What are the differences between an ocean, a sea, a bay and a gulf? | Reference.com What are the differences between an ocean, a sea, a bay and a gulf? A: Quick Answer Oceans, seas, bays and gulfs are all primarily distinguished by size. An ocean and a sea differ mainly by size as oceans are larger than seas. Similarly, the difference between a bay and a gulf is also based on size. Gulfs are larger than bays, and small bays are sometimes called coves. Full Answer Oceans are the largest bodies of water on Earth, and they all contain salt water. There are only five oceans: the Atlantic, Pacific, Arctic, Indian and Southern Oceans. The Atlantic Ocean is divided into the North and South Atlantic Oceans by the equator, and the Pacific Ocean is divided into the North and South Pacific Oceans by the same line. Seas are similar to oceans in that they contain salt water, but they are smaller in size. There are many more seas than oceans, and prominent examples include the Red Sea, the Mediterranean Sea and the Baltic Sea. Generally, seas are surrounded by land, and oceans surround land.

A bay is an indentation in land by a sea, ocean or even a lake. A large bay that is in an ocean is referred to as a gulf. Because of their size and significance, most gulfs are specifically named. The Gulf of Mexico and the Persian Gulf are common examples. Both gulfs and bays are sometimes referred to as inlets. THE BALTIC SEA ANOMALY OCEAN X Location map of the Baltic Sea The Baltic Sea is a mediterranean sea located between Central and Northern Europe, from 53ï¿½N to 66ï¿½N latitude and from 10ï¿½E to 30ï¿½E longitude. It is bounded by the Swedish part of the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the ï¿½resund, the Great Belt and the Little Belt. The Kattegat continues through Skagerrak into the North Sea and the Atlantic Ocean. The Baltic Sea is connected by artificial waterways to the White Sea via the White Sea Canal, and to the German Bight of the North Sea via the Kiel Canal.

The central part, also called the Baltic Proper, is bordered on its northern edge by the Gulf of Bothnia, on its northeastern edge by the Gulf of Finland, and on its eastern edge by the Gulf of Riga. The Baltic Sea covers about 149,000 square miles (386,000 square km). The catchment area drained by the rivers bringing fresh water into the Baltic is about four times as large as the sea itself. The Baltic proper stretches southwest-northeast on the eastern side of the Scandinavian Peninsula from latitude 54ï¿½ N to very near the Arctic Circle; its major axis, from eastern Denmark to southern Finland , is a little more than 1,000 miles (1,600 km) long, with an average width of about 120 miles (190 km). The western Baltic extends north through insular Denmark and includes the Kattegat, a strait separating peninsular Denmark (Jutland, or Jylland) from southwestern Sweden . The Kattegat is bounded on the north by the Skagerrak, a deep inlet of the North Sea that separates southern Norway from northern Jutland.

The average depth is 55 m (180 ft, 30 fathoms). The maximum depth is 459 m (1506 ft) which is on the Swedish side of the center. The surface area is about 349,644 kmï¿½ (145,522 sq mi) and the volume is about 20,000 kmï¿½ (5040 cubic miles). The periphery amounts to about 8,000 km (5,000 mi) of coastline. The busy Baltic route leads to high levels of exhaust and other pollution.

ADMINISTRATION The Helsinki Convention on the Protection of the Marine Environment of the Baltic Sea Area includes the Baltic Sea and the Kattegat, without calling Kattegat a part of the Baltic Sea, "For the purposes of this Convention the "Baltic Sea Area" shall be the Baltic Sea and the Entrance to the Baltic Sea, bounded by the parallel of the Skaw in the Skagerrak at 57ï¿½44.43'N." TRAFFIC Historically, the Kingdom of Denmark collected Sound Dues from ships at the border between the ocean and the land-locked Baltic Sea. They were collected in the ï¿½resund at Kronborg castle near Helsingï¿½r, in the Great Belt at Nyborg. In the Little Belt, the site of intake was moved to Fredericia, after that stronghold had been built. The narrowest part of Little Belt is the "Middelfart Sund" near Middelfart. OCEANOGRAPHY Geographers widely agree that the preferred physical border of the Baltic is a line drawn through the southern Danish islands, Drodgen-Sill and Langeland.

The Drogden Sill is situated north of Kï¿½ge Bugt and connects Dragï¿½r in the south of Copenhagen to Malmï¿½; it is used by the ï¿½resund Bridge, including the Drogden Tunnel. By this definition, the Danish Straits are part of the entrance, but the Bay of Mecklenburg and the Bay of Kiel are parts of the Baltic Sea. Once plastic and other waste gets into the Baltic Sea, it cannot easily escape into the open ocean, ending up on beaches as a subsurface soup that is harmful to marine organisms. The Baltic Sea has a narrow outlet to the ocean - between Sweden and Denmark - because of this the water takes 25-30 years to refresh itself. The World Wildlife Fund , reporting on the Baltic seaport of Stralsund said low oxygen levels have rendered around 70,000 square meters of the sea uninhabitable. The Baltic Sea is in a "critical" condition and in danger of dying unless pollution from the Russian city of St Petersburg is drastically cut.

