User:Island Kayaker/North Sea from German Wiki

The North Sea is an epeiric sea of the Atlantic Ocean in north-west Europe, with an average depth of 94 metres. This shelf sea is enclosed by land on three sides with a funnel-shaped opening to the north-east Atlantic. A 150-kilometre stretch of the coast is home to 80 million people; the North Sea itself is an important trade route and serves as Europe’s outlet to world markets. The southern North Sea , together with the adjacent English Channel, is the area with the densest sea traffic in the world. Under the sea there are considerable petroleum and gas deposits, which have been exploited on a large scale since the 1970s. Commercial fishing has reduced fish stocks in the last few decades; environmental problems arise owing to the fact that the effluent from Northern Europe flows directly into it or via the adjacent Baltic Sea.

Position

The North Sea lies for the most part on the European continental shelf. The only exception is a narrow area of the northern North Sea off Norway. The North Sea is bounded by the island of Great Britain to the west and by the northern and central European mainland with Norway (north-east), Denmark (east), Germany (south-east), the Netherlands (south), Belgium and France (south-west). In the south-west the North Sea becomes the English Channel after the Straits of Dover, in the east it is connected to the Baltic Sea via the Skagerrak and Kattegat, and to the north it opens in a funnel shape to the Norwegian Sea which lies in the eastern part of the North Atlantic. Apart from the obvious boundaries formed by the coasts of the countries which border it, the North Sea is bounded by an imaginary line from Lindesnes in Norway to Hanstholm in Denmark running towards the Skagerrak. The northern limit towards the Atlantic, by the nature of the area, is less well-defined. Traditionally , an imaginary line is taken to run from northern Scotland by way of the Shetlands to Ålesund in Norway; according to the Convention for the Protection of the Marine Environment of the North-East Atlantic of 1962 it runs further to the west and north from longitude 5º West and latitude 62º North, at the latitude of Geirangerfjord in Norway. The main rivers which drain into the North Sea are: from the mainland, the Scheldt, the Meuse, the Rhine, the Ems, the Weser and the Elbe, as well as the Thames in England which empties into it north of the Straits of Dover. The surface area of the North Sea is approx. 575,000 km2 (222,000 mi2), with a volume of around 54,000 km3 (12,955 mi3).

Origin of the Name

The name “North Sea” stems from the Middle High German and probably harks back to the name given by the Frisians who settled on its south coast. From the point of view, too, of the German Hanseatic Towns, the sea to the east was the “East Sea” (Baltic Sea in German is literally East Sea), and the sea to the north, the North Sea. As a result of the spread of maps used by the Hansa merchants, this name gradually became accepted throughout Europe. Other common names in use for a long period were “Mare Frisicum“, “Oceanum“ or “Mare Germanicum“ or “West Sea“, and in Denmark, which lies to the east of the North Sea, to this day, the name “Vesterhavet“ (Eng:. “West Sea“) is used as commonly as “Nordsøen“.

Geology and Hydrology

Geology

Formation

The North Sea is a geologically old sea and its formation as well as changes in its shape and size can be observed over a period of some 350 million years. The North Sea basin finally sank in the Tertiary. It received its present-day shape, however, only at the end of the last Ice Age , approximately 11,000 years ago. Even its present state is only one stage in the dynamic development of the North Sea: in the long term, a rise in sea level can be observed which, over the last 7,500 years, is in the region of 33 cm (13 in/ century (average heights at high tide on the German coast). In the last century the water level has risen some 20 to 25 cm (7.5-10 in).

During the Ice Ages, the North Sea was covered by ice several times; in the warm periods, large parts of today’s coast were covered by water. During the Wisconsin glaciation, as in other ice ages, large quantities of water were trapped in the ice of glaciers – the Scandinavian ice sheet was up to 3 km (1.86 mi) thick. The sea level at the peak of the Wisconsin glaciation was up to 120 metres (394 ft) below the present point; the coastline ran some 600 kms (375 mi) north of the present position. Large areas of the North Sea were dry at that time. The entire southern part of the North Sea was terra firme, the British Isles and the European mainland being one united land mass. During the following millennia the water level rose, although this rise underwent a deceleration over time.

