waves when blowing over the surface of a body of water forms waves that are perpendicular to the direction of the wind the friction between air and water caused by a gentle breeze on a pond causes ripples to form a strong blow over the ocean causes larger waves as the moving air pushes against the raised ridges of water the waves reach their maximum height when the rate at which they are traveling nearly matches the speed of the wind in open water when the wind blows continuously as happens in the southern hemisphere in the Roaring Forties long organized masses of water called swell roll across the ocean if the wind dies down the wave formation is reduced but already formed waves continue to travel in their original direction until they meet land the size of the waves depends on the fetch the distance that the wind has blown over the water and the strength and duration of that wind when waves meet others coming from different directions interference between the two can produce broken irregular seas constructive interference can cause individual unexpected rogue waves much higher than normal most waves are less than 3 metres 10 feet high and it is not unusual for strong storms to double or triple that height offshore constructions such as wind farms and oil platforms use mid-ocean statistics from measurements in computing the wave forces due to for instance the hundred-year wave they are designed against rogue waves however have been documented at heights above 25 metres 82 feet the top of the wave is known as the crest the lowest point between waves is the trough in the distance between the crests as the wavelength the wave is pushed across the surface of the sea by the wind but this represents a transfer of energy and not a horizontal movement of water as waves approach land and move into shallow water they change their behavior if approaching at an angle waves may bend refraction or rap 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 waves height to the water depth increases above a certain limit it breaks toppling over in a mass of foaming water this rushes in a sheet of the beach before retreating into the sea and the influence of gravity soppec tsunami a tsunami is an unusual form of wave caused by an infrequent powerful event such as an underwater earthquake or landslides 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 sea water has turned into kinetic energy creating a shallow wave a tsunami radiating outwards at a velocity proportional to the square root of the depth of the water in which therefore travels much faster in the open ocean than on a continental shelf in the deep open sea tsunamis have wavelengths of around 80 to 300 miles 130 to 480 kilometers travel at speeds of over 600 miles per hour 970 kilometers per hour and usually have a height of less than 3 feet so they often pass unnoticed at this stage in contrast ocean surface waves caused by winds have wavelengths of a few hundred feet travel at up to 65 miles per hour 105 km/h and are up to 45 feet 14 meters high 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 so as the wave radiates away from the source the front gets longer and the average energy reduces so distant chores will on average 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 an effect known as refraction which can focus the strength of the advancing tsunami on some areas and weaken it in others according to undersea topography as a tsunami moves into shallower water its speed decreases its wavelength shortens and its amplitude increases enormously behaving in the same way as a wind generated wave in shallow water but on a vastly greater scale either the trough or the crest of a tsunami can arrive at the coast first in the former case the sea draws back and leaves subtitle’ areas close to the shore exposed which provides a useful warning for people on land when the crest arrives it does not usually break but rushes inland flooding all in its path much of the destruction may be caused by the flood water draining back into the sea after the tsunami has struck dragging debris and people with it often several tsunami are caused by a single geological event and arrive at intervals of between 8 minutes and 2 hours the first wave to arrive on shore may not be the biggest or most destructive occasionally a tsunami may transform into a bore typically in a shallow bay or an estuary topic currents when 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 easterly’s dominate the tropics 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 – in the Pacific – in the Atlantic and one in the Indian Ocean 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 and anti clockwise in the southern hemisphere the water moving away from the equator is warm and that flowing in the reverse direction 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 global climate and weather forecasts are powerfully affected by the world ocean so global climate modeling makes use of ocean circulation models as well as models of other major components such as the atmosphere land surfaces aerosols and sea ice ocean models make use of a branch of physics geophysical fluid dynamics that describes the large scale flow of fluids such as sea water 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 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 mental 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 besides gyres there are temporary surface currents that occur under specific conditions when waves meet ashore 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 approach the stronger is the longshore current these currents can shift great volumes of sand or pebbles creates pits and make beaches disappear and water channels silt up a rip current can occur when water piles up near the shore from advancing waves and is funneled out to sea through a channel in the seabed it may occur at a gap in a sandbar or near a man-made structures such as a groin these strong currents can have a velocity of 3 feet 0.9 m/s can form at different places at different stages of the tide and can carry away unwary bathers 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 topic tides tides are the regular rise and fall in water level experienced by seas and oceans in response to the gravitational influences of the moon and the Sun and the effects of the Earth’s rotation during each tidal cycle at any given place the water rises to a maximum height known as high tide before ebbing away again to the minimum low tide level as the water recedes it uncovers more and more of the foreshore also known as the intertidal zone the difference in height between