Misplaced Pages

#203796

132-556: In the early 1930s, subsequent to the construction of a seawall extending from West End to the Industrial Canal which created a new shoreline for Lake Pontchartrain, Pontchartrain Beach was moved to a new location at the lake end of Elysian Fields Avenue , a location formerly offshore of Milneburg . Pontchartrain Beach included a beach with a large Art Deco style bathhouse and swimming pools , amusement rides (including

264-517: A biodiverse range of larger and smaller animal life. Light is only able to penetrate the top 200 metres (660 ft) so this is the only part of the sea where plants can grow. The surface layers are often deficient in biologically active nitrogen compounds. The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen , its assimilation, nitrification , anammox and denitrification. Some of these processes take place in deep water so that where there

396-683: A mediterranean sea ) or wholly (as inland seas ) enclosed by land . However, an exception to this is the Sargasso Sea which has no coastline and lies within a circular current, the North Atlantic Gyre . Seas are generally larger than lakes and contain salt water, but the Sea of Galilee is a freshwater lake . The United Nations Convention on the Law of the Sea states that all of the ocean

528-422: A channel in the seabed. It may occur at a gap in a sandbar or near a man-made structure such as a groyne . These strong currents can have a velocity of 3 ft (0.9 m) per second, can form at different places at different stages of the tide and can carry away unwary bathers. Temporary upwelling currents occur when the wind pushes water away from the land and deeper water rises to replace it. This cold water

660-491: A false sense of security to property owners and local residents as evident in this situation. Seawalls along the Japanese coast have also been criticized for cutting settlements off from the sea, making beaches unusable, presenting an eyesore, disturbing wildlife, and being unnecessary. After 2012's Hurricane Sandy , New York City Mayor Bill de Blasio invested $ 3,000,000,000 in a hurricane restoration fund, with part of

792-546: A few years there was also a fairly large petting zoo with many farm animals and a huge red barn house. A miniature golf course was added, when this pastime became popular. Just outside the entrance gates was the Bali Hai Tiki-style restaurant. Another popular restaurant was the Ship Ahoy, which featured hamburgers and seafood. Pontchartrain Beach was sold on September 23, 1983. The main reason it closed down

924-400: A height of less than three feet, so they often pass unnoticed at this stage. In contrast, ocean surface waves caused by winds have wavelengths of a few hundred feet, travel at up to 65 miles per hour (105 km/h) and are up to 45 feet (14 metres) high. As a tsunami moves into shallower water its speed decreases, its wavelength shortens and its amplitude increases enormously, behaving in

1056-507: A large and multidisciplinary field: it examines the properties of seawater ; studies waves , tides , and currents ; charts coastlines and maps the seabeds ; and studies marine life . The subfield dealing with the sea's motion, its forces, and the forces acting upon it is known as physical oceanography . Marine biology (biological oceanography) studies the plants , animals , and other organisms inhabiting marine ecosystems . Both are informed by chemical oceanography , which studies

1188-453: A low-pressure system, can raise the surface of the sea at high tide dramatically. The Earth is composed of a magnetic central core , a mostly liquid mantle and a hard rigid outer shell (or lithosphere ), which is composed of the Earth's rocky crust and the deeper mostly solid outer layer of the mantle. On land the crust is known as the continental crust while under the sea it is known as

1320-415: A natural barrier against future disasters like the 2004 Indian Ocean earthquake . Studies have found that an offshore tsunami wall could reduce tsunami wave heights by up to 83%. The appropriate seawall design relies on location-specific aspects, including surrounding erosion processes. There are three main types of seawalls: vertical, curved, stepped, and mounds (see table below). A report published by

1452-534: A new world of creatures living on the seabed that scientists had not previously known to exist. Some like the detrivores rely on organic material falling to the ocean floor. Others cluster round deep sea hydrothermal vents where mineral-rich flows of water emerge from the seabed, supporting communities whose primary producers are sulphide-oxidising chemoautotrophic bacteria, and whose consumers include specialised bivalves, sea anemones, barnacles, crabs, worms and fish, often found nowhere else. A dead whale sinking to

SECTION 10

#1732787159204

1584-541: A problem as it is not easy for people to predict or imagine the strength of hurricane or storm-induced waves compared to normal, expected wave patterns. An extreme event can dissipate hundreds of times more energy than everyday waves, and calculating structures that will stand the force of coastal storms is difficult and, often the outcome can become unaffordable. For example, the Omaha Beach seawall in New Zealand

1716-402: A rise of between +16-19.3 cm throughout 1900–1988. Superstorm Sandy of 2012 is an example of the devastating effects rising sea levels can cause when mixed with a perfect storm. Superstorm Sandy sent a storm surge of 4–5 m onto New Jersey's and New York's barrier island and urban shorelines, estimated at $ 70 billion in damage. This problem could be overcome by further modeling and determining

1848-536: A saline body of water and therefore solely a sea in the sense of the common use of the word, like all other saltwater lakes called sea. Earth is the only known planet with seas of liquid water on its surface, although Mars possesses ice caps and similar planets in other solar systems may have oceans. Earth's 1,335,000,000 cubic kilometers (320,000,000 cu mi) of sea contain about 97.2 percent of its known water and covers approximately 71 percent of its surface. Another 2.15% of Earth's water

1980-443: A seawall can be from the area's natural water-table , rain percolating into the ground behind the wall and waves overtopping the wall. The water table can also rise during periods of high water ( high tide ). Lack of adequate drainage can cause the seawall to buckle, move, bow, crack, or collapse. Sinkholes may also develop as the escaping water pressure erodes soil through or around the drainage system. Extreme events also pose

2112-481: A ton, are weathered black and brown. The seawall is inspected every year and whenever gaps appear or the stones sink into the sand, the government adds more boulders to keep it strong. The Union Territory of Pondicherry recorded around 600 deaths from the huge tsunami waves that struck India's coast after the mammoth underwater earthquake (which measured 9.0 on the moment magnitude scale ) off Indonesia, but most of those killed were fishermen who lived in villages beyond

