History of navigation and exploration beginning at around 3000 BC 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 ,
Austronesians on Taiwan had begun spreading into
maritime Southeast Asia. Subsequently, 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 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 the
early Medieval 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 the early fifteenth century, sailing the Indian and Pacific Oceans. With regards to maps that are vital for navigation, in the second century,
Ptolemy mapped the whole known world from the "Fortunatae Insulae",
Cape Verde or
Canary Islands, eastward to the
Gulf of Thailand. This map was used in 1492 when Christopher Columbus set out on his voyages of discovery. Subsequently,
Gerardus Mercator made a practical map of the world in 1538, his map projection conveniently making
rhumb lines straight. A fourth edition draft was published in 1986 but so far several naming disputes (such as the one over the
Sea of Japan) have prevented its ratification.
History of oceanography and deep sea exploration Scientific oceanography began with the voyages of Captain James Cook from 1768 to 1779, describing the Pacific with unprecedented precision from 71 degrees South to 71 degrees North. In the southern Atlantic in 1898/1899,
Carl Chun on the
Valdivia brought many new life forms to the surface from depths of over . The first observations of deep-sea animals in their natural environment were made in 1930 by
William Beebe and
Otis Barton who descended to in the spherical steel
Bathysphere. This was lowered by cable but by 1960 a self-powered submersible,
Trieste developed by
Jacques Piccard, took Piccard and
Don Walsh to the deepest part of the
Earth's oceans, the
Mariana Trench in the Pacific, reaching a record depth of about , a feat not repeated until 2012 when
James Cameron piloted the
Deepsea Challenger to similar depths. An
atmospheric diving suit can be worn for deep sea operations, with a new world record being set in 2006 when a US Navy diver descended to in one of these articulated, pressurized suits. At great depths, no light penetrates through the water layers from above and the pressure is extreme. For deep sea exploration it is necessary to use specialist vehicles, either
remotely operated underwater vehicles with lights and cameras or crewed
submersibles. The battery-operated
Mir submersibles have a three-person crew and can descend to . They have viewing ports, 5,000-watt lights, video equipment and manipulator arms for collecting samples, placing probes or pushing the vehicle across the sea bed when the thrusters would stir up excessive sediment.
Bathymetry is the mapping and study of the
topography of the ocean floor. Methods used for measuring the depth of the sea include single or multibeam
echosounders,
laser airborne depth sounders and the calculation of depths from satellite remote sensing data. This information is used for determining the routes of undersea cables and pipelines, for choosing suitable locations for siting oil rigs and offshore wind turbines and for identifying possible new fisheries. Ongoing oceanographic research includes marine lifeforms, conservation, the marine environment, the chemistry of the ocean, the studying and modelling of climate dynamics, the air-sea boundary, weather patterns, ocean resources, renewable energy, waves and currents, and the design and development of new tools and technologies for investigating the deep. Whereas in the 1960s and 1970s, research could focus on taxonomy and basic biology, in the 2010s, attention has shifted to larger topics such as climate change. Researchers make use of satellite-based
remote sensing for surface waters, with research ships, moored observatories and autonomous underwater vehicles to study and monitor all parts of the sea.
Law "Freedom of the seas" is a principle in
international law dating from the seventeenth century. It stresses freedom to navigate the oceans and disapproves of war fought in
international waters. Today, this concept is enshrined in the United Nations Convention on the Law of the Sea (UNCLOS), the third version of which came into force in 1994. Article 87(1) states: "The high seas are open to all
states, whether coastal or
land-locked." Article 87(1) (a) to (f) gives a non-exhaustive list of freedoms including navigation, overflight, the laying of
submarine cables, building artificial islands, fishing and scientific research. UNCLOS defines various areas of water. "Internal waters" are on the landward side of a
baseline and foreign vessels have no right of passage in these. "Territorial waters" extend to from the coastline and in these waters, the coastal state is free to set laws, regulate use and exploit any resource. A "contiguous zone" extending a further 12 nautical miles allows for
hot pursuit of vessels suspected of infringing laws in four specific areas: customs, taxation, immigration and pollution. An "exclusive economic zone" extends for from the baseline. Within this area, the coastal nation has sole exploitation rights over all natural resources. The "continental shelf" is the
natural prolongation of the land territory to the
continental margin's outer edge, or 200 nautical miles from the coastal state's baseline, whichever is greater. Here the coastal nation has the exclusive right to harvest minerals and also living resources "attached" to the seabed. In the decisive 480 B.C.
