The coast, also known as the coastline, shorelineorseashore, is defined as the area where land meets the ocean,[1] or as a line that forms the boundary between the land and the coastline.[2] Shores are influenced by the topography of the surrounding landscape, as well as by water induced erosion, such as waves. The geological composition of rock and soil dictates the type of shore which is created. The Earth has around 620,000 kilometres (390,000 mi) of coastline. Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbor important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangrovesorseagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species.[3][4] Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past and present, while the beach is at the edge of the shore, representing the intertidal zone where there is one.[5] Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 meters (3.3–164.0 feet).
According to an atlas prepared by the United Nations, 44% of all humans live within 150 km (93 mi) of the sea.[6] Due to its importance in society and its high population concentrations, the coast is important for major parts of the global food and economic system, and they provide many ecosystem services to humankind. For example, important human activities happen in port cities. Coastal fisheries (commercial, recreational, and subsistence) and aquaculture are major economic activities and create jobs, livelihoods, and protein for the majority of coastal human populations. Other coastal spaces like beaches and seaside resorts generate large revenues through tourism. Marine coastal ecosystems can also provide protection against sea level rise and tsunamis. In many countries, mangroves are the primary source of wood for fuel (e.g. charcoal) and building material. Coastal ecosystems like mangroves and seagrasses have a much higher capacity for carbon sequestration than many terrestrial ecosystems, and as such can play a critical role in the near-future to help mitigate climate change effects by uptake of atmospheric anthropogenic carbon dioxide.
Because coasts are constantly changing, a coastline's exact perimeter cannot be determined; this measurement challenge is called the coastline paradox. The term coastal zone is used to refer to a region where interactions of sea and land processes occur.[10] Both the terms coast and coastal are often used to describe a geographic location or region located on a coastline (e.g., New Zealand's West Coast, or the East, West, and Gulf Coast of the United States.) Coasts with a narrow continental shelf that are close to the open ocean are called pelagiccoast, while other coasts are more sheltered coast in a gulforbay. A shore, on the other hand, may refer to parts of land adjoining any large body of water, including oceans (sea shore) and lakes (lake shore).
Size
The Earth has approximately 620,000 kilometres (390,000 mi) of coastline. Coastal habitats, which extend to the margins of the continental shelves, make up about 7 percent of the Earth's oceans,[12] but at least 85% of commercially harvested fish depend on coastal environments during at least part of their life cycle.[13] As of October 2010,[update] about 2.86% of exclusive economic zones were part of marine protected areas.[14]
The definition of coasts varies. Marine scientists think of the "wet" (aquatic or intertidal) vegetated habitats as being coastal ecosystems (including seagrass, salt marsh etc.) whilst some terrestrial scientists might only think of coastal ecosystems as purely terrestrial plants that live close to the seashore (see also estuaries and coastal ecosystems).
While there is general agreement in the scientific community regarding the definition of coast, in the political sphere, the delineation of the extents of a coast differ according to jurisdiction.[citation needed][15] Government authorities in various countries may define coast differently for economic and social policy reasons.
The measured length of the coastline depends on the method used to measure it and the degree of cartographic generalization. Since a landmass has features at all scales, from hundreds of kilometers in size to tiny fractions of a millimeter and below, there is no obvious size of the smallest feature that should be taken into consideration when measuring, and hence no single well-defined perimeter to the landmass. Various approximations exist when specific assumptions are made about minimum feature size.
Formation
Tides often determine the range over which sediment is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, and areas with lower tidal ranges produce deposition at a smaller elevation interval. The tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves; however, tidal bores can erode as the waves surge up the river estuaries from the ocean.[21]: 421
Geologists classify coasts on the basis of tidal range into macrotidal coasts with a tidal range greater than 4 m (13 ft); mesotidal coasts with a tidal range of 2 to 4 m (6.6 to 13 ft); and microtidal coasts with a tidal range of less than 2 m (7 ft). The distinction between macrotidal and mesotidal coasts is more important. Macrotidal coasts lack barrier islands and lagoons, and are characterized by funnel-shaped estuaries containing sand ridges aligned with tidal currents. Wave action is much more important for determining bedforms of sediments deposited along mesotidal and microtidal coasts than in macrotidal coasts.[22]
Waves erode coastline as they break on shore releasing their energy; the larger the wave the more energy it releases and the more sediment it moves. Coastlines with longer shores have more room for the waves to disperse their energy, while coasts with cliffs and short shore faces give little room for the wave energy to be dispersed. In these areas, the wave energy breaking against the cliffs is higher, and air and water are compressed into cracks in the rock, forcing the rock apart, breaking it down. Sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. This forms an abrasionorcliffed coast.
