Approximately 70.8 percent of the terrestrial surface is covered by saltwater oceans, with a volume of about 1.4 billion cubic kilometers.

The oceans contain about 97 percent of the planet’s water budget. The remaining 3 percent occurs as fresh waters, three-quarters of which are locked up in the form of ice at polar latitudes. Most of the remaining fresh water is groundwater held in soils and rocks; less than 1 percent of it occurs in lakes and rivers.

In terms of percentage, atmospheric water vapour is negligible, but the transport of water evaporated from the oceans onto land surfaces is an integral part of the hydrological cycle.

 

 

The average depth of sea is 3790 m, compared with average elevation of land i.e. 875 m.

Hydrological cycle

The hydrological cycle involves the transfer of water from the oceans through the atmosphere to the continents and back to the oceans over and beneath the land surface. The cycle involves processes such as evaporation, transpiration, precipitation, infiltration, percolation, and runoff. These processes operate throughout the entire hydrosphere, which extends from about 15 kilometers into the atmosphere to roughly 5 kilometers into the crust.

About one-third of the solar energy that reaches the surface of the Earth is expended on evaporating ocean water. The resulting atmospheric moisture and humidity condense into clouds, rain, snow, and dew. Moisture is a crucial factor in determining weather. It is the driving force behind storms and is responsible for separating electrical charge, which is the cause of lightning. Moisture wets the land, replenishes subterranean aquifers, chemically weathers the rocks, erodes the landscape, nourishes life, and fills the rivers, which carry dissolved chemicals and sediments back into the oceans. For example, water plays a vital role in the carbon dioxide cycle. Calcium is weathered from continental rocks and is then returned to the oceans, where it combines to form calcium carbonates (such minerals constitute the shells of marine life). Eventually the carbonates are deposited on the seafloor and are lithified to form limestones. Some of these carbonate rocks are later dragged deep into the Earth’s interior and melted, resulting in a release of carbon dioxide (from volcanoes, for example) into the atmosphere. Cyclical processing of water, carbon dioxide, and oxygen through physical and biological systems on the Earth is fundamental to maintaining balance in the ecosphere.

Oceans

Earth is covered by one hydrosphere or one layer of connecting water. Even though the ocean is broken up into seven ocean parts, all the oceans are connected, one flowing into the other[1]. The Pacific Ocean, covering 64,186,000 square miles, is nearly as large as the Atlantic and Indian Oceans combined. It contains a little more than half of all the water in the world's oceans.

AREAS AND DEPTHS OF OCEANS
OCEAN	AREA (000’sq KM)	%  of water	DEPTH (meters)		LOCATION (maximum depth)
			Mean	Maximum
Pacific Ocean	179679	50	4028	11776	Mariana Trench
Atlantic Ocean	92544	25	3926	9460	Puerto Rico Trench
Indian Ocean	74917	21	3897	7725.	Java Trench
Arctic Ocean	13919	04	1205	5449	Nansen’s Trough
World Ocean	361059	100	3795	11776	-

Types of Coasts

Coastlines may be of two types – coastlines of submergence which have formed due to sinking of land or rise in sea levels; and coastlines of emergence which have formed due to uplift of the land or fall in sea levels.

Coastlines of Submergence

Fjord coasts- Fjords are submerged glacial U-shaped valleys marked by steep walls. Due to greater intensity of ice erosion, fjords are deeper inlands and become shallower as one approaches the sea. They are found in the temperate regions of the world and are very prominent in Scandinavia, Alaska and South America.

Ria coasts- In upland coastal regions where the mountain chains run at right angles to the sea, ria coasts were formed when the sea levels rose following end of ice age and sea waters submerged these valleys.

A ria coast differs from fjords in two aspects. First, they are not glaciated and second, there depth increases seawards.

Dalmatian coasts- Dalmatian coasts were formed when the mountain valleys which run parallel to the coastline are submerged following the rise in sea levels after end of ice age. These are longitudinal coastlines where former mountain systems rise above surface as series of islands.

Estuarine coasts- In submerged lowlands, the mouths of rivers are drowned in the sea so as to give rise to estuaries. These estuaries being de-silted by tidal action often serve as good ports.

It is to be noted that despite being deep sheltered coastlines, Ria, Fjords and Dalmatian coasts do not form good ports as the mountains in the background hinder communication with the mainland.

Coastlines of Emergence

Emergent upland coast- Faulting and movements along the coastline often thrust the coastal lands upwards thereby leading to formation of emergent upland coasts. The western coast of Indian peninsula is such emergent coast.

Uplifted lowland coast- such coasts are formed when the continental shelf gets uplifted and smooth gently sloping coastline is formed.

