WORLD OCEAN

world ocean contains the details about history of earth science and marine environment,physical ocean,bottom dewellers, water deweller and ocean's future. each title having the details of ocean and species in different place like pelagic zone and seafloor etc.,

WHY OCEAN WATER IS SALTY?

In the beginning the primeval seas must have been only slightly salty. But ever since the first rains descended upon the young Earth hundreds of millions of years ago and ran over the land breaking up rocks and transporting their minerals to the seas, the ocean has become saltier. It is estimated that the rivers and streams flowing from the United States alone discharge 225 million tons of dissolved solids and 513 million tons of suspended sediment annually to the sea. Recent calculations show yields of dissolved solids from other land masses that range from about 6 tons per square mile for Australia to about 120 tons per square mile for Europe. Throughout the world, rivers carry an estimated 4 billion tons of dissolved salts to the ocean annually. About the same tonnage of salt from the ocean water probably is deposited as sediment on the ocean bottom, and thus, yearly gains may offset yearly losses. In other words, the oceans today probably have a balanced salt input and outgo.

Past accumulations of dissolved and suspended solids in the sea do not explain completely why the ocean is salty. Salts become concentrated in the sea because the Sun's heat distills or vaporizes almost pure water from the surface of the sea and leaves the salts behind. This process is part of the continual exchange of water between the Earth and the atmosphere that is called the hydrologic cycle

Water vapor rises from the ocean surface and is carried landward by the winds. When the vapor collides with a colder mass of air, it condenses (changes from a gas to a liquid) and falls to Earth as rain. The rain runs off into streams which in turn transport water to the ocean. Evaporation from both the land and the ocean again causes water to return to the atmosphere as vapor and the cycle starts anew. The ocean, then, is not fresh like river water because of the huge accumulation of salts by evaporation and the contribution of raw salts from the land. In fact, since the first rainfall, the seas have become saltier.

HOW SALTY IS THE OCEAN?

How salty the ocean is, however, defies ordinary comprehension. Some scientists estimate that the oceans contain as much as 50 quadrillion tons (50 million billion tons) of disso

lved solids.If the salt in the sea could be removed and spread evenly over the Earth's land surface it would form a layer more than 500 feet thick, about the height of a 40-s

tory office building. The saltiness of the ocean is more understandable when compared with the salt content of a fresh-water lake. For example, when 1 cubic foot of sea water evaporates it yields about 2.2 pounds of salt, but 1 cubic foot of fresh water from Lake Michigan contains only one one-hundredth (0.01) of a pound of salt, or about one sixth of an ounce. Thus, sea water is 220 times saltier than the fresh lake water. What arouses the scientist's curiosity is not so much why the ocean is salty, but why it isn't fresh like the rivers and streams that empty into it. Further, what is the origin of the sea and of its "salts"? And how does one explain ocean water's remarkably uniform chemical composition? To these and related questions, scientists seek answers with full awareness that little about the oceans is understood.

SOURCES OF THE SALTS...
Sea water has been defined as a weak solution of almost everything. Ocean water is indeed a complex solution of mineral salts and of decayed biologic matter that results from the teeming life in the seas. Most of the ocean's salts were der

ived from gradual processes such the breaking up of the cooled igneous rocks of the Earth's crust by weathering and erosion, the wearing down of mountains, and the dissolving action of rains and streams which transported their mineral washings to the sea. Some of the ocean's salts have been dissolved from rocks and sediments below its floor. Other sources of salts include the solid and gaseous materials that escaped from the Earth's crust through volcanic vents or that originated in the atmosphere.

SALINITY AND ITS VARIABILITY...
Oceanographers report salinity (total salt content) and the concentrations of individual chemical constituents in sea water -- chloride, sodium, or magnesium for example -- in parts per thousand, for which the symbol o/oo is used. That is, a salinity of 35 o/oo means 35 pounds of salt per 1,000 pounds of sea water. Similarly, a sodium concentration of 10 o/oo means 10 pounds of sodium per 1,000 pounds of water.

