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The Guide to Life, The Universe and Everything.

1. Life / The Natural World / Oceans
2. The Universe / The Earth / General Earth

Created: 8th April 2004
The Sea
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Waves crashing onto the shore.

The Sea. Also known as 'the ocean', 'the deep blue' and the 'seven seas'. It can be described in one word: wet. Most people only get to see the fringes of the sea with their own eyes, the bit where it meets the land.

What are the Seas?

The seas cover over two thirds of the earth's surface and are home to many different forms of life. The ancient Greeks and Romans believed the ocean was a great river that surrounded the landmass of the world. Today the sea is sub-divided into areas that each have their own name. Only some of these areas are identified by location here and should each have their own entry.

The Oceans

There are five oceans that separate the continents. The two largest of these, the Atlantic and Pacific, are usually further divided at the Equator. Although these oceans appear to be one body of water a study of winds and currents will show that the northern and southern sections share little in common. The North Atlantic Ocean lies between Europe and North America. The South Atlantic between Africa and South America. The North Pacific is the area from North America to Japan. The South Pacific stretches from South America to Australia. From Australia to Africa lies the Indian Ocean. North from the Arctic circle lies the Arctic Ocean, mostly covered by Ice, it flows over the North Pole. The Southern Ocean1 similarly encircles the South Pole surrounding the land mass of Antarctica north to the latitude of 60°.

The Seas

There are several other large areas of salt water that are not quite as large as the oceans and are known as seas. These include the Mediterranean Sea with Europe to the north, Africa to the south and the Middle East to the east. The large gulf between the Italian peninsula and the Baltic countries is known as the Adriatic Sea and the smaller gulf between the Greek peninsula and Asia Minor is called the Aegean Sea. To the north of Asia Minor lies the Black Sea. The Black Sea is connected to the Aegean Sea through the Bosporus Strait, Sea of Marmara and the Dardanelles Strait. The Red Sea is found between Egypt and the Arabian peninsula. The North Sea lies between Great Britain and Scandinavia. The Baltic Sea is bordered by Sweden to the west and Northern Europe to the east. The Caribbean Sea is marked by a chain of islands, the Antilles, which run from Cuba off the coast of Mexico east to the Virgin Islands, and then south almost reaching the coast of South America. The Sea of Japan separates the Japanese Islands from mainland Asia, and the South China Sea is located off the coasts of South East Asia and China. The Ross Sea is actually a huge bay located in Antarctica and is largely covered by an ice shelf.

Other Parts of the Seas

Of the thousands of gulfs, bays, straits and estuaries only a very few will be mentioned here as somewhat unique. The Gulf of Mexico, which lies north of the Caribbean and is bordered by the United States and Mexico on three sides, it is almost large enough to be a sea in its own right. Baffin Bay, which lies between Greenland and the Canadian maritime providences, is actually a strait with water flowing freely from the North Atlantic to the Arctic Oceans; the perpetual ice cap across the northern end of this passage gave the early explorers the illusion that there was land below the ice. The most famous strait is almost certainly the Straits of Gibraltar, a narrow channel that allows passage between the North Atlantic Ocean and the Mediterranean Sea. Estuaries are a wonderful place where fresh water from rivers and streams mix with the salt-water sea. Many types of wildlife and plants require these areas to exist. A few of the largest include the Thames Estuary on the east coast of England, Chesapeake Bay on the East Coast of the United States and the Amazon River in South America; where it is said you can actually pull up a bucket of fresh water while still over two hundred kilometres away from the coast.

Seas that do not flow into the Oceans

There are a few bodies of water whose waters do not flow into the oceans, their levels controlled primarily by evaporation. Due to the effects of evaporation they tend to be saltier than the open ocean. The largest of these is the Caspian Sea located in south-west Asia, forming part of the northern border of Iran. This sea supports several species of bonefish and sturgeon, and supplies some of the finest caviar in the world. To the east of the Caspian Sea lies the Aral Sea, at least at the time of this writing. The rivers that fed this sea have been diverted to irrigate farming fields hundreds of kilometres away; as a result this sea has lost over 50% of its surface area as the water evaporates faster than it is replaced. The lowest body of water on earth is the Dead Sea, located between Israel and Jordan. Almost 400 metres below sea level, the Dead Sea has 7 times as much salt as the open ocean, far too salty to allow any fish to survive in its waters. The Great Salt Lake, located in the western United States, can only support a population of brine shrimp due to the high salt content. Ironically the Dead Sea is in reality only the size of a fairly small lake, whereas the Great Salt Lake is large enough to be considered a sea by many people.