Relief Features of Ocean floor

Like the continents, oceans floors too have relief features, which can be broadly divided into five zones: (i) Continental shelves (ii) Continental slopes and (iii) Deep Oceans Basins or Floors (iv) The Ocean Deeps (v) Submarine Canyons.

Continental Shelf

The portions of the land, which are submerged under seawater, constitute continental shelf. The continental shelf is shallow and its depth is not more than 200 meters. Its slope from the land to the sea is about 2 meters per km. The breadth of the continental shelf is not the same everywhere. The maximum breadth is almost equal to 1,100 km. found between Northern Norway and Novaya Zemlya along Berings Sea. The area of continental shelf is maximum in Asia, i.e. 9.38x10⁶ sq. km. The second place is occupied by North America (6.74x10⁶ square km.). The smallest shelf, i.e., 0.36x10⁶ square km. is found in Antarctica. Areas of the shelf are composed of hard rocks. Mud, sand and glacial deposits are also found at many places. Glacial deposits are found on the continental shelf in New England and Canada. Many drumlins rise above sea surface and appear as islands.

Types of Continental Shelves

i.          Glacier shelves

ii.         Broad river shelves

iii.        Coral shelves.

Hydrosphere
	Extent	Nature
Continental shelf	Usually 150-200 metres deep. Average width 70 kms, Mean slope < 1o About 7.5% of the total area of the oceans is covered by it.	Exclusive store house of marine food. Most of the petroleum and natural gas found here.
Continental slope	Steep slope descends to about 3660 metres from the mean sea level, mean slope varies between 2o to 5o	Since the slope is steep, not much of marine sediments are found here. Productivity less than continental shelf as light fails to penetrate the depths.
Continental rise	The average slope is low (0.5o to 1o). The general Relief is low	This marks the edge of the Continental Blocks as they rise from the ocean floor. The productivity of the region still less as compared to proceeding features.
Abyssal plains	Found at an average depth of 3,000 to 6,000 metres. These are deep sea plains carrying most of the deep-sea deposits.	The Abyssal Plains has in it feature such as, Seamount guyots, Mid Oceanic Ridges. Deep sea trenches.

Continental Slope

At the outer edge of the continental shelf, the slope suddenly steepens. This is found to be 35 to 61 meters per km. One end of the slope connects it with continental shelf while the other one merges into the ocean floors. The area occupied by continental slope is 8.5% of the total ocean area. The continental slope consists of light continental rocks, which overlie the dense rocks of ocean floors. Hence, no deposit of the coast except some fine mud reaches the continental slope.

Deep Ocean Basins or Floors

About 2/3 of ocean surface is occupied by deep ocean basins or floors. They are situated on the base of the continental slope. The depth varies from 3,000 to 6,000 meters. Many long zigzag rides, plateaus, volcanic summits, etc., exist on the basin. Many mountain tops rise steeply from the ocean floors and emerge out of sea as islands. Such mountain tops are found in Indonesia and in Pacific Ocean. Many pelagic deposits and oozes are found on the basins.

The Ocean Deeps

A depression, long and narrow, existing on the deep ocean basins are called ocean deeps. The deeps are also called trenches or troughs. Sometimes their name suggests that the trenches have a steep slope. In fact, their slope is nowhere more than 7% Due to the nonexistence of sediments, the deeps are almost empty.

Mid-Oceanic Ridges or Submarine Ridges

A mid-oceanic ridge is composed of two chains of mountains separated by a large depression. [Divergent Boundary].The mountain ranges can have peaks as high as 2,500 m and some even reach above the ocean’s surface. Running for a total length of 75,000 km, these ridges form the largest mountain systems on earth. These ridges are either broad, like a plateau, gently sloping or in the form of steep-sided narrow mountains. These oceanic ridge systems are of tectonic origin and provide evidence in support of the theory of Plate Tectonics. Iceland is a part of the mid-Atlantic Ridge

The Ocean Deposits

There are four sources of ocean deposits. They are

(1)        Terrigenous sediments: These deposits are obtained from erosion of rocks on land and are subdivided into the four subheadings:

i.          Due to the work of rivers

ii.         Due to the work of sea waves and currents.

iii.        Due to the work of winds.

iv.        Due to the work of glaciers.

The final destination of the sediment produced in these ways is mostly the seas and the oceans. They are also known as muds.

(2)        Pelagic Sediments: These sediments are found on the floors of deep seas and oceans. Their origin is the marine vegetation and animal life. The sediments consist of shells and skeletons of marine vegetation and animals. They are also known as oozes.

(3)       Sediment from Sub-Marine Volcanoes: The volcanoes submerged under the sea explode out volcanic material. This material is also very helpful in the formation of oceanic sediments. The ash of volcanic material ejected on the land also reaches the sea. They are also known as clays.

(4)        Extra Terrestrial Sediment: Meteors and their ash falling on the earth also form a part of oceanic sediments.

