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119-570: The terminology of a "seven seas" with varying definitions was part of the vernacular of several peoples (as in the prior mentioned seas of Arabic literature), long before the oceans of the world became known (to those peoples). The term can now also be taken to refer to these seven oceanic bodies of water: The World Ocean is also known as just " the sea ", the expanse emanating from any marginal sea . The International Hydrographic Organization lists over 23 distinct bodies of water called seas. The modern practice of debating which bodies of water are

238-410: A halocline . If a zone undergoes a strong, vertical chemistry gradient with depth, it contains a chemocline . Temperature and salinity control ocean water density. Colder and saltier water is denser, and this density plays a crucial role in regulating the global water circulation within the ocean. The halocline often coincides with the thermocline, and the combination produces a pronounced pycnocline ,

357-493: A mid-ocean ridge , which creates a long mountain range beneath the ocean. Together they form the global mid-oceanic ridge system that features the longest mountain range in the world. The longest continuous mountain range is 65,000 km (40,000 mi). This underwater mountain range is several times longer than the longest continental mountain range – the Andes . Oceanographers state that less than 20% of

476-582: A boundary between less dense surface water and dense deep water. Po river The Po ( / p oʊ / POH , Italian: [ˈpɔ] ) is the longest river in Italy. It flows eastward across northern Italy, starting from the Cottian Alps . The river's length is either 652 km (405 mi) or 682 km (424 mi), if the Maira , a right bank tributary, is included. The headwaters of

595-422: A depth of a few hundred meters or less. Human activity often has negative impacts on marine life within the continental shelf. Ocean temperatures depend on the amount of solar radiation reaching the ocean surface. In the tropics, surface temperatures can rise to over 30 °C (86 °F). Near the poles where sea ice forms, the temperature in equilibrium is about −2 °C (28 °F). In all parts of

714-595: A gentle breeze on a pond causes ripples to form. A stronger gust blowing over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they are travelling nearly matches the speed of the wind. In open water, when the wind blows continuously as happens in the Southern Hemisphere in the Roaring Forties , long, organized masses of water called swell roll across

833-451: A net of channels called navigli , which Leonardo da Vinci helped design. Near the end of its course, it creates a wide delta (with hundreds of small channels and five main ones, called Po di Maestra , Po della Pila , Po delle Tolle , Po di Gnocca and Po di Goro ) at the southern part of which is Comacchio , an area famous for eels . The Po Valley was the territory of Roman Cisalpine Gaul , divided into Cispadane Gaul (south of

952-496: A shallow area and this, coupled with a low pressure system, can raise the surface of the ocean dramatically above a typical high tide. The average depth of the oceans is about 4 km. More precisely the average depth is 3,688 meters (12,100 ft). Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep. "Deep ocean," which is anything below 200 meters (660 ft), covers about 66% of Earth's surface. This figure does not include seas not connected to

1071-403: A wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion. Material worn from the margins of the land eventually ends up in the sea. Here it is subject to attrition as currents flowing parallel to the coast scour out channels and transport sand and pebbles away from their place of origin. Sediment carried to the sea by rivers settles on

1190-406: A zone undergoes dramatic changes in temperature with depth, it contains a thermocline , a distinct boundary between warmer surface water and colder deep water. In tropical regions, the thermocline is typically deeper compared to higher latitudes. Unlike polar waters , where solar energy input is limited, temperature stratification is less pronounced, and a distinct thermocline is often absent. This

1309-439: Is a bay , a small bay with a narrow inlet is a cove and a large bay may be referred to as a gulf . Coastlines are influenced by several factors including the strength of the waves arriving on the shore, the gradient of the land margin, the composition and hardness of the coastal rock, the inclination of the off-shore slope and the changes of the level of the land due to local uplift or submergence. Normally, waves roll towards

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1428-598: Is a strait where pearls are fished. The second sea begins at Ra’s al-Jumha and is called Larwi . It is a big sea, and in it is the Island of Waqwaq and others that belong to the Zanj . These islands have kings. One can only sail this sea by the stars. It contains huge fish, and in it are many wonders and things that pass description. The third sea is called Harkand , and in it lies the Island of Sarandib , in which are precious stones and rubies. Here are islands with kings, but there

1547-444: Is an important reference point for oceanography and geography, particularly as mean sea level . The ocean surface has globally little, but measurable topography , depending on the ocean's volumes. The ocean surface is a crucial interface for oceanic and atmospheric processes. Allowing interchange of particles, enriching the air and water, as well as grounds by some particles becoming sediments . This interchange has fertilized life in

1666-411: Is customarily divided into five principal oceans – listed below in descending order of area and volume: The ocean fills Earth's oceanic basins . Earth's oceanic basins cover different geologic provinces of Earth's oceanic crust as well as continental crust . As such it covers mainly Earth's structural basins , but also continental shelfs . In mid-ocean, magma is constantly being thrust through

1785-399: Is due to the fact that surface waters in polar latitudes are nearly as cold as deeper waters. Below the thermocline, water everywhere in the ocean is very cold, ranging from −1 °C to 3 °C. Because this deep and cold layer contains the bulk of ocean water, the average temperature of the world ocean is 3.9 °C. If a zone undergoes dramatic changes in salinity with depth, it contains

1904-508: Is irregular, unevenly dominating the Earth's surface . This leads to the distinction of the Earth's surface into a water and land hemisphere , as well as the division of the ocean into different oceans. Seawater covers about 361,000,000 km (139,000,000 sq mi) and the ocean's furthest pole of inaccessibility , known as " Point Nemo ", in a region known as spacecraft cemetery of