2244-471: A very high range in bays or estuaries . Submarine earthquakes arising from tectonic plate movements under the oceans can lead to destructive tsunamis , as can volcanoes, huge landslides , or the impact of large meteorites . The seas have been an integral element for humans throughout history and culture. Humans harnessing and studying the seas have been recorded since ancient times and evidenced well into prehistory , while its modern scientific study

2376-414: A wide array of species including corals (only six of which contribute to reef formation). Marine primary producers  – plants and microscopic organisms in the plankton – are widespread and very essential for the ecosystem. It has been estimated that half of the world's oxygen is produced by phytoplankton. About 45 percent of the sea's primary production of living material

2508-672: A wooden roller coaster called the Zephyr), and concession stands. The park featured live music concerts, including many local musicians and touring national acts such as Elvis Presley . Other rides and amusements included the Zephyr Junior, Smoky Mary, the Wild Maus , Musik Express , Log Ride, the Ragin' Cajun (a modern, looping steel coaster), the Bug, Paratrooper, Scrambler , Calypso,

2640-529: Is "sea". The law of the sea has at its center the definition of the boundaries of the ocean, clarifying its application in marginal seas . But what bodies of water other than the sea the law applies to is being crucially negotiated in the case of the Caspian Sea and its status as "sea", basically revolving around the issue of the Caspian Sea about either being factually an oceanic sea or only

2772-449: Is a continuous circulation of water in the oceans. Warm surface currents cool as they move away from the tropics, and the water becomes denser and sinks. The cold water moves back towards the equator as a deep sea current, driven by changes in the temperature and density of the water, before eventually welling up again towards the surface. Deep seawater has a temperature between −2 °C (28 °F) and 5 °C (41 °F) in all parts of

SECTION 20

#1732787159204

2904-399: Is a form of coastal defense constructed where the sea , and associated coastal processes, impact directly upon the landforms of the coast . The purpose of a seawall is to protect areas of human habitation, conservation, and leisure activities from the action of tides , waves , or tsunamis . As a seawall is a static feature, it will conflict with the dynamic nature of the coast and impede

3036-399: Is a point of land jutting out into the sea and a larger promontory is known as a cape . The indentation of a coastline, especially between two headlands, is a bay , a small bay with a narrow inlet is a cove and a large bay may be referred to as a gulf . Coastlines are influenced by several factors including the strength of the waves arriving on the shore, the gradient of the land margin,

3168-481: Is a static feature which can conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The table below summarizes some positive and negative effects of seawalls which can be used when comparing their effectiveness with other coastal management options, such as beach nourishment . Generally, seawalls can be a successful way to control coastal erosion, but only if they are constructed well and out of materials that can withstand

3300-545: Is also a major issue with seawalls. In 2013, more than 5,000 feet (1,500 m) of seawall was found to be crumbling in Punta Gorda, Florida . Residents of the area pay hundreds of dollars each year for a seawall repair program. The problem is that most of the seawalls are over a half-century old and are being destroyed by only heavy downpours. If not kept in check, seawalls lose effectiveness and become expensive to repair. Seawall construction has existed since ancient times. In

3432-487: Is an upwelling of cold waters, and also near estuaries where land-sourced nutrients are present, plant growth is higher. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal. There is a broader spectrum of higher animal taxa in the sea than on land, many marine species have yet to be discovered and the number known to science is expanding annually. Some vertebrates such as seabirds , seals and sea turtles return to

3564-613: Is believed to be a 100-meter row of boulders in the Mediterranean Sea off the coast of Israel. Boulders were positioned in an attempt to protect the coastal settlement of Tel Hreiz from sea rise following the last glacial maximum . Tel Hreiz was discovered in 1960 by divers searching for shipwrecks, but the row of boulders was not found until storms cleared a sand cover in 2012. More recently, seawalls were constructed in 1623 in Canvey Island , UK, when great floods of

3696-556: Is called oceanography and maritime space is governed by the law of the sea , with admiralty law regulating human interactions at sea. The seas provide substantial supplies of food for humans, mainly fish , but also shellfish , mammals and seaweed , whether caught by fishermen or farmed underwater. Other human uses of the seas include trade , travel, mineral extraction , power generation , warfare , and leisure activities such as swimming , sailing , and scuba diving . Many of these activities create marine pollution . The sea

3828-478: Is contributed by diatoms . Much larger algae, commonly known as seaweeds , are important locally; Sargassum forms floating drifts, while kelp form seabed forests. Flowering plants in the form of seagrasses grow in " meadows " in sandy shallows, mangroves line the coast in tropical and subtropical regions and salt-tolerant plants thrive in regularly inundated salt marshes . All of these habitats are able to sequester large quantities of carbon and support

3960-481: Is frozen, found in the sea ice covering the Arctic Ocean , the ice cap covering Antarctica and its adjacent seas , and various glaciers and surface deposits around the world. The remainder (about 0.65% of the whole) form underground reservoirs or various stages of the water cycle , containing the freshwater encountered and used by most terrestrial life : vapor in the air , the clouds it slowly forms,

4092-401: Is likely to reduce levels of oxygen in surface waters since the solubility of oxygen in water falls at higher temperatures. Ocean deoxygenation is projected to increase hypoxia by 10%, and triple suboxic waters (oxygen concentrations 98% less than the mean surface concentrations), for each 1 °C of upper-ocean warming. The amount of light that penetrates the sea depends on the angle of

Pontchartrain Beach - Misplaced Pages Continue

4224-530: Is near the Mariana Islands , a volcanic archipelago in the West Pacific. Its deepest point is 10.994 kilometres (nearly 7 miles) below the surface of the sea. The zone where land meets sea is known as the coast and the part between the lowest spring tides and the upper limit reached by splashing waves is the shore . A beach is the accumulation of sand or shingle on the shore. A headland

4356-541: Is often rich in nutrients and creates blooms of phytoplankton and a great increase in the productivity of the sea. Tides are the regular rise and fall in water level experienced by seas and oceans in response to the gravitational influences of the Moon and the Sun, and the effects of the Earth's rotation. During each tidal cycle, at any given place the water rises to a maximum height known as "high tide" before ebbing away again to