The salinity of ocean water varies. It is affected by such factors as melting of ice, inflow of river water, evaporation, rain, snowfall, wind, wave motion, and ocean currents that cause horizontal and vertical mixing of the saltwater.

THE SALTIEST WATER...
The saltiest water (40 o/oo ) occurs in the Red Sea and the Persian Gulf, where rates of evaporation are very high. Of the major oceans, the North Atlantic is the saltiest; its salinity averages about 37.9 o/oo. Within the North Atlantic, the saltiest part is the Sargasso Sea, an area of about 2 million square miles, located about 2,000 miles west of the Canary Islands. The Sargasso Sea is set apart from the open ocean by floating brown seaweed "sargassum" from which the sea gets its name. The saltiness of this sea is due in part to the high water temperature (up to 83º F) causing a high rate of evaporation and in part to its remoteness from land; because it is so far from land, it receives no fresh-water inflow.

Abyssal plains

Abyssal plains are flat or very gently sloping areas of the deepocean basin floor. They are among the Earth's flattest and smoothest regions and the least explored. Abyssal plains cover approximately 40% of the ocean floor and reach depths between 2,200 and 5,500 m (7,200 and 18,000 ft). They generally lie between the foot of a continental rise and a mid-oceanic ridge.

There are several distinct abyssal plains across the world's oceans. Each abyssalplain starts at a continental rise and continues until it reaches a mid-oceanic ridge, resuming on the other side. Mid-oceanic ridges are huge underwater mountain chains marking major plate boundaries. These ridges are also the primary source of sea floor spreading since they are slowly pulling apart. Since the continental slope and the ridges essentially form the edge of a deep bowl, some people refer to the abyssal plain as the ocean basin. Overall, the abyssalplain represents around 40% of the ocean floor.

Other components of abyssal plain sediment include wind-blown dust, volcanic ash, chemical precipitates, and occasional meteorite fragments. Abyssal plains are often littered with nodules of manganese containing varying amounts of iron, nickel, cobalt, and copper. These pea to potato-sized nodules form by direct preciption of mineralsfrom the sea-water onto a bone or rock fragment. Currently, deposits of manganese nodules are not being mined from the sea bed, but it is possible that they could be collected and used in the future.

Of the 15 billion tons of river-carried clay, sand, and gravel that are washed into the oceanseach year, only a fraction of this amount reaches the abyssal plains. The amount of biological sediment that reaches the bottom is similarly small. Thus, the rate of sediment accumulation on the abyssal plains is very slow, and in many areas, less than an inch of sediment accumulates per thousand years. Because of the slow rate of accumulation and the monotony of the topography, abyssal plains were once believed to be a stable, unchanging environment. However, deep ocean currents have been discovered that scour the ocean floor in places. Some currents have damaged trans-oceanic communication cables laid on these plains.

Although they are more common and widespread in the Atlantic and Indian ocean basins than in the Pacific, abyssal plains are found in all major ocean basins. Approximately 40% of the planet's ocean floor is covered by abyssal plains. The remainder of the ocean floor topography consists of hills, cone-shaped or flat-topped mountains, deep trenches, andmountain chain such as the mid-oceanic ridge systems.

The abyssal plains do not support a great abundance of aquatic life, though some species do survive in this relatively barren environment. Deep sea dredges have collected specimens of unusual-looking fish, worms, and clam-like creatures from these depths.

continental slope

now let we see about another part in ocean environment that is continental slope and their environmental characteristics with species habitat

A continental slope is a relatively steep slope that extends from a depth of 100 to 200 meters at the edge of the continental shelf down to oceanic depths.the average angle of slope for a continental slope is 4 to 5 degree, although locally some parts are much steeper.

Because the continental slopes are more difficult to study than the continental shelves, less is known about them. the greater depth of water and the locally steep inclines on the continental slopes hinder rock dredging and drilling and make the results of seismic refraction and reflection harder to interpret.