2023-477: Is now degrading. Venice , which was originally built on islands off the coast, is most at risk due to subsidence, but the effect is realized in the Po delta as well. The causes are first a decrease in the sedimentation rate due to the locking of sediment behind hydroelectric dams and the deliberate excavation of sand from rivers for industrial purposes. Second, agricultural use of the river is heavy; during peak consumption

2142-407: Is one king over them. In the islands of this sea grow bamboo and rattan . The fourth sea is called Kalah and is shallow and filled with huge serpents. Sometimes they ride the wind and smash ships. Here are islands where the camphor tree grows. The fifth sea is called Salahit and is very large and filled with wonders. The sixth sea is called Kardanj ; it is very rainy. The seventh sea is called

2261-454: Is produced and magma is forced up creating underwater mountains, some of which may form chains of volcanic islands near to deep trenches. Near some of the boundaries between the land and sea, the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed. As they grate together, the continental plates are deformed and buckle causing mountain building and seismic activity. Every ocean basin has

2380-407: Is pushed across the surface of the ocean by the wind, but this represents a transfer of energy and not horizontal movement of water. As waves approach land and move into shallow water , they change their behavior. If approaching at an angle, waves may bend ( refraction ) or wrap around rocks and headlands ( diffraction ). When the wave reaches a point where its deepest oscillations of the water contact

2499-423: Is reflected back out of the water. Red light is most easily absorbed and thus does not reach great depths, usually to less than 50 meters (164 ft). Blue light, in comparison, can penetrate up to 200 meters (656 ft). Second, water molecules and very tiny particles in ocean water preferentially scatter blue light more than light of other colors. Blue light scattering by water and tiny particles happens even in

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2618-471: Is reserved mainly for agriculture and is subject to flash floods , even though the overall quantity of water is lower than in the past and lower than demand. The main products of the farms around the river are cereals including – unusually for Europe – rice , which requires heavy irrigation . The latter method is the chief consumer of surface water, while industrial and human consumption use underground water. The Po has 141 tributaries . They include (R on

2737-480: Is sometimes referred to as the World Ocean, global ocean or the great ocean . The concept of a continuous body of water with relatively unrestricted exchange between its components is critical in oceanography . The word ocean comes from the figure in classical antiquity , Oceanus ( / oʊ ˈ s iː ə n ə s / ; ‹See Tfd› Greek : Ὠκεανός Ōkeanós , pronounced [ɔːkeanós] ),

2856-839: Is the product of the islands of the northern ocean ( Baltic Sea )" and attributes its introduction into the Po Valley to the Veneti , the last link in a trade route to the north through Pannonia . Pliny ( Hist. Nat. , iii. 122) also gives the Ligurian name of the Po as Bodincus , which he translates as "bottomless". The root bod- has been generally analyzed as containing the PIE base * bhu(n)d(h) - seen in Sanskrit budhnah and Avestan buna - "bottom", Greek pythmen "foundation", Latin fundus "bottom", Old Irish bond "sole of

2975-519: The 1947 Peace Treaty of Paris as a punitive measure against Italy. These can be found on the Mont Cenis and Mongenevre passes. The former contains a reservoir dammed at the Po end and so technically constitutes part of its basin, although it contributes little to the water flow as the water is, by definition, retained by the dam. The Po is the longest river in Italy; at its widest point it is 503 m (1,650 ft) across. The vast valley around

3094-1063: The Black Sea , Caspian Sea , Red Sea , Mediterranean Sea , and Adriatic Sea . In British Colonial times the Clipper Ship Tea Route from China to England was the longest trade route in the world. It took sailors through seven seas near the Dutch East Indies : the Banda Sea , the Celebes Sea , the Flores Sea , the Java Sea , the South China Sea , the Sulu Sea , and the Timor Sea . The Seven Seas referred to those seas, and if someone had sailed

3213-669: The Busa di Tramontana to the north and the Busa di Scirocco to the south, while the mainstream, the Busa Dritta , enters Punta Maistra and exits finally past Pila lighthouse. Despite the park administration's definition of the active delta as beginning at Porto Viro, there is another active channel upstream from it at Santa Maria in Punta, where the Fiume Po divides into the Po di Goro and

3332-598: The European Union (EU) Water Framework Directive , 2000/60/EC. This takes in water management and flood risk plans antecedent. Between 2009 and 2015 the Po Valley Project (the implementation of the plan) took more than 60 measures, notably to: heighten and strengthen levees , increase flood-meadows , resume natural sediment transport and deposition points, enlarge wetlands, afforest, re-nature, promote biodiversity and recreational use. In Roman times

3451-540: The Last Glacial Maximum around 20,000 years ago, which brought the Adriatic to a high point at about 5,500 years ago. Since then the Po delta had been prograding . The rate of coastal zone progradation between 1000 BC and 1200 AD was 4 m/yr. Human factors, however, brought about a change in the equilibrium in the mid-20th century with the result that the entire coastline of the northern Adriatic

3570-695: The Miocene Epoch, the Messinian (7–5 mya ), the Messinian salinity crisis , a near drying of the Mediterranean, was caused by the sea level dropping below the sill at the Strait of Gibraltar and the equilibrium between evaporation and replenishment shifting in favor of evaporation. At that time the Po Valley and the Adriatic depression were a single canyon system thousands of feet deep. On

