North Sea

The North Sea, located between the United Kingdom and continental Europe, is one of the world's most economically important bodies of water. The impact of human activity on the North Sea is of significant concern to environmentalists.

Physical Characteristics

The North Sea is an arm of the Atlantic Ocean located between the islands of Britain and the mainland of northwestern Europe. It is bordered by the island of Great Britain to the southwest and west, by the Orkney Islands and the Shetland Islands to the northwest, by Norway to the northeast, by Denmark to the east, by Germany and the Netherlands to the southeast, and by Belgium and France to the south.

To the north, the North Sea opens to the Norwegian Sea. To the south, it is connected to a narrow waterway known as the Strait of Dover, located between southeast England and northwest France. The Strait of Dover connects the North Sea to a wider waterway, the English Channel, between southern England and northern France. The English Channel opens to the Atlantic Ocean. To the east, the North Sea is connected to a strait known as the Skagerrak, located between Norway and Denmark. The Skagerrak is connected to a strait between Sweden and Denmark known as the Kattegat, which opens to the Baltic Sea.

The North Sea covers an area of about 570,000 square kilometers. It contains about 50,000 cubic kilometers of water. The North Sea is generally shallow, with an average depth of about 94 meters (about 308 feet). By comparison, the Atlantic Ocean has an average depth of about 3,930 meters (about 12,900 feet). The southern part of the North Sea is the shallowest, with the northern part growing deeper as it approaches the much deeper Norwegian Sea.

The floor of the North Sea is rough and irregular. In the southern part, where the water is often less than 40 meters (131 feet) deep, many areas of elevated underwater land known as banks are shifted and reworked by tides and currents. These moving banks often present a hazard to navigation. The Dogger Bank, a large bank located roughly in the center of the North Sea, is only about 15 to 30 meters (49 to 98 feet) below sea level.

Several areas of greater-than-average depth, known as trenches, are located in the North Sea. In the otherwise shallow waters of the south, a trench known as Silver Pit reaches a depth of about 97 meters (318 feet). Not far north of the Dogger Bank is a trench known as Devil's Hole that reaches more than 450 meters (1,476 feet). The deepest part of the North Sea is the Norwegian Trench, a large trench that runs parallel to the southern coast of Norway. The Norwegian Trench is between 25 and 30 kilometers (15.5 and 18.5 miles) wide, with depths ranging from 300 to 700 meters (984 to 2,297 feet).

The coastline of the North Sea varies from rugged highlands in the north to smooth lowlands in the south. The coast of Norway is mountainous and broken, with thousands of rocks and small islands frequently indented by steep-sided inlets called fjords. The coasts of Scotland and northern England are high and rocky but less broken. The coasts of middle England and the Netherlands are low and marshy, with places that have been isolated from the sea by human-made dikes that regulate water levels. The coasts of southern England, France, and Belgium are low and sandy.

Geological History, Hydrology, and Climate

The shape and size of the North Sea have varied greatly over time. At the end of the Pliocene Epoch, about 1.6 million years ago, the southern half of the North Sea was part of the mainland of Europe. At that time, the Rhine River, which now empties into the North Sea in the southern part of the Netherlands, ran to a point about 400 kilometers north of London. The Thames River, which now empties into the North Sea east of London, continued eastward until it met the Rhine River.

During the Pleistocene epoch, from about 1.6 million to 10,000 years ago, vast ice sheets advanced and retreated several times and deposited a thick layer of clay on the bottom of the North Sea. At its greatest extent, the ice covered the entire North Sea. About 8,000 years ago, the ice retreated for the last time. A few hundred years later, the rising waters of the North Sea broke through the land bridge connecting England and France, forming the Strait of Dover. The modern coastlines of the North Sea were formed about 3,000 years ago.

The movements of the ice sheets were largely responsible for the rugged floor of the North Sea. The Dogger Bank and smaller banks in the southern part of the North Sea were created when the ice deposited large amounts of earth and stones in a particular area. Some of the trenches in the North Sea are believed to be located in areas where ancient rivers emptied into the North Sea when it was much smaller.

