The North Sea

The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Sea in the north. It is more than long and wide, covering .

It hosts key north European shipping lanes and is a major fishery. The coast is a popular destination for recreation and tourism in bordering countries, and a rich source of energy resources, including wind and wave power.

The North Sea has featured prominently in geopolitical and military affairs, particularly in Northern Europe, from the Middle Ages to the modern era. It was also important globally through the power northern Europeans projected worldwide during much of the Middle Ages and into the modern era. The North Sea was the centre of the Vikings' rise. The Hanseatic League, the Dutch Republic, and the British each sought to gain command of the North Sea and access to the world's markets and resources. As Germany's only outlet to the ocean, the North Sea was strategically important through both World Wars.

The coast has diverse geology and geography. In the north, deep fjords and sheer cliffs mark much of its Norwegian and Scottish coastlines respectively, whereas in the south, the coast consists mainly of sandy beaches, estuaries of long rivers and wide mudflats. Due to the dense population, heavy industrialisation, and intense use of the sea and the area surrounding it, there have been various environmental issues affecting the sea's ecosystems. Adverse environmental issuescommonly including overfishing, industrial and agricultural runoff, dredging, and dumping, among others have led to several efforts to prevent degradation and to safeguard the long-term economic benefits.

Geography

The North Sea is bounded by the Orkney Islands and east coast of Great Britain to the west
and the northern and central European mainland to the east and south, including Norway, Denmark, Germany, the Netherlands, Belgium, and France.

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively. In the north it is bordered by the Shetland Islands, and connects with the Norwegian Sea, which is a marginal sea in the Arctic Ocean.

The North Sea is more than long and wide, with an area of and a volume of . Around the edges of the North Sea are sizeable islands and archipelagos, including Shetland, Orkney, and the Frisian Islands. The North Sea receives freshwater from a number of European continental watersheds, as well as the British Isles. A large part of the European drainage basin empties into the North Sea, including water from the Baltic Sea. The largest and most important rivers flowing into the North Sea are the Elbe and the Rhine – Meuse.
Around 185 million people live in the catchment area of the rivers discharging into the North Sea encompassing some highly industrialized areas.

Major features

For the most part, the sea lies on the European continental shelf with a mean depth of .
The only exception is the Norwegian trench, which extends parallel to the Norwegian shoreline from Oslo to an area north of Bergen. It is between wide and has a maximum depth of .

The Dogger Bank, a vast moraine, or accumulation of unconsolidated glacial debris, rises to a mere below the surface. This feature has produced the finest fishing location of the North Sea. The Long Forties and the Broad Fourteens are large areas with roughly uniform depth in fathoms (forty fathoms and fourteen fathoms or deep, respectively). These great banks and others make the North Sea particularly hazardous to navigate, which has been alleviated by the implementation of satellite navigation systems. The Devil's Hole lies east of Dundee, Scotland. The feature is a series of asymmetrical trenches between long, wide and up to deep.

Other areas which are less deep are Cleaver Bank, Fisher Bank and Noordhinder Bank.

Extent

The International Hydrographic Organization defines the limits of the North Sea as follows:

''On the Southwest.'' A line joining the Walde Lighthouse (France, 1°55'E) and Leathercoat Point (England, 51°10'N).

''On the Northwest.'' From Dunnet Head (3°22'W) in Scotland to Tor Ness (58°47'N) in the Island of Hoy, thence through this island to the Kame of Hoy (58°55'N) on to Breck Ness on Mainland (58°58'N) through this island to Costa Head (3°14'W) and Inga Ness (59'17'N) in Westray through Westray, to Bow Head, across to Mull Head (North point of Papa Westray) and on to Seal Skerry (North point of North Ronaldsay) and thence to Horse Island (South point of the Shetland Islands).

''On the North.'' From the North point (Fethaland Point) of the Mainland of the Shetland Islands, across to Graveland Ness (60°39'N) in the Island of Yell, through Yell to Gloup Ness (1°04'W) and across to Spoo Ness (60°45'N) in Unst island, through Unst to Herma Ness (60°51'N), on to the SW point of the Rumblings and to Muckle Flugga () all these being included in the North Sea area; thence up the meridian of 0°53' West to the parallel of 61°00' North and eastward along this parallel to the coast of Norway, the whole of Viking Bank is thus included in the North Sea.

''On the East.'' The Western limit of the Skagerrak _line_joining_Hanstholm_()_and_the_Naze_(Lindesnes.html" ;"title="Hanstholm.html" ;"title=" line joining Hanstholm"> line joining Hanstholm () and the Naze (Lindesnes">Hanstholm.html" ;"title=" line joining Hanstholm"> line joining Hanstholm () and the Naze (Lindesnes, )].