Sediment deposited by rivers is the dominant influence on the amount of sediment located in the case of coastlines that have estuaries.[23] Today, riverine deposition at the coast is often blocked by dams and other human regulatory devices, which remove the sediment from the stream by causing it to be deposited inland. Coral reefs are a provider of sediment for coastlines of tropical islands.[24]
Like the ocean which shapes them, coasts are a dynamic environment with constant change. The Earth's natural processes, particularly sea level rises, waves and various weather phenomena, have resulted in the erosion, accretion and reshaping of coasts as well as flooding and creation of continental shelves and drowned river valleys (rias).
More and more of the world's people live in coastal regions.[25] According to a United Nations atlas, 44% of all people live within 150 km (93 mi) of the sea.[6] Many major cities are on or near good harbors and have port facilities. Some landlocked places have achieved port status by building canals.
Nations defend their coasts against military invaders, smugglers and illegal migrants. Fixed coastal defenses have long been erected in many nations, and coastal countries typically have a navy and some form of coast guard.
Growth management and coastal management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents, and poor management practices of construction often leave these communities and infrastructure vulnerable to processes like coastal erosion and sea level rise. In many of these communities, management practices such as beach nourishment or when the coastal infrastructure is no longer financially sustainable, managed retreat to remove communities from the coast.
A passenger car ferry arrives at the coast of Mariehamn, Åland.
Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.
Estuarine and marine coastal ecosystems are both marine ecosystems. Together, these ecosystems perform the four categories of ecosystem services in a variety of ways: The provisioning services include forest products, marine products, fresh water, raw materials, biochemical and genetic resources. Regulating services include carbon sequestration (contributing to climate change mitigation) as well as waste treatment and disease regulation and buffer zones. Supporting services of coastal ecosystems include nutrient cycling, biologically mediated habitats and primary production. Cultural services of coastal ecosystems include inspirational aspects, recreation and tourism, science and education.
Coasts and their adjacent areas on and offshore are an important part of a local ecosystem. The mixture of fresh water and salt water (brackish water) in estuaries provides many nutrients for marine life. Salt marshes, mangroves and beaches also support a diversity of plants, animals and insects crucial to the food chain. The high level of biodiversity creates a high level of biological activity, which has attracted human activity for thousands of years. Coasts also create essential material for organisms to live by, including estuaries, wetland, seagrass, coral reefs, and mangroves. Coasts provide habitats for migratory birds, sea turtles, marine mammals, and coral reefs.[26]
According to one principle of classification, an emergent coastline is a coastline that has experienced a fall in sea level, because of either a global sea-level change, or local uplift. Emergent coastlines are identifiable by the coastal landforms, which are above the high tide mark, such as raised beaches. In contrast, a submergent coastline is one where the sea level has risen, due to a global sea-level change, local subsidence, or isostatic rebound. Submergent coastlines are identifiable by their submerged, or "drowned" landforms, such as rias (drowned valleys) and fjords
According to the second principle of classification, a concordant coastline is a coastline where bands of different rock types run parallel to the shore. These rock types are usually of varying resistance, so the coastline forms distinctive landforms, such as coves. Discordant coastlines feature distinctive landforms because the rocks are eroded by the ocean waves. The less resistant rocks erode faster, creating inletsorbay; the more resistant rocks erode more slowly, remaining as headlandsoroutcroppings.