Bodies of Water that are not the Seas

Most inland waters do not contain salt in any significant quantity and are known as fresh water. They support a different eco-system than the sea. Only a very few will be included for the curious. The Sea of Galilee, which is known in Israel as Lake Kinneret, is in reality only a small lake located between Israel and Jordan. The waters of the Sea of Galilee flow down the Jordan River (which in turn empties into the Dead Sea). High in the Andes Mountains Lake Titicaca, located between Bolivia and Peru, is the highest navigational body of water in the world some 3,800 metres above sea level. The five Great Lakes lie between the United States and Canada. They have served as a major transportation link since man first inhabited this area. Major rivers exist throughout the world and provide an easy way to travel, as well as a source of power and irrigation.

The Waters of the Seas

Made of salt water, the sea forms an important part of the water cycle. The process of evaporation leaves the salt behind while the water vapours form clouds that produce rain perhaps thousands of kilometres away. Almost all the water on the face of the earth will at some time flow to the sea.

Commonly a blue-green-greyish colour, the sea tends to reflect the colour of the sky above or in shallow areas the features of its bottom. On stormy overcast days will appear grey and sullen. In tropical destinations, it can appear a brilliant turquoise blue and may be crystal clear, whilst in the more temperate (miserable) climates it is generally murky and dark.

Winds, Tides and Currents

The earth produces a coriolis effect due to its rotation. This combined with the location of seasonal areas of high and low areas of atmospheric pressure create prevailing winds. Although these winds can and do vary they were consistent enough to create trade routes for sailing ships.

The Equator is an imaginary line drawn around the centre of the globe, halfway between the north and south poles. The Tropic of Cancer and the Tropic of Capricorn lie north and south of the Equator marking the boundaries of the tropical regions. These imaginary lines mark the limits where the sun can be seen directly overhead, north of the Tropic of Cancer the sun is always south of the observer, while south of the Tropic of Capricorn the Sun is always north of the observer. To the north of the Equator the winds usually blow from the northeast and to the south of it they blow from the southeast. In the areas of the tropic lines the winds can be quite unreliable and it is not uncommon to have no wind for extended periods of time, these areas are known as the Doldrums. These areas also became known as the horse latitudes from the time when the calm area delayed sailing ships so long that they were forced to throw their animals overboard and let them drown to save food and water for the crew. Beyond the tropics the winds begin to blow from the west in both the northern and southern hemispheres and generally the closer you get to the poles the stronger the winds blow.

Another type of wind is caused by the fact that water changes temperature much slower than the land. The sea breeze - the winds blowing from the sea to the land - tend to blow in the afternoon, while the land breeze tends to blow in the early morning hours.

The gravitational pull of the moon, and to a lesser extent the sun, effects the surface of the sea. This effect causes the depth of the sea to vary in most areas; the difference between the highest and lowest depths is the tidal range. As the earth turns the high tide will move around with the gravitational pull of the moon. In most areas there are four tides each day, two high and two low, but in some areas there are only two. The most extreme tidal range is found in the Bay of Fundy in Canada, between New Brunswick and Nova Scotia. The tidal range here can be as much as 16 metres, in other places it may only be a few centimetres. As the tides flow in and out of certain restricted areas, such as bays and straits, a very strong current can be created making it impossible to enter or leave until the tidal flow stabilizes. The current level of the tide must be known before sailing into shallow water to avoid striking the bottom.

In many parts of the ocean there are currents that carry water thousands of miles, almost like a river in the sea. The water in these currents will be either warmer or colder than the surrounding sea because of its rapid passage. The climate of northern Europe is warmed by the Gulf Stream, and the waters of the Western United States are cooled by the North Pacific current. Sea creatures that get into these currents may find themselves at the other end in waters too cold or warm for their survival. Unusual temperatures can change the flow of these currents, such as the El Niño and La Niña phases of the Pacific Ocean.

The Perils of the Sea

The hazards that can be faced on the sea can be divided into four areas; Earth, Air, Fire and Water. Is it only a coincidence that these correspond to the four elements of ancient Greece? Often these can combine with a deadly effect. A ship can find itself being helplessly blown ashore in a storm, and after striking the shore, be smashed to bits by the waves breaking on the beach. Fire is one of the most feared of all events at sea. First there is no place to run away from the flames. To fight the fire a large amount of water must be pumped from the sea. To prevent the ship from sinking the same water must be pumped back into the sea. One of the worst disasters at sea was the burning of the cruise ship Morro Castle off the coast of New Jersey USA in 1934.