Water enters the North Sea from the Atlantic Ocean through the Strait of Dover and the Norwegian Sea. This water is relatively warm and salty. It is heated by the warm North Atlantic Current, which moves north along the western side of the British Isles and enters the Norwegian Sea. Colder, less salty water from the Baltic Sea enters through the Skagerrak, creating a counterclockwise current in the North Sea.

Freshwater enters the North Sea from the Thames, the Rhine, and other large rivers. The salt content of the North Sea varies from about thirty-four to about thirty-five parts per thousand. Higher concentrations are found off the coast of Great Britain, and lower concentrations are found off the coast of Norway.

The average temperature of the surface water in the North Sea in January varies from about 2 degrees Celsius (36 degrees Fahrenheit) east of Denmark to about 8 degrees Celsius (46 degrees Fahrenheit) between the Shetland Islands and Norway. In July, the average temperature varies from more than 15 degrees Celsius (59 degrees Fahrenheit) along the coast from the Strait of Dover to Denmark to about 12 degrees Celsius (54 degrees Fahrenheit) between the Shetland Islands and the Orkney Islands.

The average air temperature varies from between 0 and 4 degrees Celsius (32 and 39 degrees Fahrenheit) in January to 13 and 18 degrees Celsius (55 and 64 degrees Fahrenheit) in July. Winters are stormy, and gales are frequent. The average difference between low and high tide is about 4 meters and 6 meters (13 feet and 20 feet) along the coast of the British Isles and the southern coast of the European mainland. Along the northern coast of the European mainland, the difference is usually less than 3 meters (10 feet).

Human Activities

Because of its long coastline and the many rivers that empty into it, the North Sea has long been an area of important human activity. The exchange of people, goods, and ideas made possible by the North Sea profoundly influenced the cultural development of northwestern Europe during the Renaissance.

In the twenty-first century, the North Sea is one of the busiest shipping areas in the world. Adding to its economic importance is that it provides the only waterway between the Baltic Sea and the Atlantic Ocean. Because of the North Sea, the Netherlands and the United Kingdom are among the world’s leading nations regarding the volume of cargo carried by sea. The Europoort complex at Rotterdam, in the Netherlands, handles more cargo than any other European seaport and is one of the busiest in the world. Other major ports located on the North Sea include Antwerp, Belgium; Dunkirk, France; London, England; and the three ports of Hamburg, Bremerhaven, and Wilhelmshaven in Germany.

The North Sea's accessibility also made it an early area of scientific research. The Challengerexpedition, launched by the British in 1872, began a new era in oceanography. In 1902, the International Council for the Exploration of the Seas was founded in Denmark to study the North and Baltic Seas. It has since compiled the longest record of marine ecological conditions worldwide. In the twentieth and twenty-first centuries, many marine laboratories, research centers, and scientific vessels have been active in the area.

The North Sea has also long been an area of land reclamation and flood-control projects, particularly in the Netherlands. The Dutch have reclaimed land from the North Sea for centuries by building dikes. In the 1930s, a dike 30 kilometers (18.5 miles) long was built in the Netherlands, creating a large freshwater lake. Three-fifths of the land formerly under the North Sea was then reclaimed as farmland. After abnormally high tides flooded a large part of the Netherlands in 1953, the Dutch built a large flood-control system on rivers emptying into the North Sea. The British built a similar system on a smaller scale on the Thames River in 1984.

Fishing has long been a major activity in the area. The constant mixing of shallow water in the North Sea provides a rich supply of nutrients to plankton—microscopic organisms that support a wide variety of commercially important fish. The main species caught are cod, haddock, herring, and saithe. Lesser quantities of plaice, sole, and Norway pout are also caught. Sand eel, mackerel, and sprat are caught to produce fish meal.