4488-595: Is the interconnected system of all the Earth's oceanic waters, including the Atlantic , Pacific , Indian , Southern and Arctic Oceans . However, the word "sea" can also be used for many specific, much smaller bodies of seawater, such as the North Sea or the Red Sea . There is no sharp distinction between seas and oceans , though generally seas are smaller, and are often partly (as marginal seas or particularly as

4620-419: Is turned into kinetic energy, creating a shallow wave, a tsunami, radiating outwards at a velocity proportional to the square root of the depth of the water and which therefore travels much faster in the open ocean than on a continental shelf. In the deep open sea, tsunamis have wavelengths of around 80 to 300 miles (130 to 480 km), travel at speeds of over 600 miles per hour (970 km/h) and usually have

4752-491: The 2004 Indian Ocean earthquake tsunami crashed against India's south-eastern coastline killing thousands. However, the former French colonial enclave of Pondicherry escaped unscathed. This was primarily due to French engineers who had constructed (and maintained) a massive stone seawall during the time when the city was a French colony. This 300-year-old seawall effectively kept Pondicherry's historic center dry even though tsunami waves drove water 24 ft (7.3 m) above

4884-651: The Coriolis effect . The surface currents flow in a clockwise direction in the Northern Hemisphere and anticlockwise in the Southern Hemisphere. The water moving away from the equator is warm, and that flowing in the reverse direction has lost most of its heat. These currents tend to moderate the Earth's climate, cooling the equatorial region and warming regions at higher latitudes. Global climate and weather forecasts are powerfully affected by

5016-857: The Mediterranean and Red Sea with the Egyptian Hannu reaching the Arabian Peninsula and the African Coast around 2750 BC. In the first millennium BC, Phoenicians and Greeks established colonies throughout the Mediterranean and the Black Sea . Around 500 BC, the Carthaginian navigator Hanno left a detailed periplus of an Atlantic journey that reached at least Senegal and possibly Mount Cameroon . In

5148-500: The UK , seawall also refers to an earthen bank used to create a polder , or a dike construction . The type of material used for construction is hypothesized to affect the settlement of coastal organisms, although the precise mechanism has yet to be identified. A seawall works by reflecting incident wave energy back into the sea, thus reducing the energy available to cause erosion. Seawalls have two specific weaknesses. Wave reflection from

5280-612: The United Nations Environment Programme (UNEP) suggests that the tsunami of 26 December 2004 caused less damage in the areas where natural barriers were present, such as mangroves , coral reefs or coastal vegetation. A Japanese study of this tsunami in Sri Lanka used satellite imagery modelling to establish the parameters of coastal resistance as a function of different types of trees. Natural barriers, such as coral reefs and mangrove forests, prevent

5412-584: The early Mediaeval period , the Vikings crossed the North Atlantic and even reached the northeastern fringes of North America. Novgorodians had also been sailing the White Sea since the 13th century or before. Meanwhile, the seas along the eastern and southern Asian coast were used by Arab and Chinese traders. The Chinese Ming Dynasty had a fleet of 317 ships with 37,000 men under Zheng He in

Pontchartrain Beach - Misplaced Pages Continue

5544-614: The hundred-year wave ) they are designed against. Rogue waves, however, have been documented at heights above 25 meters (82 ft). The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave is pushed across the surface of the sea by the wind, but this represents a transfer of energy and not a horizontal movement of water. As waves approach land and move into shallow water , they change their behavior. If approaching at an angle, waves may bend ( refraction ) or wrap rocks and headlands ( diffraction ). When

5676-422: The oceanic crust . The latter is composed of relatively dense basalt and is some five to ten kilometres (three to six miles) thick. The relatively thin lithosphere floats on the weaker and hotter mantle below and is fractured into a number of tectonic plates . In mid-ocean, magma is constantly being thrust through the seabed between adjoining plates to form mid-oceanic ridges and here convection currents within

5808-436: The photosynthetic activity of these plants produces oxygen, which dissolves in the seawater and is used by marine animals. At night, photosynthesis stops, and the amount of dissolved oxygen declines. In the deep sea, where insufficient light penetrates for plants to grow, there is very little dissolved oxygen. In its absence, organic material is broken down by anaerobic bacteria producing hydrogen sulphide . Climate change

5940-421: The rain falling from them, and the lakes and rivers spontaneously formed as its waters flow again and again to the sea. The scientific study of water and Earth's water cycle is hydrology ; hydrodynamics studies the physics of water in motion. The more recent study of the sea in particular is oceanography . This began as the study of the shape of the ocean's currents but has since expanded into

6072-412: The swash moves beach material seawards. Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide, the power of a storm wave impacting on the foot of a cliff has a shattering effect as air in cracks and crevices is compressed and then expands rapidly with release of pressure. At the same time, sand and pebbles have an erosive effect as they are thrown against

6204-420: The water , carbon , and nitrogen cycles . The surface of water interacts with the atmosphere, exchanging properties such as particles and temperature, as well as currents . Surface currents are the water currents that are produced by the atmosphere's currents and its winds blowing over the surface of the water, producing wind waves , setting up through drag slow but stable circulations of water, as in

6336-599: The "airplanes", Haunted House, Ghost Train, bumper cars, carousel , Ferris wheel , the Monster, Trabant, Sky Ride, Hard Rock, Galaxy, Laff in the Dark, Magic Rainbow, Red Baron, and Kiddieland. As with other amusement or theme parks, over time certain older rides were changed out for new ones. In addition to rides, there were also the summertime shows which changed every few years (Skipper & Dolly dolphin show, Great American High Dive Show, Merlin's Magic Rainbow Show). For

6468-569: The Austronesian " Lapita " peoples displayed great feats of navigation, reaching out from the Bismarck Archipelago to as far away as Fiji , Tonga , and Samoa . Their descendants continued to travel thousands of miles between tiny islands on outrigger canoes , and in the process they found many new islands, including Hawaii , Easter Island (Rapa Nui), and New Zealand. The Ancient Egyptians and Phoenicians explored