HYDROGRAPHY and BIOLOGY Drodgen Sill (depth of 7 metres) sets a limit to ï¿½resund and Darss Sill (depth of 18 metres), and a limit to the Belt Sea.The shallow sills are obstacles to the flow of heavy salt water from the Kattegat into the basins around Bornholm and Gotland. The Kattegat and the southwestern Baltic Sea are well oxygenated and have a rich biology. The remainder of the Sea is brackish, poor in oxygen and in species. Thus, statistically, the more of the entrance that is included in its definition, the healthier the Baltic appears; conversely, the more narrowly it is defined, the more endangered its biology appears. ECONOMY Bulk cargoes of oil and coal come by all water routes into the Baltic, and many exports of minerals, timber , and wood products move in the opposite direction by sea around Jutland. These traditional exports represent a diminishing value in overall trade. The greatest values are in consumer goods, most of which are carried in containers by integrated land and sea transport to markets and to and from the North Sea ports of Hamburg in Germany and Rotterdam in the Netherlands.

This has led to increased interest in building a bridge between Denmark and Sweden . Shipbuilding has declined in Sweden but has continued in Poland and Finland (especially for ice-strengthened vessels); marine engines are produced in Denmark. Generally, however, light engineering, high-quality furniture production, and motor-vehicle manufacturing have replaced many of these maritime-based industries. A manned ferry carrying around 240 souls caught fire on the Baltic Sea, injuring 22 people. An explosion on the upper deck of the Lisco Gloria set the ship ablaze. It was not immediately clear what caused the explosion according to reports. The Lithuanian-flagged ferry was travelling from the German port of Kiel to Klaipeda, Lithuania . Six other ships rushed to the scene to help evacuate passengers and crew shortly after the accident. Three people were taken to hospitals by helicopter and the others were being taken back to Germany on another ferry. Unmanned ships not only are better equipped with fire sensors, but also react to emergencies quicker than a human crew. ENVIRONMENTAL ISSUES Since World War II , various nations, including the Soviet Union, the United Kingdom and the United States, have disposed of chemical weapons in the Baltic Sea, raising concerns of environmental contamination.

Even now fishermen accidentally retrieve some of these materials: the most recent available report from the Helsinki Commission notes that four small scale catches of CW munitions representing approximately 105 kilograms (231 lbs) of material were reported in 2005. This is a reduction from the 25 incidents representing 1,110 kilograms (2,447 lbs) of material in 2003. Until now, the U.S. government refuses to disclose the exact coordinates of the wreck sites. Rotting bottles leak Lost and other substances, thus slowly poisoning a substantial part of the Baltic Sea. Slimy and disgusting algae have become a daily problem for holidaymakers along the Baltic shores. Industrial emissions and untreated municipal sewage water have over the last century left the sea suffocated. This is common knowledge and efforts are being made to cope with the problem. However, something quite appalling is about to happen, something that is not as widely known. Giant animal farms are emerging around the Baltic Sea. The EU has decided to make agriculture more efficient in Poland . Russia is to become a self-sufficient meat producer. Multinational food companies are establishing themselves around the Baltic. A large pig farm pollutes as much a small town.

But, in contrast to a municipality, there is no or insufficient sewage treatment. And there are thousands of farms being established in the region. The hunger for meat is turning the Baltic into a giant cesspool of animal excrement . Agricultural and environmental policies are on a collision course, it's industry versus the environment. In this film , the beautiful landscapes of Europe and Russia stand in stark contrast to scientific warnings, to people who are affected and the corporations feathering their nests. For the first time, the people around the Baltic Sea will get this complex situation explained, learn about possible solutions and actions and hear from the politicians responsible. THE BALTIC SEA MEDIA PROJECT (BSMP) The Baltic Sea is one of the most studied seas in the world. The environmental problems are well known. The main threats derive from eutrophication, hazardous substances, over- fishing and maritime transport. The Baltic Sea is surrounded by some of the world's most environmentally conscious societies. And scientists all agree on the most important steps to take. Still, in many respects, the state of this sensitive and almost landlocked sea is deteriorating. The efforts to save the sea are spoiled by national disagreements and short-term interest.

The future and life quality of 90 million people are affected by the Baltic Sea environment. The next ten years will be critical. Can we save the sea that ties us together? Filmmakers Mattias Klum and Folke Rydï¿½n are spending ten years documenting the efforts to save the Baltic Sea. Focusing on the decision-making processes for environmental, scientific and political issues, the aim is to produce a television documentary every other year in cooperation with public service broadcasters around the region. The first programme will be completed in the autumn of 2009. At the same time, production of an international feature documentary will begin (for release in 2017) as well as creation of a range of interactive educational material for use in the whole Baltic region. A map of Northern Europe including the North and Baltic Seas FROZEN SEAS The Baltic Sea is ice-covered at the annual maximum for about 45% of its surface area on average.

The ice-covered area during such a typical winter includes the Gulf of Bothnia, the Gulf of Finland, Gulf of Riga, Vï¿½inameri in the Estonian archipelago, the Stockholm archipelago and the Archipelago Sea of Finnish territorial waters. The remainder of the Baltic itself does not freeze during a normal winter, with the exception of sheltered bays and shallow lagoons such as the Curonian Lagoon. The ice reaches its maximum extent in February or March; typical ice thickness in the northernmost areas in the Bothnian Bay, the northern basin of the Gulf of Bothnia, is about 70 cm (28 in) for landfast sea ice. The thickness decreases farther south. Freezing begins in the northern extremities of Gulf of Bothnia typically in the middle of November, reaching the open waters of the Bothnian Bay in early January. The Bothnian Sea, the basin south of Kvarken, freezes on average in late February. The Gulf of Finland and the Gulf of Riga freeze typically in late January. In 2011, the Gulf of Finland was completely frozen on 15 February.