Some 9,850 to 7,100 years ago, parts of the Elbe floodplain began to fill with water. Somewhat later the English Channel opened and the Wadden Sea (tidal mud flats) began to form. In the following period there were alternating sharp rises (transgression) and falls (regression) in sea levels. Around 5,000 years ago, (3,000 BC) the water level on the southern coast was about four metres (13 ft) below its present level and at the time of the birth of Christ it was just under two metres (6.5 ft) below the level it is today. Thereafter it rose somewhat and around the year 1000 it sank again to the level at the time of the birth of Christ, to finally rise slowly again in several stages.

Shape and Physical Division

The North Sea is a shelf sea, with an average depth of only 93 m (305 ft). The sea bed lies for the most part on the shelf and the depth increases from 25 (82 ft)or 35 m (115 ft) in the southern part, up to between 100 and 200 m (328-656 ft) on the continental slope between Norway and an area north of the Shetland Islands. The entire southern area of the sea is at the most 50 m (164 ft) deep. The exception is the Norwegian Trench: at this point the North Sea reaches a maximum depth of 725m (2379 ft). The shallowest area away from the coastal zones is the Dogger Bank. The southern part of the North Sea is traversed by numerous large sand banks.

The North Sea is generally divided into the shallow southern North Sea, the central North Sea, the northern North Sea and the Norwegian Trench with the transition zone of the Skagerrak. In the southern North Sea the English Channel becomes the Straits of Dover. The Southern Bight lies off the Dutch and Belgian coasts, the German Bight together with the Helgoland Bight lies off the German coast. The shallow area of the Dogger Bank forms the boundary of the German Bight towards the central North Sea. The tidal mudflats follow the coast from the southern part at Den Helder in the Netherlands along practically all the German North Sea Coast as far as Esbjerg in Denmark.

The shallow water area of the Dogger Bank is about half the size of the Netherlands with a depth of between 13 and , at its deepest point, 20 metres (43-66ft). It is famous as a fishing ground, and during storms the waves frequently break over it.

The Norwegian Trench is on average 250 to 300 metres (820-984ft) deep, becoming up to 725 metres (2379ft) at the transition to the Skagerrak , and plays an important part in the interchange of water between the Baltic and the Atlantic. The Norwegian Current flows along the Norwegian Trench, by way of which the largest part of the North Sea water flows into the Atlantic. [Translator’s Note: This is translated literally. I wonder whether the writer meant: ...... by way of which, the largest part of the North Sea water which flows into the Atlantic, is transported.] Furthermore, a large part of the water coming from the Baltic flowing northwards flows through here. In the central North Sea, some 200 kms (125mi) to the east of the Scottish town of Dundee, in the Devil’s Hole, we find several other troughs. These troughs, which are only a few kilometres long, go from the 90 metres (295ft) of the surrounding area down as far as 230 metres (755ft).

The Straits of Dover reach a depth of around 30 metres (100ft) and the sea bed slopes down towards the west reaching 100 metres (328ft) where the English Channel ends. Between the Netherlands and Great Britain the depths are of the order of 20 to 30 metres (66-98ft), reaching down to 45 metres (148ft)on the Frisian coast.

For fisheries and weather forecasts, for example the Hamburg Maritime Weather Service, the North Sea is divided into different areas: The western North Sea from north to south:

Viking – east of the Shetlands, bounded to the south by the Long Forties and to the east by Utsire
Long Forties - east of Scotland
Dogger – covers, among others, the area of the Dogger Bank
Southwest North Sea – the area of the German Bight

The eastern North Sea from north to south:

Utsire – west of the Norwegian coast, after the island of the same name.
Fisher – bounded to the west by the Skagerrak.
German Bight – between the Dutch, German and Danish North Sea coasts.