Environment of the Continental Slope:

The deep waters of the Continental Slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. In absorbing sunlight, surface waters are heated, while deeper waters stay cold, typically just a few degrees above freezing. Some mixing of the warm and cold waters occurs, generally in the top 100 m (330 ft) of the water column.

Adaptations to Life on the Slope:

Because of the cold environment, organisms that live at greater depths have slower metabo- lisms. As a result, they eat less frequently, are slower in digesting their food, and move more slowly.When these organisms are observed at depth with video equipment, they typically are seen sitting immobile on the bottom or floating with the current just off the bottom. Another consequence of slower metabolism is that the animals grow more slowly and attain greater ages than their counterparts that live in shallower waters. It has been determined that some deep-sea rockfish live more than 70 years. Many of the animals living in the perpetual darkness of these depths have developed light producing organs.Among organisms with these structures are shrimps and several fishes, includ- ing midshipman, flashlightfish, lampfish (fig.1), and headlightfish. Each species has its own
distinctive pattern of lights that serve various functions, such as communicating with members of their own kind (as in courtship), attracting food (Figure 1. Northern lampfish with light organs (small white circles) along its underside. This small fish, only about 6cm (2.5 in) long, also displays the dark coloration typical of many animals on deeper parts of the Continental Slope. )(like attracting moths to a flame), and avoiding being eaten (flashing a light in a predator’s eyes can give an animal a chance to get away). Another adaptation to the darkness is an absence of color diversity. With no light, colors can have no function. Therefore, animals living on the Continental Slope are generally either a dark color, like black or brown, or red (fig. 2). Among the fishes, rockfish and thornyheads are dominantly red. Red is also the basic color of many invertebrates, including certain crabs and shrimps. The red wavelengths of sunlight are absorbed in the water near the surface, and so do not penetrate to deeper areas. Because of this, red objects appear black at depth, (Figure 2. Because of the absence of light on the Continental Slope, animals living there are generally either a dark color, such as the sablefish (top), or red, such as the shortspine thornyhead (bottom)).

allowing red organisms to blend in with their dark surroundings. Most animals living on the Continental Slope are dark. Among the few exceptions is the deep-sea sole, which is mostly blue, with some black and brown. The water pressure on the sea floor at the top of the Continental Slope is more than 10 times higher than at the surface, and at the bottom of the slope the pressure can be more than 100 times higher than at the surface. To compensate for this difference in pressure, organisms have a large percentage of water in their tissues, bones, and shells that replaces other substances, such as gases and calcium. Owing to the high water content of their muscle tissues, many larger, older fish caught from deeper waters are limp and soft when brought to the surface. An example is the Dover sole, which as it grows and matures, moves deeper downslope, increasing the water content of its tissues. Because of their high water content, mature Dover sole brought to the surface become "jellied" and slimy, leading to one of the fish’s original names, "slime sole." Another such example is the shells of some deep-slope crabs, which are rigid at depth but are easily crushed when they are brought to the surface.

Different Slope Communities :

Fishes living at different depths on the Continental Slope have different life-histories. Species living near the top of the slope produce pelagic (open ocean) young that spend the first few months to years of life swimming in the upper water column and then settle out in relatively shallow water and migrate downslope as they grow and mature (fig. 3). Dover sole, sablefish, and rockfish (fig. 4) have this type of life history; however, most species living deeper, such as rattails, deep-sea soles, and slickheads, have young that live in the same depths as adults. Relatively few species occur at all or most depths on the Continental Slope. Species occu-pying (Figure 3. Juvenile rockfish swimming over Cordell Bank in the northern Gulf of the Farallones. Species of fish living near the top of the Continental Slope in the gulf produce pelagic (open-ocean) young that spend the first few months to years of life swimming in the upper water column and then settle out in relatively shallow water and migrate downslope as they grow and mature. )

one depth commonly are replaced by similar species at other depths. An exception is the eel-like hagfish, which is found at all depths on the slope. In general, the distribution of most (Figure 4. Ared-banded rockfish on the Continental Slope in the Gulf of the Farallones. Relatively few species of fish occur at all or most depths on the slope. Those occupying one depth commonly are replaced by similar species at other depths. For example, greenstriped and stripetail rockfishes live on muddy bottoms on the upper part of the slope, whereas at greater depth they are replaced by species of thornyheads. )

groups changes with increasing depth. For example, on the upper part of the slope, greenstriped and stripetail rockfishes live on muddy bottoms, whereas at greater depth, they are replaced by two species of thornyheads. Another example is skates, which are similar to rays. About five common species of skates live in the shallow waters of the slope, whereas three different species live at greater depths on the slope.