Hydrology

Temperature and salinity

The average temperature is in the summer and in the winter. The average temperatures have been trending higher since 1988, which has been attributed to climate change. Air temperatures in January range on average between and in July between . The winter months see frequent gales and storms.

The salinity averages between of water. The salinity has the highest variability where there is fresh water inflow, such as at the Rhine and Elbe estuaries, the Baltic Sea exit and along the coast of Norway.

Water circulation and tides

The main pattern to the flow of water in the North Sea is an anti-clockwise rotation along the edges.

The North Sea is an arm of the Atlantic Ocean receiving the majority of ocean current from the northwest opening, and a lesser portion of warm current from the smaller opening at the English Channel. These tidal currents leave along the Norwegian coast. Surface and deep water currents may move in different directions. Low salinity surface coastal waters move offshore, and deeper, denser high salinity waters move inshore.

The North Sea located on the continental shelf has different waves from those in deep ocean water. The wave speeds are diminished and the wave amplitudes are increased. In the North Sea there are two amphidromic systems and a third incomplete amphidromic system. p. 329 tidal map showing amphidromes
p. 157 tidal map showing amphidromes
In the North Sea the average tide difference in wave amplitude is between zero and .

The Kelvin tide of the Atlantic Ocean is a semidiurnal wave that travels northward. Some of the energy from this wave travels through the English Channel into the North Sea. The wave continues to travel northward in the Atlantic Ocean, and once past the northern tip of Great Britain, the Kelvin wave turns east and south and once again enters the North Sea. p. 94 shows the amphidromic points of the North Sea

Coasts

The eastern and western coasts of the North Sea are jagged, formed by glaciers during the ice ages. The coastlines along the southernmost part are covered with the remains of deposited glacial sediment. The Norwegian mountains plunge into the sea creating deep fjords and archipelagos. South of Stavanger, the coast softens, the islands become fewer. The eastern Scottish coast is similar, though less severe than Norway. From north east of England, the cliffs become lower and are composed of less resistant moraine, which erodes more easily, so that the coasts have more rounded contours. In the Netherlands, Belgium and in East Anglia the littoral is low and marshy. The east coast and south-east of the North Sea ( Wadden Sea) have coastlines that are mainly sandy and straight owing to longshore drift, particularly along Belgium and Denmark.

Coastal management

The southern coastal areas were originally flood plains and swampy land. In areas especially vulnerable to storm surges, people settled behind elevated levees and on natural areas of high ground such as spits and geestland. As early as 500 BC, people were constructing artificial dwelling hills higher than the prevailing flood levels. It was only around the beginning of the High Middle Ages, in 1200 AD, that inhabitants began to connect single ring dikes into a dike line along the entire coast, thereby turning amphibious regions between the land and the sea into permanent solid ground.

The modern form of the dikes supplemented by overflow and lateral diversion channels, began to appear in the 17th and 18th centuries, built in the Netherlands. The North Sea Floods of 1953 and 1962 were the impetus for further raising of the dikes as well as the shortening of the coast line so as to present as little surface area as possible to the punishment of the sea and the storms. Currently, 27% of the Netherlands is below sea level protected by dikes, dunes, and beach flats.

Coastal management today consists of several levels. The dike slope reduces the energy of the incoming sea, so that the dike itself does not receive the full impact. Dikes that lie directly on the sea are especially reinforced. The dikes have, over the years, been repeatedly raised, sometimes up to and have been made flatter to better reduce wave erosion. Where the dunes are sufficient to protect the land behind them from the sea, these dunes are planted with beach grass (''Ammophila arenaria'') to protect them from erosion by wind, water, and foot traffic.

Storm tides

Storm surges threaten, in particular, the coasts of the Netherlands, Belgium, Germany, and Denmark and low-lying areas of eastern England particularly around The Wash and Fens.
Storm surges are caused by changes in barometric pressure combined with strong wind created wave action.

The first recorded storm tide flood was the ''Julianenflut'', on 17 February 1164. In its wake, the Jadebusen, (a bay on the coast of Germany), began to form.
A storm tide in 1228 is recorded to have killed more than 100,000 people.
In 1362, the Second Marcellus Flood, also known as the ''Grote Manndrenke'', hit the entire southern coast of the North Sea. Chronicles of the time again record more than 100,000 deaths, large parts of the coast were lost permanently to the sea, including the now legendary lost city of Rungholt.

In the 20th century, the North Sea flood of 1953 flooded several nations' coasts and cost more than 2,000 lives.
315 citizens of Hamburg died in the North Sea flood of 1962.