3689-691: The North Sea or the Red Sea . There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as marginal seas ) or wholly (as inland seas ) bordered by land. The contemporary concept of the World Ocean was coined in the early 20th century by the Russian oceanographer Yuly Shokalsky to refer to the continuous ocean that covers and encircles most of Earth. The global, interconnected body of salt water

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3808-565: The Parco Regionale Veneto , one of the tracts under the authority of the Parco Delta del Po , contains the latest branches of the Po. The Po di Gnocca branches to the south followed by the Po di Maestra to the north at Porto Tolle . At Tolle downstream the Po di Venezia divides into the Po delle Tolle to the south and the Po della Pila to the north. The former exits at Bonelli. The latter divides again at Pila into

3927-415: The Po di Venezia . The fossil Po is the region of no longer active channels from the Po to the sea. It begins upstream from Ferrara . The Fiume Po currently flowing to the north of Ferrara is the result of a diversion at Ficarolo in 1152 made in the hope of relieving flooding in the vicinity of Ravenna . The diversion channel was at first called the Po di Ficarolo . The Fiume Po before then followed

4046-495: The Po di Volano , no longer connected to the Po, which ran to the south of Ferrara and exited near Volano . In Roman times it did not exit there but ran to the south as the Padus Vetus ("old Po") exiting near Comacchio , from which split the Po di Primaro exiting close to Ravenna . Before 1152 the seaward extension of today's delta, about 12 km (7.5 mi), did not exist. The entire region from Ravenna to Chioggia

4165-481: The South Pacific Ocean , at 48°52.6′S 123°23.6′W  /  48.8767°S 123.3933°W  / -48.8767; -123.3933  ( Point Nemo ) . This point is roughly 2,688 km (1,670 mi) from the nearest land. There are different customs to subdivide the ocean and are adjourned by smaller bodies of water such as, seas , gulfs , bays , bights , and straits . The ocean

4284-477: The Taglio di Porto Viro , "Porto Viro cut-off". Their intent was to stop the gradual migration of the Po toward the lagoon of Venice, which would have filled up with sediment had contact been made. The subsequent town of Taglio di Po grew around the diversionary works. The lock of Volta Grimana blocked the old channel, now the Po di Levante , which flows to the Adriatic through Porto Levante. Below Taglio di Po

4403-592: The Thames Barrier is designed to protect London from a storm surge, while the failure of the dykes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States. Most of the ocean is blue in color, but in some places the ocean is blue-green, green, or even yellow to brown. Blue ocean color is a result of several factors. First, water preferentially absorbs red light, which means that blue light remains and

4522-649: The canton of Ticino , which is essentially drained by the river Ticino rising in the Gotthard Area , and includes Lake Maggiore and Lake Lugano . A small part of the canton of Grisons drains to the Po, partly via the Ticino. The Simplon Valley in the canton of Valais is drained by the Diveria . A minute section of the Po basin belongs to France in the Vallée Étroite  [ it ; fr ] (literally,

4641-410: The carbon cycle , and the water cycle by acting as a huge heat reservoir . Ocean scientists split the ocean into vertical and horizontal zones based on physical and biological conditions. The pelagic zone is the open ocean's water column from the surface to the ocean floor. The water column is further divided into zones based on depth and the amount of light present. The photic zone starts at

4760-406: The coastline and structure of the world ocean. A global ocean has existed in one form or another on Earth for eons. Since its formation the ocean has taken many conditions and shapes with many past ocean divisions and potentially at times covering the whole globe. During colder climatic periods, more ice caps and glaciers form, and enough of the global water supply accumulates as ice to lessen

4879-452: The comuni of Alfonsine, Argenta, Cervia, Codigoro, Comacchio, Goro, Mesola, Ostellato and Ravenna. The 53,653 ha (132,580 acres) of the park contain wetlands, forest, dunes and salt pans. It has a high biodiversity , with 1,000–1,100 plant species and 374 vertebrate species, of which 300 are birds. The most recent part of the delta, which projects into the Adriatic between Chioggia and Comacchio , contains channels that connect to

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4998-604: The drainage basin – nearly three times higher than estimated. On February 24, 2010, the Po was contaminated by an oil spill coming from a refinery in Villasanta through the Lambro , the Agenzia Nazionale Stampa Associata news agency has estimated it to be about 600,000 liters. Until 1989 water resources were administered regionally or locally. The major authority on the lower Po

5117-591: The ocean floor , they begin to slow down. This pulls the crests closer together and increases the waves' height , which is called wave shoaling . When the ratio of the wave's height to the water depth increases above a certain limit, it " breaks ", toppling over in a mass of foaming water. This rushes in a sheet up the beach before retreating into the ocean under the influence of gravity. Earthquakes , volcanic eruptions or other major geological disturbances can set off waves that can lead to tsunamis in coastal areas which can be very dangerous. The ocean's surface

5236-535: The sea of Sanji , also known as Kanjli. It is the sea of China; one is driven by the south wind until one reaches a freshwater bay, along which are fortified places and cities, until one reaches Khanfu . This passage demonstrates the Seven Seas as referenced in Medieval Arabian literature : Arab seafarers may have also considered other important seas nearby which they navigated regularly, including

5355-704: The "Sibbichaean". Lightfoot does not comment on the remaining three seas. After the discovery of the Americas during the Age of Discovery, the "seven seas" were reckoned by some as: The last two of these are now reckoned to be part of the Atlantic Ocean, and the Mediterranean either part of the Atlantic or omitted. Splitting the Atlantic and Pacific into north and south and adding the Southern Ocean returns