Rivieras
Riviera is an Italian word for "shoreline",[27][28][29] ultimately derived from Latin ripa ("riverbank"). It came to be applied as a proper name to the coast of the Ligurian Sea, in the form riviera ligure, then shortened to riviera. Historically, the Ligurian Riviera extended from Capo Corvo (Punta Bianca) south of Genoa, north and west into what is now French territory past Monaco and sometimes as far as Marseilles.[27][30][31] Today, this coast is divided into the Italian Riviera and the French Riviera, although the French use the term "Riviera" to refer to the Italian Riviera and call the French portion the "Côte d'Azur".[28]
As a result of the fame of the Ligurian rivieras, the term came into English to refer to any shoreline, especially one that is sunny, topographically diverse and popular with tourists.[27] Such places using the term include the Australian RivierainQueensland and the Turkish Riviera along the Aegean Sea.[28]
Other coastal categories
Acliffed coast or abrasion coast is one where marine action has produced steep declivities known as cliffs.
Aflat coast is one where the land gradually descends into the sea.
Agraded shoreline is one where wind and water action has produced a flat and straight coastline.
Aprimary coast isone which is mainly undergoing early stage development by major long-term processes such as tectonism and climate change A secondary coast is one where the primary processes have mostly stabilised, and more localised processes have become prominent.[32]
Anemergent coast is one where the sea level has dropped relative to the land, while a submergent coat is relatively recently immersed by a relative rise of sea level.[32]
Much of the sediment deposited along a coast is the result of erosion of a surrounding cliff, or bluff. Sea cliffs retreat landward because of the constant undercutting of slopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment it will erode at a much faster rate than a cliff made of bedrock.[23]
Anatural arch is formed when a headland is eroded through by waves.
Sea caves are made when certain rock beds are more susceptible to erosion than the surrounding rock beds because of different areas of weakness. These areas are eroded at a faster pace creating a hole or crevice that, through time, by means of wave action and erosion, becomes a cave.
Astack is formed when a headland is eroded away by wave and wind action.
Astump is a shortened sea stack that has been eroded away or fallen because of instability.
Wave-cut notches are caused by the undercutting of overhanging slopes which leads to increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually removed by waves.
Awave-cut platform forms after erosion and retreat of a sea cliff has been occurring for a long time. Gently sloping wave-cut platforms develop early on in the first stages of cliff retreat. Later, the length of the platform decreases because the waves lose their energy as they break further offshore.[23]
"Coastal waters" (or "coastal seas") is a rather general term used differently in different contexts, ranging geographically from the waters within a few kilometers of the coast, through to the entire continental shelf which may stretch for more than a hundred kilometers from land.[33] Thus the term coastal waters is used in a slightly different way in discussions of legal and economic boundaries[34] (see territorial waters and international waters) or when considering the geography of coastal landforms or the ecological systems operating through the continental shelf (marine coastal ecosystems). The research on coastal waters often divides into these separate areas too.
The dynamic fluid nature of the ocean means that all components of the whole ocean system are ultimately connected, although certain regional classifications are useful and relevant. The waters of the continental shelves represent such a region.[35] The term "coastal waters" has been used in a wide variety of different ways in different contexts. In European Union environmental management it extends from the coast to just a few nautical miles[36] while in the United States the US EPA considers this region to extend much further offshore.[37][38]
Similarly, the term littoral zone has no single definition. It is the part of a sea, lake, or river that is close to the shore.[39] In coastal environments, the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged.
The identification of bodies of rock formed from sediments deposited in shoreline and nearshore environments (shoreline and nearshore facies) is extremely important to geologists. These provide vital clues for reconstructing the geography of ancient continents (paleogeography). The locations of these beds show the extent of ancient seas at particular points in geological time, and provide clues to the magnitudes of tides in the distant past.[43]
Sediments deposited in the shoreface are preserved as lenses of sandstone in which the upper part of the sandstone is coarser than the lower part (acoarsening upwards sequence). Geologists refer to these are parasequences. Each records an episode of retreat of the ocean from the shoreline over a period of 10,000 to 1,000,000 years. These often show laminations reflecting various kinds of tidal cycles.[43]
Some of the best-studied shoreline deposits in the world are found along the former western shore of the Western Interior Seaway, a shallow sea that flooded central North America during the late CretaceousPeriod (about 100 to 66 million years ago). These are beautifully exposed along the Book CliffsofUtah and Colorado.[44]
Geologic processes
The following articles describe the various geologic processes that affect a coastal zone:
Larger animals that live in coastal areas include puffins, sea turtles and rockhopper penguins, among many others. Sea snails and various kinds of barnacles live on rocky coasts and scavenge on food deposited by the sea. Some coastal animals are used to humans in developed areas, such as dolphins and seagulls who eat food thrown for them by tourists. Since the coastal areas are all part of the littoral zone, there is a profusion of marine life found just off-coast, including sessile animals such as corals, sponges, starfish, mussels, seaweeds, fishes, and sea anemones.
Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres (660 ft) deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the sunlit epipelagic zone.[45] Coastal fish can be contrasted with oceanic fishoroffshore fish, which inhabit the deep seas beyond the continental shelves.
Coastal fish are the most abundant in the world.[46] They can be found in tidal pools, fjords and estuaries, near sandy shores and rocky coastlines, around coral reefs and on or above the continental shelf. Coastal fish include forage fish and the predator fish that feed on them. Forage fish thrive in inshore waters where high productivity results from upwelling and shoreline run off of nutrients. Some are partial residents that spawn in streams, estuaries and bays, but most complete their life cycles in the zone.[46]
Plants
Many coastal areas are famous for their kelp beds. Kelp is a fast-growing seaweed that can grow up to half a meter a day in ideal conditions. Mangroves, seagrasses, macroalgal beds, and salt marsh are important coastal vegetation types in tropical and temperate environments respectively.[3][4]Restinga is another type of coastal vegetation.
The pollution of coastlines is connected to marine pollution which can occur from a number of sources: Marine debris (garbage and industrial debris); the transportation of petroleumintankers, increasing the probability of large oil spills; small oil spills created by large and small vessels, which flush bilge water into the ocean.
Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residentialwaste, particles, noise, excess carbon dioxideorinvasive organisms enter the ocean and cause harmful effects there. The majority of this waste (80%) comes from land-based activity, although marine transportation significantly contributes as well.[47] It is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. This pollution results in damage to the environment, to the health of all organisms, and to economic structures worldwide.[48] Since most inputs come from land, either via the rivers, sewage or the atmosphere, it means that continental shelves are more vulnerable to pollution. Air pollution is also a contributing factor by carrying off iron, carbonic acid, nitrogen, silicon, sulfur, pesticides or dust particles into the ocean.[49] The pollution often comes from nonpoint sources such as agricultural runoff, wind-blown debris, and dust. These nonpoint sources are largely due to runoff that enters the ocean through rivers, but wind-blown debris and dust can also play a role, as these pollutants can settle into waterways and oceans.[50] Pathways of pollution include direct discharge, land runoff, ship pollution, bilge pollution, atmospheric pollution and, potentially, deep sea mining.
The types of marine pollution can be grouped as pollution from marine debris, plastic pollution, including microplastics, ocean acidification, nutrient pollution, toxins and underwater noise. Plastic pollution in the ocean is a type of marine pollution by plastics, ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. Marine debris is mainly discarded human rubbish which floats on, or is suspended in the ocean. Plastic pollution is harmful to marine life.
Marine debris, also known as marine litter, is human-created solid material that has deliberately or accidentally been released in seas or the ocean. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood and drift seeds, are also present. With the increasing use of plastic, human influence has become an issue as many types of (petrochemical) plastics do not biodegrade quickly, as would natural or organic materials.[51] The largest single type of plastic pollution (~10%) and majority of large plastic in the oceans is discarded and lost nets from the fishing industry.[52] Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts.[53]
Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem. This increased water pollution has caused serious negative effects such as discarded fishing nets capturing animals, concentration of plastic debris in massive marine garbage patches, and increasing concentrations of contaminants in the food chain.