The ice extent depends on whether the winter is mild, moderate or severe. Severe winters can lead to ice formation around southern Sweden and even in the Danish straits. According to the 18th-century natural historian William Derham, during the severe winters of 1703 and 1708, the ice cover reached as far as the Danish straits. Frequently, parts of the Gulf of Bothnia and Gulf of Finland are frozen, in addition to coastal fringes in more southerly locations such as the Gulf of Riga. This description meant that the whole of the Baltic Sea was covered with ice. It is known that since 1720, the Baltic Sea has frozen over entirely only 20 times. The most recent case was in early 1987, which was the most severe winter in Scandinavia since that date. The ice then covered 400,000 km2 (150,000 sq mi).

During the winter of 2010ï¿½11, which was quite severe compared to those of the last decades, the maximum ice cover was 315,000 km2, which was reached on 25 February 2011. The ice then extended from the north down to the northern tip of Gotland, with small ice-free areas on either side, and the east coast of the Baltic Sea was covered by an ice sheet ca. 25ï¿½100 km (16ï¿½62 mi) wide all the way to Gdańsk. This was brought about by a stagnant high-pressure area that lingered over central and northern Scandinavia from ca. 10 to 24 February. After this, strong southern winds pushed the ice further into the north, and much of the waters north of Gotland were again free of ice, which had then packed against the shores of southern Finland. The effects of the afore-mentioned high-pressure area did not reach the southern parts of the Baltic Sea, and thus the entire sea did not freeze over. However, floating ice was additionally observed near Świnoujście harbour in January 2010.

In the recent years prior to 2011, the Bothnian Bay and the Bothnian Sea were frozen with solid ice near the Baltic coast and dense floating ice far from it. In 2008, there was almost no ice formation except for a short period in March. Piles of drift ice on the shore of Puhtulaid, near Virtsu, Estonia, in late April During winter, fast ice, which is attached to the shoreline, develops first, rendering the ports unusable without the services of icebreakers. Level ice, ice sludge, pancake ice, and rafter ice form in the more open regions. The gleaming expanse of ice is similar to the Arctic , with wind-driven pack ice and ridges up to 15 m (49 ft). Offshore of the landfast ice, the ice remains very dynamic all year, and it is relatively easily moved around by winds and therefore forms pack ice, made up of large piles and ridges pushed against the landfast ice and shores. In spring, the Gulf of Finland and the Gulf of Bothnia normally thaw in late April, with some ice ridges persisting until May in the eastern extremities of the Gulf of Finland.

In the northernmost reaches of the Bothnian Bay, ice usually stays until late May; by early June it is practically always gone. The ice cover is the main habitat for two large mammals, the grey seal (Halichoerus grypus) and the Baltic ringed seal (Pusa hispida botnica), both of which feed underneath the ice and breed on its surface. Of these two seals, only the Baltic ringed seal suffers when there is not adequate ice in the Baltic Sea, as it feeds its young only on ice. The grey seal is adapted to reproducing also with no ice in the sea. The sea ice also harbours several species of algae that live in the bottom and inside unfrozen brine pockets in the ice. Aland Island, Baltic Sea - is an area with significant environmental issues HISTORY In the early Middle Ages, Norse (Scandinavian) merchants built a trade empire all around the Baltic. Later, the Norse fought for control of the Baltic against Wendish tribes dwelling on the southern shore. The Norse also used the rivers of Russia for trade routes, finding their way eventually to the Black Sea and southern Russia. This Norse-dominated period is referred to as the Viking Age.

Since the Viking age, the Scandinavians have referred to the Baltic Sea as Austmarr ("Eastern Lake"). "Eastern Sea", appears in the Heimskringla and Eystra salt appears in Sï¿½rla ï¿½ï¿½ttr. Saxo Grammaticus recorded in Gesta Danorum an older name, Gandvik, "-vik" being Old Norse for "bay", which implies that the Vikings correctly regarded it as an inlet of the sea. Another form of the name, "Grandvik", attested in at least one English translation of Gesta Danorum, is likely to be a misspelling.) In addition to fish the sea also provides amber, especially from its southern shores. The bordering countries have traditionally exported lumber, wood tar, flax, hemp and furs by ship across the Baltic. Sweden had from early medieval times exported iron and silver mined there, while Poland had and still has extensive salt mines. Thus the Baltic Sea has long been crossed by much merchant shipping. The lands on the Baltic's eastern shore were among the last in Europe to be converted to Christianity.

This finally happened during the Northern Crusades: Finland in the twelfth century by Swedes, and what are now Estonia and Latvia in the early thirteenth century by Danes and Germans (Livonian Brothers of the Sword). The Teutonic Order gained control over parts of the southern and eastern shore of the Baltic Sea, where they set up their monastic state. Lithuania was the last European state to convert to Christianity. World's oldest - 9,000 year old stationary fishing trap is similar to baskets in use by cultures all over the world today. ARCHAEOLOGY - JUNE 2012 Swedish marine archaeologists have found what they believe are the worldï¿½s oldest stationary fishing traps on the bottom of the Baltic Sea; the oldest dates back at least 9,000 years. Archaeologist Arne Sjostrom, of Sodertorn University, Stockholm, found the remains of 7 basket traps, constructed from hazel rods and bound together, in an ancient river valley off Swedenï¿½s southern coast, now submerged at a depth of 5-12 meters.

