The Water Planet Earth

Background information; by edgardowelelo@yahoo.com, Master of the Game

With water generally so available to us at the turn of a tap, it is easy to forget how essential it is for life on Planet Earth. Water, collected in the great ocean basins, regulates the Planet Earth’s temperature and climate as well as providing numerous habitats for plant and animal life. Earth is a unique Planet blessed with a vast quantity of liquid water. In prehistoric times, the ocean basins filled with water and became the cradle for the evolution of life.

WATER WORLD (THE WATER PLANET EARTH)

From space, Planet Earth is BLUE. It floats like a jewel in the inky black void. The reflection of the sun’s light from the vast expanse of water covering its surface creates its germ – like blue colour. In the entire solar system, Earth is the only Planet that has water in its liquid form in such quantities. That is what makes Earth unique. Water has been the cradle of life throughout most of the Planet’s 4600 – million – year history. The earliest forms of life – a simple collection of organic compounds – evolved in water and stayed there. They were bathed in a nutrient soup that remained at a suitable temperature and never dried up. From these early beginnings, life on Earth evolved and diversified through the millennia. Fish, worms, amphibians, reptiles, birds, mammals and every plant, both above and below the water, started their evolutionary journey in the ocean. It is only because of water; and its combination of special properties, that life on Earth – as we know it – exists at all.The oceans are critical to life on Planet Earth. They absorb carbon dioxide from the air keeping it cooler than it would otherwise be; they store heat and are the source of fresh water for all plants and animals on land.

THE BLUE PLANET EARTH

Planet Earth is special in our solar system because it is blessed with an abundance of life. One of the key factors in the evolution of life is the position of Earth in relation to the sun. Earth is 150 million km (93 million miles) away from the sun. Some planets within our galaxy, such as Mercury and Venus are closer, while others, such as Pluto, are further away. Because the sun radiates immense heat, conditions on a Planet are determined by how close it is to the sun. Mercury, which is only 60 million km (37 million miles) from the sun, has daytime temperatures of 350⁰C (662⁰F) – hot enough to melt many metals – and any water that existed evaporated long ago. At the other extreme, Pluto, which is 5900 million km (3666 million miles) from the sun, is permanently frozen, with surface temperatures of about – 230⁰C (-382⁰F). Fortunately, Earth lies between the extremes, and has a milder surface temperature. This, combined with the unique properties of the water molecule, results in a world where water can exist in a liquid state. As yet, no other planet in our solar system, or in the universe as whole, has been found to have such a favorable set of conditions for life.

OCEAN ORIGINS

As a result of a cosmic explosion known as the BIG BANG, (an estimated 15 billion years) ago), space, time and matter were created simultaneously; the UNIVERSE was born. Over 10 billion years later, an interstellar cloud of swirling gas and dust condensed and began to heat up. Nuclear reactions began to occur in the intense heat, and pressure built up at its centre: what we now know as the sun began to shine. The young sun began to exert a gravitational pull on the rest of the cloud and grew, exerting a still stronger pull, until it contained all but a few bits of debris and some gasses, which were both far away and travelling fast enough to remain isolated. These particles and gases eventually coalesced and the planets, including EARTH itself, were formed. Our solar system is thought to have been created in this way about 4.6 billion years ago. The great heat produced during the formation of the Planet Earth probably meant that the entire planet was molten. The more dense materials sank to the centre, while lighter ones floated to the surface. As the Planet Earth gradually cooled, these lighter surface materials formed a thin CRUST. Volcanic activity continued unabated, with molten lava from beneath erupting up at the surface, releasing water vapour and other gases. Much of our water may have landed on Earth as ice – laden comets. About 4000 million years ago, the atmosphere was dominated by water vapour, but as Earth continued cooling, water vapour in the atmosphere began to condense and fall as RAIN. Streams developed into rivers, and gradually the low – lying areas filled with water. The oldest sedimentary (water – formed) rocks found to date suggest that these early seas formed about 3800 million years ago. Today, just over 70 per cent of the Planet Earth’s surface is covered by water. If the Earth were flat and even, like a ball, the depth of the water layer lying on its surface would be 3.7 km (2.25 miles) deep. Luckily, Earth has a complicated topography, which includes extensive depressions – the ocean basins – which have filled with water. Most of the Planet’s water (nearly 98 per cent) is stored within these basins. There is a constant and critical recycling of water around the Planet Earth. As the sun heats the surfaces of the oceans, water vapour rising into the atmosphere forms clouds. These are driven around the globe by winds, and when the conditions are right, they condense and water falls as RAIN, SNOW or HAIL. This process of water changing from its liquid state in the oceans to gas in the atmosphere and back again to liquid is known as the HYDROLOGICAL CYCLE, and is essential to life on land. Without it much of the world would be barren.

THE NATURE OF WATER

The special properties of water, including the way it changes when heated and cooled, make it unique. Most substances expand when heated and contract when cooled, but water behaves differently. As it freezes, water increases in volume by about 9 per cent and becomes lighter, which is why ICE floats. If this were not the case, we would not recognize the planet. Ice would sink to the bottom of high – latitude lakes, seas and oceans, and once shielded from the heat of the sun by the water above, more freezing would occur until these bodies of water would just be frozen blocks. There would be no ocean circulation on a grand scale, so warm water from the tropics would not reach the POLAR REGIONS. The tropics would be intolerably hot, the poles permanently frozen and the temperature latitudes would freeze for much of the year. Water can also dissolve more substances than any other solvent. It is especially good at dissolving salts. Sodium chloride, for example, is made up of one ion of sodium and one of chlorine, both with strong opposite charges. Without water, these ions form tight bonds, resulting in salt crystals. However, weakly charged water molecules are attracted to these strongly charged salt molecules and cluster around them, weakening the bonds between the ions. Gradually the ions separate and float off, surrounded by a cluster of water molecules. In other words, the salt dissolves. Water has a great capacity to store heat. In order to heat up water just a little, a substantial quantity of heat is required and likewise, as water cools, a lot of heat is lost. The oceans store heat from the sun’s radiation during the daytime, particularly in summer. On the other hand, they lose heat at night and during the winter. The process of heating up and cooling down is significantly slower for water than for land. As a result, oceans have an impact on neighboring land, buffering the more extreme temperatures that would otherwise occur daily and seasonally. That is why COASTS experience a milder climate than the inland areas of a large continental mass. Furthermore, ocean currents ensure that heat is transported around the Planet Earth. On a global scale, if EARTH were not covered by such extensive oceans, we would experience blisteringly hot temperatures in the day and freezing cold temperatures at night.

THE IMPORTANCE OF WATER

The water’s super – efficiency as a solvent makes it the basis for all forms of life. The chemical compounds and processes that make up what we call “life” occur in water. It is not surprising then, that the bodies of most organisms are about 65 per cent water and most marine life contains about 80 per cent water and some, such as JELLYFISH, as much as 95 per cent. Outside an organism’s body, water’s solvent properties are equally important. The salinity of water determines what animals can live there. Some can survive only in fresh water, where the salt content is very low; many can tolerate a higher salt content and live in the sea; yet others can eke out an existence in highly saline habitats such as salt marshes. Plants and animals that survive in places where salinity fluctuates dramatically, such as estuaries, have had to evolve more complicated ways of regulating their own internal body fluid concentration. Water also contains dissolved gases, including oxygen. Oxygen in water comes from two (2) sources: it is absorbed at the surface from air, or it comes from plants as a by – product of photosynthesis. This makes water an ideal place for animals to live, as they are bathed in a convenient solvent that provides them with oxygen. However, as water temperatures rises, its oxygen content decreases, making the topical oceans poorer in oxygen than the temperate oceans. Moreover, as water depth increases, the less surface – absorbed oxygen there is available; also, as there is no light, there is   little or no oxygen from photosynthesis. At about 500 m (1640 feet) there is a layer of sea water that contains hardly any oxygen at all. Despite this, some animals, such as SHRIMPS and FISH, do manage to live here. To survive in such oxygen – poor water, they have had to adapt. First, they are relatively inactive, so they use less energy, and second, they have enlarged gills to extract as much oxygen from the water as possible.

SIGNS OF LIFE

Fossil evidence of the first known organisms – resembling present – day blue – green algae or cyanobacteria – has been found in rock 3600 million years old. For about 1600 million years these single – celled life forms were possibly the only living things on the Planet Earth. However, there were significant changes during those years. Since Earth’s creation, its atmosphere had probably consisted largely of water vapour; methane and ammonia. But the single – celled organisms now living in the oceans were photosynthesizing (creating simple sugars probably by using first chemical then later the sun’s energy). A crucial by –product of photosynthesis is oxygen. Gradually the atmosphere changed as oxygen became available. Moreover; the ozone layer formed and screened the developing life from the effects of ULTRA VIOLET RADIATION. The stage was set for more complicated life forms. About 600 million years ago, the first, known multi – celled animals evolved. All organisms contain water and rely on its solvent properties to live. Jellyfish are 95 per cent water.

OCEAN EXPLORATION

The earliest evidence that man lived by the sea comes not from the remains of BOATS but from piles of discarded shells found in refuse tips dating from about 40,000 years ago. As the sea level rose after the last ice age, there is probably much more archaeological evidence hidden under water; but boats are unlikely to be found. Being made of wood, skin and fibres, they do not preserve well, but they undoubtedly played an important part in survival and exploration. As time went by, boats became increasingly sophisticated and people ventured further and further away from known territory, braving the OPEN OCEANS in their quest for new land.