A growing concern regarding plastic pollution in the marine ecosystem is the use of microplastics. Microplastics are beads of plastic less than 5 millimeters wide,[54] and they are commonly found in hand soaps, face cleansers, and other exfoliators. When these products are used, the microplastics go through the water filtration system and into the ocean, but because of their small size they are likely to escape capture by the preliminary treatment screens on wastewater plants.[55] These beads are harmful to the organisms in the ocean, especially filter feeders, because they can easily ingest the plastic and become sick. The microplastics are such a concern because it is difficult to clean them up due to their size, so humans can try to avoid using these harmful plastics by purchasing products that use environmentally safe exfoliates.
Because plastic is so widely used across the planet, microplastics have become widespread in the marine environment. For example, microplastics can be found on sandy beaches[56] and surface waters[57] as well as in the water column and deep sea sediment. Microplastics are also found within the many other types of marine particles such as dead biological material (tissue and shells) and some soil particles (blown in by wind and carried to the ocean by rivers). Population density and proximity to urban centers have been considered the main factors that influence the abundance of microplastics in the environment.
Between 1901 and 2018, the average global sea level rise was 15–25 cm (6–10 in), with an increase of 2.3 mm (0.091 in) per year since the 1970s.[58]: 1216 This is faster than the sea level has risen over the past 3,000 years, if not longer.[58]: 1216 The rate accelerated to 4.62 mm (0.182 in)/yr for the decade 2013–2022.[59]Climate change due to human activities is the main cause.[60]: 5, 8 Between 1993 and 2018, melting ice sheets and glaciers accounted for 44% of sea level rise, with another 42% resulting from thermal expansionofwater.[61]: 1576
Sea level rise lags behind changes in the Earth's temperature, and sea level rise will therefore continue to accelerate between now and 2050 in response to warming that has already happened.[62] What happens after that depends on human greenhouse gas emissions. Sea level rise would slow between 2050 and 2100 if there are very deep cuts in emissions. It could then reach slightly over 30 cm (1 ft) from now by 2100. With high emissions it would accelerate. It could rise by 1.01 m (3+1⁄3ft) or even 1.6 m (5+1⁄3ft) by then.[60][58]: 1302 In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming amounts to 1.5 °C (2.7 °F). It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F).[60]: 21
^Steinhaus, Hugo (1954). "Length, shape and area". Colloquium Mathematicum. 3 (1): 1–13. doi:10.4064/cm-3-1-1-13. The left bank of the Vistula, when measured with increased precision would furnish lengths ten, hundred and even thousand times as great as the length read off the school map. A statement nearly adequate to reality would be to call most arcs encountered in nature not rectifiable.
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^ abcKolb, Martina (2013). Nietzsche, Freud, Benn, and the Azure Spell of Liguria. Toronto, Ontario: University of Toronto Press. p. 30. ISBN978-1-4426-4329-1.
^The more common ones are puntellare and litorale.
^Mantoura, R. F. C; Martin, Jean-Marie; Wollast, R, eds. (1991). Ocean margin processes in global change: report of the Dahlem Workshop on Ocean Margin Processes in Global Change, Berlin, 1990, March 18-23. Chichester, New York: Wiley. ISBN978-0-471-92673-3. OCLC22765791.
^ abLeeder, M. R. (2011). Sedimentology and sedimentary basins: from turbulence to tectonics (2nd ed.). Chichester, West Sussex, UK: Wiley-Blackwell. pp. 436–437. ISBN978-1-4051-7783-2.
^ abcFox-Kemper, B.; Hewitt, Helene T.; Xiao, C.; Aðalgeirsdóttir, G.; Drijfhout, S. S.; Edwards, T. L.; Golledge, N. R.; Hemer, M.; Kopp, R. E.; Krinner, G.; Mix, A. (2021). Masson-Delmotte, V.; Zhai, P.; Pirani, A.; Connors, S. L.; Péan, C.; Berger, S.; Caud, N.; Chen, Y.; Goldfarb, L. (eds.). "Chapter 9: Ocean, Cryosphere and Sea Level Change"(PDF). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, New York, US.
^National Academies of Sciences, Engineering, and Medicine (2011). "Synopsis". Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia. Washington, DC: The National Academies Press. p. 5. doi:10.17226/12877. ISBN978-0-309-15176-4. Box SYN-1: Sustained warming could lead to severe impacts