Carbon dating of one of the baskets estimates it to be around 9,000 years old and Sjostrom is ï¿½pretty confident this is the worldï¿½s oldest stationary fishing trap that has been found so far.ï¿½ This find mirrors the discovery of similar fishing traps in the North Sea at submerged sites in what was Doggerland. It has been estimated that the human inhabitants of Doggerland during the Mesolithic acquired 60% of their protein from sea foods (including salmon, flounder, cod, & oysters). So abundant were these marine resources, that they left their nomadic game hunting lifestyle and settled down into sedentary communities. The super-successful fish trap developed during the Mesolithic, is essentially identical in design to those still used in parts of the world to this day. Artists impressions of the 'Baltic Anomaly.' The discovery was made on June 19, 2011 by the Swedish based ï¿½Ocean X Teamï¿½ during a dive in the Baltic Sea between Sweden and Finland while searching for an old shipwreck.

The group describes themselves as treasure hunters and salvage operators who specialize in underwater searches for sunken ï¿½antique high-end alcoholic beverages and historic artifactsï¿½. In March 2012, Ocean X formalized a partnership with entertainment producers Titan TV to produce a TV documentary series and documentary film. JUNE 2011 - OCEAN X - BALTIC SEA ANOMALY The Baltic Sea anomaly is a 60-metre (200 ft) circular rock-like formation on the floor of the Baltic Sea, discovered by Peter Lindberg, Dennis ï¿½sberg and their Swedish ï¿½Ocean Xï¿½ diving team in June 2011. The team reported that the formation rests on a pillar and includes a structure similar in appearance to a staircase, leading to a dark hole. Commentators have suggested that the structure could be a World War II anti- submarine device, a battleship gun turret, sediment dropped by a fishing trawler, or a flying saucer. Several experts have stated that it is most likely a natural geological formation.

According to Ocean X, the formation has an appearance of ï¿½rough graniteï¿½, is round, 3 to 4 metres (9.8 to 13.1 ft) thick and approximately 60 metres (200 ft) in diameter, stands on an 8-meter (26 ft) tall pillar-like feature, and is located at a depth of 85 to 90 metres (279 to 295 ft). There is also another smaller object not far away. The object is at the end of what resembles a 300-metre (980 ft) ï¿½runwayï¿½. The Ocean X team has published one additional close-up sonar scan on their Web site and nine additional close-up sonar scans on their YouTube page that appear to show a 90-degree angle and other features of the object. On their second expedition, they reported that they found something that looks like a staircase and a round black hole that goes directly into the structure. Dennis Asberg, September 28, 2012: ï¿½It is not an object which is man made in modern time.

What ever it is itï¿½s either from during the ice age or pre-ice age.ï¿½ ï¿½ Peter Lindberg, February 24, 2013 ï¿½The object is older than 140.000 yrs. Older than thatï¿½ with straight angles/lines ï¿½ rounded cornersï¿½ much like a ï¿½dinner plateï¿½ and separate from the base below.ï¿½ There are THREE objects of interest ï¿½ 1) the main 60 meter circular anomaly, 2) a smaller secondary object lying approx. 200 meters from the 1st anomaly with an area shaped like two ï¿½Gothic church windowsï¿½ and 3) a third anomaly ï¿½ a 28 meters high and 275 meters wide rock outcrop with a crack running through it, lying some 1500 metres South of the circular object, direct on the other end of the ï¿½trailï¿½.

The team has stated Anomaly 2 might turn out to be the most interesting than the first, and they plan to dive on it this time around There are two holes on the anomaly. One is 25 centimeters in diameter, and the other is 2 meters surrounded by a square formation. Itï¿½s not yet known where the holes lead. ï¿½What I do not believe because I know, is the fact that we found a round hole approx 25 cm in diameter going straight into the surface of the circle, how odd is not that? How deep? No idea, we just saw it for some seconds before we decided to back off to preserve the visibility for the divers that was going down later on." It looks like there are stair-like structures on the top right side (North-East) as well as the lower bottom left (South-West) of the 60 meter circular object.

(Peter confirmed the ï¿½staircaseï¿½ reference was only an example to describe what he saw and that steps on the lower south-west side are comprised of 8 steps with each step a 1 meter drop starting from the missing section on the left.) ï¿½The staircase comment was slipped from my mouth, and probably too early. I have seen something that looks like a stair, or steps, on the Multi Beam raw data. And it looks like they are going from the missing part on the left side of the side scan image from last year and down to the bottom. I could only count eight of them and that should mean that every step should be like a meter high which is a bit to high for a person to use. If there actually are something that looks like steps they probably just natural.ï¿½ Peter Lindberg ï¿½ June 28, 2012: ï¿½Someone asked about the stairs, there is stair shaped formations but I do not know if I have got it right. I thought they were on one side but on the Multi beam image they appeared to be on an other side.