Salinity of Oceans

Salt in the ocean comes from rocks on land eroded by rivers; and hydrothermal vents at Oceanic floor and through minerals dissolved in volcanic eruptions inside oceans. Two of the most prevalant ions in seawater are sodium(77%) and chloride(13%). Together, they make up over 90 percent of all dissolved ions in the ocean. Sodium and Chloride are 'salty.'

The concentration of salt in seawater (salinity) is about 35 parts per thousand or 35 grams per 1000 grams, on average. Stated in another way, about 3.5 percent of the weight of seawater comes from the dissolved salts.

By some estimates, if the salt in the ocean 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-story office building.

Factors affecting salinity of Oceans

The salinity of the ocean varies from place to place, especially at the surface. Much of the ocean has salinity between 34ppt and 36ppt, but there are places that tend to be higher or lower. This is so because salinity varies depending on several factors

1. Evaporation and Precipitation - The salinity of water in the surface layer of oceans depend mainly on evaporation and precipitation. Areas with high evaporation tend to have higher salinity as fresh water evaporates leaving the salts behind and those with lower rate of evaporation have lower salinity (like the Polar areas). Similarly areas having high precipitation tend to have lower salinity due to addition of fresh water by rains. For example the equatorial areas tend to have lower salinity.

2. Influx of fresh water from rivers and land based glaciers - Generally polar areas tend to have lower salinity as a lot of fresh water is added by Land based Glaciers thereby lowering the Salinity. Similarly water bodies which are fed by large rivers tend to have lower salinity. For example Bay of Bengal has lower salinity than Arabian Sea as it is fed by large rivers like Ganga, Brahmaputra, Godavari, Mahanadi, Krishna, Cauvery, Irrawaddy etc.

3. Degree of intermixing with other Seas/Oceans - Generally Partially or wholly enclosed seas if not fed by large rivers or glaciers tend to have a higher salinity as compared to open seas. This is so because the water there evaporates thereby increasing the Salinity and the water does not mix with other ocean waters which can neutralize the high salinity. For example Red Sea has high salinity.

4. Intermixing by Winds and Ocean Currents - Winds and Ocean Currents also transport water from one place to other and affect the salinity of Oceans. For example North Sea has high salinity despite lying in high latitudes due to presence of saline water brought by North Atlantic Drift.

Temperature of ocean water

There are three layers in the oceans from surface to the bottom in the tropics viz.:

(i) The first layer represents the top-layer of warm oceanic water and is 500m thick with temperature ranging between 20° and 25°C. This layer is present within the tropics throughout the year but it develops in mid-latitudes only during summer,

(ii) The Thermocline layer represents vertical zone of oceanic water below the first layer and is characterized by rapid rate of decrease of temperature with increasing depth

(iii) The third layer is very cold and extends upto the deep ocean floor.

The polar areas have only one layer of cold water from the surface (sea-level) to the deep ocean floor.

The major source of the temperature of the oceanic water is the sun. Though negligible, some of the heat is also received from bottom of ocean floor from interiors of earth.

Factors affecting temperature of Ocean waters

1. Latitudes: The temperature of surface water decreases from equator towards the poles because the sun’s rays become more and more slanting and thus the amount of insolation decreases poleward accordingly.

2. Unequal distribution of land and water: The temperature of ocean water varies in the northern and the southern hemispheres because of dominance of land in the former and water in the latter. The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than their counter­parts in the southern hemisphere and thus the tempera­ture of surface water is comparatively higher in the former than the latter.

The isotherms are not regular and do not follow latitudes in the northern hemisphere because of the existence of both warm and cold land- masses whereas they (isotherms) are regular and follow latitudes in the southern hemisphere because of the dominance of water. The temperature in the enclosed seas in low latitudes becomes higher because of the influence of surrounding land areas than the open seas e.g., the average annual temperature of surface water at the equator is 26.7°C (80°F) whereas it is 37.8°C (100°F) in the Red Sea and 34.4°C (94°F) in the Persian Gulf.

3. Prevailing wind: Wind direction largely af­fects the distribution of temperature of ocean water. The winds blowing from the land towards the oceans and seas (e.g., offshore winds) drive warm surface water away from the coast resulting into upwelling of cold bottom water from below. Thus, the replacement of warm water by cold water introduces longitudinal variation in temperature. Contrary to this, the onshore winds pile up warm water near the coast and thus raise the temperature.

For example, trade winds cause low temperature (in the tropics along the eastern margins of the oceans or the western coastal regions of the conti­nents) because they blow from the land towards the oceans whereas these trade winds raise the tempera­ture in the western margins of the oceans or the eastern coastal areas of the continents because of their onshore position.