 

EARLY VOYAGERS

One of the earliest sea voyages, at least 40,000 years ago, would have involved the migration of people from Southeast Asia to Papua New Guinea and Australia. Although the sea level was then much lower and therefore the stretch of water they had to cross was probably only 40 km (25 miles) wide, they would have needed sturdier craft than those used on inland waterways. Ocean – going vessels developed independently in many parts of the world. European trade was flourishing in the Mediterranean 5000 years ago. Ships also helped people to spread west through the Pacific, colonizing the islands some 4000 years ago. The Arabs, too had extensive trading networks with India, Arabia and Africa, demonstrating an early understanding of the monsoon wind patterns of the Indian Ocean and the use of stars as a navigational aid. With this knowledge they could cross wide stretches of open water without using landmarks as guides.

MAPPING THE WORLD

Europeans had a hunger for both trade routes and knowledge in the middle of the last millennium. Money was made available to explorers who wanted to chart the oceans and open up trade. One of the first to make his name was CHRISTOPHER COLUMBUS, who, in 1492, was credited with having discovered the NEW WORLD (North and South America). The Portuguese explorer FERDINAND MAGELLAN set off in 1519 to circumnavigate the world, but was killed in the PHILIPPINES. The journey was completed under the leadership of JUAN DEL CANO, and the vastness of the Pacific Ocean was officially discovered. Although these early explorers could measure latitude accurately, they struggled with longitude because a clock that could keep reliable time at sea had not been invented. It was not until 1760, when a clock – maker called JOHN HARRISON perfected his chronometer, that the problem was solved. Soon after, JAMES COOK set sail with the best navigational equipment the world had known. During his three voyages, between 1768 and 1780, COOK mapped the PACIFIC OCEAN, charted the east coast of Australia and surmised that there was a continent of ice to the south.

A SCIENCE IS BORN

Exploration of the OCEANS sank into insignificance behind the great and exciting new continental discoveries: strategic and commercial interests dominated. However, when the problem of longitude was solved, and accurate positioning of both marine and coastal features could be given, information about the seas and oceans became valuable to both traders and naval commanders. Understanding of the OCEANS progressed in fits and starts, but a major turning point was the CHALLENGER EXPEDITION in 1872. Under the guidance of two British biologists, this ship circumnavigated the globe and many important discoveries were made. They dredged up animals from 8000 m (26,000 feet), thus demonstrating that the abyssal depths were not lifeless. The foundations for the modern science of OCEANOGRAPHY had been laid. Equipment used today is highly sophisticated. It includes SUBMERSIBLES, which can be manned or remotely operated, and even SATELLITES which can study the OCEANS from high above. Despite great advances, our understanding of the oceans is still superficial. We know more about the surface of Mars than we do about most of the SEA FLOOR.

A GIANT JIGSAW (THE WATER PLANET EARTH)

For many centuries PEOPLE thought that the EARTH was established, stable and unchanging. But this view could not have been further from the truth. It was as early as 1596 that the Dutch map maker ABRAHAM ORTELIUS pondered the fact that the coasts of Africa and Europe might fit snugly against the Americas on the other side of the Atlantic, and proposed that they might have been joined at one time. Supporting evidence mounted over the centuries. Coal deposits and other geological features were found to be similar in Africa and the Americas, and fossils of the extinct reptile Mesosaurus have been found both along the west coast of southern Africa and the east coast of South America.

In 1912, a German scientist called ALFRED WEGENER collated all this evidence and proposed the idea of continental drift. He (ALFRED WEGENER) suggested that there used to be ONE SUPERCONTINENT, which he named PANGAEA, and that in geological time this continent had broken apart, its various pieces separating out to their MODERN – DAY POSITIONS. At first, his ideas were received with scepticism because there was no known mechanism by which CONTINENTAL DRIFT could occur. It was not until the late 1960s that a solution was found and his ideas were truly accepted.

MID – OCEAN RIDGES

After World War II, the use of SONAR revolutionized surveys of the SEA FLOOR. Accurate mapping of the ocean basins was now possible. Far from being merely the flat plains previously imagined, gigantic mountain ranges, isolated seamounts and deep trenches were discovered. It was the mapping of a great mid – ocean mountain range that, incredibly, extends through  all the ocean basins that was the key to understanding CONTINENTAL DRIFT. This continuous MID – OCEAN RIDGE is by far the largest geological feature on EARTH, but we only ever see glimpses of it where the tips of its submarine mountains break the surface, creating islands such as the AZORES and ICELAND in the ATLANTIC. As geologists began to investigate part of the range that extends up the Atlantic (The Mid – Atlantic Ridges), they (Geologists) found evidence that the ocean floor was spreading apart, thus supporting WEGENER’S idea of CONTINENTAL DRIFT. ROCKS near the centre of the ridge were younger than those further away. Moreover; the further away from the ridge the geologists looked, the more overlying sediment there was, suggesting the Rocks beneath had been there longer. The final piece of evidence came when the magnetism of the rocks was examined. Every so often, in geological time, the Earth’s polarity reverses so that the magnetic north switches to the south. Magnetic particles in MOLTEN ROCKS (Magma/Liquid Rocks) align themselves to the new direction. Geologists found a series of parallel hands or stripes in the rocks of the mid – Atlantic ridge, each one signifying a change in Earth’s polarity. These bands run along the length of the ridge. They also discovered that the bands on either side of the ridge are mirror images of each other. Here, then, was the evidence that continents were moving apart, WEGENER’S THEORY was accepted.

PLATE TECTONICS

It is now recognized that the surface of the Planet Earth is divided into 13 major plates(For example, Pacific plate, Eurasian plate, North American plate, African plate, Antarctic plate, Somali plate, Indo – Australian plate, Philippine plate, Arabian plate, Burma plate, Scotia plate, Nazca plate, Juan De Fuca plate, Caribbean plate, Tonga plate, Cocos plate, Solomon plate, Fiji Micro plate, Bismarck plate, South American plate) and a number of smaller ones, all floating on the partly molten layer of the MANTLE beneath. Some of these plates carry CONTINENTS, but others are purely oceanic. Those that do carry CONTINENTS are responsible for CONTINENTAL DRIFT. Continents move at the same rate as the plates are moving apart or together – 2 cm (0.75 in) per year in the ATLANTIC and 18 cm (7 in) per year in the EASTERN PACIFIC. It is thought that currents within the fluid rock of the mantle below cause the plates to move.Where a current rises up MOLTEN ROCK breaks through the CRUST at a mid – oceanic ridge; where it moves down through the mantle, a plate does one of two things, depending on its nature. Plates which are 50 – 100 km (30 – 60 miles) thick, consist of the SURFACE CRUST of the Earth and a part of the upper mantle, both of which are Rock. The CRUST PART varies in nature. CONTINENTAL CRUST, or LAND, is thicker (30 – 40 km/18¹/₂-25 miles deep) but less dense than OCEANIC CRUST (only 6 km/3¹/₄, miles deep). This difference in density accounts for the oceans themselves. Despite being thinner, the denser oceanic crust floats lower in the liquid rock of the mantle than the lighter continental crust. Water flows by gravity to the lower areas, thus creating the oceans. With the ocean floors spreading along the mid – ocean ridges, Earth would be expanding unless somewhere material were being forced back into the mantle. When an oceanic plate collides with a continental plate, the heavier, oceanic plate moves beneath. At this point – or subduction zone, as it is called – deep oceanic trenches are created and a line of volcanic activity is found along the continental edge. This is best illustrated in the EAST PACIFIC. The expanding East Pacific Rise (a mid – ocean ridge) is pushing the NAZCA plate towards South America. This oceanic plate is being forced under the lighter South America plate, causing many EARTHQUAKES. The continental crust of South America is buckling under the pressure, creating the ANDES MOUNTAINS, and as the less dense materials contained within the NAZCA PLATE melt, they rise and burst out as VOLCANOES. But when two continental plates collide, both are light and neither sinks back into the mantle. As the landmasses (continents) are pushed together, tremendous pressure builds, rocks distort under the force and great mountain ranges are squeezed up. It is the collision of the Asian landmass and the northward – moving Indian sub – continent, for example, that has created the HIMALAYAS. The ANDES were formed by the oceanic Nazca Plate moving beneath the South American plate. The lighter materials from the Nazca Plate rise to the surface as they melt, erupting as VOLCANOES in the ANDES.

THE BREAK – UP OF PANGAEA/PANGEA

The continents (Landmasses) have been floating around for many hundreds of millions of years, colliding to form SUPERCONTINENTS, which then break up again. The last supercontinent that existed was the one named PANGAEA (PANGEA) by ALFRED WEGENER. PANGAEA/PANGEA was surrounded by a single super – ocean he called PANTHALASSA, the predecessor of the PACIFIC OCEAN. There was also a shallow, tropical ocean he called the TETHYS SEA. Some 200 – 220 million years ago, PANGAEA/PANGEA, it began to break up by a process known as CONTINENTAL DRIFT. The continents (landmasses) are still moving today. NORTH AMERICA began to separate from the fused continents (landmasses) of SOUTH AMERICA and AFRICA, creating a gap which was the start of the NORTHERN ATLANTIC OCEAN. The line of separation marked the beginning of the MID – ATLANTIC RIDGE. As the SPLIT widened, two (2) giant continents (landmasses) were formed: LAURASIA to the North, which combined North America and Eurasia, and GONDWANALAND to the South, which consisted of South America, Africa, India, Arabia, Australia and the Antarctic continent.