5474-399: The Adriatic and therefore is called the active delta by the park authorities, whereas the fossil delta contains channels that no longer connect the Po to the Adriatic (but once did). The active delta was created in 1604 when the city of Venice diverted the main stream, the Po grande or Po di Venezia , from its channel north of Porto Viro to the south of Porto Viro in a channel then called

5593-531: The Apennines filled the valley and the central Adriatic generally to a depth of 1,000 m (3,300 ft) to 2,000 m (6,600 ft) but from 2,000 m (6,600 ft) to 3,000 m (9,800 ft) off the current mouth of the Po, with pockets as deep as 6,000 m (20,000 ft). At the start of the Pleistocene the valley was full. Cycles of transgression and regression are detectable in

5712-442: The Earth's biosphere . Oceanic evaporation , as a phase of the water cycle, is the source of most rainfall (about 90%), causing a global cloud cover of 67% and a consistent oceanic cloud cover of 72%. Ocean temperatures affect climate and wind patterns that affect life on land. One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where

5831-623: The Elder has the most to say about the Padus of his times. Herodotus had expressed doubt concerning the existence of a river in Europe, Eridanos , which flowed into the northern sea, he said, from which amber came. He believed it was a Greek name (there are other Eridanos rivers in Greece), "invented by some poet," but makes no conjectures as to where it might be. Pliny points out that in his own time

5950-479: The Eridanos had become wrongly identified with the Padus . He does not know when or how, but like Herodotus, he blames the poets. Amber is supposed to have come from there. Phaëthon , son of the sun, struck by lightning changed into poplars and exuded tears every year, which is the source of amber (a myth of Pausanias ). Expressing surprise at the ignorance of the poets, Pliny says "There can be no doubt that amber

6069-839: The Ministry of Public Works, headed by a chairman appointed by the Head of State and the Council of Ministers. Its headquarters are in Venice. Its domain is the management and protection of the water system in Veneto , Mantua , Trento , Bolzano and Friuli-Venezia Giulia . In 1989 in response to the major geologic problems that were developing along the river Law no. 183/89 was passed authorizing The Po Basin Water Board (Autorità di bacino del fiume Po), which would direct operations concerning all

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6188-456: The Moon are 20x stronger than the Moon's tidal forces on the Earth.) The primary effect of lunar tidal forces is to bulge Earth matter towards the near and far sides of the Earth, relative to the moon. The "perpendicular" sides, from which the Moon appears in line with the local horizon, experience "tidal troughs". Since it takes nearly 25 hours for the Earth to rotate under the Moon (accounting for

6307-403: The Moon's 28 day orbit around Earth), tides thus cycle over a course of 12.5 hours. However, the rocky continents pose obstacles for the tidal bulges, so the timing of tidal maxima may not actually align with the Moon in most localities on Earth, as the oceans are forced to "dodge" the continents. Timing and magnitude of tides vary widely across the Earth as a result of the continents. Thus, knowing

6426-471: The Moon's gravity, oceanic tides are also substantially modulated by the Sun's tidal forces, by the rotation of the Earth, and by the shape of the rocky continents blocking oceanic water flow. (Tidal forces vary more with distance than the "base" force of gravity: the Moon's tidal forces on Earth are more than double the Sun's, despite the latter's much stronger gravitational force on Earth. Earth's tidal forces upon

6545-400: The Moon's position does not allow a local to predict tide timings, instead requiring precomputed tide tables which account for the continents and the Sun, among others. During each tidal cycle, at any given place the tidal waters rise to maximum height, high tide, before ebbing away again to the minimum level, low tide. As the water recedes, it gradually reveals the foreshore , also known as

6664-577: The Narrow Valley) running from Mont Thabor to the Italian ski resort of Bardonecchia . Although in France, Vallée Étroite is so remote it is essentially administered by Italy (telephone network, rubbish collections, etc. ). Further minuscule parts of the Po's basin (measurable in the hundreds of metres of linear distance) within France are found in the form of small streamheads forced into France by

6783-693: The New Testament . A chapter titled The Seven Seas according to the Talmudists, and the four Rivers compassing the Land includes the "Great Sea" (now called the Mediterranean Sea), the "Sea of Tiberias" ( Sea of Galilee ), the "Sea of Sodom" ( Dead Sea ), the "Lake of Samocho" (probably the (mostly) dried-up Hula Lake, called Semechonitis by Josephus and lake Sumchi in the Talmud), also called

6902-648: The Okeanos is represented with a dragon-tail on some early Greek vases. Scientists believe that a sizable quantity of water would have been in the material that formed Earth. Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. This is called atmospheric escape . During planetary formation , Earth possibly had magma oceans . Subsequently, outgassing , volcanic activity and meteorite impacts , produced an early atmosphere of carbon dioxide , nitrogen and water vapor , according to current theories. The gases and

7021-513: The Po are formed by a spring seeping from a stony hillside at Pian del Re, a flat place at the head of the Val Po under the northwest face of Monviso . The Po then extends along the 45th parallel north before ending at a delta projecting into the Adriatic Sea near Venice . It is characterized by its large discharge (several rivers over 1,000 km have a discharge inferior or equal to