the high tide and low tide has known as the tidal range or tidal amplitude most places experience two high tides each day occurring at intervals of about 12 hours and 25 minutes this is half that 24 hours and 50 minute it takes for the earth to make a complete revolution and return the moon to its previous position relative to an observer the moon’s mass has some 27 million times smaller than the Sun but it is 400 times closer to the earth tidal force our tide raising force decreases rapidly with distance so the moon has more than twice as great an effect on tides as the Sun a bulge is formed in the ocean at the place where the 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 as the moon rotates around the earth so do these ocean bulges move around the earth the gravitational attraction of the Sun is also working on the Seas but its effect on tides is less powerful than that of the moon and when the Sun Moon and Earth are all aligned full moon and new moon the combined effect results in the high spring tides in contrast when the Sun is at 90 degrees from the moon as viewed from Earth the combined gravitational effect on tides is less causing the lower neap tides tidal flows of sea water are resisted by the waters inertia and can be affected by land masses in places like the Gulf of Mexico where land constrains the movement of the bulges only one set of tides may occur each day in shore from an island there may be a complex daily cycle with four high tides the island straits at Chalky’s on you booyah experienced 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 where there is a funnel-shaped Bay or estuary the tidal range can be magnified the Bay of Fundy is the classic example of this and can experience spring tides of 15 meters 49 feet 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 anti cyclones pushes down on the water and is associated with abnormally low tides while low pressure areas may cause extremely high tides 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 feet 5 meters surge during a hurricane that overwhelmed the city killing over 3500 people and destroying 3636 homes topic ocean basins the 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 mostly solid outer layer of the mantle on land the crust is known as the continental crust while under the sea it is known as the oceanic crust the latter is composed of relatively dense basalt and as 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 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 processes accompanied by friction as the plates grind together the movement proceeds in jerks which cause earthquakes heat is produced in magma is forced up creating underwater mountains some of which may form chains of volcanic islands near to deep trenches near some of the boundaries between the land and sea the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed as they grate together the continental plates are deformed and buckle causing mountain building and seismic activity the Earth’s deepest trench as the Mariana Trench which extends for about 2,500 kilometers 1,600 miles across the seabed it is near the Mariana Islands a volcanic archipelago in the West Pacific and though it averages just 68 kilometers 42 miles wide its deepest point is 10.99 four kilometres nearly seven miles below the surface of the sea an even longer trench runs alongside the coast of Peru and Chile reaching a depth of 8,000 65 metres 26400 60 feet and extending for approximately five thousand nine hundred kilometers 3,700 miles it occurs where the oceanic Nazca plate slides under the continental South American plate and is associated with the up thrust and volcanic activity of the Andes topic posts the zone where land meets sea is known as the coast in the part between the lowest spring tides and the upper limit reached by splashing waves as the shore a beach is the accumulation of sand or shingle on the shore a headland is a point of land jutting out into the sea and a larger promontory is known as a Cape the indentation of a coastline especially between two headlands is a bay a small bay with a narrow Inlet as a cove and a large bay may be referred to as a gulf 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 offshore 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 and these are known as constructive waves as they tend to move material up the beach and have little erosive effect storm waves arrive on shore in rapid succession and are known as destructive waves as the swash moves Beach material see words 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 this tends to undercut the cliff and normal weathering processes such as the action of frost follows causing further destruction gradually a wave-cut platform develops at the foot of the cliff and this has a protective effect reducing further wave erosion material worn from the margins of the land eventually ends up in the sea here it is subject to attrition as currents flowing parallel to the coast scour out channels in transport sand and pebbles away from their place of origin sediment carried to the sea by rivers settles on the seabed causing Delta’s to form in estuaries all these materials move back and forth under the influence of waves tides and currents dredging removes material and deepens channels but may have unexpected effects elsewhere on the coastline governments make efforts to prevent flooding of the land by the building of breakwaters sea walls dikes and levees and other sea defenses for instance the thames barrier is designed to protect london from a storm surge while the failure of the dikes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States land reclamation in Hong Kong also permitted the construction of Hong Kong International Airport through the leveling and expansion of two smaller islands topic C level over most of geologic time the sea level has been higher than it is today the main factor affecting sea level over time as the result of changes in the oceanic crust with a downward trend expected to continue in the very long term at the last glacial maximum some 20,000 years ago the sea level was 120 metres 390 feet below its present-day level for at least the last 100 years sea level has been rising at an average rate of about 1.8 millimeters 0.071 in per year 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 meters 1,600 feet 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 ground water for irrigation and other agricultural and human needs the rising trend from global warming is expected to continue until at least the end of the 21st century topic water cycle the sea plays a part in the water