Then, some 170 million years ago, Gondwanaland began to break up. South America and Africa moved to the northeast, while India, on its own, started to move north. Some 35 million years later, South America and Africa broke apart, creating the southern Atlantic Ocean. The mid – ocean ridges of the north and south Atlantic joined up to form one long, continuous ridge. As the Atlantic continued to spread, the remains of PANTHALASSA, now the PACIFIC began to shrink. It is still shrinking to this day. The TETHYS SEA was gradually closed by the northward movement of Africa and what we know as SOUTHERN EUROPE. INDIA finally reached ASIA, and the HIMALAYAN MOUNTAINS were born. The mid – Indian Ocean ridge extended down to separate AUSTRALIA and ANTARCTICA as it does today, causing Australia to move north.

SEASCAPES

On a global scale, PLATE TECTONICS shape the TOPOGRAPHY of the Earth’s crust. This is true for both continental crust (land) and oceanic crust (the ocean floor). It also means that all around the world very similar features can be found underwater.In broad terms, there are only two zones:the edges of the continents and the ocean floor.

1. CONTINENTAL EDGES

Sea level is much higher today than it was 15,000 to 20,000 years ago, so the margins of all continental crusts have been flooded. This has created extensive, new, shallow underwater habitats which are ideal for colonization by plants and animals. Although these regions, known as CONTINENTAL SHELVES, make up only 8 per cent of the world’s oceans, they are where the majority of marine life is concentrated.

Continental shelves are nearly flat and typically about 150 m (500 feet) deep, though their range is 120 – 400 m (400-1300 feet). This uniformity of depth is explained by the fact that they are simply the outer edges of flat continents which have become flooded. However, they do vary greatly in width. Some continental shelves are very short because an oceanic plate is butting up against the edge of the continental crust and compressing it. The Pacific edge of SOUTH AMERICA, for example, has a very short underwater continental shelf of only 1 km (0.6 mile). Most of the continental edge has been squashed to form the Andes range. Indeed, much of the Pacific Rim is characterized by short continental shelves with active volcanic and Earthquake zones. By contrast, the Atlantic continental shelves are much wider and non – volcanic: they are simply the flooded edges of the continental crust. The Atlantic Ocean is expanding, and the four (4) plates that are separating carry the continents of Africa, South America, North America and Eurasia. Therefore, as the edges of the Atlantic are not marked by zones where an oceanic plate is being pushed beneath a continental plate, there are no VOLCANOES or EARTHQUAKES around its perimeter. The true edge of all continents now lies UNDER WATER and is called the CONTINENTAL SLOPE. The slope extends steeply from150 m (500 feet) or so down to about 3000 m (9850 feet). Deep canyons riddle the slope, many of which are carved by the sediment from a river. Sediments flow down the slope and into the canyons, forming great fans at the bottom. These are so extensive that they merge to form an immense band of sediment (called the CONTINENTAL RISE), which runs along the base of the slope. The Ganges fan is the most impressive, having a colossal cone extending some 2500 km (1550 miles) beyond the edge of the continental slope and reaching a depth of 5000 m (16,400 feet).

2. THE OCEAN FLOOR(OCEANIC CRUST)

At the bottom of the continental slope and beneath the sediment of the continental rise is the ROCK of the ocean floor. This is where the CONTINENTAL CRUST (LAND) ends and the OCEANIC CRUST begins. Further out to sea, beyond the sediment of the continental rise, much of the sea floor is smothered in a blanket of ooze – like sediment. This does not originate on land, but comes from dead plants and animals that rain down from above. These extensive, usually flat areas are called abyssal plains. However, abyssal plains are not utterly featureless. They are peppered with submarine volcanoes called SEAMOUNTS, which, if they rise to the surface waters, form important oases for marine life in an otherwise relatively barren ocean. When SEAMOUNTS are high enough to break the surface, they form volcanic islands, such as the GALAPAGOS ISLANDS and the HAWAIIAN CHAIN. Another feature of the abyssal plains are guyots – seamounts with strangely flat tops. Opinion varies as to how guyots became truncated, but as they are drowned volcanic islands, the most plausible argument is that their tops were eroded away when they were islands. Trenches are also a feature of the deep ocean. Formed at the point where an oceanic plate collides with a continental plate and descends into the mantle, their sides plummet to phenomenal depths. Most oceanic trenches are found around the Pacific Rim because the oceanic plates that make up the Pacific are being forced beneath continental plates along their perimeters. The bottom of the deepest trench of all, the MARIANAS TRENCH in the western Pacific, lies 11 km (7 miles) beneath the surface of the sea. MOUNT EVEREST would fit inside this trench and its peak would still be 2000 m (6500 feet) beneath the surface. The abyssal plains have an almost undetectable rise towards the mid – ocean ridges. Closer to the ridge there is less sediment as the rocks are younger, and at the ridge itself the nature of the seabed changes all together. When two oceanic plates separate, there is a gap or valley in the middle. This is called the CENTRAL RIFT VALLEY, and within it is a whole new world. Sea water seeps down through the cracks and crevices of the broken crust, heats up to extreme temperatures (as much as 350⁰C/662⁰F) in the hot rocks beneath and is forced out again in deep – sea hot springs or HYDROTHERMAL VENTS. Dissolved in the emerging water are minerals, particularly sulphides. As this mineral – laden hot water makes contact with the surrounding, cooler sea water, it rapidly cools and the minerals solidity. Chimneys of solidified minerals build up, with black “smoke” or sulphide – particles pouring out of the top. These hydrothermal vents are one of the very few habitats on Planet Earth where life does not rely on the energy of the sun.

LIGHT IN THE SEA

One of the reasons that the oceans are so full of life is that sea water is largely transparent. Plants need LIGHT to grow, and if light did not penetrate beyond the surface, there would be only a thin scum of life in the oceans. However, not all light penetrates very far; the amount and type of light that gets through depends on the quality of the water. Turbid water at a river mouth lets in less light than the clear water of the open ocean, for example. Of the sunlight striking the ocean surface between 3 and 30 per cent is reflected off immediately, depending on the angle of the sun to the water. Light that penetrates the surface does not do so equally. Sea water absorbs red wavelengths quickly so objects that appear red at the surface look grey or black at depth. Underwater photographers, use flashlights for this reason. If they did not, their pictures would turn out mostly blue, for it is blue light that penetrates the furthest.

FORCES OF NATURE (THE WATER PLANET EARTH)

The combined effects of the sun, the moon and the rotation of the Planet Earth govern the OCEANS and, in turn, our climate. We swim, sail and surf in the SEA. We build sand castles on the beach and stand on CLIFF – TOPS to let the wind blow through our hair. We ski on snow, fish from rivers and drink pure water from SPRINGS without a thought. We enjoy the warmth of summer and cold of winter. In short, we take salt water; fresh water and the changing seasons for granted. But they are all products of the rotation of the EARTH and its orbit around one particular star; the SUN. Despite being 150 million km (93 million miles) away, the SUN is the heat engine of the Planet Earth. Its power is awesome. Even after travelling so far through space, the SUN’S RAYS release 130 trillion horsepower per second on Earth. It creates all the winds, from light zephyrs to rampaging HURRICANES, and drives ocean currents; it controls our climate and, in partnership with the MOON, it influences tides. Almost all life in the sea and on land is directly or indirectly affected by it.

SUNPOWER

Of the SUN’S ENERGY that reaches the Planet Earth, about 30 per cent is reflected back immediately, the remainder being absorbed by the atmosphere and Earth’s surface. This energy fuels the Planet, and most importantly, the oceans.

WINDS

In the days when sail was the only means of moving across the ocean, mariners were well aware that to cross from EUROPE to the AMERICAS it was necessary to sail south to catch the northeasterly winds, which would blow them west across the Atlantic. These winds were so reliable and so often used for trade, they became known as the trade winds. To return, mariners had to sail north up the Gulf Stream and catch winds known as the WESTERLIES, which blew then back to Europe. Winds are driven by heat from the sun, most of this energy being absorbed in the TROPICS. Here, the SUN’S RAYS strike the atmosphere at right angles, which has two effects, both of which ensure more heat is absorbed by Earth. First, fewer rays are deflected off the atmosphere, so more pass through. Second, the distance the rays have to travel through the atmosphere before they hit the surface of the Earth is shorter. As air at the EQUATOR heats up, it becomes less dense and rises. To fill the gap being produced beneath, air rushes in from adjacent areas, creating winds. These are the trade winds. Instead of the trade winds simply blowing south in the Northern hemisphere and north in the Southern hemisphere, both these sets of winds blow slightly west as well. This affect, caused by the rotation of the Earth, was what made them so useful to early sailors. Known as the CORIOLIS EFFECT (after the French scientist who first described it), it applies to all moving particles on the Earth’s surface. Those in the Northern hemisphere move slightly to the right and those in the Southern hemisphere to the left. Imagine standing at the NORTH POLE and throwing a ball to someone at the EQUATOR. At the Pole, even though the EARTH is spinning (in an anticlockwise direction), you are turning only slowly, but the person at the EQUATOR is moving at about 1500 kph (930 mph). By the time the ball you have thrown reaches the EQUATOR, the person will have moved left of his starting place. So it appears that rather than travelling straight towards the other person, the ball has curved to the right. On a day – to – day basis in our own lives, the Coriolis Effect is too small to be noticeable, but it has dramatic consequences on the winds and currents, which move great distances over the Earth’s surface.