6600-405: The Earth , clarified the process of sedimentation , and assisted the study of volcanism and earthquakes . A characteristic of seawater is that it is salty. Salinity is usually measured in parts per thousand ( ‰ or per mil), and the open ocean has about 35 grams (1.2 oz) solids per litre, a salinity of 35 ‰. The Mediterranean Sea is slightly higher at 38 ‰, while the salinity of

6732-420: The Earth is closest to the Moon because it is also where the effect of the Moon's gravity is stronger. On the opposite side of the Earth, the lunar force is at its weakest and this causes another bulge to form. As the Moon rotates around the Earth, so do these ocean bulges move around the Earth. The gravitational attraction of the Sun is also working on the seas, but its effect on tides is less powerful than that of

SECTION 50

#1732787159204

6864-411: The Earth to make a complete revolution and return the Moon to its previous position relative to an observer. The Moon's mass is some 27 million times smaller than the Sun, but it is 400 times closer to the Earth. Tidal force or tide-raising force decreases rapidly with distance, so the moon has more than twice as great an effect on tides as the Sun. A bulge is formed in the ocean at the place where

6996-506: The Global Positioning System, GPS) indicate a mean rate of sea level rise of 1.6–1.8 mm/yr over the twentieth century. The Intergovernmental Panel on Climate Change (IPCC) (1997) suggested that sea level rise over the next 50 – 100 years will accelerate with a projected increase in global mean sea level of +18 cm by 2050 AD. This data is reinforced by Hannah (1990) who calculated similar statistics including

7128-754: The Living Seawalls project was announced as a finalist for the international environment award the Earthshot Prize . Since 2022 it has become part of Project Restore, under the auspices of the Sydney Institute of Marine Science . Some further issues include a lack of long-term trend data of seawall effects due to a relatively short duration of data records; modeling limitations and comparisons of different projects and their effects being invalid or unequal due to different beach types; materials; currents; and environments. Lack of maintenance

7260-413: The Moon, and when the Sun, Moon and Earth are all aligned (full moon and new moon), the combined effect results in the high "spring tides". In contrast, when the Sun is at 90° from the Moon as viewed from Earth, the combined gravitational effect on tides is less causing the lower "neap tides". A storm surge can occur when high winds pile water up against the coast in a shallow area and this, coupled with

7392-556: The Southern Hemisphere in the Roaring Forties , long, organised masses of water called swell roll across the ocean. If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. The size of the waves depends on the fetch , the distance that the wind has blown over the water and the strength and duration of that wind. When waves meet others coming from different directions, interference between

7524-576: The Thames estuary occurred, prompting the construction of protection for further events in this flood-prone area. Since then, seawall design has become more complex and intricate in response to an improvement in materials, technology, and an understanding of how coastal processes operate. This section will outline some key case studies of seawalls in chronological order and describe how they have performed in response to tsunamis or ongoing natural processes and how effective they were in these situations. Analyzing

7656-510: The Vancouver Seawall is a prime example of how seawalls can simultaneously provide shoreline protection and a source of recreation which enhances human enjoyment of the coastal environment. It also illustrates that although shoreline erosion is a natural process, human activities, interactions with the coast, and poorly planned shoreline development projects can accelerate natural erosion rates. On December 26, 2004, towering waves of

7788-517: The added CO 2 is absorbed by the oceans, forming carbonic acid and lowering the pH (now below 8.1 ) through a process called ocean acidification . The extent of further ocean chemistry changes, including ocean pH, will depend on climate change mitigation efforts taken by nations and their governments. The amount of oxygen found in seawater depends primarily on the plants growing in it. These are mainly algae, including phytoplankton , with some vascular plants such as seagrasses . In daylight,

7920-427: The artificial barrier which reinforces the effectiveness of seawalls. At least 43 percent of Japan's 29,751 km (18,486 mi) coastline is lined with concrete seawalls or other structures designed to protect the country against high waves, typhoons, or even tsunamis. During the 2011 Tōhoku earthquake and tsunami , the seawalls in most areas were overwhelmed. In Kamaishi , 4-metre (13 ft) waves surmounted

8052-411: The behavior of elements and molecules within the oceans: particularly, at the moment, the ocean's role in the carbon cycle and carbon dioxide 's role in the increasing acidification of seawater. Marine and maritime geography charts the shape and shaping of the sea, while marine geology (geological oceanography) has provided evidence of continental drift and the composition and structure of

SECTION 60

#1732787159204

8184-529: The bottom of the ocean provides food for an assembly of organisms which similarly rely largely on the actions of sulphur-reducing bacteria. Such places support unique biomes where many new microbes and other lifeforms have been discovered. Humans have travelled the seas since they first built sea-going craft. Mesopotamians were using bitumen to caulk their reed boats and, a little later, masted sails . By c. 3000 BC, Austronesians on Taiwan had begun spreading into maritime Southeast Asia . Subsequently,

8316-467: The boundaries between the land and sea, the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed. As they grate together, the continental plates are deformed and buckle causing mountain building and seismic activity. The Earth's deepest trench is the Mariana Trench which extends for about 2,500 kilometres (1,600 miles) across the seabed. It

8448-516: The case of the ocean sustaining deep-sea ocean currents . Deep-sea currents, known together as the global conveyor belt , carry cold water from near the poles to every ocean and significantly influence Earth's climate. Tides , the generally twice-daily rise and fall of sea levels , are caused by Earth's rotation and the gravitational effects of the Moon and, to a lesser extent, of the Sun . Tides may have

8580-437: The coast scour out channels and transport sand and pebbles away from their place of origin. Sediment carried to the sea by rivers settles on the seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides and currents. Dredging removes material and deepens channels but may have unexpected effects elsewhere on the coastline. Governments make efforts to prevent flooding of

8712-446: The composition and hardness of the coastal rock, the inclination of the off-shore slope and the changes of the level of the land due to local uplift or submergence. Normally, waves roll towards the shore at the rate of six to eight per minute and these are known as constructive waves as they tend to move material up the beach and have little erosive effect. Storm waves arrive on shore in rapid succession and are known as destructive waves as