or hydrological cycle in which water evaporates from the ocean travels through the atmosphere as vapor condenses falls as rain or snow thereby sustaining life on land and largely returns to the sea even in the Atacama Desert where little rain ever falls dense clouds of fog known as the cabmen chaka blow in from the sea and support plant life in Central Asia and other large land masses there are indirect basins which have no outlet to the sea separated from the ocean by mountains or other natural geologic features that prevent the water draining away the caspian sea is the largest one of these its main inflow is from the river Volga there is no outflow and the evaporation of water makes it saline as dissolved minerals accumulate the RLC and Pyramid Lake in the western United States are further examples of large inland saline water bodies without drainage some in doric lakes are less salty but all are sensitive to variations in the quality of the inflowing water topic 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 the ocean’s surface layer holds large amounts of dissolved organic carbon that is exchanged rapidly with the atmosphere the deep layers concentration of dissolved inorganic carbon as about 15 percent higher than that of the surface layer and it remains there for much longer periods of time thermohaline circulation exchanges carbon between these two layers carbon enters the ocean as atmospheric carbon dioxide dissolves in the surface layers and is converted into carbonic acid carbonate and bicarbonate co2 gas co2 AQ co2 AQ + h2o h2 co3 h2 co3 hco3 minus plus h plus h co 3 – co 32 – plus 2 h plus IT can also enter through rivers as dissolved organic carbon 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 topic acidification see water is slightly alkaline and had an average pH of about 8.2 over the past 300 million years more recently anthropogenic activities have steadily increased the carbon dioxide content of the atmosphere about 30 to 40 percent of the added co2 as absorbed by the oceans forming carbonic acid and lowering the pH now below eight point one through a process called ocean acidification the pH is expected to reach seven point seven representing a three-fold increase in hydrogen ion concentration by the year 2100 which is a significant change in a century 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 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 because their ability to form shells will be reduced and the carbonate compensation depth will rise closer to the sea surface affected planktonic organisms will include the snail like mollusks known as pteropods and single-celled algae called cockle it affords 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 in turn adversely impacting other reef dwellers 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 a particular concern as the manner in which the combination of acidification with the expected additional stressors of higher temperatures and lower oxygen levels will impact the Seas topic life in the sea 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 marine habitats range from surface water to the deepest oceanic trenches including coral reefs kelp forests seagrass Meadows tide pools muddy sandy and rocky sea beds in the open pelagic zone the organisms living in the sea range from whales 30 metres 100 feet long to microscopic phytoplankton and zooplankton fungi and bacteria 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 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 experiment 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 topic 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% 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 polar seas with ice shelves sea ice and icebergs to temperate and tropical waters coral reefs the so called rainforests of the sea occupy less than 0.1% of the world’s ocean surface yet their ecosystems include 25% of all marine species 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 Reformation topic algae and plants Marine primary producers plants and microscopic organisms in the plankton are widespread and very essential for the ecosystem it has been estimated that half of the world’s oxygen is produced by phytoplankton about 45% of the Seas primary production of living material is contributed by diatoms much larger algae commonly known as seaweeds are important locally Sargassum forms floating drifts while kelp forms sea bed forests flowering plants in the form of sea grasses grow in meadows in sandy shallows mangroves lined the coast in tropical and subtropical regions and salt tolerant plants thrive in regularly inundated salt marshes all of these habitats are able to sequester large quantities of carbon and support a bio diverse range of larger and smaller animal life light is only able to penetrate the top 200 meters 660 feet so this is the only part of the sea where plants can grow 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 an Amex and denitrification some of these processes take place in deep water so that where there is an upwelling of cold waters and also 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 topic animals and other marine life 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 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 life style and many invertebrate phyla are entirely marine in fact the oceans teem with life and provide many varying micro habitats one of these is the surface film which even though tossed about by the movement of waves provides a rich environment and is home to bacteria fungi micro algae protozoa fish eggs and various larvae the pelagic zone contains macro and microphone 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 minut 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 neck tonic organisms to large squid sharks porpoises dolphins and whales some marine creatures make large migrations either to other regions of the ocean on a seasonal basis or vertical migrations daily often ascending to feed at night and descending to safety by day ships can introduce or spread invasive species through the discharge of ballast water or the transport of organisms that have accumulated as part of the fouling community on the hulls of vessels the demersal zone supports many animals that feed on benthic organisms or seek protection from predators and 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 the dehydrating air as home to barnacles mollusks and crustaceans the neritic zone has many organisms that need light to flourish here among algal encrusted rocks live sponges echinoderms polychaete worms sea anemones and