Similarly, the eastern margins of the oceans in the middle latitudes (western coasts of Europe and North America) have relatively higher temperature than the western margins of the oceans because of the onshore position of the westerlies.

4. Ocean currents: Surface temperatures of the oceans are controlled by warm and cold currents. Warm currents raise the temperature of the affected areas whereas cool currents lower down the temperature. For example, the Gulf Stream raises the temperature near the eastern coasts of N. America and the western coasts of Europe.

Kuro Shivo drives warm water away from the eastern coast of Asia and raises the temperature near Alaska. Labrador cool current lowers down the tem­perature near north-east coast of N. America. Similarly, the temperature of the eastern coast of Siberia becomes low due to Kurile cool current.

5. Other Minor factors:

(i) Submarine ridges spewing hot magma,

(ii) Local weather conditions like storms, cyclones, hurricanes, fog, cloudiness, evaporation and conden­sation, and

(iii) Location and shape of the sea - Longitudinally more extensive seas in the low latitudes have higher temperature than the latitudinally more extensive seas as the Mediterranean Sea records higher temperature than the Gulf of California.

The enclosed seas in the low latitudes record relatively higher temperature than the open seas whereas the enclosed seas have lower temperature than the open seas in the high latitudes (Baltic Sea records 0°C (32°F) and open seas have 4.4°C or 40°F).

TIDES

Tides are defined as slight oscillations of sea level that occur approximately twice a day and attain exaggerated proportion in marginal seas, straits and estuaries. The major cause of the tides is the gravitational pull of the moon and, to a lesser extent, of the sun, as it is further from the earth.

Lunar Tides

As the moon travels in its orbit in the same direction as the earth’s rotation, a period of 24 hours 50 minutes elapses between two successive occasions when the moon is vertically above a point. The highest level the water reaches is called a high tide and the lowest level is called the low tide. High and low tide occur twice each during the period of 24 hrs. 50 minutes, giving an interval of about 12-1\2 hours between successive high (or low) tides.

Neap and Spring Tides

When the earth, the moon and the sun are in a straight line, the gravitational force is at its greatest because tide-producing forces of both sun and moon complement each other and they ‘pull’ together. This produces tides of unusually great ranges, called the spring tides. These occur about twice a month; at new moon, when the sun and the moon are in conjunction: and at full moon, when they are in opposition.

When the earth, the moon and the sun are not in a straight line, but are at right angles to the earth, the gravitational force is less, as the sun and the moon are not pulling together. This happens during phases of first and third quarter, i.e. at half moon, the sun’s tide producing force tends to balance the tide producing force of the moon, resulting in tides of usually small range known as neap tides. Amplitude or tidal range refers to the difference between high tide and low tide; it is high at spring tides and low at neap tides.

Perigean and Apogean Tides

When the moon is nearest to the earth in its orbit (at perigee), its tide producing power is greater than average, resulting in perigean tides. These are 15-20 per cent greater than average. When the moon is farthest from the earth (in apogee), the tides are called apogean tides, which are about 15-20 per cent less than average. Coincidence of spring and perigean tides results in an abnormally great tidal range; while when neap and apogean tides coincide, the range is abnormally small.

River Tides

Tides are experienced in the lower parts of many of the great rivers. These are known as tidal rivers, where either the coastal area has recently subsided, or the ocean level rises, causing the lower part of the river to be drowned. River tides are distinguishable from ocean tides by one characteristic: the interval between high tide and the next low tide.

THE SEAS

With respect to their communication with the ocean the SEAS are classed into

(i)      Marginal (fringing) seas,

(ii)     Continental seas, or Mediterranean sea.

MARGINAL SEA

MARGINAL SEA is a semi-enclosed sea that borders a continent, and lies on a submerged portion of a continental mass, rather than within an ocean basin; for example: Sea of Okhotsk, Sea of Japan, Yellow Sea, Celebes Sea, Baltic Sea, North Sea, Red Sea, Persian Gulf.

The MARGINAL SEAS are characterized by a more or less free links with the oceans and, in a number of instances, are separated from it by a chain islands or by peninsulas.  A relatively unobstructed communication of Marginal seas with the oceans is a factor determining their mutual similarity with respect to the ‘salinity’, ‘temperature’, and the abundance of ‘organic life’.  They are swept by the ocean ‘tides’ and are subject to the influence of oceanic ‘currents’.  On the other hand, some Marginal seas have close ties with land and are under sway of its effects.  Among examples of this type of bodies are the Bering Sea, the sea of Okhotsk, the Japan Sea, the East China Sea, the South China Sea, the Caribbean Sea and other seas. 