Battle of Salamis, the Greek general
Themistocles trapped the far larger fleet of the Persian king
Xerxes in a narrow channel and attacked vigorously, destroying 200 Persian ships for the loss of 40 Greek vessels. At the end of the
Age of Sail, the British Royal Navy, led by
Horatio Nelson, broke the power of the combined French and Spanish fleets at the 1805
Battle of Trafalgar. With steam and the industrial production of steel plate came greatly increased firepower in the shape of the
dreadnought battleships armed with long-range guns. In 1905, the Japanese fleet decisively defeated the Russian fleet, which had travelled over , at the
Battle of Tsushima. Dreadnoughts fought inconclusively in the
First World War at the 1916
Battle of Jutland between the
Royal Navy's
Grand Fleet and the
Imperial German Navy's
High Seas Fleet. In the
Second World War, the British victory at the 1940
Battle of Taranto showed that naval air power was sufficient to overcome the largest warships, foreshadowing the decisive sea-battles of the
Pacific War including the Battles of the
Coral Sea,
Midway,
the Philippine Sea, and the climactic
Battle of Leyte Gulf, in all of which the dominant ships were
aircraft carriers. Submarines became important in naval warfare in World War I, when German submarines, known as
U-boats, sank nearly 5,000 Allied merchant ships, including the
RMS Lusitania, which helped to bring the United States into the war. In World War II, almost 3,000 Allied ships were sunk by U-boats attempting to block the flow of supplies to Britain, but the Allies broke the blockade in the
Battle of the Atlantic, which lasted the whole length of the war, sinking 783 U-boats. Since 1960, several nations have maintained fleets of nuclear-powered
ballistic missile submarines, vessels equipped to launch
ballistic missiles with
nuclear warheads from under the sea. Some of these are kept permanently on patrol.
Travel Sailing ships or
packets carried mail overseas, one of the earliest being the Dutch service to
Batavia in the 1670s. These added passenger accommodation, but in cramped conditions. Later, scheduled services were offered but the time journeys took depended much on the weather. When steamships replaced sailing vessels,
ocean-going liners took over the task of carrying people. By the beginning of the twentieth century, crossing the Atlantic took about five days and shipping companies competed to own the largest and fastest vessels. The
Blue Riband was an unofficial accolade given to the fastest liner crossing the Atlantic in regular service. The
Mauretania held the title with for twenty years from 1909. The
Hales Trophy, another award for the fastest commercial crossing of the Atlantic, was won by the
United States in 1952 for a crossing that took three days, ten hours and forty minutes. The great liners were comfortable but expensive in fuel and staff. The age of the trans-Atlantic liners waned as cheap intercontinental flights became available. In 1958, a regular scheduled air service between New York and Paris taking seven hours doomed the Atlantic ferry service to oblivion. One by one the vessels were laid up, some were scrapped, others became cruise ships for the
leisure industry and still others floating hotels.
Trade Maritime trade has existed for millennia. The
Ptolemaic dynasty had developed trade with India using the Red Sea ports, and in the first millennium BC, the Arabs, Phoenicians,
Israelites and Indians traded in luxury goods such as spices, gold, and precious stones. The Phoenicians were noted sea traders and under the Greeks and Romans, commerce continued to thrive. With the collapse of the Roman Empire, European trade dwindled but it continued to flourish among the kingdoms of Africa, the Middle East, India, China and southeastern Asia. From the 16th to the 19th centuries, over a period of 400 years, about 12–13 million Africans were shipped across the Atlantic to be sold as slaves in the Americas as part of the
Atlantic slave trade. Large quantities of goods are transported by sea, especially across the Atlantic and around the Pacific Rim. A major trade route passes through the
Pillars of Hercules, across the Mediterranean and the
Suez Canal to the Indian Ocean and through the
Straits of Malacca; much trade also passes through the
English Channel.
Shipping lanes are the routes on the open sea used by cargo vessels, traditionally making use of trade winds and currents. Over 60 percent of the world's container traffic is conveyed on the top twenty trade routes. Increased melting of Arctic ice since 2007 enables ships to travel the
Northwest Passage for some weeks in summertime, avoiding the longer routes via the Suez Canal or the
Panama Canal. Shipping is supplemented by
air freight, a more expensive process mostly used for particularly valuable or perishable cargoes. Seaborne trade carries more than US$4 trillion worth of goods each year.
Bulk cargo in the form of liquids, powder or particles are carried loose in the
holds of
bulk carriers and include
crude oil,
grain,
coal,
ore,
scrap metal,
sand and
gravel. Other cargo, such as manufactured goods, is usually transported within
standard-sized, lockable containers, loaded on purpose-built
container ships at
dedicated terminals. Before the rise of
containerization in the 1960s, these goods were loaded, transported and unloaded piecemeal as
break-bulk cargo. Containerization greatly increased the efficiency and decreased the cost of moving goods by sea, and was a major factor leading to the rise of
globalization and exponential increases in
international trade in the mid-to-late 20th century.