Fisheries :

Currently productive commercial fisheries on the Continental Slope off California’s coast catch Dover sole, sablefish, deep-living rockfishes, and thornyheads . Many of these fishes occupy similar habitats and generally are caught as a group. One increasingly active fishery is for rattails, a deep-living fish with a large head and a long tail that tapers to a point. Another fishery
exists for spot prawn, a rather large, spotted shrimp that lives on muddy bottoms along the slope. Smaller fisheries include one for a large shell-less snail (a nudibranch) that is sold for scientific research. One major fishery of note is for hagfish, the skin of which is used to make what are sold as "eel skin" wallets. Hagfish are not true eels but are a primitive group of fish that have no bones and no jaws. Instead of bones, they have cartilage, and instead of jaws, they have a large sucker-like mouth similar to that of a lamprey or a leech. Once attached, hagfish use a tongue with many tiny teeth to dig into their prey. Once inside, the prey is eaten from the inside out. Besides its unique method of eating, the hagfish has another interesting trait—it produces copious amounts of slime, probably used to discourage predators, and giving the fish its nickname, the "slime eel."

Continental shelf

where is continental shelf? what is continental shelf?, where it starts and where it ends, so we have lot of questions about continental shelf, lte we see about continental shelf and nature of continental shelf, species living in, and etc., first we see about different definitions for continental shelf

• The continental shelf is an undersea extension which can stretch for many miles out to the sea in some cases. Many nations have asserted mineral and land rights to their associated continental shelves, since this region of the ocean is rich in natural resources such as marine life.

• There are actually several parts to the continental shelf. The first part is the shelfitself, which starts below the shoreline of a continent. The shelf slopes gently as it stretches towards the deeper part of the ocean, until it reaches a certain point and drops off sharply, causing the waters above to rapidly become much deeper. This drop is called thecontinental break, and it occurs uniformly at around 460 feet (140 meters) of depth.t has been theorized that the continental break may mark the former sea level of the world's oceans.

• the continental shelf, a shallow submarine platform at the edge of a continent inclines very gently seaward, generally at an angle 0.1 degeree.Continental shelves vary in width.on the pacific coast of north America the shelf is only a few kilometers wide. On the Pacific off Newfoundland in the Atlantic ocean it is about 500 kilometers.portions of the shelves in the Arctic Ocean off siberia and northern Europe are even wider. Water depth over a continental shelf tends to increase regularly away from land, with the outer edge of the shelf being about 100 to 200 meters below sea level.

OCEAN-INTRODUCTION !

The oceans, which began to be scientifically explored 200 years ago,hold the key to how the Earth works. For example, the ocean’s sediments provide a record of climatic signals over the last 200 million years. Although our improving knowledge of the oceans has revolutionised our understanding of the planet as a whole (the best example being the sea-going expeditions after World War 2, which led to the theory of plate tectonics in the late 1960s) much more remains to be discovered – not only in the use of oceans to the benefit of humankind and the environment, but also in mitigating hazards around the continental margins. About 21% of the world’s population, 1147 million people, live within 30km of a coastline. Within the framework of plate tectonics, the birth of a new ocean spreading centre often involves the rupturing of a continent and this leads to the production of a pair of rifted continental margins (like opposing sides of the Atlantic Ocean today). Ocean floor is generated continuously at the global system of spreading ridges, and the ocean crust moves away from the ridge. After its journey across the deep ocean basin, seafloor may disappear at an ocean trench, where the oceanic plate is subducted, often beneath a continent – as around the Pacific Ocean today. Therefore, most of the scientific questions of OCEAN are related to spreading ridges and continental margins, whether created by rifting (Atlantic) or subduction (Pacific).