8844-598: The continental shelf. Alternatively, marine habitats can be divided vertically into pelagic (open water), demersal (just above the seabed) and benthic (sea bottom) habitats. A third division is by latitude : from polar seas with ice shelves, sea ice and icebergs, to temperate and tropical waters. Coral reefs, the so-called "rainforests of the sea", occupy less than 0.1 percent of the world's ocean surface, yet their ecosystems include 25 percent of all marine species. The best-known are tropical coral reefs such as Australia's Great Barrier Reef , but cold water reefs harbour

8976-522: The currents. Most of the smallest organisms are the larvae of fish and marine invertebrates which liberate eggs in vast numbers because the chance of any one embryo surviving to maturity is so minute. The zooplankton feed on phytoplankton and on each other and form a basic part of the complex food chain that extends through variously sized fish and other nektonic organisms to large squid , sharks , porpoises , dolphins and whales . Some marine creatures make large migrations, either to other regions of

9108-436: The depths of the ocean; however, the relative proportions of dissolved salts vary little across the oceans. The most abundant solid dissolved in seawater is sodium chloride . The water also contains salts of magnesium , calcium , potassium , and mercury , amongst many other elements, some in minute concentrations. A wide variety of organisms , including bacteria , protists , algae , plants, fungi , and animals live in

9240-410: The destruction may be caused by the flood water draining back into the sea after the tsunami has struck, dragging debris and people with it. Often several tsunami are caused by a single geological event and arrive at intervals of between eight minutes and two hours. The first wave to arrive on shore may not be the biggest or most destructive. Wind blowing over the surface of the sea causes friction at

9372-413: The direction of the wind. The friction between air and water caused by a gentle breeze on a pond causes ripples to form. A strong blow over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they are travelling nearly matches the speed of the wind. In open water, when the wind blows continuously as happens in

9504-485: The disruption of sediment movement and transport patterns. Combined with a high construction cost, this has led to increasing use of other soft engineering coastal management options such as beach replenishment . Seawalls are constructed from various materials, most commonly reinforced concrete , boulders, steel, or gabions . Other possible construction materials include vinyl, wood, aluminum, fiberglass composite, and biodegradable sandbags made of jute and coir . In

9636-571: The early fifteenth century, sailing the Indian and Pacific Oceans. In the late fifteenth century, Western European mariners started making longer voyages of exploration in search of trade. Bartolomeu Dias rounded the Cape of Good Hope in 1487 and Vasco da Gama reached India via the Cape in 1498. Christopher Columbus sailed from Cadiz in 1492, attempting to reach the eastern lands of India and Japan by

9768-454: The earthquake zone, as the tsunami washed over walls that were supposed to protect the plants. Arguably, the additional defense provided by the seawalls presented an extra margin of time for citizens to evacuate and also stopped some of the full force of energy which would have caused the wave to climb higher in the backs of coastal valleys. In contrast, the seawalls also acted in a negative way to trap water and delay its retreat. The failure of

9900-408: The exchange of sediment between land and sea. Seawall designs factor in local climate, coastal position, wave regime (determined by wave characteristics and effectors), and value (morphological characteristics) of landform. Seawalls are hard engineering shore-based structures that protect the coast from erosion. Various environmental issues may arise from the construction of a seawall, including

10032-404: The extension of height and reinforcement of current seawalls which needs to occur for safety to be ensured in both situations. Sea level rise also will cause a higher risk of flooding and taller tsunamis. Seawalls, like all retaining walls , must relieve the buildup of water pressure . Water pressure buildup is caused when groundwater is not drained from behind the seawall. Groundwater against

10164-450: The first century BCE, Romans built a seawall or breakwater at Caesarea Maritima creating an artificial harbor (Sebastos Harbor). The construction used Pozzolana concrete which hardens in contact with seawater. Barges were constructed and filled with the concrete. They were floated into position and sunk. The resulting harbor/breakwater/seawall is still in existence today – more than 2000 years later. The oldest known coastal defense

10296-422: The food chain or precipitated into the deeper, more carbon-rich layers as dead soft tissue or in shells and bones as calcium carbonate . It circulates in this layer for long periods of time before either being deposited as sediment or being returned to surface waters through thermohaline circulation. The oceans are home to a diverse collection of life forms that use it as a habitat. Since sunlight illuminates only

10428-402: The force of ongoing wave energy. Some understanding is needed of the coastal processes and morphodynamics specific to the seawall location. Seawalls can be very helpful; they can offer a more long-term solution than soft engineering options, additionally providing recreation opportunities and protection from extreme events as well as everyday erosion. Extreme natural events expose weaknesses in

10560-596: The four antique carousels is located on the boardwalk in Myrtle Beach, South Carolina . Also, the crest of the Zephyr currently resides at Kenner Memorial Park, among with remnants of Bali Hai restaurant. The hand-painted carousel horses were donated by Harry J. Batt Jr. and John A. Batt to New Orleans' City Park . The Park did not acknowledge the gifts or recognize the Batts for their donation. The land formerly housing

10692-580: The gap and a circular movement of surface currents known as a gyre is formed. There are five main gyres in the world's oceans: two in the Pacific, two in the Atlantic and one in the Indian Ocean. Other smaller gyres are found in lesser seas and a single gyre flows around Antarctica . These gyres have followed the same routes for millennia, guided by the topography of the land, the wind direction and

10824-570: The globe. Seawater with a typical salinity of 35 ‰ has a freezing point of about −1.8 °C (28.8 °F). When its temperature becomes low enough, ice crystals form on the surface. These break into small pieces and coalesce into flat discs that form a thick suspension known as frazil . In calm conditions, this freezes into a thin flat sheet known as nilas , which thickens as new ice forms on its underside. In more turbulent seas, frazil crystals join into flat discs known as pancakes. These slide under each other and coalesce to form floes . In

10956-442: The interface between air and sea. Not only does this cause waves to form, but it also makes the surface seawater move in the same direction as the wind. Although winds are variable, in any one place they predominantly blow from a single direction and thus a surface current can be formed. Westerly winds are most frequent in the mid-latitudes while easterlies dominate the tropics. When water moves in this way, other water flows in to fill