PRINCIPAL SEAS
Sea	Area (inSq. km.)	Average depth(in meters)
South China Sea	2974600	1200
Caribbean Sea	2756000	2400
Mediterranean Sea	2503000	1485
Bering Sea	2268180	1400
Gulf of Mexico	1542985	1500
Sea of Okhotsk	1527570	840
East China Sea	1249150	180
Hudson Bay	1232300	120
Sea of Japan	1007500	1370
Andaman Sea	797700	865
North Sea	575300	90
Black Sea	461980	1100
Red Sea	437700	490
Baltic Sea	422160	55
Persian Gulf (Arabian Gulf)	238790	24
Gulf of St. Lawrence	237760	120
Gulf of California	162000	810
English Channel	89900	54
Irish Sea	88500	60
Bass Strait	75000	70

GULFS (BAYS) varying in their shape and size, indenting the land and broadly and freely communicating with the ocean,  such as the Bay of Biscay, the Gulf of Guinea, the Bay of Bengal, the Gulf of Alaska, are also set apart. Some seas for instance the Arabian Sea, may also be referred to as Gulfs.

CONTINENTAL SEA 

It is a partially enclosed sea, lying on or within a continent in the structural sense, linked with the open ocean through a narrow strait, for example Baltic Sea, Hudson Bay, Yellow Sea, Mediterranean Sea.

CONTINENTAL SEAS communicate with the ocean only through narrow and comparatively shallow straits.  They include MEDITERRANEAN SEA with an average depth of 1498 metres and maximum depth of 4594 metres and a strait near the Gibraltar (about 320 metres deep); the BLACK SEA with a mean depth of 1271 metres and a link to the Mediterranean through the Bosporus strait (46 m deep); the sea of azov (8-13 metres deep).

A completely closed basin is the Caspian sea, which at the end of Pleistocene had lost all connection with the Azov – Black Sea basin and, consequently, with the ocean. 

SEVEN SEAS

We have got only four oceans but SEVEN SEAS (especially in historical Tales).  The proverbial seven seas are made up by dividing the first three oceans into north and south along the Equator and adding Arctic to them, thus: (i) North Pacific, (ii) South Pacific, (iii)  North Atlantic, (iv) South Atlantic, (v) North Indian, (vi) South Indian and (vii) Arctic.

LIFE IN THE OCEAN

The living organisms of the ocean can be divided into three groups, according to ‘where’ and ‘how’ they live in the ocean.

• The lowest order group is called PLANKTON.  Plankton is made up of the ocean’s smallest-usually microscopic-plants and animals.  These tiny plants and animals float freely with the movements of ocean water, are true ‘drifters’, and form the basis for the oceanic food chain.
• The Second group is composed of the animals that swim in the water. This group is called NEKTONS and includes fish, sea mammals such as whales, and invertebrates such as the squid and octopus.
• The third group is the plants and animals that live near or on the ocean floor.  This group is called the BENTHOS.  It includes coral and such burrowing or crawling animals as the barnacle, crab, Lobster, and oyster, and plants such as seaweed.

CORALS

Coral Polyps – The living organism of the category of marine animals which are responsible for building coral reefs are called as coral polyps. Polyps are shallow water organisms which have a soft body covered by a calcareous skeleton. The polyps sequester calcium carbonate from sea water to form hard skeletons known as corallites or exoskeleton .The polyps live in colonies fastened to the rocky sea floor. Exoskeletons is the exterior skeleton of coral polyps or the house of the polyps. The corals build their own shell of calcium carbonate in which they are protected from predators.

Coral Reefs – The reefs of cemented and compact , rigid , massive structures of numerous corallites or Exoskeletons are called coral reefs .

Zooxanthella- Corals polyps live in a symbiotic relationship with single cell autotrophic algae known as Zooxanthella. Tissues of corals themselves are colourless; they receive their coloration from Zooxanthella living within them. They provide more than 60% of total food requirement of living corals and recycle the excreta and waste of corals. In return corals provide them shelter in their bodies .

Ideal Conditions for the formation of Coral Reefs

1.       Perpetually warm waters: Corals thrive in tropical waters where diurnal & annual temperature  ranges are very narrow.

2.       Shallow water: Coral require fairly good amount of sunlight to survive. Ideal depths for coral growth are 45 m to 55 m below sea surface, where there is abundant sunlight.

3.       Clear salt water: Clear salt water is suitable for coral growth, while both fresh water and highly saline water are harmful.

4.       Abundant Plankton: Adequate supply of oxygen and microscopic marine food, called plankton, is essential for growth.

5.       Little or no pollution: Corals are highly fragile and are vulnerable to climate change and pollution and even a minute increase in marine pollution can be catastrophic.

6.       No turbulence: turbulence in ocean waters due to storms, cyclones or river discharge is harmful for growth of corals.

Coral Bleaching

Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. Corals may also be stressed by temperature , light or nutrients .When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.