The ocean cover nearly 71% of the earth's surface,but hemispherewise, the extent is 81% in the southern hemisphere and 61% in the northern. the average depth of the oceans is of the order of $ km though the deep trenches go down to a depth of more than 10km. atmosphere and oceanic process are inter connected. winds, waves and weather, are sun-powered and ther is profound interaction at the land-air and land-sea interfaces. the distribution and juxtaposition of the oceans and land masses have intimate relationship with the climatic pattern

How do the lithosphere, hydrosphere and biosphere interact at mid-ocean ridges, and what role did these interactions play in the origin of life on Earth?

Huge cracks in the Earth’s surface are formed when the tectonic plates that make up our planet’s outer shell move apart. These cracks run mostly through the ocean basins, forming a 60,000km globe-encircling volcanic system known as mid-ocean ridges. With only one exception (Iceland) this volcanic belt is completely hidden from view beneath two to four kilometres of ocean. Nevertheless, it is along these ridges that molten rock (“magma”) generated at depths between 20 to 80km within the Earth rises and erupts on the seafloor, slowly resurfacing vast areas of our planet as that seafloor spreads away from these ridges. The results are bizarre landscapes (strictly speaking, “bathyscapes”), of toxic hot springs and an abundance of life thriving independently of sunlight, all of which are constantly being remodeled by volcanic eruptions and earthquakes. This is an interesting and largely unknown part of our planet for sure, but how important is this volcanic activity and the life it supports to the world as a whole? What part does it play, for example, in the production of mineral deposits, in controlling the chemical composition of the oceans, in the deep-sea food chain, and in the origin of life? In view of the enormous length of the ridges and their relative inaccessibility, answering these questions has required - and still requires - a global, coordinated international scientific collaboration.

Science programme A panel of 20 eminent geoscientists from all parts of the world decided on a list of nine broad science themes -Groundwater, Hazards,Earth& Health, Climate, Resources, Megacities,Deep Earth, Ocean, and Soils.The next step is to identify substantive science topics with clear deliverables within each broad theme.A ‘key-text’ team has now been set up for each, tasked with working out an Action Plan. Each tea will produce a text that will be published as a theme prospectus like this one. A series of Implementation Groups will then be created to set the work under the nine programmes in motion. Every effort will be made to involve specialists from countries with particular interest in (and need for) these programmes. Mid-ocean ridges are the site of the most active volcanism and frequent earthquakes on our planet

Recent effort has shown just how important the ridges are for the deep ocean and potentially for humankind. The energy released by the cooling volcanic rock at the ridges is equal to about half of what is generated by the human race through burning fossil fuels and from nuclear power. At present this energy dissipates on and near the seafloor, driving the circulation of vast amounts of seawater through the oceanic crust. The output of this circulation is hot (up to 400°C) and acidic hydrothermal fluids, which carry dissolved metals and are laden with dissolved gases such as methane and hydrogen sulphide. When they vent on the seafloor, reactions between the hot, metalladen vent fluids and the surrounding cold deep-sea water lead to the precipitation of metal sulphides, a reaction that has generated some of the largest metal ore bodies on Earth. Hot, sulphide and metal-laden fluids do not sound like the ideal place for life to thrive, but it is precisely around these vents that the highest concentrations of biomass in the deep sea are found. The animals found at the hydrothermal vents are often quite strange by our standards, including giant worms without guts that feed by relying on bacteria in their tissues that in turn harness the energy from the normally toxic chemical, hydrogen sulphide.

These and numerous other unique vent animals have much to teach us about how they can withstand, and even flourish in, the dynamic and hostile environment they inhabit. Furthermore, the microbes found in hydrothermal vents can live in even more extreme environments, and we have just begun to explore the enormous diversity of metabolic pathways (chains of biochemical reactions) found in bugs both above and below the seafloor. We already know that some can live at temperatures greater than any other form of life on the planet can tolerate, and in fact many scientists believe that it was in places like this that life first evolved on Earth. Mid-ocean ridges are the site of the most active volcanism and frequent earthquakes on our planet.