I will come back to the stairs when I can study an image from a different angle." REGIONAL BRANDING 2013 - STOCKHOLM In 2013 the Nordic Place Branding Conference 2013 was held in Stockholm. Representatives from cities, regions and government agencies in the five Nordic countries met to listen to speakers discussing their various place branding efforts. Several of the speakers talked about the challenge to get stakeholders, such as citizens of the location and business, to support branding efforts. Another issue that came up was what was place branding is all about: is mostly it a matter of marketing yourself by creating clever campaigns and taglines or of developing your place and its people and live by your values? Words or deeds? Or both? The need to put the Baltic Sea Region on the map, both in terms of creating a ï¿½we-feelingï¿½ in the region and making the region known globally, has been a much-discussed issue for some time. For the Baltic Sea Region, building a brand is obviously about smart communication: telling people in the region and outside world that we exist, and that we do a lot of good things here, in each country and together, in collaboration.

Come and visit, invest, start a business, live, work or study here should be the messages. But it is also about working together and solving real, concrete problems and unlocking opportunities in order to build a better, cleaner, more prosperous and attractive region ï¿½ through common strategies, projects and activities. Ocean and Sea | Scholastic Ocean and Sea Grades 9–12 Oceans and seas are the bodies of salt water that cover about 71% of the Earth's surface; they are referred to in total as the world ocean. Several centuries ago the "seven seas" were considered the navigable oceans. They were the Atlantic, Pacific, Indian, and Arctic oceans; the Mediterranean and Caribbean seas; and the Gulf of Mexico. At present, however, oceanographers consider all other oceans and seas as belonging to the Atlantic, Pacific, or Indian oceans. The Arctic Ocean, the Mediterranean and Caribbean seas, and the Gulf of Mexico are considered marginal seas of the Atlantic Ocean. These, in turn, have their own marginal bays and seas.

Narrow, shallow straits separate the marginal seas from the Atlantic: the Straits of Florida (Gulf of Mexico), the Strait of Gibraltar (Mediterranean), and many gaps between the islands of the Greater and Lesser Antilles (Caribbean Sea). Many other large bodies of water have been designated as seas, but all are marginal to the great oceans. The largest of these are the Bering Sea, Coral Sea, East China Sea and South China Sea, Sea of Japan, Sea of Okhotsk, Yellow Sea, and Philippine Sea, bordering the Pacific; the Arabian Sea, Red Sea, and Bay of Bengal, bordering the Indian Ocean; and the Scotia Sea, North Sea, Labrador Sea, Weddell Sea, Norwegian Sea, and Greenland Sea, bordering the Atlantic Ocean. Marginal seas differ from the major oceans primarily in size, but also in depth and bottom topography. The boundaries between the oceans are based on geographic criteria and have little to do with physical water-mass boundaries. The Atlantic is separated from the Indian Ocean by the 20° east meridian.

It is separated from the Pacific Ocean, in the south, by a line extending from Cape Horn at the tip of South America to the South Shetland Islands off Antarctica's tip; and, in the north, by the narrowest part of the Bering Strait. The dividing line between the Pacific and Indian oceans extends along an arc through the Malay Peninsula, Sumatra, Java, and Timor to Cape Londonderry in Australia; to Tasmania; and then along the 147° east meridian to Antarctica. Reference is sometimes made to the Antarctic, or Southern, Ocean. This encircles the Antarctic continent and consists of the southernmost sectors of the three principal oceans. Despite the lack of definitive geographic boundaries, the meteorological and oceanographic conditions in the high southern latitudes combine to produce a well-defined circumpolar current called the West Wind Drift. Any reference to an Antarctic Ocean refers roughly to the waters bound by this current; otherwise, as noted, the Atlantic, Pacific, and Indian oceans are considered to extend down to Antarctica. Oceanic regions constitute a much larger percentage of the Earth's surface in the Southern Hemisphere (81%) than in the Northern Hemisphere (61%).

This factor is reflected by major differences in oceanic circulation and weather patterns between the two hemispheres. Origin An explanation of the origin of the world's oceans must account for both the great ocean basins as well as the source of the water filling them. Perhaps surprisingly, neither the basins nor the volume of water in them has remained constant over the history of the Earth. The Water As the cosmic dust collapsed billions of years ago to form the planet Earth, water was probably locked into rock-forming compounds. These compounds (hydrated silicates) would have slowly released the trapped water during the first billion years or so of Earth history and formed the primordial ocean. The duration and time of initiation of this process are not exactly known; this is because rocks containing the record of that time span have been destroyed in the succeeding 3 billion years. Water would not have been released at the earliest stage of the Earth's development, however; the reason is that a molecule of water is lighter than a molecule of any of the lighter elements, or "volatiles" (such as neon), that would have escaped into space during the intense heat that accompanied the formation of the planet.

On the other hand, the origin of the primordial ocean must have occurred during the first billion years; this must be true because some of the earliest rocks found on Earth show evidence of deposition in a large body of water. The time required to accumulate the volume of water in the present oceans is unknown. The water was released during the cooling of the Earth. Early after its initiation it attained a volume not drastically different from that of the modern oceans. That the volume has not changed greatly during the last few hundred million years is inferred from evidence indicating that the interiors of the continental landmasses have never been inundated by deep oceans. Any incursions of seawater on the continents that did occur were in response to tectonic changes (that is, changes due to deformations of the Earth's crust). The most recent changes in ocean volume have accompanied the ice ages during the last 2 million to 3 million years. The northern polar ice cap has expanded and contracted with great regularity; the volume of the oceans has fluctuated correspondingly as water is alternately locked into or released from the ice cap. These fluctuations, however, have accounted for changes in sea level of no more than 200 m (660 ft).