7140-565: The Po is called the Po Basin or Po Valley (Italian Pianura Padana or Val Padana ); the main industrial area and the largest agricultural area in the country - accounting for 35% of Italian agricultural production . In 2002, more than 16 million people lived in the area, at the time nearly one-third of the population of Italy. The two main economic uses of the valley are for industry and for agriculture. The industrial centres, such as Turin and Milan, are located on higher terrain, away from

7259-539: The Po) and Transpadane Gaul (north of the Po). The Po has a drainage area of 74,000 km in all, 70,000 of those being in Italy, of which 41,000 is in montane environments and 29,000 on the plain. The slope of the Po's river valley decreases from 0.35% in the west to 0.14% in the east, a low gradient. Along its path lie 450 standing lakes. Almost all of the rest of the non-Italy basin is in Switzerland , primarily in

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7378-462: The Po). It is, with the Rhône and Nile , one of the three Mediterranean rivers with the largest water discharge. As a result of its characteristics, the river is subject to heavy flooding. Consequently, over half its length is controlled with embankments . The river flows through many important Italian cities, including Turin , Piacenza , Cremona and Ferrara . It is connected to Milan through

7497-557: The Po, for which the European Environment Agency cited the city. Since 2005, all sewage from Milan is treated in plants at Nosedo, San Rocco and Peschiera Borromeo. These treat the sewage from over 2.5 million inhabitants. In 2005, water from the Po was found to contain much benzoylecgonine , passed by cocaine users in urine . Based on these figures, cocaine consumption was estimated to be about 4 kg daily, or 27 doses per day per thousand young adults in

7616-455: The Po. Nine gates are 6.5 m (21 ft) high and two are 8 m (26 ft) high for sediment-scouring purposes. A spillway to the right passes through a hydroelectric station of 4 generators of 76 MW each operated by a 3.5–11 m (11–36 ft) head of water. The spillway connects to a diversionary canal subtending a 12 km (7.5 mi) loop of the Po. A ship lock 85 m (279 ft) long and 12 m (39 ft) wide next to

7735-476: The Seven Seas it meant he had sailed to, and returned from, the other side of the world. The term in modern usage originated from Greece, where the seven seas were considered as: The meaning of septem maria ( Latin ) in Ancient Rome is different than the phrase "seven seas" in the modern era. The navigable network in the mouths of the Po river discharges into saltmarshes on the Adriatic shore and

7854-741: The World Ocean, such as the Caspian Sea . The deepest region of the ocean is at the Mariana Trench , located in the Pacific Ocean near the Northern Mariana Islands . The maximum depth has been estimated to be 10,971 meters (35,994 ft). The British naval vessel Challenger II surveyed the trench in 1951 and named the deepest part of the trench the " Challenger Deep ". In 1960, the Trieste successfully reached

7973-421: The amounts in other parts of the water cycle. The reverse is true during warm periods. During the last ice age, glaciers covered almost one-third of Earth's land mass with the result being that the oceans were about 122 m (400 ft) lower than today. During the last global "warm spell," about 125,000 years ago, the seas were about 5.5 m (18 ft) higher than they are now. About three million years ago

8092-479: The atmosphere are thought to have accumulated over millions of years. After Earth's surface had significantly cooled, the water vapor over time would have condensed, forming Earth's first oceans. The early oceans might have been significantly hotter than today and appeared green due to high iron content. Geological evidence helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption)

8211-407: The bottom of the trench, manned by a crew of two men. Oceanographers classify the ocean into vertical and horizontal zones based on physical and biological conditions. The pelagic zone consists of the water column of the open ocean, and can be divided into further regions categorized by light abundance and by depth. The ocean zones can be grouped by light penetration into (from top to bottom):

8330-406: The elder of the Titans in classical Greek mythology . Oceanus was believed by the ancient Greeks and Romans to be the divine personification of an enormous river encircling the world. The concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion,

8449-528: The flow in places nearly dries up, causing local contention. As a result of decreased flow, salt water is intruding into the aquifers and coastal ground water. Eutrophication in standing waters and streams of low flow is on the increase. The valley is subsiding due to the extraction of ground water. Always prone to fog, the valley is subject to heavy smog due to industrial atmospheric emissions, especially from Turin . The city of Milan had no sewage treatment plants. Sewage went through channels directly into

8568-467: The foot". The word Bodincus appears in the place name Bodincomagus , a Ligurian town on the right bank of the Po downstream from today's Turin. The Po, along with other rivers in northern Italy , was the scene of numerous military episodes throughout the Middle Ages and all the major cities and coastal lordships were equipped with real river fleets. Particularly violent were the clashes between

8687-412: The formation of unusually high rogue waves . Most waves are less than 3 m (10 ft) high and it is not unusual for strong storms to double or triple that height. Rogue waves, however, have been documented at heights above 25 meters (82 ft). The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave

8806-694: The institution of two regional parks in the regions in which it is situated: Veneto and Emilia-Romagna . The Po Delta Regional Park in Emilia-Romagna, the largest, consists of four parcels of land on the right bank of the Po and to the south. Created by law in 1988, it was managed by a consortium, the Consorzio per la gestione del Parco , to which Ferrara and Ravenna provinces belong as well as nine comuni : Comacchio , Argenta , Ostellato , Goro , Mesola , Codigoro , Ravenna , Alfonsine , and Cervia . Executive authority resided in an assembly of

8925-421: The interface between water and air is called swell – a term used in sailing , surfing and navigation . These motions profoundly affect ships on the surface of the ocean and the well-being of people on those ships who might suffer from sea sickness . Wind blowing over the surface of a body of water forms waves that are perpendicular to the direction of the wind. The friction between air and water caused by