As such they provide a unique natural laboratory for long-term monitoring of the interaction between submarine volcanoes, earthquakes, and changes in physical conditions in the deep ocean. For example, recent studies have indicated that moderate-sized earthquakes along the oceanic transform faults (which offset the spreading ridges) appear to be associated with much higher numbers of foreshocks but lower numbers of aftershocks in comparison to continental counterparts. Moreover, changes in ocean tides appear to have triggered seismicity in the vicinity of submarine volcanoes. New knowledge obtained from studying the way the rocky shell of the Earth (lithosphere) interacts with the hydrosphere in the mid-ocean ridge volcanic-tectonic system has important implications for applied research and the forecasting of volcanic and earthquake hazards on land. Volcanic, tectonic, and hydrothermal processes at mid-ocean ridges also control the chemical composition of the Earth’s oceanic lithosphere (the rocks that form the ocean floor) and the landscape of the vast abyssal plains.

Beneath fast-spreading ridges, such as the East Pacific Rise, a steady-state lens of magma is often imaged, providing molten rock for the relatively frequent intrusion of magma sheets (dykes) and for the seafloor eruption events that they feed. The magma lens also supplies heat to drive hot-water (hydrothermal) circulation in the ocean crust. At the slow and ultraslow ridges, such as the Mid-Atlantic Ridge and the Gakkel Ridge under the Arctic Ocean, however, magmatic events are much less frequent and the tectonic extension of the lithosphere by faulting is a significant component of seafloor spreading. We are only at the early stage of understanding what controls the cycles of magmatic/tectonic events at mid-ocean ridges. Mid-ocean ridges and hotspots, such as Iceland, the Azores, and Galapagos islands, exhibit the greatest flow of heat from the Earth’s mantle to the bottom of the oceans. The effects of such hotspots are manifested by shallowing and even emergence of the ocean floor (the two most dramatic cases being Hawaii in the Pacific ocean basin and Iceland at the Mid-Atlantic Ridge), increases in the thickness of the oceanic crust, changes in the style and intensity of seafloor volcanism, and evolving geometry of the seafloor spreading centres. When a hotspot interacts with a mid-ocean ridge spreading centre, the lava that erupts on the ocean floor (and on the hotspot islands) also contains important information on the chemical composition of Earth’s mantle.

However, we do not yet know whether most of the hotspots found on the ocean basins have deep roots inside Earth’s lower mantle, or are caused by anomalies in Earth’s upper mantle.

PORTO NOVO MARINE

Porto Novo, perched atop a hill overlooking the Bay of Bengal, is 34 km south of Cuddalore and is known as ‘Parangipettai’ in Tamil meaning ‘European village’.

Porto Novo was occupied by the Portuguese, Dutch and British successively during the colonial period. Under the European rule, Porto Novo emerged as an important harbor and major trade center with industries like ship building and fishing. The first iron foundry in Asia was built here. The place is associated with the second war of Mysore. Except for a flag mast and plaque, all other remnants of the colonial rule have disappeared and today, it is a fishing village.

Porto Novo is a major pilgrim center of Muslims. Saint Malumiyar, Araikasu Nachiyar, Hafiz Mir Sahib and Sayed Saheb are the famous dargahs situated here. The Centre for Advanced Studies in Marine Biology of Annamalai University is located here and its Marine Biology Museum is worth a peep.

The temple town of Chidambaram is nearby. Pichavaram, Poompuhar and Neyveli are the nearby places of tourist interest. Pondicherry is 60 km away.

Nearest airport is at Chennai. Parangipettai Railway Station is on the Chidambaram - Viluppuram rail route of Southern Railways. The National Highway 7A connects Porto Novo to Tuticorin port. Tamil Nadu State Transport Coorporation buses ply from Porto Novo to nearby towns.