The major fishing nations in the region are Norway, Denmark, the United Kingdom, and the Netherlands. In 1983, the nations of Europe created the Common Fisheries Policy. This arrangement establishes the number of species each nation may catch in the open waters of the North Sea. This policy does not apply to fish caught in coastal waters, which are considered to belong to a particular nation. Upon its creation, the European Union adopted this policy, reformed it, and extended it to its member states in 2014.

and Oil

New economic resources were discovered in the North Sea in the second half of the twentieth century. In 1959, the first known source of natural gas in the North Sea was identified. This source was an extension into the sea of a large natural gas field in the northeastern part of the Netherlands. By the end of the 1970s, many natural gas production sites were developed in the North Sea. These sites are located primarily along an east and west line for about 150 kilometers (93 miles) between the Netherlands and England. A smaller number of natural gas sources are located in the central and northern regions of the North Sea.

Norway was the first nation to obtain oil from the North Sea, and it began operating its first offshore oil well in 1971. The United Kingdom began extracting oil from the North Sea in 1975. The oil wells are primarily located in the northern and central regions of the North Sea. By the 1980s, offshore oil wells operated from north of the Shetland Islands to about 650 kilometers (404 miles) to the south. New oil deposits continued to be discovered in the North Sea in the twenty-first century, with several new sites discovered at the beginning of 2023 alone. In 2024, oil discoveries were made in the Balder area of the Central North Sea, on the Svalin Field in the North Sea, and in several other existing North Sea oil fields. 

Oil is found in the North Sea in a basin of sedimentary rock thousands of meters thick. Almost all of the world’s oil supply is found in similar basins. Such basins are believed to exist in areas where the Earth's outer layer has been stretched and thinned. This causes a basin to form beneath the outer layer, which collects sediments for millions of years. Organic matter is transformed into oil if the sediments are subjected to certain temperatures and pressures. Seismic measurements using controlled explosions have confirmed that the outer layer of land beneath the central portion of the North Sea is about half as thick as the same layer elsewhere. The stretching and thinning of this area took place millions of years ago when Europe and the island of Great Britain were drifting apart.

Significance

The most critical issue facing the nations that border the North Sea is the impact of human activity in the area. Pollution from ships and land-based operations is a significant concern. Although international agreements on limiting pollution of the North Sea have been in place since 1969, enforcement remains problematic. Events, such as the Ecofisk oil well blowout, which spilled more than 30 million liters of oil into the North Sea in 1977, highlight the importance of controlling contamination. Smaller and more routine North Sea oil spills occurred regularly in the twenty-first century, alarming environmentalists and activists. In 2024, Oil Change International released a report charging that the oil and gas policies of five major North Sea countries were not aligned with the Paris Climate Agreement and that those countries needed to advance their policies to cut oil and gas production to be in line with the agreement's stipulations. Still, these countries continue to extend new opportunities for oil and natural gas exploration in the North Sea, seemingly incongruent with the Paris Agreement. 

A significant problem is the disposal of offshore equipment that is no longer in use. As long ago as 1958, international agreements stated that all such equipment must be removed from the sea. However, because of the extremely high cost of removing large installations, new agreements were made in 1989 that allowed such equipment to be disposed of at sea. The agreement required that the water where the equipment is disposed of be at least 100 meters deep and that at least 35 meters of water remain above the disposed debris. This policy met with worldwide controversy in 1995 when the Shell company decided to dispose of an unused oil well known as the Brent Spar in this way. Under intense pressure from environmentalists and organizations, such as Greenpeace, Shell reversed this decision and made plans to remove the Brent Spar entirely.

The problem of oil pollution from mud used to lubricate drills in offshore oil wells is less dramatic but possibly even more critical. Studies have indicated that oil from this and other sources is far more widespread than previously thought. The most significant impact was on an organism known as the burrowing brittle star. The digging of this animal brings oxygen into sediments, encouraging other organisms to grow there. The burrowing brittle star is also an important food source for many fish. The number of burrowing brittle stars per square meter fell from more than one hundred in unpolluted waters to zero within 1 or 2 kilometers (.5 to 1 mile) of oil wells. Such losses may have been a significant factor in the decrease in North Sea fish, such as cod, whose population fell by two-thirds between 1980 and 1995.