Food Fish and other fishery products are among the most widely consumed sources of protein and other essential nutrients. In 2011, the total world production of fish, including
aquaculture, was estimated to be 154 million tonnes, of which most was for human consumption. The harvesting of wild fish accounted for 90.4 million tonnes, while annually increasing aquaculture contributes the rest. In order to avoid overexploitation, many countries have introduced
quotas in their own waters. However, recovery efforts often entail substantial costs to local economies or food provision.
Artisan fishing methods include rod and line, harpoons, skin diving, traps, throw nets and drag nets. Traditional fishing boats are powered by paddle, wind or outboard motors and operate in near-shore waters. The
Food and Agriculture Organization is encouraging the development of local fisheries to provide food security to coastal communities and help alleviate poverty.
Aquaculture About 79 million tonnes (78M long tons; 87M short tons) of food and non-food products were produced by aquaculture in 2010, an all-time high. About six hundred species of plants and animals were cultured, some for use in seeding wild populations. The animals raised included
finfish, aquatic
reptiles, crustaceans, molluscs,
sea cucumbers,
sea urchins, sea squirts and jellyfish. Various methods are employed. Mesh enclosures for finfish can be suspended in the open seas, cages can be used in more sheltered waters or ponds can be refreshed with water at each high tide.
Shrimps can be reared in shallow ponds connected to the open sea. Ropes can be hung in water to grow algae, oysters and mussels. Oysters can be reared on trays or in mesh tubes. Sea cucumbers can be ranched on the seabed. Captive breeding programmes have raised
lobster larvae for release of juveniles into the wild resulting in an increased lobster harvest in
Maine. At least 145 species of seaweed – red, green, and brown algae – are eaten worldwide, and some have long been farmed in Japan and other Asian countries; there is great potential for additional
algaculture. Few maritime flowering plants are widely used for food but one example is
marsh samphire which is eaten both raw and cooked. A major difficulty for aquaculture is the tendency towards monoculture and the associated risk of widespread
disease. Aquaculture is also associated with environmental risks; for instance,
shrimp farming has caused the destruction of important
mangrove forests throughout
southeast Asia.
Leisure Use of the sea for leisure developed in the nineteenth century, and became a significant industry in the twentieth century. Maritime leisure activities are varied, and include
beachgoing,
cruising,
yachting,
powerboat racing and
fishing; commercially organized voyages on
cruise ships; and trips on smaller vessels for
ecotourism such as
whale watching and coastal
birdwatching.
Sea bathing became the vogue in Europe in the 18th century after
William Buchan advocated the practice for health reasons.
Surfing is a sport in which a wave is ridden by a surfer, with or without a
surfboard. Other marine
water sports include
kite surfing, where a
power kite propels a rider on a board across the water,
windsurfing, where the power is provided by a fixed, manoeuvrable sail and
water skiing, where a
powerboat is used to pull a skier. Beneath the surface,
freediving is necessarily restricted to shallow descents.
Pearl divers can dive to with baskets to collect
oysters. Human eyes are not adapted for use underwater but vision can be improved by wearing a
diving mask. Other useful equipment includes
fins and
snorkels, and
scuba equipment allows underwater breathing and hence a longer time can be spent beneath the surface. The depths that can be reached by divers and the length of time they can stay underwater is limited by the increase of pressure they experience as they descend and the need to prevent
decompression sickness as they return to the surface. Recreational divers restrict themselves to depths of beyond which the danger of
nitrogen narcosis increases.
Deeper dives can be made with specialised equipment and training. Forms of
sustainable marine energy include
tidal power,
ocean thermal energy and
wave power. Electricity
power stations are often located on the coast or beside an estuary so that the sea can be used as a heat sink. A colder heat sink enables more efficient power generation, which is important for expensive
nuclear power plants in particular. in Brittany generates 0.5 GW. Tidal power uses generators to produce electricity from tidal flows, sometimes by using a dam to store and then release seawater. The Rance barrage, long, near
St Malo in
Brittany opened in 1967; it generates about 0.5 GW, but it has been followed by few similar schemes. The first offshore wind farm was installed in Denmark in 1991, and the installed capacity of worldwide offshore wind farms reached 34 GW in 2020, mainly situated in Europe.
Extractive industries The seabed contains large reserves of minerals which can be exploited by dredging. This has advantages over land-based mining in that equipment can be built at specialised
shipyards and
infrastructure costs are lower. Disadvantages include problems caused by waves and tides, the tendency for excavations to silt up and the washing away of
spoil heaps. There is a risk of coastal erosion and environmental damage.