11088-547: The land by the building of breakwaters , seawalls , dykes and levees and other sea defences. For instance, the Thames Barrier is designed to protect London from a storm surge, while the failure of the dykes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States. The sea plays a part in the water or hydrological cycle , in which water evaporates from

11220-523: The land to breed but fish, cetaceans and sea snakes have a completely aquatic lifestyle and many invertebrate phyla are entirely marine. In fact, the oceans teem with life and provide many varying microhabitats. One of these is the surface film which, even though tossed about by the movement of waves, provides a rich environment and is home to bacteria, fungi , microalgae , protozoa , fish eggs and various larvae. The pelagic zone contains macro- and microfauna and myriad zooplankton which drift with

11352-648: The levels of salinity in different seas, the relative composition of the dissolved salts is stable throughout the world's oceans. Seawater is too saline for humans to drink safely, as the kidneys cannot excrete urine as salty as seawater. Although the amount of salt in the ocean remains relatively constant within the scale of millions of years, various factors affect the salinity of a body of water. Evaporation and by-product of ice formation (known as "brine rejection") increase salinity, whereas precipitation , sea ice melt, and runoff from land reduce it. The Baltic Sea , for example, has many rivers flowing into it, and thus

11484-508: The mantle tend to drive the two plates apart. Parallel to these ridges and nearer the coasts, one oceanic plate may slide beneath another oceanic plate in a process known as subduction . Deep trenches are formed here and the process is accompanied by friction as the plates grind together. The movement proceeds in jerks which cause earthquakes, heat is produced and magma is forced up creating underwater mountains, some of which may form chains of volcanic islands near to deep trenches. Near some of

11616-416: The minimum "low tide" level. As the water recedes, it uncovers more and more of the foreshore , also known as the intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude. Most places experience two high tides each day, occurring at intervals of about 12 hours and 25 minutes. This is half the 24 hours and 50 minute period that it takes for

11748-480: The money dedicated to building new seawalls and protection from future hurricanes. A New York Harbor Storm-Surge Barrier has been proposed, but not voted on or funded by Congress or the State of New York. In Florida, tiger dams are used to protect homes near the coast. General: Related types of walls: Specific walls: Sea A sea is a large body of salt water . There are particular seas and

11880-454: The normal high-tide mark. The barrier was initially completed in 1735 and over the years, the French continued to fortify the wall, piling huge boulders along its 1.25 mi (2 km) coastline to stop erosion from the waves pounding the harbor. At its highest, the barrier running along the water's edge reaches about 27 ft (8.2 m) above sea level. The boulders, some weighing up to

12012-539: The northern Red Sea can reach 41‰. In contrast, some landlocked hypersaline lakes have a much higher salinity, for example, the Dead Sea has 300 grams (11 oz) dissolved solids per litre (300 ‰). While the constituents of table salt ( sodium and chloride ) make up about 85 percent of the solids in solution, there are also other metal ions such as magnesium and calcium , and negative ions including sulphate , carbonate , and bromide . Despite variations in

12144-730: The novel means of travelling westwards. He made landfall instead on an island in the Caribbean Sea and a few years later, the Venetian navigator John Cabot reached Newfoundland . The Italian Amerigo Vespucci , after whom America was named, explored the South American coastline in voyages made between 1497 and 1502, discovering the mouth of the Amazon River . In 1519 the Portuguese navigator Ferdinand Magellan led

12276-484: The ocean depths caused by the movement of deep water masses. A main deep ocean current flows through all the world's oceans and is known as the thermohaline circulation or global conveyor belt. This movement is slow and is driven by differences in density of the water caused by variations in salinity and temperature. At high latitudes the water is chilled by the low atmospheric temperature and becomes saltier as sea ice crystallizes out. Both these factors make it denser, and

12408-440: The ocean on a seasonal basis or vertical migrations daily, often ascending to feed at night and descending to safety by day. Ships can introduce or spread invasive species through the discharge of ballast water or the transport of organisms that have accumulated as part of the fouling community on the hulls of vessels. The demersal zone supports many animals that feed on benthic organisms or seek protection from predators and

12540-471: The ocean, travels through the atmosphere as vapour, condenses , falls as rain or snow , thereby sustaining life on land, and largely returns to the sea. Even in the Atacama Desert , where little rain ever falls, dense clouds of fog known as the camanchaca blow in from the sea and support plant life. In central Asia and other large land masses, there are endorheic basins which have no outlet to

12672-423: The open pelagic zone. The organisms living in the sea range from whales 30 metres (98 feet) long to microscopic phytoplankton and zooplankton , fungi, and bacteria. Marine life plays an important part in the carbon cycle as photosynthetic organisms convert dissolved carbon dioxide into organic carbon and it is economically important to humans for providing fish for use as food. Life may have originated in

12804-750: The park is now occupied by the University of New Orleans Research & Technology Park , home to numerous corporate tenants, the Navy's Space and Naval Warfare Systems Center (SPAWAR) and the UNO Advanced Technology Center office building. A mile-long sand beach is still at the same area where Pontchartrain Beach once was. It is inaccessible and off limits to the general public, having been deemed hazardous due to underwater drop offs and riprap which pose dangers for swimmers. Water quality had increased dramatically in recent decades and

12936-462: The performance of seawalls, and analyses of these can lead to future improvements and reassessment. Sea level rise creates an issue for seawalls worldwide as it raises both the mean normal water level and the height of waves during extreme weather events, which the current seawall heights may be unable to cope with. The most recent analyses of long, good-quality tide gauge records (corrected for GIA and when possible for other vertical land motions by

13068-430: The process of freezing, salt water and air are trapped between the ice crystals. Nilas may have a salinity of 12–15 ‰, but by the time the sea ice is one year old, this falls to 4–6 ‰. Seawater is slightly alkaline and had an average pH of about 8.2 over the past 300 million years. More recently, climate change has resulted in an increase of the carbon dioxide content of the atmosphere; about 30–40% of