Tsunamis

Though rare, the North Sea has been the site of a number of historically documented tsunamis. The Storegga Slides were a series of underwater landslides, in which a piece of the Norwegian continental shelf slid into the Norwegian Sea. The immense landslips occurred between 8150 BCE and 6000 BCE, and caused a tsunami up to high that swept through the North Sea, having the greatest effect on Scotland and the Faeroe Islands.
The Dover Straits earthquake of 1580 is among the first recorded earthquakes in the North Sea measuring between 5.6 and 5.9 on the Richter scale. This event caused extensive damage in Calais both through its tremors and possibly triggered a tsunami, though this has never been confirmed. The theory is a vast underwater landslide in the English Channel was triggered by the earthquake, which in turn caused a tsunami. The tsunami triggered by the 1755 Lisbon earthquake reached Holland, although the waves had lost their destructive power. The largest earthquake ever recorded in the United Kingdom was the 1931 Dogger Bank earthquake, which measured 6.1 on the Richter magnitude scale and caused a small tsunami that flooded parts of the British coast.

Geology

Shallow epicontinental seas like the current North Sea have since long existed on the European continental shelf. The rifting that formed the northern part of the Atlantic Ocean during the Jurassic and Cretaceous periods, from about , caused tectonic uplift in the British Isles.
Since then, a shallow sea has almost continuously existed between the uplands of the Fennoscandian Shield and the British Isles. This precursor of the current North Sea has grown and shrunk with the rise and fall of the eustatic sea level during geologic time. Sometimes it was connected with other shallow seas, such as the sea above the Paris Basin to the south-west, the Paratethys Sea to the south-east, or the Tethys Ocean to the south.

During the Late Cretaceous, about , all of modern mainland Europe except for Scandinavia was a scattering of islands. By the Early Oligocene, , the emergence of Western and Central Europe had almost completely separated the North Sea from the Tethys Ocean, which gradually shrank to become the Mediterranean as Southern Europe and South West Asia became dry land. The North Sea was cut off from the English Channel by a narrow land bridge until that was breached by at least two catastrophic floods between 450,000 and 180,000 years ago. Since the start of the Quaternary period about , the eustatic sea level has fallen during each glacial period and then risen again. Every time the ice sheet reached its greatest extent, the North Sea became almost completely dry, the dry landmass being known as Doggerland, whose northern regions were themselves known to have been glaciated. The present-day coastline formed after the Last Glacial Maximum when the sea began to flood the European continental shelf.

In 2006 a bone fragment was found while drilling for oil in the North Sea. Analysis indicated that it was a Plateosaurus from 199 to 216 million years ago. This was the deepest dinosaur fossil ever found and the first find for Norway.

File:Doggerland.svg, Map showing hypothetical extent of Doggerland (c. 8,000 BC), which provided a land bridge between Great Britain and continental Europe
File:North Sea -.jpg, North Sea from De Koog, Texel island
File:Mediterranean Rupelian.jpg, The North Sea between and , as Central Europe became dry land

Nature

Fish and shellfish

Copepods and other zooplankton are plentiful in the North Sea. These tiny organisms are crucial elements of the food chain supporting many species of fish. Over 230 species of fish live in the North Sea. Cod, haddock, whiting, saithe, plaice, sole, mackerel, herring, pouting, sprat, and sandeel are all very common and are fished commercially. Due to the various depths of the North Sea trenches and differences in salinity, temperature, and water movement, some fish such as blue-mouth redfish and rabbitfish reside only in small areas of the North Sea.

Crustaceans are also commonly found throughout the sea. Norway lobster, deep-water prawns, and brown shrimp are all commercially fished, but other species of lobster, shrimp, oyster, mussels and clams all live in the North Sea. Recently non-indigenous species have become established including the Pacific oyster and Atlantic jackknife clam.

Birds

The coasts of the North Sea are home to nature reserves including the Ythan Estuary, Fowlsheugh Nature Preserve, and Farne Islands in the UK and the Wadden Sea National Parks in Denmark, Germany and the Netherlands. These locations provide breeding habitat for dozens of bird species. Tens of millions of birds make use of the North Sea for breeding, feeding, or migratory stopovers every year. Populations of black-legged kittiwakes, Atlantic puffins, northern gannets, northern fulmars, and species of petrels, seaducks, loons (divers), cormorants, gulls, auks, and terns, and many other seabirds make these coasts popular for birdwatching.

Marine mammals

The North Sea is also home to marine mammals. Common seals, grey seals, and harbour porpoises can be found along the coasts, at marine installations, and on islands. The very northern North Sea islands such as the Shetland Islands are occasionally home to a larger variety of pinnipeds including bearded, harp, hooded and ringed seals, and even walrus. North Sea cetaceans include various porpoise, dolphin and whale species.

Flora

Plant species in the North Sea include species of wrack, among them bladder wrack, knotted wrack, and serrated wrack. Algae, macroalgal, and kelp, such as oarweed and laminaria hyperboria, and species of maerl are found as well. Eelgrass