other invertebrates 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 bio diverse habitat for reef dwelling organisms there is less sea life on the floor of deeper sees but marine life also flourishes around sea mounts that rise from the depths where fish and other animals congregate to spawn and feed close to the seabed live demersal fish that feed largely on pelagic organisms are benthic invertebrates exploration of the deep sea by submersibles revealed a new world of creatures living on the seabed that scientists had not previously known to exist some like the d’être vores rely on organic material falling to the ocean floor others cluster round deep sea hydrothermal vents where mineral rich flows of water emerge from the seabed supporting communities whose primary producers are sulphide oxidizing chemoautotrophs consumers include specialised bivalves sea anemones barnacles crabs worms and fish often found nowhere else 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 sulfur reducing bacteria such places support unique biomes where many new microbes and other life forms have been discovered pick humans in the sea topic history of navigation and exploration you humans have traveled the seas since they first built seagoing craft Mesopotamians were using bitumen to cut their reed boats and a little later masted sails by sea 3000 BC austronesians on Taiwan had begun spreading into maritime Southeast Asia subsequently the Austronesian Lapita people’s displayed great feats of navigation reaching out from the Bismarck Archipelago to as far away as Fiji Tonga and Samoa their descendants continued to travel thousands of miles between tiny islands on outrigger canoes and in the process they found many new islands including Hawaii Easter Island Rapa Nui and New Zealand the ancient Egyptians and Phoenicians explored the Mediterranean and red sea with the Egyptian hanout reaching the Arabian Peninsula and the African coast around 20 750 BC in the 1st millennium BC Phoenicians and Greeks established colonies throughout the Mediterranean and the Black Sea around 500 BC the Carthaginian navigator Hondo left a detailed periplus of an Atlantic journey that reached at least Senegal and possibly Mount Cameroon in the early media eval period the Vikings crossed the North Atlantic and even reached the north eastern fringes of North America novgorodians had also been sailing the white sea since the 13th century or before meanwhile the seas along the eastern and southern Asian coasts were used by Arab and Chinese traders the Chinese Ming Dynasty had a fleet of 317 ships with 37,000 men under jung-hee in the early 15th century sailing the Indian and Pacific Oceans in the late 15th century Western European Mariners started making longer voyages of exploration in search of trade Bartolomeu Dias rounded the Cape of Good Hope in 1487 and Vasco da Gama reached India via the Cape in 1498 Christopher Columbus sailed from Cadiz in 1492 attempting to reach the eastern lands of India and Japan by the novel means of traveling westwards he made landfall instead on an island in the Caribbean Sea and a few years later the Venetian navigator John Cabot reached Newfoundland the Italian America Vespucci after whom America was named explored the South American coast line in voyages made between 1497 and 1502 discovering the mouth of the Amazon River in 1519 the Portuguese navigator Ferdinand Magellan led the first expedition to sail around the world as for the history of navigational instrument a compass was first used by the ancient Greeks and Chinese to show where North lies in the direction in which the ship is heading the latitude and angle which ranges from zero degrees at the equator to ninety degrees at the poles was determined by measuring the angle between the Sun moon or a specific star in the horizon by the use of an astrolabe Jacob’s staff or sextant the longitude aligned on the globe joining the two poles could only be calculated with an accurate chronometer to show the exact time difference between the ship and a fixed point such as the Greenwich meridian in 1759 John Harrison a clock maker designed such an instrument and James Cook used it in his voyages of exploration nowadays the Global Positioning System GPS using over 30 satellites enables accurate navigation worldwide with regards to maps that are vital for navigation in the second century Ptolemy mapped the whole known world from the fortunate eye instantly Cape Verde or Canary Islands eastward to the Gulf of Thailand this map was used in 1492 when Christopher Columbus set out on his voyages of discovery subsequently gerardus mercator made a practical map of the world in 1538 his map projection conveniently making rum lines straight by the 18th century better maps had been made and part of the objective of James Cook on his voyages was to further map the ocean scientific study has continued with the depth recordings of the disc Aurora the oceanic research of the Challenger voyages 1872 to 1876 the work of the Scandinavian seaman Roald Amundsen and Fridtjof Nansen the Michael SARS expedition in 1910 the German meteor expedition of 1925 the Antarctic Survey work of Discovery – in 1932 and other sins furthermore in 1921 the International hydrographic organization was set up and it constitutes the authority on hydrographic surveying and nautical charting topic history of oceanography and deep-sea exploration scientific oceanography began with the voyages of Captain James Cook from 1768 to 1779 describing the Pacific with unprecedented precision from 71 degrees south to 71 degrees north John Harrison’s chronometer supported cooks accurate navigation and charting on two of these voyages permanently improving the standard attainable for subsequent work other expeditions followed in the 19th century from Russia France the Netherlands and the United States as well as Britain on HMS Beagle which provided Charles Darwin with ideas and materials for his 1859 book On the Origin of Species the ship’s captain Robert Fitzroy charted the season coasts and published his for vol report of the ship’s three voyages in 1839 Edward Forbes his 1854 book distribution of marine life argued that no life could exist below around 600 metres 2,000 feet this was proven wrong by the British biologists WB carpenter and cy Ville Thompson who in 1868 discovered life in deepwater by dredging whyville thompson became chief scientist on the Challenger expedition of 1872 to 1876 which effectively created the science of Oceanography on her 68,000 890 nautical mile 120 7580 kilometers journey round the globe HMS challenger discovered about 4,700 new marine