SURFACE CURRENTS

Ocean surface currents are driven by persistent winds. The movement of the air literally pushes the water along. However, because of the CORIOLIS EFFECT, currents do not move in the same direction as the winds that drive them, but at 45 degrees to the wind. In the Northern hemisphere it is 45 degrees to the right, and in the Southern, 45 degrees to the left. The equatorial currents driven by the trade winds do not move towards the Equator, but flow parallel to it. The Coriolis effect is negligible on water particles at the surface, because they are moved by wind friction and therefore in the same direction as the wind. But once out of the wind, under the surface, the Coriolis force takes effect. Indeed, the deeper you go, the more effect it has and the further the water is deflected from the path of the prevailing wind. This is because the drag between each layer of moving water causes a deflection. The strength of the water motion also decreases with depth, so the end result is a narrowing spiral of water movement, turning away from the direction of wind. At about 90 m (300 feet) – the depth at which winds no longer have an impact – the water can end up flowing in exactly the opposite direction to the wind. However, the overall result is that a body of water moves at right angles to the wind pushing it.

When prevailing winds blow parallel to a coast (particularly a west coast), the top layers of water move offshore at right angles to the wind and cold, deep water rises to replace it, creating an upwelling. This cold water is full of nutrients, which nourish marine life. The upwelling on the PERUVIAN COAST of SOUTH AMERICA is very large and supports a massive fishery. By contrast, California has an upwelling that is an unpredictable and short – lived. Less significant, certainly in terms of fisheries, are equatorial upwellings. These occur more commonly in the Pacific. As the equatorial currents on either side of the Equator move west, the water beneath moves north (or right) in the Northern hemisphere and South (or left) in the Southern hemisphere and deep, cold water rises in the middle to replace it. A combination of global winds and the Coriolis Effect produces huge gyres or circular movements of surface water in the ocean basins. The Atlantic, Pacific and Indian Oceans each have two – one in the North, which rotates in a clockwise direction, and one in the South, which rotates in an anticlockwise direction.

HURRICANES

In TROPICAL OCEANS, where water temperature can rise to over 27⁰C (81⁰F), water evaporates and heat is transferred to the atmosphere. As the air warms, it becomes less dense and rises in a spiral, drawing yet more air upwards.

SOMETHING TO KNOW AND UNDERSTAND

HEAT from the SUN drives our weather patterns. It causes evaporation and clouds to develop; it creates wind as air heats up and these winds then drive both the clouds and ocean currents.

WAVES

Waves are perhaps the most familiar feature of the ocean. We sail on them, play in them, surf them and scare ourselves when they get too big. But as well as providing entertainment and thrills, waves can be very destructive. They (waves) store a lot of energy, which is released as they break. The bigger the wave, the more energy released, and sometimes we are not ready for the impact: boats sink, piers are destroyed, houses get washed away and even human life is lost. Waves, like many aspects of the ocean, are not always as predictable as we would like them to be.

MAKING WAVES

Waves are created by wind. As a breeze blows over water; surface tension, which holds the water smooth, breaks and ripples are created. The wind pushes the back of each tiny crest, and eddies form at the front, reinforcing the shape of the developing wave. Within the wave itself, water is moving in circles, riding up and forward as the crest passes over and down and backwards through the trough. So energy from the wind is not being used to move a body of water through the ocean, rather it is being stored and transported through the ocean itself. As the wind continues to blow, more energy is transferred, stored and moved. The height of waves is determined by the fetch, or distance, over which the wind is blowing.  Being the largest ocean on the Planet Earth, the PACIFIC has the longest fetch and therefore, usually the highest waves. In a big storm waves can reach 15 m (50 feet) high, although the highest wave ever recorded was 34 m (112 feet).

BREAKING WAVES

As waves approach the shore, they make contact with the SEABED and the resulting friction slows the waves down. They get closer and closer; stacking up against each other. As this happens the height and steepness of the waves increase.  As water at the top of the waves keeps going at the same speed, and water at the bottom slows down even more, the crests spill over themselves and the waves break. The energy carried in them is released on to the shore. Different types of shoreline produce different types of wave. A very gentle gradient will create waves that spill over a long distance. By contrast, a steeply shelving shoreline creates waves that break very suddenly and violently as they hit the shallow.

TSUNAMIS

Sometimes called TIDAL WAVES, these giant waves have nothing whatsoever to do with tides, and are now more commonly called TSUNAMIS (from Japanese tsu = harbour; nami = wave). They originate in submarine earthquakes, volcanic eruptions, or sometimes giant mudslides. When a shift occurs along a fault line on the sea floor, or a volcano erupts, the shock wave produced radiates outward, travelling at speeds of up to 700 kph (435 mph). At the surface of the open ocean the wave created is small – 1m (3.25 feet) high at most – and often goes unnoticed by ships. But as it reaches the continental slope, the wave slows down and in places the energy of the wave is channeled by the SEABED. With enormous power behind it and great speed propelling it, the wave builds in height very quickly, and the results can be devastating. Tsunamis are most common in the Pacific Ocean because of all the volcanic activity around its rim. The explosion of KRAKATOA in Indonesia in 1883 sent tsunamis halfway around the world, killing 36,000 people. In 1998, an earthquake produced a tsunami 10 m (33 feet) high, which destroyed villages along the coast of PAPUA NEW GUINEA, killing over 3000 inhabitants.

GYRES

GYRES are characterized by having strong currents along their western boundary which carry the water towards the POLES, and a gentler, less definable current, running east. The spiralling movement of water in ocean gyres creates a centre where the sea level is higher than the rest of the gyre. In the Northern Atlantic Gyre, for example, is the SARGASSO SEA, where sea level is about a metre or so higher than the surrounding ocean. The centre mound of water in a gyre is not right in the middle, however; owing to the rotation of the Earth, the centre is nearer its western boundary. This squashes the western current against the land and means that the water flows faster through the narrow gap. In the North, the speed of most ocean currents is about 10 km (6 miles) per day, but western boundary currents, such as the GULF STREAM in the NORTH ATLANTIC and the KOROSHIO CURRENT in the NORTH PACIFIC, may reach speeds of 90 – 160 km (60 – 100 miles) per day. These currents are strong and consistent, but as they head north and are gradually deflected east, they lose the land barrier, the pressure eases off, the water moves more slowly and the currents begin to meander. These meandering bodies of water can become isolated from the main flow of the current and form little satellite gyres, called “rings.” These remain adrift within the main ocean gyres. Ocean currents in the Southern hemisphere tend to be slower than those in the North. The centre of the gyre is less pronounced, so the effect on the western boundary is reduced. Moreover, gyres in the south are bordered by a continuous cold current, which sweeps around the SOUTHERN OCEAN, uninterrupted by any landmass. This current is called the Antarctic Circumpolar Current and is responsible for keeping Antarctica isolated from the warming effects of global currents.

CLIMATE CONTROL (OCEAN CURRENTS)

The difference in temperature between ANTARCTICA in the grip of winter and the hottest desert in summer may seem considerable to us, but far from being a place extremes, Earth is benign compared to what it would be without the oceans. These massive bodies of water act as storage heaters, slowly soaking up heat from the sun, and gradually releasing it in other places around the globe. They play a key role in regulating climate.

DEEP OCEAN CIRCULATION

In 1751 a British captain by the name of HARRY ELLIS heaved up a bucket of water from depths while off the coast of West Africa. Noting how cold it was in comparison to the balmy temperature of the surface waters, he subsequently used it to chill his wine. No scientist could be sure where this cold water came from, but they guessed that it had to have originated in the freezing waters of the poles. In POLAR REGIONS the sun barely heats up the water at all so it remains cold and dense. Polar water is also saltier than other waters, because when it freezes, its salt content stays in the unfrozen water, making it more concentrated. The combination of extreme cold and extra salt makes this water so dense that it sinks to the bottom of the ocean. As it descends, it displaces the cold, dense, salty water already there and pushes it along the ocean floor towards the Equator. Over many years, cold water from both poles spreads through the oceans, pushed along by new water descending. It gradually mixes with the warmer waters above and, over centuries, eventually reaches the surface. In addition to these movements, water is also circulated around the globe by what is called the GREAT OCEAN CONVEYER BELT. The two main places where cold water from the POLAR REGIONS is known to feed this conveyer belt are in the ATLANTIC near GREENLAND and in the south around ANTARCTICA. Water from the GULF STREAM cools as it reaches GREENLAND, sinks to the deep ocean, passes down the length of the Atlantic and combines with cold water from the Antarctic. The water then moves east. Channeled by deep sea trenches and mid – ocean ridges, some water peels off and runs up the western side of continents – the cold – water HUMBOLDT CURRENT alongside SOUTH AMERICA and the BENGUELA CURRENT running up southern Africa being example of this. The bulk of this conveyer belt of water moves eastwards, branching up into the Indian Ocean, and the rest continuing around until it reaches the Pacific, where it travels North around NEW ZEALAND. This cold, oxygen – rich and nutrient – laden water emerges as upwellings just south of India and in the Northern Pacific respectively, creating areas of great productivity. Once at the surface the water heats up and travels west again, the two loops of the current meeting in the southern Indian Ocean, before it moves back into the Atlantic and up to GREENLAND. This multi – ocean circulation transfers heat around the globe and helps regulate the planet’s climate.