Hydrology

Basic Data

The salt content of the sea water is dependent on place and time of year and is in the region of 15 to 25 parts per thousand around river mouths and up to 32 to 35 ppth in the northern North Sea.

The temperature can reach 25º C (77ºF) in summer and 10º C (50ºF) in winter. In any case, the temperature varies depending to a great degree on the influence of the Atlantic and the water depth, in particular because of the ocean currents. In the deeper northern North Sea, in an area south and east of the Shetlands, the water temperature remains at a nearly constant 10º C (50ºF) all year round because of the water flowing in from the Atlantic, while the greatest temperature variations are found on the very shallow Wadden Sea coast , where ice can form in very cold winters.

Water Circulation

The salt water from the North Sea flows through the English Channel and along the Scottish and English coasts out of the Atlantic and into the North Sea. The greatest fresh water suppliers are the rivers which flow into the Baltic, which then overflow via the Skagerrak into the North Sea. The North Sea rivers drain a land area of 841,500 km2 (324 905 mi2) and supply approximately 296 to 354 km3 (71-85 mi3) of fresh water annually. The Baltic rivers drain almost twice as large an area (1,650,000 km2, 637,068 mi2) and contribute 470 km3 (113 mi3) of fresh water yearly.

Along the Danish and Norwegian coasts the water flows back into the Atlantic via the Norwegian Current. This moves at a depth of some 50 to 100 metres (165-328ft). The brackish water of the Baltic and the fresh water contributed by the North Sea and the fjords result in the Current having a relatively low salinity. A part of the warmer water flowing in from the Atlantic turns northwards again along the Current and results in a warmer core in the waters. In winter the Current has a temperature of 2 to 5ºC (36º-41ºF) and the salinity is below 34.8 ppth. The Atlantic water in the North Sea, divided from the Current by a front, is, on the other hand, at over 6º C (43ºF) with a salinity of 35 ppth.

In approximately one to two years, the water in the North Sea is completely exchanged. Within the Sea, fronts based on temperature, salinity, nutrients and pollution can be clearly identified and they are more clearly defined in summer than in winter. Large fronts are the Frisian Front , which divides water coming from the Atlantic from water originating in the English Channel, and the Danish Front, which divides coastal waters from water in the central North Sea. The inflow of water from large rivers mixes very slowly with North Sea water. Water from the Rhine and Elbe, for example, can still be clearly differentiated from sea water off the northwest coast of Denmark.

The most important rivers which flow directly into the North Sea are :

Rhine / Meuse (Netherlands) 2,524 m³ (89,134ft³ )/ sec
Elbe ( Lower Saxony /Schleswig-Holstein) 856 m³ (30 229ft³ )/sec
Glomma (Norway) 603 m³ (21 295ft³)/sec
IJsselmeer (Netherlands) 555 m³ (19600ft³)/ sec
Weser ( Lower Saxony /Bremen) 358 m³(12,643ft³)/sec
Skjern Â (Denmark) 206 m³ (7275ft³)/sec
Firth of Tay (Scotland) 203 m³ (7169ft³)/sec
Moray Firth
- (various rivers including the Spey) 168 m³ (5933ft³)/sec
Scheldt (Belgium/Netherlands) 126 m³ (4450ft³)/sec
Humber (England) 125 m³ (4415ft³)/sec
River Forth (Scotland) 112 m³ (3955ft³)/sec
Ems (Lower Saxony ) 88 m3 (3108ft³)/ sec
River Tweed (England) 85 m³(3002ft³)/sec
Thames (England) 76 m³ (2684ft³)/sec

Tides

The tides are caused by the tide wave from the North Atlantic, as the North Sea itself is too small and too flat to have any appreciable influence. Ebb and flow alternate in a cycle of 12.5 hours. The tide wave , owing to the Coriolis effect, flows around Scotland and then in counter-clockwise direction along the English coast and reaches the German Bight some 12 hours after arriving in Scotland. In so doing , it runs around 3 amphidromic points: a central point lies shortly before the Straits of Dover. It is formed by the tide wave which is transported across the English Channel. It influences the tides in the narrow area of De Hoofden in the Southern Bight between southern England and the Netherlands. The other amphidromic system consists of two points close to each other which form a tide wave. The two other points just off the coast of southern Norway and lying on a line between southern Denmark and the West Frisian Islands form one single area around which the tides flow. Its central point lies on the Jutland Bank at 55° 25' N, 5° 15' E.