9044-482: The intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude. When the sun and moon are aligned (full moon or new moon), the combined effect results in the higher "spring tides", while the sun and moon misaligning (half moons) result in lesser tidal ranges. In the open ocean tidal ranges are less than 1 meter, but in coastal areas these tidal ranges increase to more than 10 meters in some areas. Some of

9163-929: The land of Israel. And what are the seven seas? The sea of Tiberias, the Sea of Sodom, the Sea of Helath, the Sea of Hiltha, the Sea of Sibkay, the Sea of Aspamia and the Great Sea. And what are the four rivers? The Jordan, the Yarmuk, the Keramyhon and Pigah." According to this and other passages, the Talmudic Seven Seas include: Various transliterations for the sea names from Hebrew exist. For Helath: Chelath and Shelyith . For Hiltha: Chiltha and Chultha . For Sibkay: Sibchi and Somcho . And for Aspamia: Apamia . The 17th century churchman and scholar John Lightfoot mentions this set of seas in his Commentary on

9282-739: The largest tidal ranges in the world occur in the Bay of Fundy and Ungava Bay in Canada, reaching up to 16 meters. Other locations with record high tidal ranges include the Bristol Channel between England and Wales, Cook Inlet in Alaska, and the Río Gallegos in Argentina. Tides are not to be confused with storm surges , which can occur when high winds pile water up against the coast in

9401-457: The late Roman Republic and the early Roman Empire , long after the valley had been occupied successively by prehistoric and historic peoples: Ligures , Etruscans , Celts , Veneti , Umbri , and Romans. At that late date, the ancient authors were attempting to explain the provenance of the name. Perhaps the earliest of these, Polybius (2nd century BC), uses Pados (in Greek) and says that it

9520-530: The list to seven. Detailed reckonings of the divisions of the world ocean into oceans and seas is not limited to lists of seven. For example, the International Hydrographic Organization recognizes many marginal seas ; some saltwater lakes and the freshwater Sea of Galilee also have "sea" in their names. Ocean The ocean is the body of salt water that covers approximately 70.8% of Earth . In English ,

9639-471: The majority of Earth's surface. It includes the Pacific , Atlantic , Indian , Southern/Antarctic , and Arctic oceans. As a general term, "the ocean" and "the sea" are often interchangeable. Strictly speaking, a "sea" is a body of water (generally a division of the world ocean) partly or fully enclosed by land. The word "sea" can also be used for many specific, much smaller bodies of seawater, such as

9758-536: The name of Atriatic to the sea now called the Adriatic. A history of Venice states: The expression "to sail the seven seas" was a classical flourish signifying nautical skill. It was applied to the Venetians long before they sailed the oceans. It is plausible that the English idiom is borrowed from this Venetian idiom, with a loss of geographic context. The Persians used the term "the Seven Seas" to refer to

9877-408: The ocean faces many environmental threats, such as marine pollution , overfishing , and the effects of climate change . Those effects include ocean warming , ocean acidification and sea level rise . The continental shelf and coastal waters are most affected by human activity. The terms "the ocean" or "the sea" used without specification refer to the interconnected body of salt water covering

9996-693: The ocean, deep ocean temperatures range between −2 °C (28 °F) and 5 °C (41 °F). Constant circulation of water in the ocean creates ocean currents . Those currents are caused by forces operating on the water, such as temperature and salinity differences, atmospheric circulation (wind), and the Coriolis effect . Tides create tidal currents, while wind and waves cause surface currents. The Gulf Stream , Kuroshio Current , Agulhas Current and Antarctic Circumpolar Current are all major ocean currents. Such currents transport massive amounts of water, gases, pollutants and heat to different parts of

10115-508: The ocean, on land and air. All these processes and components together make up ocean surface ecosystems . Tides are the regular rise and fall in water level experienced by oceans, primarily driven by the Moon 's gravitational tidal forces upon the Earth. Tidal forces affect all matter on Earth, but only fluids like the ocean demonstrate the effects on human timescales. (For example, tidal forces acting on rock may produce tidal locking between two planetary bodies.) Though primarily driven by

10234-469: The ocean. If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. The size of the waves depends on the fetch , the distance that the wind has blown over the water and the strength and duration of that wind. When waves meet others coming from different directions, interference between the two can produce broken, irregular seas. Constructive interference can lead to

10353-419: The oceans absorb CO 2 from the atmosphere , a higher concentration leads to ocean acidification (a drop in pH value ). The ocean provides many benefits to humans such as ecosystem services , access to seafood and other marine resources , and a means of transport . The ocean is known to be the habitat of over 230,000 species , but may hold considerably more – perhaps over two million species. Yet,

10472-425: The oceans could have been up to 50 m (165 ft) higher. The entire ocean, containing 97% of Earth's water, spans 70.8% of Earth 's surface, making it Earth's global ocean or world ocean . This makes Earth, along with its vibrant hydrosphere a "water world" or " ocean world ", particularly in Earth's early history when the ocean is thought to have possibly covered Earth completely. The ocean's shape

10591-434: The oceans have been mapped. The zone where land meets sea is known as the coast , and the part between the lowest spring tides and the upper limit reached by splashing waves is the shore . A beach is the accumulation of sand or shingle on the shore. A headland is a point of land jutting out into the sea and a larger promontory is known as a cape . The indentation of a coastline, especially between two headlands,