species and made 492 deep-sea soundings 133 bottom dredges 151 open water trawls in 263 cereal water temperature observations in the southern Atlantic in 1898 1899 Carl Chun on the Valdivia brought many new life-forms to the surface from depths of over 4,000 metres 13,000 feet the first observations of deep sea animals in their natural environment were made in 1930 by William Beebe and Otis Barton who descended to 434 metres 1424 feet in the spherical steel bathysphere this was lowered by cable but by 1960 as self powered submersible Trieste developed by Jacques Piccard took Picard and Don Walsh to the deepest part of the Earth’s oceans the Mariana Trench in the Pacific reaching a record depth of about 10,000 915 meters 35,000 810 feet a feat not repeated until 2012 when James Cameron piloted the deep-sea challenger to similar depths an atmospheric diving suit can be worn for deep sea operations with a new world record being set in 2006 when a US Navy diver descended to 2,000 feet 610 meters in one of these articulated pressurized suits at great depths no light penetrates through the water layers from above and the pressure is extreme for deep-sea exploration it is necessary to use specialist vehicles either remotely operated underwater vehicles with lights and cameras or manned submersibles the battery-operated MIR submersibles have a three-man crew and can descend to 20,000 feet 6,000 meters they have viewing ports 5000 watt lights video equipment and manipulator arms for collecting samples placing probes or pushing the vehicle across the seabed when the thrusters would stir up excessive sediment but the Matri is the mapping and study of the topography of the ocean floor methods used for measuring the depth of the sea include single or multi beam echo Sounders laser airborne depth Sounders and the calculation of depths from satellite remote sensing data this information is used for determining the roots of undersea cables and pipelines for choosing suitable locations for siting oil rigs and offshore wind turbines and for identifying possible new fisheries ongoing oceanographic research includes marine life forms conservation the marine environment the chemistry of the ocean the studying and modeling 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 whereas in the 1960’s and 1970’s research could focus on taxonomy and basic biology in the 2010s attention has shifted to larger topics such as climate change 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 topic law you Freedom of the Seas is a principle in international law dating from the 17th century it stresses freedom to navigate the oceans and disapproves of war fought in international waters today this concept is enshrined in the United Nations Convention on the law of the sea UNCLOS the third version of which came into force in 1994 article 87 1 states the high seas are open to all states whether coastal or landlocked article 87 102 F gives a non-exhaustive list of freedoms including navigation over flight the laying of submarine cables building artificial islands fishing and scientific research the safety of shipping is regulated by the International Maritime Organization its objectives include developing and maintaining a regulatory framework for shipping maritime safety environmental concerns legal matters technical cooperation and maritime security UNCLOS defines various areas of water internal waters are on the landward side of a baseline and foreign vessels have no right of passage in these territorial waters extend to 12 nautical miles 22 kilometres 14 miles from the coastline and in these waters the coastal state is free to set laws regulate use and exploit any resource a contiguous zone extending of further 12 nautical miles allows for hot pursuit of vessels suspected of infringing laws in four specific areas customs taxation immigration and pollution an exclusive economic zone extends for 200 nautical miles 370 kilometers 230 miles from the baseline within this area the coastal nation has sole exploitation rights over all natural resources the continental shelf is the natural prolongation of the land territory to the continental margins outer edge or 200 nautical miles from the coastal states baseline whichever is greater here the coastal nation has the exclusive right to harvest minerals and also living resources attached to the seabed topic lore control of the sea is important to the security of a maritime nation and the naval blockade of a port can be used to cut off food and supplies in time of war battles have been fought on the sea for more than 3,000 years in about 1210 bc soupy luma – the king of the Hittites defeated and burned a fleet from Alesia modern Cyprus in the decisive 480 BC Battle of Salaam ease the Greek general Themistocles trapped the far larger fleet of the Persian King Xerxes in a narrow channel and attacked vigorously destroying 200 Persian ships for the loss of 40 Greek vessels at the end of the age of sail the English Navy led by Horatio Nelson broke the power of the combined French and Spanish fleets at the 1805 Battle of Trafalgar with steam and the industrial production of steel plate came greatly increased firepower in the shape of the dreadnought battleships armed with long-range guns in 1905 the Japanese fleet decisively defeated the Russian fleet which had traveled over 18,000 nautical miles 33,000 kilometers at the Battle of Tsushima dread-nots fought inconclusively in the first world war at the 1916 Battle of Jutland between the Royal Navy’s Grand Fleet and the Imperial German Navy’s high seas fleet in the Second World War the British victory at the 1940 Battle of Toronto showed that naval air power was sufficient to overcome the largest warships foreshadowing the decisive sea battles of the Pacific War including the battles of the Coral Sea Midway the Philippine Sea and the climactic Battle of Leyte Gulf in all of which the dominant chips were aircraft carriers submarines became important in naval warfare in World War one when German submarines known as u-boats sank nearly 5000 allied merchant ships including however the RMS Lusitania so helping to bring the United States into the war in World War two almost 3,000 Allied ships were sunk by u-boats attempting to block the flow of supplies to Britain but the Allies broke the blockade in the Battle of the Atlantic which lasted the whole length of the war sinking 783 u-boats since 1960 several nations have maintained fleets of nuclear-powered ballistic missile submarines vessels equipped to launch ballistic missiles with nuclear warheads from under the sea some of these are kept permanently on