GIANT THERMOSTAT

The oceans absorb and lose heat slowly, the surface changing no more than 1⁰C (2⁰F) a day in any one place, and only 10⁰C (18⁰F) in a year. (By comparison, land can change as much as 80⁰C (144⁰F in a day). The process is slow because water conducts heat away from or to the surface. As the water surface heats up, heat is transferred to DEEP WATER and stored there. The reverse happens on cooling: heat is lost to the atmosphere slowly because it has to travel up from the depths. There is a further delay in redistributing the heat because ocean currents take time to move around the globe. Despite the time lag, the heat storage capacity of water combined with both the vertical and horizontal movement of currents around the globe provide efficient means of transferring a lot of heat from one part of the world to another. This has a big impact on the surrounding landmasses (continents). For example, as warm equatorial water moves to the cold North, via the Gulf Stream and North Atlantic Drift it begins to lose heat to the atmosphere. The air is gradually warmed and blown across Western Europe by the prevailing westerly winds. So in winter, when the sun’s rays are too weak to give much warmth, the North Atlantic Ocean acts as a radiator, producing relatively mild winters and a so – called maritime climate, rather than the freezing winters and scorching hot summers of the rest of the continent.

ELNINO – SOUTHERN OSCILLATION (ENSO)

The role of winds, currents and oceans in regulating the WORLD’S CLIMATE is fundamental, but often we are blithely unaware of it. Only when the pattern is altered do we take notice, and the ELNINO – SOUTHERN OSCILLATION, which affects the whole world has made us do just that. In the waters off the coast of PERU is an upwelling that supports huge numbers of anchovy exploited by humans, as well as large seabird colonies. Towards the end of the year, the winds die down, the upwelling decreases for a while and the water warms up. This annual event is called ELNINO. In some years, however, the effect is very pronounced. Without winds driving water offshore, the warm, nutrient – poor equatorial waters flow back east, smothering any remaining cold water.

The surface water becomes a few degrees warmer and the anchovy that thrive in cold water disappear. The fishery collapses, thousands of birds fail to breed and many die. Water level rises too, causing flooding in low – lying coastal areas, while TORRENTIAL RAINS batter parts of South America and other suffer drought. It was some time before ELNINO became linked to what is called the Southern Oscillation – a giant seesaw – like system of high and low pressure between the Pacific and Indian Oceans. When there is exceptionally high pressure in the Pacific, it is matched by exceptionally low pressure in the Indian Ocean and vice versa. During normal conditions, predictable Indian monsoons bring rain for the crops. But when there are major changes in pressure, the rains fail and famine results. On the other side of the Pacific, ELNINO events occur at the same time, so rather than there being a number of localized vagaries, there is one big global atmospheric and oceanic event. In 1982-83 the strongest ENSO in living memory occurred. South America’s anchovy fishery collapsed and the continent endured drought and floods. Hawaii and Tahiti were battered by cyclones while Australia, India and southern Africa suffered droughts, and in some areas famine ensued. However, not all the effects are disastrous. Warm – water fish, such as SKIPJACK TUNA, YELLOWFIN TUNA and SPANISH MACKEREL, were caught off Peru, which helped fishermen through disaster.

GREEN HOUSE GASES

The nature of Earth’s surfaces – the oceans, landmasses and ice – caps – are important in regulating the amount of heat from the sun that is reflected and absorbed. Only 4 per cent of the incoming radiation is dispelled straight back out. The rest is used, bounced between the Earth and its atmosphere until it is also eventually lost. However, some atmospheric gases impede this process. The so – called greenhouse gases (carbon dioxide in particular) are transparent to incoming, longer wavelengths of light, but are more opaque to the outgoing shorter wavelengths of light (infrared) or heat. It is estimated that without this greenhouse effect, Earth would be 33⁰C (59⁰F) colder. The amount of carbon dioxide in our atmosphere has increased by 25 per cent in the last century, and Earth’s overall temperature is believed to be changing as a result. As more heat is trapped by the atmosphere, global temperatures will rise and the currently frozen ice – caps will begin to melt. An increase in sea level, which will flood many low – lying areas, is only one of the predicted outcomes. Global climate will change and with it some valuable habitats such as sea ice will shrink.

MOON POWER

Sea level has been rising and falling each day for billions of years. This phenomenon has a huge impact on MARINE LIFE, particularly on the plants and animals living on the COAST, which are alternately submerged and exposed with each tide. Life just offshore is also affected, as tides are important in water circulation: even far away from land, marine life uses tides to synchronize behavior, most commonly reproduction.

DAILY TIDES

Tides are created by the gravitational pull of the moon and the sun, and by the rotation of the Earth and Moon. Everything in the universe exerts some gravitational pull on everything else, but in order for there to be an effect, these objects must be relatively close to each other. The gravitational pull of the moon on Earth, which is on average only 376,000 km (234,000 miles) away, is stronger than that of the sun which is 150 million Km (93 million miles away). Centrifugal force and the moon’s gravitational pull vary at different points around the world. On the side of the Earth that is nearest the moon, the moon’s gravity literally pulls the water in the oceans towards it. On the opposite side of the planet, the centrifugal force exerts a stronger influence than the moon, and that too pulls water with it.  So water is pulled in opposite directions. These opposing forces create budges, or high tides, in the oceans on opposite sides of the Earth at the same time. Between the two budges are areas of water where the impact of the forces is even. Because water has been pulled away to the budges, these areas experience low tides. As the Earth is spinning on its own axis in a 24 – hour cycle, every point on it passes through the “budges” twice a day. On land the effect is not noticeable, but we can clearly see the effect on oceans in the tidal highs and lows. However, tides have other forces working on them. Friction between water and the Earth’s crust slows the movement of water down, thus high tides are a little offset from a line drawn between the Earth and the Moon – they occur a little behind it. Also, the moon’s orbit around Earth is not in time with the Earth’s own 24 – hour spin. In fact, the moon gains by 50 minutes each day, which means that a spot on the Earth is 50 minutes into its next day before it is in direct line with the moon again. Tides, therefore, also slip by 50 minutes each day.

SPRING AND NEAP TIDES

Despite the SUN being so much larger than the MOON, it is 400 times further away, which means that its gravitational pull on Earth is only about two – fifths as strong as the moon’s. Nevertheless it does exert an influence on the oceans, and produce bulges in the same way as the moon. When the SUN is directly in line with the moon (and the Earth) its gravity either pulls with the moon or against it, depending on where the Moon is. For example, if the Moon is between the SUN and Earth (new moon), the gravitational pulls of both the Moon and the SUN act together to produce particularly high and low tides. Equally, if the MOON is FULL and on the opposite side of the Earth to the SUN, both will be pulling water and working with the centrifugal force, so tides will also be higher. These twice – monthly tides are called SPRING TIDES, which relates to their height rather than the time of year when they occur. It is when the Moon is at right angles to the SUN, either waxing or waning that the tides are less extreme, the tidal range is low and we have NEAP TIDES. This happens because Moon’s and the sun’s gravitational pulls are partly cancelling each other out.

REAL TIDES

TIDAL PATTERNS are not easily described, partly because huge landmasses (continents) get in the way and partly because of the TOPOGRAPHY of the ocean floor. Most COASTS do experience two high tides and two low tides each day, but they can vary in strength, and some places have only one tide per day rather than two. When the Moon is directly over the EQUATOR, this is the area most strongly affected by its gravity; it has less impact towards the POLES. Likewise, when the Moon’s orbit takes it away from the EQUATOR, the further north (and south) it orbits, the greater the pull in those places. Combine this with the CORIOLS effect, mid – ocean ridges and other underwater features that disrupt the flow of water, and the result is a range of different tidal patterns across the globe. Throughout most of the PACIFIC OCEAN, For example, one of the two high tides each day is higher than the other. By contrast, most of the ATLANTIC OCEAN has relatively even tides occurring twice a day. Other places, such as the GULF OF MEXICO, much of ANTARCTICA and a few isolated areas in the western Pacific experience only one tide per day. In most of the ocean basins, tides affect the height of the water by 1-3 m (3.25 -10 feet). But in areas where water flow is restricted, such as a partly enclosed bay, tidal range can be more. In the Bay of Fundy, Nova Scotia, for example, the tidal range is 15 m (49 feet) on spring tides, and a strong tidal current is present much of the time as a lot of water has to move in and out of the bay. This current mixes nutrients in the water, and as a result, the sea is very rich. Summer plankton blooms feed krill, which in turn feed humpback whales, which return each year to take advantage of this bounty.

NOTE AND REMEMBER

TSUNAMIS (often called TIDAL WAVES) can travel across very deep oceans faster than a JUMBO JET. In 1960 an EARTHQUAKE in Chile sent a shock wave across the PACIFIC which reached Japan just 21 hours later.