10710-537: The oceans may have always been on the Earth since the beginning of the planet's formation. In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity . The origin of Earth's oceans is unknown. Oceans are thought to have formed in the Hadean eon and may have been the cause for the emergence of life . Plate tectonics , post-glacial rebound , and sea level rise continually change

10829-451: The photic zone, the mesopelagic zone and the aphotic deep ocean zone: The pelagic part of the aphotic zone can be further divided into vertical regions according to depth and temperature: Distinct boundaries between ocean surface waters and deep waters can be drawn based on the properties of the water. These boundaries are called thermoclines (temperature), haloclines (salinity), chemoclines (chemistry), and pycnoclines (density). If

10948-418: The power of a storm wave impacting on the foot of a cliff has a shattering effect as air in cracks and crevices is compressed and then expands rapidly with release of pressure. At the same time, sand and pebbles have an erosive effect as they are thrown against the rocks. This tends to undercut the cliff, and normal weathering processes such as the action of frost follows, causing further destruction. Gradually,

11067-541: The presidents of the provinces, the mayors of the comuni and the board of directors. They employed a Technical-Scientific Committee and a Park Council to carry out directives. In 1999 the park was designated a World Heritage Site by UNESCO and was added to "Ferrara, City of the Renaissance, and its Po Delta." From 2012 the park is managed by the Ente di Gestione per i Parchi e la Biodiversità - Delta del Po , composed by

11186-484: The right bank, L on the left, looking downstream ): The Reno (R) was a tributary of the Po until the middle of the eighteenth century when the course was diverted to lessen the risk of devastating floods. The Tanaro is about 50 km (31 mi) longer than the upper Po at their confluence near Alessandria . The longest tributaries of the Po are Adda (313 km), Oglio (280 km), Tanaro (276 km) and Ticino (248 km). The Po Delta wetlands have been protected by

11305-402: The river. However, transit is severely hampered during summer months by low water levels. At the village of Isola Serafini in the comune of Monticelli d'Ongina , Piacenza Province , 40 km (25 mi) downstream from Piacenza, a 362 m (1,188 ft) long, 20 m (66 ft) high gate dam featuring eleven 30 m (98 ft) openings gated by vertical lift gates, crosses

11424-612: The river. They rely for power on the numerous hydroelectric stations in or on the flanks of the Alps, and on the coal/oil power stations which use the water of the Po basin as coolant. Drainage from the north is mediated through several large, scenic lakes, commonly referred to as the Italian Lakes , and shared with Switzerland. The streams are now controlled by so many dams as to slow the river's sedimentation rate, causing geologic problems. The expansive, moist and fertile flood plain

11543-455: The seabed between adjoining plates to form mid-oceanic ridges and here convection currents within the mantle tend to drive the two plates apart. Parallel to these ridges and nearer the coasts, one oceanic plate may slide beneath another oceanic plate in a process known as subduction . Deep trenches are formed here and the process is accompanied by friction as the plates grind together. The movement proceeds in jerks which cause earthquakes, heat

11662-407: The seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides and currents. Dredging removes material and deepens channels but may have unexpected effects elsewhere on the coastline. Governments make efforts to prevent flooding of the land by the building of breakwaters , seawalls , dykes and levees and other sea defences. For instance,

11781-509: The seven seas is separate from the etymology of the term. Plausible etymologies are discussed below including the Po river delta in the north Adriatic sea. The phrase’s association with the world oceans in the late 19th century is characterized by Rudyard Kipling’s 1896 book The Seven Seas . The Arabs and their near neighbours considered the Seven Seas ( Arabic : البحار السبعة ) to be the seas that they encountered in their voyages to The East. They were trading routes in ancient times and since

11900-474: The severity, resulting in a "decrease in precipitation during critical crop growing seasons". In July 2022, the Italian government declared a state of emergency in the regions Emilia-Romagna, Lombardy, Piedmont, Veneto and Friuli-Venezia Giulia. Water levels decreased and revealed large riverbed areas and lost objects. The Po is first certainly identified in the Graeco-Roman historians and geographers of

12019-401: The shore at the rate of six to eight per minute and these are known as constructive waves as they tend to move material up the beach and have little erosive effect. Storm waves arrive on shore in rapid succession and are known as destructive waves as the swash moves beach material seawards. Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide,

12138-399: The source of the food supply which sustains most of the ocean ecosystem . Ocean photosynthesis also produces half of the oxygen in the Earth's atmosphere. Light can only penetrate a few hundred more meters; the rest of the deeper ocean is cold and dark (these zones are called mesopelagic and aphotic zones). The continental shelf is where the ocean meets dry land. It is more shallow, with

12257-719: The southwest the Apennine Mountains bordered a land mass termed Tyrrhenis geologically. Their orogeny was just being completed in the Miocene. On the north the Alpine Orogeny had already created the Alps . At the end of the Messinian the ocean broke through the sill and the Mediterranean refilled. The Adriatic transgressed into all of northern Italy. In the subsequent Pliocene sedimentary outwash primarily from

12376-502: The station passes some traffic through the canal, but above the dam traffic is mainly barges. The average flow at the dam is 854 m /s, with a 12,800 m /s maximum. The historic average flow for June is 1,805 cubic metres per second. In late June 2022, the flow measured in Ferrara fell below an average of 145 cubic metres per second. Climate change has caused several droughts across Northern Italy, with predictions for their frequency and