Patrol topic travel sailing ships or packets carried mail overseas one of the earliest being the Dutch service to Batavia in the 1670s these added passenger accommodation but in cramped conditions later scheduled services were offered but the time journeys took depended much on the weather when steam ships replaced sailing vessels ocean-going liners took over the task of carrying people by the beginning of the 20th century crossing the Atlantic took about five days and shipping companies competed to own the largest and fastest vessels the blue ribbon was an unofficial accolade given to the fastest liner crossing the Atlantic in regular service the Mauretania held the title with twenty six point zero six knots forty eight point two six km/h for 20 years from 1909 the hails trophy another award for the fastest commercial crossing of the Atlantic was won by the United States in 1952 for a crossing that took three days ten hours and forty minutes the great liners were comfortable but expensive in fuel and staff the age of the transatlantic liners waned as cheap intercontinental flights became available in 1958 a regular scheduled air service between New York and Paris taking seven hours doomed the Atlantic ferry service to oblivion one by one the vessels were laid up some were scrapped others became cruise ships for the leisure industry and still others floating hotels the sea is still a route by which boat people travel in small sometimes unseaworthy craft often having paid money to people smugglers for their passage some may be fleeing persecution but most are economic migrants attempting to reach countries where they believe their prospects are brighter topic trade maritime trade has existed for millennia the Ptolemaic dynasty had developed trade with India using the Red Sea ports and in the 1st millennium BC the Arabs Phoenicians Israelites and Indians traded in luxury goods such as spices gold and precious stones the Phoenicians were noted sea traders and under the Greeks and Romans commerce continued to thrive with the collapse of the Roman Empire European trade dwindled but it continued to flourish among the kingdoms of Africa the Middle East India China and southeastern Asia from the 16th to the 19th centuries about 13 million people were shipped across the Atlantic to be sold as slaves in the Americas 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 to the Indian Ocean and through the Straits of Malacca much trade also passes through the English Channel shipping lanes are the routes on the open sea used by cargo vessels traditionally making use of trade winds and currents over 60% of the world’s container traffic is conveyed on the top-20 trade routes increased melting of Arctic ice since 2007 enables ships to travel the Northwest Passage for some weeks in summertime avoiding the longer routes via the Suez Canal or the Panama Canal 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 dollars worth of goods each year there are two main kinds of freight bulk cargo and breakbulk 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 or scrap metal sand and gravel breakbulk 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 the use of containers has greatly increased the efficiency and decreased the cost of moving them with most Freight now travelling in standard sized lockable contain loaded on purpose-built container ships at dedicated terminals freight forwarding firms booked cargo arrange pickup in delivery and managed documentation topic food fish and other fishery products are among the most important sources of protein and other nutrients that are essential for a balanced diet and a good health in 2009 sixteen point six percent of the world’s intake of animal protein and six point five percent of all protein consumed come from fishes in order to fulfill this need coastal countries have exploited marine resources in their exclusive economic zone although fishing vessels are increasingly venturing further afield to exploit stocks in international waters in 2011 total world production of fish including aquaculture was estimated to be 154 million tonnes of which most was for human consumption the harvesting of wild fish accounted for 94 million tons while annually increasing aquaculture contributes the rest the Northwest Pacific is by far the most productive area with twenty point nine million tonnes 27 percent of the global marine catch in 2010 in addition the number of fishing vessels in 2010 reached four point three six million whereas the number of people employed in the primary sector of fish production in the same year amounted to fifty four point eight million people modern fishing vessels include fishing trawlers with a small crew stern trawlers / sailors longline 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 per Sainz other sames trawls dredges gill nets and long lines and the fish species most frequently targeted are herring cod and cho v tuna flounder mullet squid and salmon over-exploitation itself has become a serious concern it does not only cause the depletion of fish stocks but also substantially reduce the population of predatory fish populations Myers and W worm estimated that industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation in order to avoid over exploitation many countries have introduced quotas in their own waters however recovery efforts often entail substantial costs to local economies or food provision nonetheless research published in nature in April 20 18 pound that the aggressive effort of the Indonesian Minister of maritime affairs and Fisheries of Indonesia Susi piteous Duty to curtail illegal fishing has reduced total fishing effort by at least 25 percent potentially generate a 14 percent increase in catch and a 12 percent increase in profit therefore the paper concluded that many nations can recover their fisheries while avoiding these short-term costs by sharply addressing illegal unreported and unregulated IUU fishing artisan fishing methods include rod and line harpoons skin diving traps throw nets and drag Nets traditional fishing boats are powered by paddle wind or outboard motors and operate in near shore waters the Food and Agriculture Organization is encouraging the development of local fisheries to provide food security to coastal communities and help alleviate poverty as well as the wild stock about 79 million tons 78 M long tons 87 M short tons of food and non-food products were produced by aquaculture in 2010 an all-time high about 600 species of plants and animals were cultured some for use in seeding wild populations the animals raised included fin fish aquatic reptiles