13200-418: The quality of the inflowing water. Oceans contain the greatest quantity of actively cycled carbon in the world and are second only to the lithosphere in the amount of carbon they store. The oceans' surface layer holds large amounts of dissolved organic carbon that is exchanged rapidly with the atmosphere. The deep layer's concentration of dissolved inorganic carbon is about 15 percent higher than that of

13332-417: The rocks. This tends to undercut the cliff, and normal weathering processes such as the action of frost follows, causing further destruction. Gradually, a wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion. Material worn from the margins of the land eventually ends up in the sea. Here it is subject to attrition as currents flowing parallel to

13464-409: The same way as a wind-generated wave in shallow water but on a vastly greater scale. Either the trough or the crest of a tsunami can arrive at the coast first. In the former case, the sea draws back and leaves subtidal areas close to the shore exposed which provides a useful warning for people on land. When the crest arrives, it does not usually break but rushes inland, flooding all in its path. Much of

13596-468: The sand beach was reopened at one point, until a pair of drownings occurred and the beach was re-closed. The Lake Pontchartrain Basin Foundation has undertaken the task of restoring Pontchartrain Beach for use as a public recreation area. While no opening date has been given officially, a phased approach was expected to begin in the summer of 2016. Seawall A seawall (or sea wall )

13728-463: The sea . The sea commonly refers to the Ocean , the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas , second-order sections of the oceanic sea (e.g. the Mediterranean Sea ), or certain large, nearly landlocked bodies of water. The salinity of water bodies varies widely, being lower near the surface and the mouths of large rivers and higher in

13860-479: The sea and all the major groups of animals are represented there. Scientists differ as to precisely where in the sea life arose: the Miller-Urey experiments suggested a dilute chemical "soup" in open water, but more recent suggestions include volcanic hot springs, fine-grained clay sediments, or deep-sea " black smoker " vents, all of which would have provided protection from damaging ultraviolet radiation which

13992-436: The sea could be considered as brackish . Meanwhile, the Red Sea is very salty due to its high evaporation rate. Sea temperature depends on the amount of solar radiation falling on its surface. In the tropics, with the sun nearly overhead, the temperature of the surface layers can rise to over 30 °C (86 °F) while near the poles the temperature in equilibrium with the sea ice is about −2 °C (28 °F). There

14124-537: The sea level has been higher than it is today. The main factor affecting sea level over time is the result of changes in the oceanic crust, with a downward trend expected to continue in the very long term. At the last glacial maximum , some 20,000 years ago, the sea level was about 125 metres (410 ft) lower than in present times (2012). For at least the last 100 years, sea level has been rising at an average rate of about 1.8 millimetres (0.071 in) per year. Most of this rise can be attributed to an increase in

14256-399: The sea under the influence of gravity. A tsunami is an unusual form of wave caused by an infrequent powerful event such as an underwater earthquake or landslide, a meteorite impact, a volcanic eruption or a collapse of land into the sea. These events can temporarily lift or lower the surface of the sea in the affected area, usually by a few feet. The potential energy of the displaced seawater

14388-671: The sea, separated from the ocean by mountains or other natural geologic features that prevent the water draining away. The Caspian Sea is the largest one of these. Its main inflow is from the River Volga , there is no outflow and the evaporation of water makes it saline as dissolved minerals accumulate. The Aral Sea in Kazakhstan and Uzbekistan, and Pyramid Lake in the western United States are further examples of large, inland saline water-bodies without drainage. Some endorheic lakes are less salty, but all are sensitive to variations in

14520-657: The seabed provides a range of habitats on or under the surface of the substrate which are used by creatures adapted to these conditions. The tidal zone with its periodic exposure to the dehydrating air is home to barnacles , molluscs and crustaceans . The neritic zone has many organisms that need light to flourish. Here, among algal-encrusted rocks live sponges , echinoderms , polychaete worms, sea anemones and other invertebrates. Corals often contain photosynthetic symbionts and live in shallow waters where light penetrates. The extensive calcareous skeletons they extrude build up into coral reefs which are an important feature of

14652-427: The seabed. These provide a biodiverse habitat for reef-dwelling organisms. There is less sea life on the floor of deeper seas but marine life also flourishes around seamounts that rise from the depths, where fish and other animals congregate to spawn and feed. Close to the seabed live demersal fish that feed largely on pelagic organisms or benthic invertebrates. Exploration of the deep sea by submersibles revealed

14784-566: The seafloor. The Living Seawalls project, which was launched in Sydney , Australia, in 2018, aims to help many of the marine species in Sydney Harbour to flourish, thus enhancing its biodiversity , by modifying the design of its seawalls. It entails covering parts of the seawalls with specially-designed tiles that mimic natural microhabitats - with crevices and other features that more closely resemble natural rocks. In September 2021,

14916-481: The seas, which offers a wide range of marine habitats and ecosystems , ranging vertically from the sunlit surface and shoreline to the great depths and pressures of the cold, dark abyssal zone , and in latitude from the cold waters under polar ice caps to the warm waters of coral reefs in tropical regions . Many of the major groups of organisms evolved in the sea and life may have started there. The ocean moderates Earth's climate and has important roles in

15048-481: The seawall began in 1917, and since then this pathway has become one of the most used features of the park by both locals and tourists and now extends 22 km in total. The construction of the seawall also provided employment for relief workers during the Great Depression and seamen from HMCS  Discovery on Deadman's Island who were facing punishment detail in the 1950s (Steele, 1985). Overall,

15180-474: The seawall – the world's largest, erected a few years ago in the city's harbor at a depth of 63 m (207 ft), a length of 2 km (1.2 mi) and a cost of $ 1.5 billion – and eventually submerged the city center. The risks of dependence on seawalls were most evident in the crisis at the Fukushima Dai-ichi and Fukushima Dai-ni nuclear power plants , both located along the coast close to

15312-418: The slope under the effect of gravity. The larger the breaking waves, the longer the beach and the more oblique the wave approach, the stronger is the longshore current. These currents can shift great volumes of sand or pebbles, create spits and make beaches disappear and water channels silt up. A rip current can occur when water piles up near the shore from advancing waves and is funnelled out to sea through