The Basins The events of formation of the initial ocean basins that held the primordial ocean are unknown. This is because they have been destroyed by subsequent geologic events. The history of the present ocean basins, however, is well known. All of the continental landmasses as they are now known began to break up about 200 million years ago from two great supercontinents called Gondwanaland and Pangea. As the continents drifted to their present positions, the great ocean basins were left in their wake. This concept has been refined within the framework of the theories of continental drift and plate tectonics. Each ocean basin has evolved in a slightly separate manner, but the overall history of each basin has a similar series of events. The origin of the Atlantic Ocean basin is best known and serves as a good example of the processes involved. About 150 million years ago forces at work beneath the crust of the Earth split the supercontinents into large fragments. One such fragment contained North America joined to Eurasia; another contained South America joined to Africa. By 135 million years ago, North America had separated from Eurasia, leaving a small, restricted ocean basin with no open ocean circulation.

At the same time, the early South Atlantic basin was formed by the separation of South America and Africa. The two parts of the Atlantic were not connected with a pathway for deep circulation until about 65 million years ago; this was after the South Atlantic had widened to approximately 3,000 km (1,800 mi) and the North Atlantic had widened as a result of a separation between Greenland and Europe. The process continues today as new (basaltic) ocean crust is added at the Mid-Atlantic Ridge, widening the Atlantic Ocean. The same process has formed the Pacific Ocean basin, but there the pattern was complicated by other factors. The Pacific Ocean basin is surrounded by the great marginal trench systems; these are accompanied by volcanic island arcs and violent earthquake activity. The trenches mark the location where great slabs of oceanic crust are being reabsorbed back into the Earth by a process called subduction. As a result, there is seismic activity along the boundaries of the Pacific Ocean basin.

This process is active along the Aleutian Trench to the north; the Kuril-Japan-Mariana Trench System and the Mindanao Trench to the west; the New Hebrides, Tonga, and Kermadec trenches to the south; and the Middle American and Peru-Chile trenches to the east. New oceanic crust is being produced in the Pacific Ocean basin along the East Pacific Rise in the southern and eastern parts of the basin. The history of the Indian Ocean basin is less clear. India and Australia separated from Antarctica about 80 million years ago. India slid past Australia about 45 million years ago and rammed into Asia, leaving behind a deep ocean basin that widened in an east-west direction beginning about 35 million years ago. The pattern of seafloor formation in this relatively small ocean basin has not been completely determined, however, owing to the complexities found there. Physiography of the Seafloor The seafloor is shaped into a host of volcanic features. They grade from long submarine mountain chains, which are larger than their continental equivalents, to deep trenches that are thousands of times larger than those found on land.

The shape of all these physiographic features is related to the origin of the slice of ocean floor on which they are found. The shape of the seafloor, in turn, affects the origin and distribution of some of the great oceanic circulation systems. These systems play a role in the distribution of the oceanic nutrients that control biogenic productivity in the oceans. Ridges, Plains, and Trenches Perhaps the most striking feature on the seafloor is the mid-oceanic ridge system that, through branches, extends across all the major ocean basins. Typically, the central axis of this system is marked by a steep-walled valley, usually about 40 km (25 mi) wide and 1.6 km (1 mi) deep. Small segments of the ridge extend above sea level to form islands (for example, Iceland, the Azores, and the GalÃ¡pagos Islands). Most of the ridge crest, however, is at a depth of approximately 2.5 km (1.5 mi). The seafloor continues to deepen away from the crests of the mid-oceanic ridge system out to the extensive, flat abyssal plains. These plains constitute the largest segment of the seafloor.

The depths of the individual plains are roughly uniform; the deepest of them occur in the Pacific Ocean (6,000 m/20,000 ft), and the shallowest occur in the Atlantic Ocean (5,000 m/ 16,000 ft). In selected areas, usually at the margins of the ocean basins, the abyssal plains descend into steep oceanic trenches. There the greatest depths in the oceans are found. Examples of these trenches include the Peru-Chile Trench (Pacific), 8,055 m (26,428 ft); the Puerto Rico Trench (Atlantic), 9,200 m (30,200 ft); the Tonga Trench (Pacific), 10,880 m (35,700 ft); and the deepest hole in the ocean, the Mariana Trench (Pacific), 11,022 m (36,163 ft). Associated with most of these major trench systems are volcanic island arcs found on the landward side of the trenches.

Fracture Zones and Seamounts Superimposed on the features of the seafloor previously mentioned are many other smaller-scale, but very important, physiographic features. Segments of the mid-oceanic ridges are commonly offset laterally by parallel, linear fracture zones thousands of kilometers long. These oceanic fracture zones are characterized by ridges and valleys separated by steep rock cliffs that are hundreds to several thousands of meters high. These fracture zones can be traced out into the abyssal plains, where the traces of the cliffs are lost beneath the sediment. The abyssal plains are also dotted with numerous isolated mountains called seamounts; these extend in some cases above sea level to become islands. Characteristically, these seamounts belong to large groups of such features, which may be randomly dispersed over a large area or arranged in a line. Seafloor Spreading The origins of many of these strikingly different physiographic features are linked together by the concept of seafloor spreading. The seafloor is produced by the cooling of upwelling molten material at spreading centers characterized by the mid-oceanic ridges. The ridges are broken and discontinuous because of fracture zones along which transform faulting occurs.