As a result, the tidal range in southern Norway is less than half a metre (1.5ft), but increases the further any given coast lies from the amphidromic point. Shallow coasts and the funnel effect of narrow straits increase the tidal range. The tidal range is at its greatest at The Wash on the English coast, where it reaches 6.80 metres (22ft). On the German North Sea coast, the tidal range varies between two and four metres (6.5-13ft) depending on the shape and position of the coast. In shallow water areas the real tidal range is strongly influenced by other factors such as the position of the coast and the wind at any given moment or the action of storms. In river estuaries, high water level in the rivers can considerably amplify the effect of high tide.

Flora, fauna, and environmental protection

Strong tides, shallow waters rich in seaweed and kelp forests, a rich variety of structures and the presence of large amounts of nutrients in the sea make for diversity of life in the North Sea .

Types of biotopes

The North Sea presents a series of very distinct habitat types, occupied by different biocoenoses (or ecological communities). Thus a distinction is made within coastal biotopes between the different types of coast, such as cliffs, or rocky or sandy coasts, and the aquatic habitats themselves. In the case of the North Sea, salt marshes and mudflats represent important transition areas, which stand out as being areas of changing living conditions independent of low and high tides. The North Sea is home to the world’s largest and most biodiverse mudflats. Furthermore the areas around the estuaries, characterised by the mixing of fresh water and the salt water of the North Sea , represent a unique habitat. Aquatic habitats can be divided into the open-sea areas (the pelagic zone) and the sea bottom (the benthic zone). Benthic habitats are in turn differentiated according to depth and the characteristics of the sea bed. Thus , they can be rocky, gravelly or sandy and they may have more or less of a mud layer, or even none at all.

Environmental Protection

The North Sea suffers by the direct discharge of pollutants, the pollutant content which rivers carry with them, and above all the impact which human use implies. Coastal protection measures have a marked influence on landscape change in the whole of the southern North Sea area. Tourism and leisure activities play an ambivalent role in this matter – on the one hand they place a large burden on coastal areas, but on the other, they give a direct economic incentive to maintain the coast largely undamaged and “pretty”. Due to overfishing, stocks, in particular of North Sea herring, shrank in the 1970s. The cod population, despite a 1983 EEC Regulation, has gone down sharply in the last few years. To protect the North Sea , countries bordering it made various agreements The Bonn Agreement of 1969 was the first international agreement on environmental protection in the North Sea and covered exclusively the possible negative effects of petroleum production. The Agreements of Oslo (1972) and Paris (1974) concerned themselves for the first time on a larger scale with pollutants in the sea; as a result of these, the riparian States approved in 1992 the Oslo-Paris Convention. The riparian States are responsible for environmental protection on the coasts and to this end have made different national regulations. In Germany, the biggest National Parks are the Wadden Sea National Parks in Schleswig-Holstein, Niedersachsen and Hamburg.

Coasts and islands

Northern North Sea: fjords, skerries, and cliffs

The North Sea is bounded by its largest island, Great Britain, to the west; however, only its East Coast faces the North Sea . The largest groups of islands which lie entirely in the North Sea are the Shetland and the Orkney Islands.

The northern North Sea coasts bear the impression of the enormous glaciers which covered them during the different Ice Ages. Thereby a split, craggy coastal landscape was formed . The fjords arose by the action of glaciers which dragged their way through them from the highlands , cutting and scraping deep trenches in the land. During the subsequent rise in sea level , they filled with water. They very often display steep coastlines and , for the North Sea, are extremely deep. Fjords are particularly common on the coast of Norway.