Principal Terms

Baltic Sea: the body of water between Scandinavia and Eastern Europe

bank: an elevated area of land beneath the surface of the ocean

fjord: a steep-sided narrow inlet eroded into the face of a seaside cliff, typical of Scandinavia but found throughout the world

Norwegian Sea: the body of water north of the North Sea

strait: a narrow waterway connecting two larger bodies of water

trench: a long, narrow, depressed area in the ocean floor

Bibliography

Exarheas, Andreas. “Oil Discovery Made in North Sea.” Rigzone, 13 April 2023, www.rigzone.com/news/oil‗discovery‗made‗in‗north‗sea-13-apr-2023-172526-article. Accessed 15 Apr. 2023.

Flemming, Nicholas Coit, Council for British Archaeology, and English Heritage. Submarine Prehistoric Archaeology of the North Sea: Research Priorities and Collaboration With Industry. York: Council for British Archaeology, 2004.

Gaffney, Vincent, Kenneth Thomson, and Simon Fitch, editors. Mapping Doggerland: The Mesolithic Landscapes of the Southern North Sea. Oxford: Archaeopress, 2007.

Glennie, Kw. Petroleum Geology of the North Sea: Basic Concepts and Recent Advances. 4th ed., New York: John Wiley & Sons, 2009.

Harvie, Christopher. Fool’s Gold: The Story of North Sea Oil. London: Hamish Hamilton, 1994.

Ilyina, Tatjana. The Fate of Persistent Organic Pollutants in the North Sea: Multiple Years Model Simulations of ?-HCH, a-HCH and PCB 153. Berlin: Springer-Verlag, 2007.

Ozsoy, Emin, and Alexander Mikaelyan, editors. Sensitivity to Change: Black Sea, Baltic Sea, and North Sea. Boston: Kluwer Academic Publishers, 1997.

Rannard, Georgina, and Erwan Rivault. “North Sea Oil Spills a Wildlife Threat - Activists.” BBC, 13 Apr. 2023, www.bbc.com/news/science-environment-65254022. Accessed 15 Apr. 2023.

Shennan, Ian, and Julian E. Andrews, editors. Holocene Land-Ocean Interaction and Environmental Change Around the North Sea. Special Publication No. 166. London: Geological Society of London, 2000.

Smith, Norman J. North Sea Oil and Gas, British Industry and the Offshore Supplies Office. vol. 7. Edited by John Cubitt. Boston: Elsevier, 2011.

Smith, Norman J. The Sea of Lost Opportunity: North Sea Oil and Gas, British Industry and the Offshore Supplies Office. Oxford: Elsevier, 2011.

Stackl, Valentina. “New Report Reveals North Sea Countries’ Oil and Gas Plans Breach Paris Agreement.” Oil Change International, 12 Mar. 2024, priceofoil.org/2024/03/12/new-report-reveals-north-sea-countries-oil-and-gas-plans-breach-paris-agreement. Accessed 20 July 2024.

Thimont, Maddy. “Common Fisheries Policy.” Institutes for Government, 17 Feb. 2017, www.instituteforgovernment.org.uk/article/explainer/common-fisheries-policy. Accessed 15 Apr. 2023.

"Troubled Waters: How North Sea Countries Are Fueling Climate Disaster." Oil Change International, 12 Mar. 2024, priceofoil.org/2024/03/12/north-sea-troubled-waters. Accessed 20 July 2024.

Warren, E. A., and P. C. Smalley. North Sea Formation Waters Atlas. London: Geological Society, 1994.

“What Does more North Sea Oil and Gas Mean for UK Energy Supply and Net Zero?” London School of Economics, 2 May 2024, www.lse.ac.uk/granthaminstitute/explainers/what-does-more-north-sea-oil-and-gas-mean-for-uk-energy-supply-and-net-zero. Accessed 20 July 2024.

Ziegler, Karen, Peter Turner, and Stephen R. Daines, editors. Petroleum Geology of the Southern North Sea: Future Potential. London: Geological Society, 1997.