Navigation

The sea is a vast highway without any markers to tell you where you are. Before the invention of a reliable timepiece it was almost impossible to fix how far east or west your ship was until land was sighted. A glance at any early map of the world will show how distorted the coastlines are in this direction. Today satellites are positioned in orbit around the earth that can locate a ship's position within a few metres on any point on the Earth, unless of course, you have a power failure. Errors in navigation and uncharted reefs have damaged or destroyed an uncountable number of ships. One of the most famous was the HMS Pandora, which sank after striking the Great Barrier Reef in 1791. She had several of the accused mutineers from the HMS Bounty on board and was searching for the rest.

Collision at Sea

As vast as the sea is, a constant lookout must be maintained to prevent collision with other ships, items that may have been discarded into the sea and natural hazards such as icebergs. A ship at sea can not just stop at night as you can on land, therefore a watch must be kept 24 hours a day. One of the most famous collisions involved the cruise ships Stockholm and Andrea Doria in 1956 near the Nantucket Lightship.

Rogue Waves and Tidal Waves

One of the strangest phenomena of the sea is the rogue wave. These may be generated by a storm hundreds of kilometres away. Sometime a wave will be generated that it is so strong that it will continue to cross the sea and can strike a vessel from an unexpected direction.

Tidal waves, in spite of their name, have nothing to do with tides. They are more properly called tsunamis. These are caused by earthquakes in or near the sea. Instead of being a small wave at the surface they are a wall of moving water that may extend several hundred metres below the surface. In deep water they are no more hazardous than a rogue wave. However when they reach shallow water they begin to grow in height due to the vast quantity of moving water. When they reach land they will carry their force far inland leaving death and destruction behind when they recede back to the sea. There was an earthquake near Prince William Sound in Alaska in March, 1964. Although the earthquake itself caused considerable local damage, the tsunamis that followed not only devastated the port of Valdez, but caused damage to the US west coast and as far away as Hilo, Hawaii.

Storms at Sea

No sea story seems complete without at least one scene showing the crew fighting for their lives in a storm at sea. Storms tend to be seasonal and careful planning can reduce the risk of being caught in one. In the summer months the superheated air of the Tropics can become quite unstable and cause large rotating storms with winds of well over a hundred kilometres per hour. These are known as Hurricanes, Typhoons and Tropical Cyclones in various parts of the world. These storms tend to develop in certain areas and follow tracks that, although they can very greatly, follow a basic pattern that have been plotted over the years. Another type of storm takes place in the winter months when cold air flows from the Arctic region and forms fierce storms as it reaches the relatively warmer air of the temperate zones. With any storm the lower the atmospheric pressure falls the more severe the storm will be.

If you spend enough time on the sea you will almost certainly face a storm at some time, no matter how carefully you plan your voyage. If the storm reaches you far from shore there is no place to seek shelter so you must know the best way for your vessel to face the onslaught. This varies depending on many factors. The film The Perfect Storm tells the true story2 of the loss of the fishing boat Andrea Gail in 1991 while returning from the North Atlantic.

Sea Life

The aforementioned inhabitants of the sea include fish, eels, rays, octopus, jellyfish, shrimp, crabs and lobster. Tiny organisms called plankton exist in many areas of the sea. The largest of the mammals also live in the sea, the various species of whales. There are basically two species of whales, baleen and toothed. The baleen whales have specially formed plates in their mouths that strain plankton from the sea for their food supply. The toothed whales are primarily carnivores that hunt their prey. Their smaller cousins porpoises, dolphins, manatees and dugongs can be founds in many parts of the world. Great colonies of seals live along rocky coastlines and walruses can be found in the arctic. There are even some animals that are able to survive at the bottom of the sea where there is no light, numbing cold and crushing pressure. These creatures are some of the weirdest looking. The Sea Floor is a realm all its own. The other animals that live near the surface are more pleasing to the eye and in many cases can be very beautiful with striking, colourful markings. Many species only exist in certain areas of the sea, while others like the great whales range around the globe. Just like the land areas of the earth some places are teeming with sea life while others are as barren as the desert.

Although they all nest on land to lay eggs and rear their young, one of the most commonly seen animals of the sea are the birds. The species of seabirds varies greatly from place to place around the world and most only venture a few hundred kilometres from shore. There are a few such as the albatross that spend most of the year far out at sea. One of the strangest classes of seabirds are the penguins which nest in the southern oceans and can not fly. Their wings have evolved into flippers that allow them to swim far from their nesting grounds. Their movement is sometimes described as 'flying underwater'.