crustaceans molluscs sea cucumbers sea urchins sea squirts and jellyfish integrated mera culture has the advantage that there is a readily available supply of planktonic food and waste is removed naturally various methods are employed mesh enclosures for fin fish can be suspended into 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 ropes can be hung in water to grow algae oysters and mussels oysters can be reared on trays or in mesh tubes sea cucumbers can be ranched on the seabed captive breeding programs have raised lobster larvae for release of juveniles into the wild resulting in an increased lobster harvest in Maine at least 145 species of seaweed red green and brown algae are eaten worldwide and some have long been farmed in Japan and other Asian countries there is great potential for additional alga culture few maritime flowering plant are widely used for food but one example is Marsh samphire which is eaten both raw and cooked a major difficulty for aquaculture as the tendency towards monoculture and the associated risk of widespread disease in the 1990s disease wiped out China’s farmed ferrars scallop and white shrimp and required their replacement by other species aquaculture is also associated with environmental risks for instance shrimp farming has caused the destruction of important mangrove forests throughout Southeast Asia Topic leisure use of the sea for leisure developed in the 19th century and became a significant industry in the 20th century maritime leisure activities are varied and includes self organized trips cruising yachting powerboat racing and fishing commercially organized voyages on cruise ships and trips on smaller vessels for ecotourism such as whale watching and coastal bird-watching humans enjoy venturing into the sea children paddle and splash in the shallows and many people take pleasure in bathing and relaxing on the beach this was not always the case with sea bathing becoming the vogue in Europe in the 18th century after dr.William buck and advocated the practice for health reasons surfing is a sport in which a wave is written by a surfer with or without a surfboard other marine water sports include kite surfing where a power kite propels a man board across the water windsurfing where the power is provided by a fixed maneuverable sail and water skiing where a powerboat is used to pull a skier beneath the surface free diving is necessarily restricted to shallow descent pearl divers have traditionally greased their spins put cotton in their ears and clips on their noses and dive 240 feet 12 meters with baskets to collect oysters human eyes are not adapted for use under water but vision can be improved by wearing a diving mask other useful equipment includes fins and snorkel and scuba equipment allows underwater breathing and hence a longer time can be spent beneath the surface the depths that can be reached by divers in 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 100 feet 30 meters beyond which the danger of nitrogen narcosis increases deeper dives can be made with specialized equipment and training topic power generation 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 forms of green marine energy include tidal power marine current power osmotic power ocean thermal energy and wave 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 one kilometre 0.62 miles long near st.Malo in Brittany opened in 1967 it generates about 0.5 gigawatts but it has been followed by few similar schemes 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 megawatts commercial wave power plant Osprey was built in northern Scotland in 1995 about 300 metres 1,000 feet offshore it was soon damaged by waves then destroyed by a storm marine current power could provide populated areas close to the sea with a significant part of their energy needs in principle it could be harnessed by open flow turbines seabed systems are available but limited to a depth of about 40 metres 130 feet offshore wind power is captured by wind turbines placed out at sea it has the advantage that wind speeds are higher than on land the wind farms are more costly to construct offshore the first offshore wind farm was installed in Denmark in 1991 and the installed capacity of European offshore wind farms reached 3 gigawatts in 2010 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 topic extractive industries the seabed contains enormous reserves of minerals which can be exploited by dredging this has advantages over land-based mining and 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 in the washing away of spoil heaps there is a risk of coastal erosion and environmental damage sea floor massive sulfide deposits are potential sources of silver gold copper lead and zinc and trace metals since their discovery in the 1960s they form when geothermally heated water is emitted from deep sea hydrothermal vents known as black smokers the ores are of high quality but prohibitively costly to extract 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 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 drilling for oil in the sea has environmental impacts animals may be disorientated by seismic waves used to locate deposits probably causing the Beeching of whales toxic substances such as mercury lead and arsenic may be released the infrastructure may cause damage an oil may be spilt large quantities of methane clathrate exist on the seabed and in ocean sediment at a temperature of around 2 degrees Celsius 36 degrees Fahrenheit and these are of interest as a potential energy source some estimates put the amount available at between 1 and 5 million cubic kilometers 0.242 1.2 million cubic miles 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 favor of more convenient sources in suitable location 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 the sea holds enormous quantities of valuable dissolved minerals 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 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 is normally only undertaken where fresh water from other sources as 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 has returned to the sea topic marine pollution many substances enter the sea as a result of human activities combustion products are transported in the air and deposited into the sea by precipitation Industrial outflows and sewage contribute heavy metals pesticides PCBs disinfectants household cleaning products and other synthetic chemicals these become concentrated in the surface film and in marine sediment especially ester I mud the result of all this contamination is largely unknown because of the large number