LIVING IN THE SEA (THE WATER PLANET EARTH)

Numerous ocean habitats support varied and complex ecosystems: in them a great diversity of plant and animal life forms has evolved. The number and variety of animals and plants that can be found in the OCEANS is overwhelming. From the tiniest bacteria (only thousandths of a millimetre across) to the largest animal on the Planet Earth (the 33 – m/108 – foot blue whale), marine life comes in all shapes and sizes. Moreover; it all survives, feeds, and reproduces in equally diverse ways. One of the reasons the oceans sustain so many life forms –  many more than can be found on land – is that they offer three (3) dimensions for occupation: a fish easily achieves neutral buoyancy in water; whereas birds expend a great deal of energy simply staying aloft. Thus, the available living space for marine life forms is an estimated 250 times greater than for those on land. Nevertheless, although the oceans offer a vast area to live in, most marine life is concentrated near the surface, in the upper 200 m (656 feet) where sunlight penetrates. Even within this shallow zone, life is not evenly distributed – most of it lives near land, on or above the continental shelf.

WHERE TO LIVE

Conditions vary greatly in different parts of the ocean, so there are numerous places to live and ways to make a living. Clearly, there are great differences between living in an icy world, in open water, on a coral reef or in the abyssal depths. In some places, life appears effortless for plants and animals: food is abundant, mates are numerous and so long as predators are avoided the living is easy. In other places it seems more of a struggle.

ON THE EDGE

COASTAL REGIONS are among the hardest places to survive. Land animals that rely on the SEA for a living spend part of their time in water for which they are not necessarily well designed. Few plants and animals do well both on land and under water; there always has to be some compromise. Birds that feed by swimming under water, such as guillemots, are not good fliers. Penguins have given up aerial flight altogether for more efficient “flight” under water. Similarly, marine animals that have to breed on land often move very inefficiently when out of the water. Seals and sea lions manage an ungainly shuffle at best. The intertidal zone is probably one of the toughest places to live. Plants and animals on a rocky shore suffer great physical stress when the tide goes out. They are left literally high and dry. Some such as crabs and snails, run from the problem, seeking shelter in tide pools or in damp cracks and overhangs. Seaweeds remain stuck where they are, and some survive only if they originally settle in a place that keeps them moist during low tide. MOLLUSCS such as mussels and limpets shut themselves in to reduce water loss. Others are adapted to tolerate it; the seaweeds Fucus can cope with losing a remarkable 90 per cent of its water content with each low tide. It is not only drying out that organisms have to deal with. They get battered by waves and during LOW TIDE they may be exposed to extremes of temperature, they may experience a drop in salinity if it rains and, of course, many of them rely on water for food, so when the tide is out they cannot feed. Life on the intertidal zone of a rocky shore is far from easy. POLAR REGIONS present another set of extremes.

For part of the year the POLAR SEAS are in total darkness, and during the summer they enjoy 24 hours of SUNLIGHT. Temperatures hover above freezing in the summer but can plunge to below – 50⁰C ( -58⁰F) in winter. Many warm – blooded animals escape the dark and bitter cold of winter by migrating away as the sea freezes over. However, some hardly types, such as WEDDELL SEALS in the ANTARCTIC and WALRUSES in the ARCTIC stay behind, enduring the severest of conditions. In order to breathe they have to use holes in the ice that are kept open by currents or, in the case of WEDDELL SEALS, use their teeth to keep a hole open.

BATHED IN WATER

The richest, most diverse habitats occur in shallow, rocky places in both temperate and tropical seas. Enough sunlight reaches the SEABED to allow plants to grow, and stable ecosystems can be built on such foundations. CORAL REEFS are the most diverse of all. Although the water surrounding them is low in nutrients, recycling on a REEF is so efficient that the community is largely self – sufficient. Temperate habitats are also exuberant, but are restricted by their seasonality. MARINE LIFE is concentrated in a COASTAL WATER for good reason: all the advantages of a solid, three – dimensional living space are on offer. By contrast the vast open ocean has one severe disadvantage for animals: there is no place to attach to, nothing to burrow into or hide behind. Nevertheless, compared to the inter -tidal zone or the freezing poles, it is an easier place to live – often warm, well lit and with no shortage of water. The only thing creatures have to do is stay afloat and avoid being eaten. Staying afloat can be achieved in two main ways: by increasing water resistance to slow the inevitable sinking process, and by increasing buoyancy. MICROSCOPIC PLANTS and ANIMALS (which form PLANKTON) have large surface areas for their size, which increases drag as they sink: extra appendages and a flat shape add resistance. Greater buoyancy can be achieved by storing fat, which is less dense than water and therefore floats. Many small plankton, such as tiny crustaceans and fish larvae, have little fat droplets. Even larger, open – ocean swimmers, such as TUNA and SHARKS, use fat to increase their buoyancy. Marine mammals do too, and the stored blubber also helps to maintain their body temperature. Most FISHES use air for buoyancy, having evolved swim bladders (pockets of air) to regulate their depth in the water. Avoiding predators is far more demanding. In the open ocean, where there is plenty of light, most animals have very well – developed eyes, both for finding food and spotting predators. Transparency is a great advantage used by many JELLYFISH and smaller creatures. Go below the sunlight surface waters to a depth of 200 m (656 feet) and life becomes harder. The pressure exerted by water is considerable, but most critically there is not enough light to support plant life. Without plants, animals depend on the rain of food from above, and that is hardly abundant. Only about 5 per cent of food produced in the sea above is not used there and sinks to support animals living at depth. Because food is so limited, there are comparatively few animals living in the twilight zone (200 – 1000 m//656 – 3281 feet), and fewer living in the inky blackness beneath.

NOTE AND REMEMBER; Phytoplankton are responsible for nearly half of the photosynthesis in the world, producing half the oxygen in the atmosphere.

BLUE WHALES

Twice the size of the biggest dinosaurs, blue whales are the largest animals that have ever lived on Planet Earth. In every dimension their size is incomparable. Adult females are the largest, able to weigh as much as 200 tonnes and measure 33 m (108 feet) in length. Their tongue alone weighs the same as an elephant. When they exhale, the thunderous blow reaches 9 m (30 feet) high and, on a quiet day, can be heard miles away. Because they (whales) are so big, so rich in blubber and so audible, BLUE WHALES were once hunted to near extinction.

HUNTING WHALES

For many years blue whales were not sought by whaling ships. Swimming at a remarkable 20 knots, they were simply too fast to be caught by sailing boats. On the odd occasions they were caught, they were too powerful to overcome and, in any case, when a blue whale is harpooned and dies, it sinks, which made them hard to handle. It was not until 1864, when a Norwegian whaling captain commissioned a purpose – built steam – powered boat, that blue whales were targeted. Soon the North Atlantic and Pacific stocks began to be depleted. When shore – based whaling stations sprang up in 1904, the Antarctic population suffered. But it was the advent of factory ships which processed the dead whales from a fleet of many smaller ships, that heralded disaster for blue whales. The whalers had the speed to chase them, the harpoons to kill them and the freedom to stay at sea for long periods because they no longer had to return to shore after each catch. The southern summer of 1930 – 1931 marked the peak of the slaughter: 28,325 blue whales were killed by only 41 ships. It is thought that a total of 350,000 blue whales have been killed worldwide. 90 per cent of those in Antarctic waters. At last, in 1965, the International Whaling Commission decreed that blue whales should be protected. But by then, for most populations, it was already too late. An estimated 650 were left in the Southern Ocean, and there has been no visible recovery. It appears that the ALASKAN population was wiped out altogether. Only in California waters, since 1980, has there been a marked comeback, and now approximately 2000 blue whales feed there.

BIG EATERS

BLUE WHALES have big appetites.  In order to maintain such a huge body they probably need about 1.5 million calories each day. But as they feed for only half the year (the other half is spent in warn tropical water where they breed and where there is little or no food), they actually need 3 million or more calories per day. BLUE WHALES eat mostly KRILL, a small shrimp – like crustaceans. They (Blue whales) feed by engulfing huge mouthfuls of KRILL and WATER: in order to consume enough with each gulp, they have throat pleats stretching from their lower jaw along their body, which distend enormously when a mouthful is taken. In order to sieve the KRILL from the water: the enormous tongue forces water through the 270 – 400 tightly spaced, 1-m (3.25-foot_ – long baleen plates that hang from the upper jaw.

LONERS (LIVING ALONE/SINGLY)

Blue whales are usually seen ALONE (Solitary). Occasionally, two or more adults can be seen feeding together; but most sightings of two blue whales are mother and calf. Very little is known about their breeding behaviour: and what we do know comes from records kept during the whaling days. Females mature at five years old. After mating, the gestation is 11-12 months and a calf of 7 m (23 feet) and 3 tonnes is born. After only seven months of feeding on rich milk, the calf is weaned and starts to feed on KRILL.  At this stage it is 16 m (52.5 feet) long and weighs 23 tones. That means that a calf grows 4 cm (1.5 in) and gains 90 kg (198lb) per day while nursing. To achieve this it drinks up to 100 litres (22 gallons) of milk each day. This extraordinary transfer of energy takes a toll on the mother, who loses about one – third (50 tonnes) of her body weight. When the pair return to higher latitudes for the summer: the mother can resume feeding and regain her fat stores.

PYRAMIDS OF LIFE

On LAND, the plant world is dominated by TREES, BUSHES and GRASSES, but in the OCEANS it is dominated by  MICROSCOPIC CELLS. Whatever size and shape they come in, the key thing that plants the world over have in common is the ability to photosynthesize. This chemical reaction uses energy from the SUN to combine carbon dioxide and water to produce simple sugars, the building blocks of carbohydrates. Oxygen happens to be a by – product of the reaction. Apart from a few extraordinary habitats, such as the HYDROTHERMAL and cold vents in the deep ocean, photosynthesis makes the biological world go around. Most of the ocean’s photosynthesis occurs in PLANKTON, a community of microscopic single – celled plants (phytoplankton) and animals (ZOOPLANKTON), that drifts around in surface waters. Only the plants photosynthesize. However, PLANKTON can refer to anything that lives by drifting in the sea, so large JELLYFISH and floating seaweed can also be included.