Newly formed material moves away from the ridge crest; tens of millions of years later, it is subducted in an oceanic trench. Continental Shelves, Slopes, and Rises The margins of all the continents extend seaward as a broad, flat, shallow shelf. These continental shelves dip gently seaward and are usually less than 200 m (660 ft) below sea level. The continental shelves compose only a small portion (7.6%) of the seafloor. They are disproportionately important, however, because the shallow depths make it possible to exploit their natural resources. The shelves abruptly end at the shelf breaks, where the seafloors rapidly descend along the continental slopes to the abyssal depths. At the bases of the continental slopes, which cover about 15.3% of the oceanic area, are the continental rises; these represent a series of sediment slumps from the slopes above that have spilled down onto the deep seafloor or ocean basins. The basins cover about 75.9% of the oceanic area. Only 1.2% of the ocean is greater than 6,000 m (19,686 ft) in depth.

Importance of the Oceans and Seas Oceans and seas are now understood to be integral parts of the entire geologic process of continental weathering, runoff, and deposition. This progression is followed by either uplift and subaerial exposure or subduction into the depths of the Earth during the process of plate tectonics and seafloor spreading. The oceans and seas, also known as the hydrosphere, are responsible for the regulation of many major processes that occur on the surface of the Earth. Much of the precipitation that falls on land areas is derived from oceanic evaporation. The hydrosphere acts as a tremendous heat reservoir, exerting a dominant effect on temperature extremes over large land areas. The movement of ocean currents also creates moderating effects in some areas at latitudes where weather extremes might otherwise make life unpleasant. Oceans also act as reservoirs for numerous other substances that provide a buffering effect on the levels of various gases in the atmosphere; and in some cases they provide a dilution of otherwise toxic materials that humans have introduced into salt and fresh waters. Oceans and seas represent a place of recreation, a means of transportation, and a storehouse of food, mineral resources, and energy.

Their potential as a source of immeasurable resources is just beginning to be realized. Transportation The ocean provides tremendous potential as a means of transportation. The major portion of goods distributed worldwide are shipped by water. It is the least expensive method of transport and one that provides a livelihood for a significant percentage of the world's population. Food As a biological entity, oceans represent a highly productive environment. The basic biological habitats of the ocean can be divided into pelagic (water region) and benthic (seafloor region) environments. The pelagic zone can be divided into the neritic zone, down to 200 m (660 ft) and over the continental shelf; and the oceanic zone, below 200 m. The neritic and the upper oceanic (epipelagic zone) regions correspond to the photic zone, in which photosynthesis is possible.

The benthic habitat is also divided into the intertidal zone (between high and low tide); the sublittoral zone (down to 200 m); the bathyal zone (200 to 4,000 m/660 to 13,000 ft); the abyssal zone (4,000 to 5,000 m/13,000 to 16,000 ft); and the hadal zone (deeper than 5,000 m). The photic zone is the most highly productive area; it contains numerous benthic, planktonic (free-floating), and nektonic (free-swimming) marine creatures. Below the photic zone the biomass decreases considerably. The only food source for marine life is the constant rain of organic matter from above. The lack of light and food has produced numerous adaptations in deep-sea life, resulting in some very strange forms at these depths. Throughout recorded history people have used the ocean as a source of food. Yet even at present rates of removal, the food-resource potential of the oceans has barely been touched.

At present, most countries remove only certain choice species from the ocean. This fishing industry practice has led to the depletion of aquatic populations of these few species, whereas, at the same time, other species have remained almost untouched. Depletion of such populations in once-choice fishing grounds has caused considerable international dispute among the governments and fishing fleets of many countries. The conflicts have resulted in expansion of offshore fishing limits in many parts of the world. Depletion has also forced the development of techniques for fish farming and the cultivation and seeding of many bottom areas in order to enhance shellfish production. A change in attitudes about the consumption of various aquatic species may also help alleviate fishing pressures on certain species and encourage a more balanced exploitation of fisheries resources. Research in fisheries biology is still in its infancy. The behavior, food requirements, and breeding habits of most fish are not well known. Further investigation, however, may lead to a situation where human beings can depend more heavily on the ocean as a food source without creating a drastic impact on the overall ecology of the ocean. Water The ocean is a source of fresh water in many highly arid, nearshore areas where the cost of transporting water from regions where naturally occurring fresh water is abundant is greater than the cost of desalinization.

Most current desalination methods resemble a distilling process. Other methods that are available but not in widespread use are freezing, reverse osmosis, and ionic processes. Current costs of desalination are not so high as to be prohibitive to domestic and some industrial users; however, whether new developments will bring costs down to a level where agricultural and other industrial users will find the use of desalinized water practical remains uncertain. Energy Theoretically, the ocean represents a tremendous source of energy. Yet current use of the oceans by the energy industry is restricted for the most part to the use of seawater as a coolant in nearshore nuclear power plants. This particular use has produced considerable response from groups concerned with the environmental impact of the discharge of heated water from these reactors. Some energy can be extracted from the ocean by making use of the change in sea level caused by tidal cycles. The use of this method is currently limited, however. Numerous other methods are mostly in experimental stages at present. Several of these methods make use of the temperature differential that exists across the thermocline. Other methods would make use of wave and current energy. Yet most of these designs suffer from one or more disadvantages.