Firths have a similar structure to fords, but are mostly shallower with broader bays in which small islands may often be found. The glaciers which formed them influenced the land over a wider area and scraped away larger surface areas. Firths are to be found mostly on the Scottish and northern English coasts. Individual islands in the firths , or islands and the coast, are often joined up by sandbars or spits made up of sand deposits known as “Tombolos”.

Towards the south the firths give way to a cliff coast, which were formed above all from the moraines of Ice Age glaciers. The horizontal impact of waves on the North Sea coast gives rise to eroded coasts; the eroded material is an important source of sediment for the mudflats on the other side of the North Sea. Large estuaries (funnel-shaped river mouths) with their corresponding mud and marshy flats disrupt the cliff landscape. The Humber and Thames in southern England have these large mouths. In southern Norway, as well as on the Swedish Skagerrak coast , skerries are to be found. Formed by similar action to that which created the fjords and firths, the glaciers in these places affected the land to an even greater extent , so that large areas were carried away. The coastal brim (Strandflaten), which is found especially in southern Norway, is the lowland area between the sea and the mountains. It consists of plates of bedrock, and often extends for kilometres, reaching under the sea, at a depth of only a few metres.

Southern North Sea: shoals and mudflats

The shallow-water coasts of the southern and eastern coast all the way up to Denmark were basically formed by Ice Age activity, but their shape is determined for the most part by the sea and sediment deposits. The whole of the coastal zone is shallow, the tides flood large areas and uncover them again. The water deposits sediments. In the microtidal area (a tidal range of up to 1.35 metres (4.43ft)), such as on the Dutch or Danish coasts, barrier beaches with dunes are formed. In the mesotidal area (a tidal range of between 1.35 and 2.90 metres (4.43-9.5ft)), barrier islands are formed; in the macrotidal area (above 2.90 metres (9.5ft) tidal range), such as at the mouth of the Elbe, underwater sandbanks form. The Dutch West Frisian and the German East Frisian Islands are barrier islands. They arose along the breakers’ edge where the water surge piled up sediment, and behind which sediment was carried away by the breaking waves. In this way, over time, sandplates arose, which finally were only ever covered by storm floods. The first plants began to colonise the sandbanks and the land began to stabilise.

Even though today they are established islands, some of them continue to be in motion. On the East Frisian Island of Juist for example, since the year 1650 there are 5 different proven sites for the church, as the spot for building the church had to keep pace with the ever-moving island. At times, Juist even consisted of two islands, before it grew together once again. The neighbouring island of Wangerooge in the last 300 years has moved a distance equivalent to its own length to the east. In this process, depending on the prevailing conditions, land is eroded on the western coasts, whilst sediments are deposited on the eastern coasts. As a result, western coasts are today increasingly protected by human action. The canals between the islands serve as passages for the tides, so that in these places the current prevents the islands gradually joining one to another.

The North Frisian Islands, on the other hand, arose from the remains of old Geestland islands, where the land was partially removed by storm floods and water action and then separated from the mainland. For this reason they are often higher and their cores less exposed to changes than the islands to the south. Beyond the core, however, the same processes as on the West and East Frisian Islands are at work, particularly evident on Sylt, where in the south of the island, a break threatens, whilst the harbour at Lister silts up. The Danish Wadden Sea Islands, the next in the chain to the north, arose from sandbanks. Right up into the 20th Century, the silting up of the islands was a serious problem. To protect the islands, small woods were planted. On the southeastern coast there are several broad estuaries, such as the Meuse, Rhine, Weser, Elbe or Eider. In particular , the Southern Bight has been changed by land reclamation, as the Dutch have been especially active in this matter; the largest project of this type was the diking and reclamation of the IJsselmeer. The Wadden Sea stretches between Esbjerg (Denmark) in the north and Den Helder (Netherlands) in the west. This landscape is influenced by the ebb and flow of the tides; important sections of it have been declared a National Park. The island of Helgoland is an exception, as it was not formed by sediment deposition; in fact it is considerably older and is composed of Early Triassic sandstone.