MARINE PYRAMIDS

Viewed simply, a food chain or web is just a series of links between living things that depend on each other for food. The plants, or primary producers, are the first in line. Next come the first group of consumers, the herbivores, followed by various other consumers each feeding on the group before. However, not all energy is passed on to the next level. Some of energy created by PHYTOPLANKTON is lost in simply living, and not all phytoplankton are eaten before they die. Similarly, herbivores and carnivores use energy to live and to reproduce, and some of what they eat passes through them without being digested. This loss of energy between each level is substantial and, on average, only 10 per cent is passed on. As a result, there are fewer animals at each level.

On land, this typically creates a PYRAMID OF LIFE: there are more plants than herbivores, more herbivores than carnivores and so on. In the OCEAN, however, the pyramid is normally inverted. The number of primary producers is lower than the herbivores, which in turn is lower than the carnivores. But if you look at actual production within any one level, a pyramid does exist. PHYTOPLANKTON reproduce within a matter of hours or days (but the standing stock is low as they are eaten very quickly), ZOOPLANKTON take weeks, and fishes can take a year. So in terms of how much is actually produced at any one level, the pyramid still stands. Because each level has less energy, there is a limit on the number of levels that can exist. At the top of the food chain, energy runs out, so animals such as sharks and killer whales, are fewer in number and reproduce less often, and are therefore less commonly seen than those lower down, such as smaller fishes. The best strategy for animals at the top of the PYRAMID is to bypass as many levels of consumer as possible and feed nearer the bottom of the food chain: that way they harness more energy for themselves. Not surprisingly, it is the largest animals in the OCEANS that have achieved this. WHALE SHARKS, the largest fish of all, feed on PLANKTON, as do BLUE WHALES, the largest mammal.

PHYTOPLANKTON – THE FIRST LINK IN THE CHAIN

Bathed in water, which contains dissolved carbon dioxide, and, because of their size, needing only a minimal amount of sunlight to fuel their photosynthesis, phytoplankton are pretty well cared for in most places. The only other nutrients they need in any quantity are nitrogen, phosphorus and silica, all of which are found in SEA WATER. Being so minute, some as small as 0.0002mm, their individual requirements are not large. Phytoplankton are essential to life in the oceans: a staggering 90 per cent of primary production (the creation of organic compounds from carbon dioxide) in the oceans occurs in these microscopic plants. In shallow coastal waters, a community can develop based on larger marine plants – SEAWEEDS and ALGAE – which grow on the SEA FLOOR. Indeed, in nutrient – rich water that receives a lot of sun (even if only seasonally), plants, such as the giant KELP FORESTS of California, rival the productivity of phytoplankton. But COASTAL WATERS make up a tiny percentage of the oceans, and these small productive zones cannot begin to support the abundance of life found in the oceans. Since PHYTOPLANKTON needs LIGHT, it exists only in the upper 200 m (656 feet) of water. Here it flourishes and soon uses up all the available nutrients unless they are replaced. Clearly, It is not limited by water, and nor is it limited by carbon dioxide, as more is continually being absorbed from the atmosphere. It is nitrogen and phosphorus (and in some places silica and iron) that are limiting nutrients. In areas of upwelling, where nutrients are constantly replenished, phytoplankton do well. Similarly, seasonal storms, which affect temperate latitudes, mix the water thoroughly, ensuring that when spring returns, there are enough nutrients in the water for PHYTOPLANKTON to bloom. The POLAR REGIONS also have a PLANKTON bloom, but it comes later in the year when the annual sea ice has all but melted. TROPICAL WATER might be expected to have the highest primary productivity as the water is warm and there is year – round sunlight. But tropical waters are characterized by having a low nutrient content, and this limits phytoplankton numbers. Indeed, productivity in tropical water is only a quarter of what it is in temperate seas.

ZOOPLANKTON – THE FIRST CONSUMERS

Where there is a source of food, there is nearly always an animal to eat it. ZOOPLANKTON are animals of the PLANKTON WORLD and many of them graze on PHYTOPLANKTON. In contrast to LAND HERBIVORES, few plankton are strict vegetarians: most ZOOPLANKTON will indulge in a little animal flesh occasionally. The most abundant tiny herbivores are COPEPODS, making up about 70 per cent of the ZOOPLANKTON. They (COPEPODS) are minute crustaceans that use their legs like paddles to draw water towards their mouth so that they can extract phytoplankton. Far from being unselective in their diet, they actively seek out phytoplankton using both sight and smell”. COPEPODS are also carnivorous, catching other zooplankton (and sometimes each other) with claw – like appendages. On LAND, plants grow large and store food. Some of it is eaten, but most plant matter eventually dies and is decomposed by BACTERIA and FUNGI. In the OCEAN things are very different: most PHYTOPLANKTON gets eaten. Being single – celled, their growth potential is small, so they turn excess energy into reproducing by simple division, which they do frequently. That is why, in higher latitudes when spring arrives and there is enough light for photosynthesis, the PHYTOPLANKTON population increases, sometimes explodes, before the ZOOPLANKTON population has had time to graze it down. Most ZOOPLANKTON do not last long either. They live only a few weeks which give them time to collect enough energy to breed before dying (if they are not eaten first).  In the TROPICAL OCEANS, ZOOPLANKTON can breed all year, but at higher latitudes, where the feeding season is short, the breeding season is correspondingly curtailed. Those animals in the ZOOLPANKTON that are not permanent residents but merely larval stages of other animals do not reproduce at all. These ZOOPLANKTON spend only a short part of their lives in the PLANKTON community: but this period is important in dispersal, ensuring the colonization of new places. Swarming the OCEANS are carnivores, which feed exclusively on ZOOPLANKTON. Some are ZOOPLANKTON themselves, being merely a little bigger or a little more aggressive than those they eat. Other feeders include fishes, jellyfish and even some of the biggest animals on the PLANET, the BALEEN WHALES.

NEKTON – THE SWIMMERS

Members of the PLANKTON are at the whim of ocean currents, but larger animals, some of which depend on the PLANKTON community for food, are free to swim where they please. Fishes, marine mammals and squid are the most numerous of the group known as NEKTON, which also includes TURTLES, SEA SNAKES and PENGUINS. Animals that feed exclusively on PLANKTON range from small fishes, such as sardines, anchovies and herring, to manta rays and whale sharks. Their style of acquiring food varies as much as their size. Fish usually pick off individual zooplankton drifting by, while whale sharks simply open their mouths as they swim along and let the plankton enter. Whale sharks have fine, comb – like structures on their gills to sieve out larger planktonic animals as the water passes through. The ability of these animals to swim means that they can move between the best feeding grounds as the productivity of each place changes with the seasons. TUNA, for example, make long journeys right across the PACIFIC and ATLANTIC, following the areas of highest productivity. WHALES migrate from the TROPICS, where they breed, to the POLAR REGIONS to take advantage of the huge plankton boom that occurs each POLAR SUMMER. Many sea birds time their breeding to coincide with PHYTOPLANKTON blooms, for shortly after ZOOPLANKTON numbers increase, small fishes arrive to feed, and birds rely on an abundance of small fish to satisfy their growing chicks. In most ocean habitats, simple food chains like this do not exists; instead, there is a complex web of dependence, creating a more stable ecosystem.

THE CARBON CYCLE

The recycling of carbon between the ocean, the atmosphere and land is an essential ongoing process for life on Planet Earth. Most carbon in its inorganic form, carbon dioxide, is found in the atmosphere and dissolved in sea water: thus the oceans are an immense carbon dioxide store. When plants photosynthesize, they convert inorganic carbon into organic carbon compounds or simple sugars. In the OCEANS it is the MICROSCOPIC PLANTS called PHYTOPLANKTON, that are responsible for nearly all the conversion of carbon dioxide into useful sugars. Most of the organic carbon moves up the FOOD CHAIN/WEB as one animal eats another: in order to live, organisms use the sugars for energy and by doing so convert the carbon back into carbon dioxide. This is released into the water or the air; where it can be reabsorbed by plants. But some organic carbon takes another path. PHYTOPLANKTON might die before being eaten, some carbon is excreted as faeces by animals and, in the end,  the animals themselves die. All this dead organic carbon rains down on the SEA FLOOR; where much of it is converted back to carbon dioxide by decaying bacteria. When not used by bacteria or eaten by scavengers, dead organic carbon builds up, layer upon layer, and over geological time is converted into DEPOSITS of FOSSIL FUELS, OIL, GAS and COAL.

NOTE AND REMEMBER

WHALES and DOLPHINS produce greasy tears that protect their eyes from the stinging effects of salty sea water. DIATOMS are microscopic marine plants that are particularly abundant in temperate waters. Along with other phytoplankton, they form the first stage in the food chain/web.

EATING AT SEA

Water provides a three – dimensional habitat in which to live and feed. That fact alone vastly increases the methods by which animals can obtain their food. Many of them simply strain it from the water passing by,  probably the easiest method, while others scrape it off rocks, eat it out of the sand or hunt it down.