In addition to engineering problems, high generation costs and great distances between suitable generating sites and the power market may exist. The Sun replenishes the oceanic energy reserves at a much greater rate than human beings could ever remove energy from the oceans. The problems of economically removing this energy—most of which is diffused over the entire ocean—are, however, at present so insurmountable as to make widespread dependence on this energy resource impractical. Oil Since the 1960s the production of oil from wells on the continental shelves has increased drastically. At this point it represents a substantial percentage of the world's petroleum production. Later evidence indicates that oil deposits also reside on the continental slope. Current drilling and maintenance technology, however, has not yet advanced to a state where tapping of these additional reserves is practical in a routine manner. Estimates of offshore reserves far surpass presently known onshore reserves. A need for additional energy supplies will no doubt stimulate the technological advancements necessary to take advantage of these reserves. A major consideration is minimizing damage to the environment, especially damage related to oil spills. Minerals Economically important minerals are constantly introduced into the ocean from a variety of sources; most of the material accumulates on the ocean bottom.

Rivers dump vast quantities of particulate mineral materials into the oceans each year. Volcanic eruptions and hydrothermal solutions introduce many metals in both solution and solid form. Heavy minerals have a tendency to accumulate in superficial placer deposits; these can be located using a variety of geophysical techniques and then can be mined by dredging. Phosphate rocks are also mined from nearshore areas. Salt domes, which are subbottom bedrock deposits, are mined by pumping hot water down to melt the sulfur and to force the molten material back up the drill string. The deep sea as well as nearshore environments store vast amounts of economically important oceanic mineral resources. Large areas of the ocean bottom, mostly in temperate and tropical regions, are covered with calcareous oozes; these deep-sea oozes are the product of deposition of calcium-carbonate skeletons accreted by planktonic and benthonic microorganisms. This material could be useful in the manufacture of various building supplies, most notably cement. In higher latitudes the ocean-bottom sediments are dominated by siliceous oozes. The product of silica-secreting microorganisms, these oozes serve as an efficient filtering and insulating material.

Ocean Pollution Oceans clearly play an essential role in life on Earth; yet because of their vastness, humans have tended to use their waters as dumping grounds for many waste materials. This practice has increased as land areas for such wastes diminish. Oceans also receive all of the pollutants that are fed to them by the rivers of the world. Even when ships are not actively engaged in dumping wastes, they are themselves sources of pollution; most notable are the giant tankers that have caused numerous massive oil spills. As a result, by the early 21st century, ocean studies indicate that what had once been thought impossible is becoming a reality. The oceans as a whole are showing signs of environmental pollution. Even the surface waters of the oceans are increasingly plagued by obvious litter. Some of this litter washes ashore to render beaches unsightly, while other such debris entangles and kills many sea birds and mammals every year. More insidious than these litter problems are the effects of toxic contaminants from wastes that are dumped into the ocean. The wastes' chemicals can upset delicate marine ecosystems as they are absorbed by organisms all along the food chain. Even the paints being used on many ships can be hazardous.

The need to address the matter of ocean pollution has been recognized at national and international levels. The U.S. Congress, for example, passed an act in 1988 that would prohibit ocean dumping by 1991; in that same year, 65 nations agreed to cease burning toxic wastes at sea by 1994 should acceptable alternative practices be found. The latter action remains under debate, however, with several nations continuing the practice of ocean burning of toxic wastes. The U.S. act may prove as unenforceable as a prior one in 1977 that attempted the same prohibition. Worldwide, the problem of ocean pollution remains. Craig Amerigian and Michael T. Ledbetter Broad, William J., The Universe Below: Discovering the Secrets of the Deep Sea (1997). Chircop, Aldo, et al., eds., Ocean Yearbook 20 (2006). Earle, Sylvia A., National Geographic Atlas of the Ocean: The Deep Frontier (2001). Geyer, Richard A., Handbook of Geophysical Exploration at Sea, 2d ed. (1991).

Gwynn, Richard, Way of the Sea: The Use and Abuse of the Oceans (1992). Kunzig, Robert, Mapping the Deep: The Extraordinary Story of Ocean Science (2000). Lamson, Cynthia, ed., The Sea Has Many Voices: Oceans Policy for a Complex World (1994). Longhurst, Alan, Ecological Geography of the Sea (1998). Neal, Philip, Oceans Under Threat (1990). Paine, Lincoln, The Sea and Civilization: A Maritime History of the World (2013). Prager, Ellen J., with Sylvia A. Earle, The Oceans (2001). Stow, Dorrik, Oceans: An Illustrated Reference (2005). Sverdrup, Keith A., et al., An Introduction to the World's Oceans, 10th ed. (2008). Weir, Gary E., An Ocean in Common: American Naval Officers, Scientists, and the Ocean Environment (2001). World Conservation Union Staff, Random House Atlas of the Oceans (1991). ×

Question: Of which ocean is the White Sea a gulf?
Answer: ARCTIC