12495-468: The streams forming the Oxus River . The Babylonian Talmud mentions seven seas and four rivers that surround the land of Israel. In Tractate Bava Batra , fol. 74b , it reads: When R. Dimi came he said R. Yohanan said: "What is the meaning of the verse, 'For he hath founded it upon the seas and established it upon the floods.' (Ps. 24:2)? This refers to the seven seas and four rivers that surround

12614-412: The surface and is defined to be "the depth at which light intensity is only 1% of the surface value" (approximately 200 m in the open ocean). This is the zone where photosynthesis can occur. In this process plants and microscopic algae (free floating phytoplankton ) use light, water, carbon dioxide, and nutrients to produce organic matter. As a result, the photic zone is the most biodiverse and

12733-456: The system forms). As the world's ocean is the principal component of Earth's hydrosphere , it is integral to life on Earth, forms part of the carbon cycle and water cycle , and – as a huge heat reservoir – influences climate and weather patterns. The motions of the ocean surface, known as undulations or wind waves , are the partial and alternate rising and falling of the ocean surface. The series of mechanical waves that propagate along

12852-451: The term ocean also refers to any of the large bodies of water into which the world ocean is conventionally divided. The following names describe five different areas of the ocean: Pacific , Atlantic , Indian , Antarctic/Southern , and Arctic . The ocean contains 97% of Earth's water and is the primary component of Earth's hydrosphere and is thereby essential to life on Earth. The ocean influences climate and weather patterns,

12971-457: The time of Muhammad , they are the places where Islam spread and is widely practised. In the 9th century AD, author Ya'qubi wrote: Whoever wants to go to China must cross seven seas, each one with its own color and wind and fish and breeze, completely unlike the sea that lies beside it. The first of them is the Sea of Fars , which men sail setting out from Siraf . It ends at Ra’s al-Jumha; it

13090-589: The valley and the Adriatic as far as its centre and in the southern Adriatic. From the Pleistocene alternation of maritime and alluvial sediments occur as far west as Piacenza . The exact sequences at various locations have been studied extensively. Apparently the sea advanced and receded over the valley in conformance to an equilibrium between sedimentation and glacial advance or recession at 100,000-year intervals and 100 m (330 ft) to 120 m (390 ft) fluctuation of sea level. An advance began after

13209-434: The very clearest ocean water, and is similar to blue light scattering in the sky . Ocean water represents the largest body of water within the global water cycle (oceans contain 97% of Earth's water ). Evaporation from the ocean moves water into the atmosphere to later rain back down onto land and the ocean. Oceans have a significant effect on the biosphere . The ocean as a whole is thought to cover approximately 90% of

13328-555: The water resources in the Po basin (see under Po Valley ). Its headquarters have been in Parma since its inception in 1990. It considers itself a synergy among all the institutions concerned with the preservation and development of the Po basin. It is administered by officials chosen from the administrations of the constituent regions and provinces. In 2009 the water board began its Integrated River Basin Management Plan to meet

13447-498: The waterway was navigable as far upstream as Turin . Today the waterway is navigable for substantial craft (up to 1350 tonnes —the European Class IV waterway standard ) from Cremona to the river delta on the Adriatic . Passage by smaller vessels is available for some distance above Cremona. In the lower reaches the surrounding basin is generally flat and it is served by a complicated network of small canals linked to

13566-476: The world, and from the surface into the deep ocean. All this has impacts on the global climate system . Ocean water contains dissolved gases, including oxygen , carbon dioxide and nitrogen . An exchange of these gases occurs at the ocean's surface. The solubility of these gases depends on the temperature and salinity of the water. The carbon dioxide concentration in the atmosphere is rising due to CO 2 emissions , mainly from fossil fuel combustion. As

13685-598: Was colloquially called the "Seven Seas" in ancient Roman times. Pliny the Elder , a Roman author and fleet commander, wrote about these lagoons , separated from the open sea by sandbanks: All those rivers and trenches were first made by the Etruscans , thus discharging the flow of the river across the marshes of the Atriani called the Seven Seas, with the famous harbor of the Etruscan town of Atria which formerly gave

13804-592: Was dense swamps, explaining why the Via Aemilia was constructed between Rimini and Piacenza and did not begin further north. The Mediterranean Basin is a depression in the Earth 's crust caused by the African Plate slipping under the Eurasian Plate . Typically in geologic history the depression is filled with sea water under various geologic names such as Tethys Sea . In the last period of

13923-775: Was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago. In the Nuvvuagittuq Greenstone Belt , Quebec , Canada, rocks dated at 3.8 billion years old by one study and 4.28 billion years old by another show evidence of the presence of water at these ages. If oceans existed earlier than this, any geological evidence either has yet to be discovered, or has since been destroyed by geological processes like crustal recycling . However, in August 2020, researchers reported that sufficient water to fill

14042-533: Was the Magistrato alle Acque di Venezia , first formed in the 16th-century Republic of Venice . It made all the decisions concerning the diversion of the lower river. Most part of the delta is still in Veneto . In 1907 under the Kingdom of Italy the agency became the Magistrato alle Acque and took responsibility for all the water resources in northeastern Italy. Currently it is a decentralized institution of

14161-484: Was to be identified with the Eridanos of the poets. Moreover, the country people call it Bodencus . This implies that a "country" population either remained from prehistoric times or adopted the name in use by that substrate. The name has been segmented as Bod-encus or Bod-incus , the suffix being characteristic of the ancient Ligurian language of northern Italy, southern France, Corsica and elsewhere. Pliny

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