There is still a lot of the sea that is unexplored. It is said that we know more about the surface of the moon than the ocean floor, which shows how truly mind boggling it actually is. We know more about a ball of rock up in space than a bit of water here on earth, but there you go. New things are being discovered all the time and advances in engineering mean that more humans will be able to journey into the depths in better submarines3 and find out what other really strange things there are down there.

Islands in the Seas

Some areas of the sea contain small areas of dry land called islands. These may be the tops of mountain ranges or submarine volcanoes. In other places islands are only an area of the sea floor that extends above the surface, such as the Bahamas. In tropical areas the shallow water surrounding an island is often home to a coral reef.

Coral is a type of marine animal that surrounds itself with a hard mineral substance and feeds on tiny bits of plankton that float by. Over a period of many years the homes built by the coral begin to form long walls beneath the sea. These are coral reefs. These are delicate ecosystems consisting of coral formations and the various creatures which use them for food or shelter. Eventually the reef may grow to such an extent that it rises within a few centimetres of the ocean's surface. It will then begin to trap sediment and form a circular island. The water left between reef and island becomes a lagoon. In some cases the reef forms on a shallow area that does not extend above sea level and these are known as atolls. The largest reef is the Great Barrier Reef, off the coast of Australia, which can be seen from space.

In many places the sea meets the land in gentle slopes called beaches, which can be sandy, shingle or just plain rocky. The continents are surround by shallow area of the sea known as the continental shelf. Beyond that the sea floor drops to several kilometres below the surface.

Uses of the Sea

A large part of the human diet comes from the sea. As methods of fishing have become more efficient, combined with the effects of pollution of the estuaries4, the seemingly unlimited resources of the sea are becoming threatened. Many countries jealously guard their fishing grounds and impose strict limits on quantity and seasons when certain species can be taken. International agreements try to control fishing in the open ocean.

The sea also provides a vast highway that can take people and goods to any seaport in the world. Even with modern air travel, the immense tonnage of goods that can be carried by a ship makes commercial sea transport an important part of modern commerce.

The sea is also an important military resource that can allow an entire army and its supplies to be transported to any trouble spots, as well as guarding the country's own coasts from threat and illegal smuggling of goods and persons.

The sea is also used by humans for recreational activities such as swimming, sailing, diving, water-skiing, para-sailing and snorkelling. From a simple picnic on the beach to a trans-ocean voyage the sea holds an allure that can be beyond explanation.

Stories of the Sea

Stories about the sea abound, from Shakespeare's play The Tempest and Samuel Taylor Coleridge's poem 'The Rime of the Ancient Mariner' to recent films such as Jaws and The Abyss. Stories of the Marie Celeste and the Bermuda Triangle serve to root the sea as a mysterious and frightening place in our consciousness; others like Moby Dick, Mutiny of the Bounty and James Michner's Hawaii fill our heads with wanderlust; stories such as those surrounding the wreck of the Whaleship Essex and the RMS Titanic show how powerful the sea is compared to mankind's technology.


1 Previously called the Antarctic Ocean.
2 At least as true as Hollywood gets.
3 Waterproof tin cans.
4 Which are the breeding grounds for many species.


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ENTRY DATA
Written and Researched by:

bethal
Florida Sailor

Edited by:

ZarquonsSingingFish

Referenced Entries:

The World's Best Beaches
The Discovery of Fire
The Great Lakes of North America
Sea Monkeys - 'artemia salina'
Inhabitants of the USA
The European Union
Water
Swimming
Alaska and Hawaii, USA
Great Salt Lake, Utah, USA
Impressions of the Amazon
Antarctica
The Moon and the Tides
New Brunswick, New Jersey, USA
The RMS Titanic
The Mary Celeste
Jordan
Coriolis Force - a Convenient Fiction
The Wreck of the Whaleship Essex
Australia
Radio-Controlled Clocks
Wonderful Rivers
They Discovered America
Whale Evolution - The Fossil Evidence
Mexico
Oceans: the Sea Floor
Common Salt (Sodium Chloride)

Related BBC Pages:

Nature's Forecasters
BBC Science & Nature
BBC Weather

Referenced Sites:

Morro Castle
tsunamis
The Perfect Storm
Andrea Gail
Monterey Bay Aquarium Re...

Please note that the BBC is not responsible for the content of any external sites listed.
Photo supplied by:

The Rev Jack Russell



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