of substances involved in the lack of information on their biological effects the heavy metals of greatest concern are copper lead mercury cadmium and zinc which may be bio accumulated by marine invertebrates they are cumulative toxins and are passed up the food chain much floating plastic rubbish does not biodegrade instead disintegrating over time and eventually breaking down to the molecular level rigid plastics may float for years in the center of the Pacific Gyre there is a permanent floating accumulation of mostly plastic waste and there is a similar Garbage Patch in the Atlantic foraging sea birds such as the albatross and petrol 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 micro plastics may sink threatening filter feeders on the seabed most oil pollution in the sea comes from cities and Industry oil is dangerous for marine animals it can clog the feathers of seabirds reducing their insulating effect and the birds buoyancy and be ingested when they preen themselves in an attempt to remove the contaminant marine mammals are less seriously affected but may be chilled through the removal of their insulation blinded dehydrated or poison 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 the marine environment has self-cleansing properties and naturally occurring bacteria will act overtime 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 runoff of fertilizers from agricultural land as 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 with added nitrogen algal blooms and red tides can lower the oxygen level of the water and kill marine animals such events have created dead zones in the Baltic Sea and the Gulf of Mexico some algal blooms are caused by cyanobacteria that makes shellfish that filter feed on them toxic harming animals like sea otters nuclear facilities too can pollute the Irish Sea was contaminated by radioactive cesium-137 from the former Sellafield nuclear fuel processing plant and nuclear accidents may also cause radioactive material to seep into the sea as did the disaster at the Fukushima Daiichi nuclear power plant in 2011 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 agreement to control ocean dumping which had been ratified by 89 countries by the 8th of June 2012 Marples 7378 says a convention to minimize pollution of the Seas by ships by May 2013 152 maritime nations had ratified Marple topic indigenous Sea Peoples you several nomadic indigenous groups in maritime Southeast Asia live in boats and derive nearly all they need from the sea the mo can people live on the coasts of Thailand and Burma and islands in the Andaman Sea the Biagio people are originally from the Sulu Archipelago Mindanao in northern Borneo some sea gypsies are accomplished free divers able to descend to depths of 30 metres 98 feet though many are adopting a more settled land-based way of life the indigenous peoples of the Arctic such as the Chukchi Inuit Inuvialuit and yup at hunt marine mammals including seals and whales and the Torres Strait Islanders of Australia include ownership of the Great Barrier Reef among their possessions they live a traditional life on the islands involving hunting fishing gardening and trading with neighboring peoples in Papua and mainland Aboriginal Australians topic in culture the see appears in human culture in contradictory ways as both powerful but serene and is beautiful but dangerous it has its place in literature art poetry film theatre classical music mythology and dream interpretation the ancients personified it believing it to be under the control of a being who needed to be appeased and symbolically it has been perceived as a hostile environment populated by fantastic creatures the Leviathan of the Bible Scylla in Greek mythology Ison aid in Japanese mythology and the cracking of late Norse mythology civilizations have advanced through maritime trade in the exchange of ideas the sea and ships have been depicted in art ranging from simple drawings on the walls of huts in la mère to seascapes by Joseph Turner in Dutch Golden Age painting artists such as Jan poor cellies Hendrik doubles willem van de Velde the elder and his son and let old back wiesen celebrated the sea in the Dutch navy at the peak of its military prowess the Japanese artist Katsushika Hokusai created color prints of the moods of the sea including the Great Wave off Kanagawa music – has been inspired by the ocean sometimes by composers who lived or work near the shore and saw its many different aspects sea shanties songs that were chanted by Mariners to help them perform arduous tasks have been woven into compositions and impressions in music have been created of calm waters crashing waves and storms at sea classical see related music includes Richard Wagner’s The Flying Dutchman Claude Debussy’s lemare 1903 205 Charles Villiers Stanford’s songs of the sea 1904 and songs of the fleet 1910 Edward Elgar see pictures 1899 and Ralph Vaughan Williams AC Symphony 1903 – 1909 as a symbol the sea has for centuries played a role in literature poetry and dreams 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 and death in his epic poem The Odyssey written in the eighth century BC Homer describes the ten-year voyage of the Greek hero Odysseus who struggles to return home across the seas many hazards after the war described in the Iliad the sea is a recurring theme the haiku poems of the Japanese Edo period poet Matsuo Basho song way Bajau 1644 to 16 94 in modern literature see inspired novels have been written by Joseph Conrad drawn from his experience at sea Herman Wouk and Herman Melville in the works of psychiatrist Carl Jung the sea symbolises the personal and the collective unconscious in dream interpretation the depths of the sea symbolizing the depths of the unconscious mind although the origin of life on Earth is still a matter of debate scientist and writer Rachel Carson in her award-winning 1951 book the sea around us wrote 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 you topic see also seize Wikipedia book topic notes topic references topic cited texts Cotterell Arthur Edie mm world mythology Paragon is B and nine seven eight oh seven five two five three oh three seven six CS one mayn’t extra text authors list link Kindersley Dorling 2011 illustrated encyclopedia of the ocean Dorling Kindersley ISBN nine seven eight one four oh five three three 308 five Stowe Doric 2004 encyclopedia of the oceans oxford university press ISBN o one nine eight six oh six eight seven seven topic external links oceans at Curley National Oceanic and Atmospheric Administration


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