In the last two decades, the corals around the globe have been experiencing massive bleaching, wherein they lose their colours and turn pale / white as they are unable to support the algae within them because of changes in sea water temperatures (very high or very low), high solar irradiance (too much of light), lowering of nutrients and salinity due to too much of surface run-off or mixing of fresh water near the coast, overfishing, heavy storms or pollution (oil drilling/spilling, coral trading, chemicals in agriculture, marine activities).

Corals can survive without the algae for short periods and revert back to original health with the re-entrance of the algae once the sea conditions return to normal, but if the stress factors stay longer, the corals begin to starve and die. The coral reefs, eventually, collapse due to erosion. A healthy coral reef system can even resist coral bleaching, but increasing global warming and frequent episodes of bleaching weaken even the healthy reef systems.

Ocean currents

Fast-flowing current of seawater generated by the wind or by variations in water density and temperature[2] between two areas. Ocean currents are partly responsible for transferring heat from the Equator to the poles and thereby evening out the global heat imbalance.

There are three basic types of ocean current: drift currents are broad and slow-moving; stream currents are narrow and swift-moving; and upwelling currents bring cold, nutrient-rich water from the ocean bottom.

Stream currents include the Gulf Stream and the Japan (or Kuroshio) Current. Upwelling currents, such as the Gulf of Guinea Current and the Peru (Humboldt) current, provide food for plankton, which in turn supports fish and sea birds. At approximate five-to-eight-year intervals, the Peru Current that runs from the Antarctic up the West coast of South America, turns warm, with heavy rain and rough seas, and has disastrous results for Peruvian wildlife and for the anchovy industry. The phenomenon is called El Niño (Spanish `the Child´) because it occurs towards Christmas.

Pacific Ocean Currents

OCEAN CURRENTS
	Name of Current	Properties	Area/Ocean
1.	Gulf stream	Warm	Eastern coast of USA Atlantic ocean
2.	Kuroshio	Warm	Eastern coast of China & Japan/Pacific ocean
3.	All Equatorial	Warm	Equatorial regions currents
4.	Brazil current	Warm	Eastern coast of Brazil/S. Atlantic
5.	Florida current	Warm	Gulf of Mexico/Atlantic
6.	Guinea current	Warm	West African coast/Atlantic
7.	North Atlantic	Warm	Norway coast/N.
	drift		Atlantic ocean
8.	Canary current	Cold	N. Atlantic ocean
9.	Labrador current	Cold	Labrador sea & Dam’s Strait /N. Atlantic ocean
10.	Benguela current	Cold	S. West African coast Atlantic
11.	Falkland current	Cold	Near Falkland/S. Atlantic
12.	Peru or Humboldt current	Cold	West South American coast/ S. Pacific
13.	Kuril & Okhotsk	Cold	North Pacific ocean current
14.	East Australian	Warm	S. Pacific current
15.	California	Cold	N.E. Pacific
16.	Aleutian current	Warm	N.E. Pacific
17.	Antilles current	Warm	Caribbean Sea
18.	Renal current	Warm	Bay of Biscay/N. Atlantic
19.	Irminger current	Warm	Near Iceland/N. Atlantic
20.	East Greenland current	Cold	East coast of Greenland
21.	West wind drift	Cold	South oceans
Saragasso sea in middle of North Atlantic sea. Mozambique, Agulhas & West Australian currents are warm, in the south west Indian oceans. There is no counter equatorial current in Indian ocean

Winds in the northern Pacific produce generally clockwise currents; a northward current from the equator flows past the Philippines and is joined by currents from the East Indies and China Sea at Taiwan to form the Kuroshio. The Kuroshio Current, off the shores of Japan, is the largest current. It can travel between 25 and 75 miles a day, 1 - 3 miles per hour, and extends some 3300 feet deep. The Gulf Stream is close to this current's speed. A cold current from the Bering Sea enters the Okhotsk and Japan seas, causing freezing in winter. In the South Pacific the trade winds cause anticlockwise equatorial currents which branch opposite southern Chile, to flow north as the cooling Peru Current (Humboldt Current), and south round Cape Horn.

Atlantic Ocean Currents

The trade winds, which determine the course of the ocean currents, have their origin in high-pressure areas in the centre of both the North and South Atlantic. They produce a warm equatorial current which divides and flows south as the Brazil current, and north through the Caribbean Sea and Gulf of Mexico, emerging as the Gulf Stream or North Atlantic Drift, which has an enormous warming influence on the climate of northwest Europe. A cold current flows south from the Arctic Ocean and, as the Labrador current, passes beneath the Gulf Stream off the Newfoundland Grand Banks. Between 40º and 80º west, and 25º and 30º north, there is an area of calm occupied by the Sargasso Sea, in which float extensive banks of weed.