15444-411: The spread of tsunamis and the flow of coastal waters and mitigated the flood and surge of water. A cost-benefit approach is an effective way to determine whether a seawall is appropriate and whether the benefits are worth the expense. Besides controlling erosion, consideration must be given to the effects of hardening a shoreline on natural coastal ecosystems and human property or activities. A seawall

15576-583: The successes and shortcomings of seawalls during severe natural events allows their weaknesses to be exposed, and areas become visible for future improvement. The Vancouver Seawall is a stone seawall constructed around the perimeter of Stanley Park in Vancouver, British Columbia . The seawall was constructed initially as waves created by ships passing through the First Narrows eroding the area between Prospect Point and Brockton Point. Construction of

15708-429: The sun, the weather conditions and the turbidity of the water. Much light gets reflected at the surface, and red light gets absorbed in the top few metres. Yellow and green light reach greater depths, and blue and violet light may penetrate as deep as 1,000 metres (3,300 ft). There is insufficient light for photosynthesis and plant growth beyond a depth of about 200 metres (660 ft). Over most of geologic time,

15840-430: The surface and loops back on itself. It takes a thousand years for this circulation pattern to be completed. Besides gyres, there are temporary surface currents that occur under specific conditions. When waves meet a shore at an angle, a longshore current is created as water is pushed along parallel to the coastline. The water swirls up onto the beach at right angles to the approaching waves but drains away straight down

15972-473: The surface layer and it remains there for much longer periods of time. Thermohaline circulation exchanges carbon between these two layers. Carbon enters the ocean as atmospheric carbon dioxide dissolves in the surface layers and is converted into carbonic acid , carbonate , and bicarbonate : It can also enter through rivers as dissolved organic carbon and is converted by photosynthetic organisms into organic carbon. This can either be exchanged throughout

16104-453: The temperature of the sea due to climate change , and the resulting slight thermal expansion of the upper 500 metres (1,600 ft) of water. Additional contributions, as much as one quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human needs. Wind blowing over the surface of a body of water forms waves that are perpendicular to

16236-432: The two can produce broken, irregular seas. Constructive interference can cause individual (unexpected) rogue waves much higher than normal. Most waves are less than 3 m (10 ft) high and it is not unusual for strong storms to double or triple that height; offshore construction such as wind farms and oil platforms use metocean statistics from measurements in computing the wave forces (due to for instance

16368-431: The upper layers, the major part of the ocean exists in permanent darkness. As the different depth and temperature zones each provide habitat for a unique set of species, the marine environment as a whole encompasses an immense diversity of life. Marine habitats range from surface water to the deepest oceanic trenches , including coral reefs, kelp forests , seagrass meadows , tidepools , muddy, sandy and rocky seabeds, and

16500-549: The wall may result in hydrodynamic scour and subsequent lowering of the sand level of the fronting beach. Seawalls may also accelerate the erosion of adjacent, unprotected coastal areas by affecting the littoral drift process. Different designs of man-made tsunami barriers include building reefs and forests to above-ground and submerged seawalls. Starting just weeks after the disaster, in January 2005, India began planting Casuarina and coconut saplings on its coast as

16632-460: The water sinks. From the deep sea near Greenland, such water flows southwards between the continental landmasses on either side of the Atlantic. When it reaches the Antarctic, it is joined by further masses of cold, sinking water and flows eastwards. It then splits into two streams that move northwards into the Indian and Pacific Oceans. Here it is gradually warmed, becomes less dense, rises towards

16764-426: The wave reaches a point where its deepest oscillations of the water contact the seabed , they begin to slow down. This pulls the crests closer together and increases the waves' height , which is called wave shoaling . When the ratio of the wave's height to the water depth increases above a certain limit, it " breaks ", toppling over in a mass of foaming water. This rushes in a sheet up the beach before retreating into

16896-445: The world ocean, so global climate modelling makes use of ocean circulation models as well as models of other major components such as the atmosphere , land surfaces, aerosols and sea ice. Ocean models make use of a branch of physics, geophysical fluid dynamics , that describes the large-scale flow of fluids such as seawater. Surface currents only affect the top few hundred metres of the sea, but there are also large-scale flows in

17028-605: The world's largest seawall, which cost $ 1.5 billion to construct, shows that building stronger seawalls to protect larger areas would have been even less cost-effective. In the case of the ongoing crisis at the nuclear power plants, higher and stronger seawalls should have been built if power plants were to be built at that site. Fundamentally, the devastation in coastal areas and a final death toll predicted to exceed 10,000 could push Japan to redesign its seawalls or consider more effective alternative methods of coastal protection for extreme events. Such hardened coastlines can also provide

17160-763: Was designed to prevent erosion from everyday waves only, and when a storm in 1976 carved out ten meters behind the existing seawall, the whole structure was destroyed. The addition of seawalls near marine ecosystems can lead to increased shadowing effects in the waters surrounding the seawall. Shadowing reduces the light and visibility within the water, which may disrupt the distribution as well as foraging capabilities of certain species. The sediment surrounding seawalls tends to have less favorable physical properties (Higher calcification levels, less structural organization of crystalline structure, low silicon content, and less macroscale roughness) when compared to natural shorelines, which can present issues for species that reside on

17292-661: Was due to declining attendance. In 1943, Corporal Douglas O'Brien, a World War II serviceman from Springfield, Massachusetts , fell 75 feet (23 m) to his death from the top of the Zephyr roller coaster. He was 32 years old. Several of the rides – including the Airplanes and many Kiddieland rides – ended up in Gulf Shores, Alabama , at a small amusement park, which was subsequently wiped out by Hurricane Ivan in 2004. The Ragin' Cajun moved to Six Flags Great Escape in 1984 and opened as Steamin' Demon . One of

17424-407: Was not blocked by the early Earth's atmosphere. Marine habitats can be divided horizontally into coastal and open ocean habitats. Coastal habitats extend from the shoreline to the edge of the continental shelf . Most marine life is found in coastal habitats, even though the shelf area occupies only 7 percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of

#203796