FILTERING FOOD

Given that so much of the food in the ocean is PLANKTON, many animals have evolved ways of filtering it out of the water. WHALES do it by using BALEEN, whale sharks and fishes use their GILLS, while COPEPODES use their HAIRS. But many filter feeders live in the SEA FLOOR and cannot swim around to find food. These include BARNACLES and some TUBE WORMS, which use modified legs to snatch particles floating by in the water and pass them to their mouth. Even the ANEMONE CRAB collects suspended particles using efficient, net – like appendages which it throws into the oncoming current. PLANKTON are trapped by numerous CORAL REEF INVERTEBRATES. Sea fans grow in flat, lattice – like structures at right angles to the prevailing current. When the individual animals or POLYPS of the sea fan, extend their tentacles, very little escapes the trap. Basketstars unfold their highly branched arms and spread their extensive net, trapping larger plankton and unwary small fish. Numerous little hooks then impale their prey before it is fed down to the mouth. Other animals are more active and actually create a flow of water by tiny beating hairs. These armies of hairs draw water through the body of the animal so that particles can be extracted. Both SEA SQUIRTS and SPONGES use this method, but some are also designed to maximize water movement by using the chimney technique. In the same way that air blowing over the top of a chimney draws air up through it, so water passing over sea squirts and tall sponges draws water through their bodies. In sea squirts a strand of mucus inside the body traps the passing particles, and the mucus is then bundled up and digested. In SPONGES, the water is moved along in small tunnels by whip – like hairs, where cells along the tunnel walls trap and ingest particles of floating food.

EATING OFF THE FLOOR

What little PLANKTON is missed by the innumerable traps, joins the rain of faecal matter and dead material that falls from above. The OCEAN FLOOR is littered with organic matter, which is soon eaten by the BACTERIA that thrive there. As on LAND, BACTERIA play an important part in breaking down organic matter for recycling. Bacteria, in turn, provide a valuable food source for animals living within the SEDIMENT. These microscopic animals move between grains of sand hunting down bacteria. The combination of fine sediment, detritus and living animals creates a grainy soup, which is ingested wholesale by a wide range of larger animals. Little fish called SLEEPER GOBIES live and feed on sandy sea beds. They spend much of the day simply scooping up mouthfuls of sand, from which they extract food. SEA CUCUMBERS – sausage – shaped animals which come in many varieties – are a familiar sight to divers. Some of them are FILTER – FEEDERS, spreading branches into the water to trap passing food. Others are DENTRITUS – FEEDERS, inching their way across the sea bed using an array of busy feeding tentacles to pick up food from the sediment. In the same way that FILTER – FEEDERS keep the water clearer of suspended matter than it might otherwise be, DETRITUS EATERS keep the SEA FLOOR in good shape. Sediment is turned over, passed through their guts and the organic matter extracted, leaving a cleaner sea bed in their wake.

NOTE AND REMEMBER

SPONGES are the vacuum cleaners of sea water. They filter water so fast that a small sponge, the size of a FIST, will process about 5000 litres (1100 gallons) of water a day.

GRAZING

In shallow water, where SUNLIGHT penetrates, nutrients abound and there is a solid SEA FLOOR to provide anchorage, algae grow profusely. ALGAE can be single – celled and appear like slime, or they can grow in short clumps or in mats. They can even grow to 30 m (98 feet) or so, like the giant KELP of California. ALGAE are one of the most important components of all shallow – water communities but are often overlooked. Where they grow luxuriantly, numerous animals have evolved to exploit them. Some, such as snails, limpets, sea hares and abalone, literally scrape off the surface film of algae. The MOLLUSCS have teeth arranged along a muscular tongue, which works rather like a file. As they craw over rock, they scrape the algae off into their mouths, but by doing so they wear down their teeth, which have to be continually replaced. SEA URCHINS also graze algae, and are important in many habitats because they clean the SEA BED, making room for colonizing animals to grow. However, they can become a problem. With such a steady supply of food, if their numbers go unchecked by predators, they proliferate and can eat their way through huge stands of seaweeds or kelp. In areas of California where sea urchin numbers have increased due to a low sea otter population, FORESTS of GIANT KELP have been temporarily reduced to rocky “deserts”. Fishes are also important grazers, particularly on CORAL REEFS where, among others, PARROTFISHES and SURGEONFISHES graze away at the flourishing algae and keep them in check. It is only because of these grazing fish that CORAL can grow at all: algae grow so fast on SHALLOW REEFS that CORAL LARVAE settling out of the PLANKTON and trying to make a start on the reef would soon be overgrown.

PREDATION

The world of predators and prey is an ARMS RACE, each player developing weapons and tactics accordingly. In the marine world there are essentially two (2) types of predators – those that feed on sedentary animals and those that feed on freely moving animals. Most invertebrates fall into the former category, while most vertebrates are in the latter. Feeding on creatures that cannot move is more like grazing than hunting. Nevertheless, the animals that do this are TRUE PREDATORS. The crown – of – thorns starfish, for example everts its stomach over coral and digests it in situ. Since they cannot move to avoid predation, more sedentary animals have some form of protection. BIVALVES, such as mussels and oysters, have hard shells which they can close, but predators have found a way around this. Some snails have drill – like mouthparts which bore a hole on the oyster’s shell. Digestive enzymes are secreted into the hole, and the resulting soup is sucked out. By contrast, starfish open bivalves with brute force and evert their stomachs to digest the contents. Most free – swimming hunters of the ocean track down their prey using sight, but once within range, they use a wide variety of tactics to catch their food. Camouflage, stealth and ambush often play a part, but in the open water, where there is nothing to hide behind, speed is most often used. TUNAS and BILLFISHES are all remarkably fast swimmers, attacking their prey at lightning speed. Ambush predators are usually found on or near the SEA FLOOR. They sit and wait for their prey to come ever closer and, once the sticking distance has been reached, they pounce on their unwary victims. Some ambush predators, such as stonefish, can be so well camouflaged they are almost impossible to see.

BREATHING UNDER WATER

GILLS are the underwater equivalent of lungs, absorbing oxygen and getting rid of carbon dioxide. GILLS are also important in regulating the salt content of a fish’s body. They lose a lot of water to the sea by osmosis, and as sea water is the only source of water available, fishes are obliged to drink it. They then have to get rid of the salt taken in, so they excrete it via their gills. As sharks swim, water passes through their mouths and over their gills. When at rest, sharks actively pump water over their gills by opening and closing their mouths. They also have small holes called SPIRACLES just behind their eyes through which water enters, before it passes over the gills.  In rays and skates, which spend most of their time on the seabed, spiracles are the only way water can get in as their mouths are usually buried in sediment. Other fish also pump water over their gills, but in a more efficient way. They have flaps covering their gills which effectively seals them. As they open their mouths and close these flaps, a vacuum is created which fills with water. Subsequently they close their mouth and water is forced over the gills and through the flaps.

PREHISTORIC SURVIVORS

SHARKS AND THEIR RELATIVES

There are about 1100 species of sharks, rays and skates in the world. They differ from other fishes in that their skeletons are made of CARTILAGE rather than bone, and also they have been around for a very long time. Over 100 million years ago, creatures similar to the sharks we know today were hunting in the ocean. The design was obviously good because, although they have diversified considerably, unlike many of their prehistoric contemporaries, their line did not die out. SHARKS live throughout the OCEANS at almost all depths. Some, such as the MEGAMOUTH, which lives in the DEEP OCEAN, are rarely seen. Very occasionally they are brought to the surface in nets, usually dead. Another little known shark is the smallest, the SPINY PYGMY SHARK, which is only 25 cm (10 in) long and also lives at depth. The slow – moving Greenland shark inhabits ARCTIC WATERS and is seldom encountered. By far the majority of sharks are concentrated in TROPICAL COASTAL WATERS where the water is warm and prey is plentiful.

JAWS

Not all sharks have big teeth. Some, such as WHALE SHARKS and BASKING SHARKS feed on PLANKTON and do not need substantial teeth. Ironically, these are the largest of the group: whale sharks grow to 12 m (39 feet) (although individuals of 18 m (59 feet have been seen), and basking sharks reach an amazing 10 m (33 feet). Smaller species, such as horn sharks, which live in temperate waters, have rows of tiny teeth. Similar in size to very coarse sand, they grow so close together that they form a rough, hard plate, perfect for crushing small crustaceans. Stingrays have a similar set of minute teeth. Nevertheless, the large predatory species, such as bull sharks, tiger sharks and great white sharks, are famous for their teeth, which are triangular, serrated and very sharp. When a tooth gets damaged or lost during feeding, there is always another one just behind ready to replace it. Rows of teeth are continually forming at the back and slowly moving forward to the leading edge of the mouth. TIGER SHARKS are thought to get through an astonishing 24,000 teeth in ten years.

 

HUNTING

SHARKS have a number of ways of hunting down their prey. They can hear well, detecting sounds many kilometres away.  They have an extraordinarily good sense of smell, particularly for blood. At distances of 100 m (328 feet) or so they can feel vibrations in the water. Homing in on any of these cues, they begin to use sight. Their vision is very good, and most of them can see better in dim light than their prey. Great white sharks hunt well in poor visibility by swimming low in the water and watching for the silhouette of an elephant seal or fur seal swimming near the surface. Close to, sharks pick up very weak electrical charges that radiate from all animals. Even a tiny fish hiding in the sand, moving its gills slightly to breathe produces an electrical signal. A small hammerhead shark scanning the sea floor for any electrical cue can home in on such a signal.