Indian Ocean Currents

The Mozambique and Agulhas currents are warm and move southwards; in the east, the colder Western Australian current crosses the Indian Ocean moving northwards. North of the equator the currents vary with the monsoon. From November to March, there are northeast winds and the current flows from the North-east as North East Monsoon Drift. From May to September, southwest winds reverse the current to flow as South West Monsoon Drift. This is the only example of an annual reversal of direction by a large oceanic current.

Arctic Ocean

The warm surface waters of the Atlantic flow up into the Arctic regions, passing between Greenland and Norway, where they are chilled by contact with the icy Arctic waters, and gradually sink to the bottom. Finally they return, along the east side of Greenland and down Davis Strait, as a cold current carrying with it the icebergs that are a danger to navigation in the Atlantic.

TSUNAMI

Tsunami Warning Systems

The word tsunami is derived from the Japanese composition - 'tsu' means 'harbor' and 'name' means 'wave'. A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, generally an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier cavings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.

Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train".

Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous and they can affect entire ocean basins; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with over 230,000 people killed in 14 countries bordering the Indian Ocean.

Classification

Based on the distance from the source and the travel time tsunamis are classified in to three types by UNESCO-IOC. They are:

Local Tsunami originates from a nearby source for which its destructive effects are confined to coasts within 100 km or less than 1 hour tsunami travel time from its source. These can often be the most dangerous because there is often little warning between the triggering event and the arrival of the tsunami.

Regional Tsunami is capable of creating destruction in a particular geographic region, generally within 1,000 km or 1-3 hours tsunami travel time from its source. Regional tsunamis occasionally have very limited and localized effects outside the region.

Distant Tsunami (also called an ocean-wide, distant, tele or far-field tsunami) is a tsunami that originates from a far away source, which is generally more than 1,000 km away from the area of interest or more than 3 hours tsunami travel time from its source. A distant tsunami is capable of causing widespread destruction, not only in the immediate region of its generation, but across an entire ocean.

Generation Mechanisms

The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to earthquakes, landslides, volcanic eruptions, glacier calving or more rarely by meteorites and nuclear tests. The waves formed in this way are then sustained by gravity. Tides do not play any part in the generation of tsunamis.

Seismicity

Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. 

Landslides

In the 1950s, it was discovered that larger tsunamis than had previously been believed to be caused by earthquakes could be caused by giant submarine landslides. These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb. 

Meteotsunamis

Some meteorological conditions, such as deep depressions that cause tropical cyclones and sudden fast moving weather systems can generate a storm surge, called a meteotsunami, which can raise tides several metres above normal levels..

Destruction

Tsunamis cause damage by two mechanisms: the smashing force of a wall of water traveling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris and material with it.

Tsunami Warning Systems

Tsunami warning systems exist in many places around the world. As scientists continuously monitor seismic activity (earthquakes), a series of buoys float off the coast and monitor changes in sea level. Unfortunately, since tsunamis are not very tall in height when they are out at sea, detection is not easy and there are many false alarms.

Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or cancelled. To provide the earliest possible alert, initial warnings are normally based only on seismic information.

Alert	Effect	Action
Warning	Inundating wave possible	Full evacuation suggested
Watch	Danger level not yet known	Stay alert for more info
Advisory	Strong currents likely	Stay away from the shore
Information	Minor waves at most	No action suggested

Ocean observing instruments used to detect tsunamis:

Tide Gauges- Tide gauges measure the height of the sea-surface and are primarily used for measuring tide levels.

The DART System- In 1995 the National Oceanic and Atmospheric Administration (NOAA) began developing the Deep-ocean Assessment and Reporting of Tsunamis (DART) system. An array of stations is currently deployed in the Pacific Ocean. These stations give detailed information about tsunamis while they are still far off shore. Each station consists of a sea-bed bottom pressure recorder which detects the passage of a tsunami.

Satellites- Satellite altimeters measure the height of the ocean surface directly by the use of electro-magnetic pulses. These are sent down to the ocean surface from the satellite and the height of the ocean surface can be determined by knowing the speed of the pulse, the location of the satellite and measuring the time that the pulse takes to return to the satellite.

ITEWS- Indian Tsunami Early Warning System. The system implemented in phases became full-fledged 24X7 operational early warning systems at the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, under the Earth System Sciences Organization (ESSO), Govt. of India in October 2007.

The Indian Tsunami Early Warning System has the responsibility to provide tsunami advisories to Indian Mainland and the Island regions. Acting as one of the Regional Tsunami Advisory service Providers (RTSPs) for the Indian Ocean Region, ITEWS also provide tsunami advisories to the Indian Ocean rim countries along with Australia & Indonesia

The Tsunami Early Warning System comprises a real-time network of seismic stations, Bottom Pressure Recorders (BPR), tide gauges and 24 X 7 operational warning center to detect tsunamigenic earthquakes, to monitor tsunamis and to provide timely advisories following the Standard Operating Procedure (SOP), to vulnerable community by means of latest communication methods with back-end support of a pre-run model scenario database and Decision Support System (DSS).