Seafloor massive sulphide deposits are potential sources of
silver,
gold,
copper,
lead and
zinc and trace metals since their discovery in the 1960s. They form when
geothermally heated water is emitted from deep sea hydrothermal vents known as "black smokers". The ores are of high quality but prohibitively costly to extract. There are large deposits of
petroleum and
natural gas, in rocks beneath the seabed.
Offshore platforms and
drilling rigs
extract the oil or gas and store it for transport to land. Offshore oil and gas production can be difficult due to the remote, harsh environment. Drilling for oil in the sea has environmental impacts. Animals may be disorientated by
seismic waves used to locate deposits, and there is debate as to whether this causes the
beaching of whales. Toxic substances such as
mercury, lead and
arsenic may be released. The infrastructure may cause damage, and oil may be spilt. Large quantities of
methane clathrate exist on the seabed and in
ocean sediment, of interest as a potential energy source. Also on the seabed are
manganese nodules formed of layers of
iron,
manganese and other hydroxides around a core. In the Pacific, these may cover up to 30 percent of the deep ocean floor. The minerals precipitate from seawater and grow very slowly. Their commercial extraction for
nickel was investigated in the 1970s but abandoned in favour of more convenient sources. In suitable locations,
diamonds are gathered from the seafloor using suction hoses to bring gravel ashore. In deeper waters, mobile seafloor crawlers are used and the deposits are pumped to a vessel above. In Namibia, more diamonds are now collected from marine sources than by conventional methods on land.
desalination plant The sea holds large quantities of valuable dissolved minerals. The most important,
Salt for table and industrial use has been harvested by solar evaporation from shallow ponds since prehistoric times.
Bromine, accumulated after being leached from the land, is economically recovered from the Dead Sea, where it occurs at 55,000 parts per million (ppm).
Fresh water production Desalination is the technique of removing salts from seawater to leave
fresh water suitable for drinking or irrigation. The two main processing methods,
vacuum distillation and
reverse osmosis, use large quantities of energy. Desalination is normally only undertaken where fresh water from other sources is in short supply or energy is plentiful, as in the excess heat generated by power stations. The brine produced as a by-product contains some toxic materials and is returned to the sea.
Indigenous sea peoples Several
nomadic indigenous groups in
Maritime Southeast Asia live in boats and derive nearly all they need from the sea. The
Moken people live on the coasts of
Thailand and
Burma and islands in the
Andaman Sea. Some Sea Gypsies are accomplished
free-divers, able to descend to depths of , though many are adopting a more settled, land-based way of life. The indigenous peoples of the Arctic such as the
Chukchi,
Inuit,
Inuvialuit and
Yup'iit hunt marine mammals including seals and whales, and the
Torres Strait Islanders of Australia include the Great Barrier Reef among their possessions. They live a traditional life on the islands involving hunting, fishing, gardening and trading with neighbouring peoples in Papua and mainland
Aboriginal Australians.
In culture '' by
Katsushika Hokusai, The
Ancients personified it, believing it to be under the control of a
being who needed to be appeased, and symbolically, it has been perceived as a hostile environment populated by fantastic creatures; the
Leviathan of the
Bible,
Scylla in
Greek mythology,
Isonade in
Japanese mythology, and the
kraken of late
Norse mythology. The sea and ships have been
depicted in art ranging from simple drawings on the walls of huts in
Lamu The Japanese artist
Katsushika Hokusai created colour
prints of the moods of the sea, including
The Great Wave off Kanagawa. This contrasts with certain other religious traditions; for instance, the sea in biblical literature is often associated with chaos and danger, while in
Hindu mythology, it plays a role in cosmic cycles such as the
Samudra Manthan, the churning of the ocean. Islamic scholarship, including classical
tafsir (Qur'anic exegesis), emphasizes that the sea is not merely a physical reality but a theological symbol that calls believers to reflect on God's greatness and their own dependence on Him. Music too has been inspired by the ocean, sometimes by composers who lived or worked near the shore and saw its many different aspects.
Sea shanties, songs that were chanted by mariners to help them perform arduous tasks, have been woven into compositions and impressions in music have been created of calm waters, crashing waves and storms at sea. As a symbol, the sea has for centuries played a role in
literature,
poetry and
dreams. Sometimes it is there just as a gentle background but often it introduces such themes as storm, shipwreck, battle, hardship, disaster, the dashing of hopes and death.
Homer describes the ten-year voyage of the Greek hero
Odysseus who struggles to return home across the sea's many hazards after the war described in the
Iliad. The sea is a recurring theme in the
Haiku poems of the Japanese
Edo period poet
Matsuo Bashō (松尾 芭蕉) (1644–1694). In the works of psychiatrist
Carl Jung, the sea symbolizes the personal and the
collective unconscious in
dream interpretation, the depths of the sea symbolizing the depths of the
unconscious mind. ==Environmental issues==