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 lies in the very north-eastern part of the Atlantic.
The North Sea is more than 970 kilometres (600 mi) long and 580 kilometres (360 mi) wide, with an area of 570,000 square kilometres (220,000 sq mi) and a volume of 54,000 cubic kilometres (13,000 cu mi). 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 watershed. Around 185 million people live in the catchment area of the rivers discharging into the North Sea encompassing some highly industrialized areas.
For the most part, the sea lies on the European continental shelf with a mean depth of 90 metres (300 ft). 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 20 and 30 kilometres (12 and 19 mi) wide and has a maximum depth of 725 metres (2,379 ft).
The Dogger Bank, a vast moraine, or accumulation of unconsolidated glacial debris, rises to a mere 15 to 30 m (50 to 100 ft) 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 73 and 26 m or 240 and 85 ft 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 200 miles (320 km) east of Dundee, Scotland. The feature is a series of asymmetrical trenches between 20 and 30 kilometres (12 and 19 mi) long, one and two kilometres (0.6 and 1.2 mi) wide and up to 230 metres (750 ft) deep.
Other areas which are less deep are Cleaver Bank, Fisher Bank and Noordhinder Bank.
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 to 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 (60°51′N 0°53′W / 60°51′N 0°53′W / 60.850; -0.883) 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 being thus included in the North Sea.
On the East. The Western limit of the Skagerrak [A line joining Hanstholm (57°07′N 8°36′E / 57°07′N 8°36′E / 57.117; 8.600) and the Naze (Lindesnes, 58°N 7°E / 58°N 7°E / 58; 7)].
mainly entering via the north entrance exiting along Norwegian coast
• Localization of the tide-gauges listed
• Tide times after Bergen
(negative = before)
• The three amphidromic centers
marshes = green
mudflats = greenish blue
lagoons = bright blue
dunes = yellow
sea dikes= purple
moraines near the coast= light brown
rock-based coasts = grayish brown
- Temperature and salinity
The average temperature in summer is 17 °C (63 °F) and 6 °C (43 °F) 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 0 to 4 °C (32 to 39 °F) and in July between 13 to 18 °C (55 to 64 °F). The winter months see frequent gales and storms.
The salinity averages between 34 to 35 grams per litre (130 to 130 g/US gal) 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 in shore.
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. In the North Sea the average tide difference in wave amplitude is between zero and eight metres (26 ft).
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 still travels 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 into the North Sea.
Selected tide ranges
|Tidal range [m]
||Geographical and historical features
||Mouth of River Dee in Scotland
||Mouth of Tyne estuary
||Kingston upon Hull
||northern side of Humber estuary
||southern side of Humber estuary farther seaward
||Lincolnshire coast north of the Wash
||mouth of Great Ouse into the Wash
||eastern edge of the Wash
||East Anglian coast north of Thames Estuary
||inner end of Thames Estuary
||dune coast east of the Strait of Dover
||dune coast west of Rhine–Meuse–Scheldt delta
||inner end of the southernmost estuary of Rhine–Meuse–Scheldt delta
||borderline of estuary delta and sedimentation delta of the Rhine
||mouth of the Uitwateringskanaal of Oude Rijn into the sea
||northeastern end of Holland dune coast west of IJsselmeer
||east of IJsselmeer, outlet of IJssel river, the eastern branch of the Rhine
||island in front of Ems river estuary
||east side of Ems river estuary
||seaward end of Weser estuary
||Bremer Industriehäfen, inner Weser estuary
||Bremen Weser barrage
||artificial tide limit of river Weser, 4 km upstream of the city centre
|| Bremerhaven 1879
|| before onset of
Weser Correction (Weser straightening works)
|| Bremen city centre 1879
|| before onset of
Weser Correction (Weser straightening works)
|| Bremen city centre 1900
Große Weserbrücke, 5 years after completion of
Weser Correction works
||seaward end of Elbe estuary
||Hamburg St. Pauli
||St. Pauli Piers, inner part of Elbe estuary
||Sylt island in front of Nordfriesland coast
||coast of Wadden Sea in Nordfriesland
||northern end of Wadden Sea in Denmark
||Danish dune coast, entrance of Ringkøbing Fjord lagoon
||Danish dune coast, entrance of Nissum Bredning lagoon, part of Limfjord
||Skagerrak. Hanstholm and Skagen have the same values.
||Skagerrak, Southern end of Norway, east of an amphidromic point
||North of that amphidromic point, rhythm of the tides irregular
||Rhythm of the tides regular
The German North Sea coast
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.
(Closure-dike) is a major dam in the Netherlands
The southern coastal areas were originally amphibious 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.:[302,303] As early as 500 BC, people were constructing artificial dwelling hills higher than the prevailing flood levels.:[306,308] 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 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 9 metres (30 ft) 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 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 as 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.:[79,86]
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 20 metres (66 ft) 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.