The Warning Centre is capable of issuing Tsunami bulletins in less than 10 minutes after any major earthquake in the Indian Ocean thus leaving us with a response/lead time of about 10-20 minutes for near source regions in the Andaman & Nicobar and a few hours in the case of mainland.

Marine Pollution

Marine pollution refers to degradation of marine water due to galaxy of factors like

Discharge from Land :-

Urban Sewage -  Pollution can enter the ocean directly. Sewage or polluting substances flow through sewage, rivers, or drainages directly into the ocean. This is often how minerals and substances from mining camps find their way into the ocean. The release of other chemical nutrients into the ocean’s ecosystem leads to reductions in oxygen levels, the decay of plant life, a severe decline in the quality of the sea water

Industrial Discharge :- Pollutants enter rivers and the sea directly from urban sewerage and industrial waste discharges, sometimes in the form of hazardous and toxic wastes. Inland mining for copper, gold. etc., is another source of marine pollution. Most of the pollution is simply soil, which ends up in rivers flowing to the sea. However, some minerals discharged in the course of the mining can cause problems, such as copper, a common industrial pollutant, which can interfere with the life history and development of coral polyps . Recent studies show that degradation, particularly of shoreline areas that is Neretic province , has accelerated dramatically in the past three centuries as industrial discharge and runoff from farms and coastal cities has increased. Minamata - This highly toxic mercury  bioaccumulated in shellfish and fish in Minamata Bay and the Shiranui Sea, which, when eaten by the local populace, resulted in mercury poisoning .

Polluted runoff from roads and highways can be a significant source of water pollution in coastal areas. About 75% of the toxic chemicals that flow into Puget Sound are carried by stormwater that runs off paved roads and driveways, rooftops, yards and other developed land .

Agricultural Run off :- rivers that empty into the ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. An excess of oxygen depleting chemicals in the water can lead to hypoxia and the creation of a dead zone . Rivers and Streams bring with them the typically compounds containing nitrogen or phosphorus , causing Eutrophication – and algae Bloom which causes lack of oxygen and severe reductions in water quality, fish, and other animal populations.

2.  Pollution caused by the ship -

a. Ships can pollute waterways and oceans in many ways. Oil spills can have devastating effects on marine ecosystem .and is very difficult to clean up, and last for years in the sediment and marine environment. Eg Mumbai high 1982 incident .  Recent Chennai oil spill .

b. Discharge of cargo residues from bulk carriers can pollute ports, waterways and oceans. In many instances vessels intentionally discharge illegal wastes despite foreign and domestic regulation prohibiting such actions. It has been estimated that container ships lose over 10,000 containers at sea each year (usually during storms

c. Ballast water taken up at sea and released in port is a major source of unwanted exotic marine life. The invasive freshwater zebra mussels, native to the Black, Caspian and Azov seas, were probably transported to the Great Lakes via ballast water from a transoceanic vessel. Invasive species can take over once occupied areas, facilitate the spread of new diseases, introduce new genetic material, alter underwater seascapes and jeopardize the ability of native species to obtain food. Invasive species are responsible for about $138 billion annually in lost revenue and management costs in the US alone and unaccounted biodiversity loss.

d. The increased presence of loud or persistent sounds from ships, sonar devices, oil rigs, and even from natural sources like earthquakes can disrupt the migration, communication, hunting, and reproduction patterns of many marine animals, particularly aquatic mammals like whales and dolphins.

Atmospheric Pollution :- Climate change is raising ocean temperatures and raising levels of carbon dioxide in the atmosphere. These rising levels of carbon dioxide are acidifying the oceans. This, in turn, is altering aquatic ecosystems and modifying fish distributions, with impacts on the sustainability of fisheries and the livelihoods of the communities that depend on them. Healthy ocean ecosystems are also important for the mitigation of climate change .

Littering - Solid waste like bags, foam, and other items dumped into the oceans from land or by ships at sea are frequently consumed, with often fatal effects, by marine mammals, fish, and birds that mistake it for food. Discarded fishing nets drift for years, ensnaring fish and mammals. In certain regions, ocean currents corral trillions of decomposing plastic items and other trash into gigantic, swirling garbage patches. One in the North Pacific, known as the Pacific Trash Vortex, is estimated to be the size of Texas. A new, massive patch was discovered in the Atlantic Ocean in early 2010.

Deep sea mining is a relatively new mineral retrieval process that takes place on the ocean floor. Ocean mining sites are usually around large areas of polymetallic nodules . deep sea mining raises questions about environmental damages to the surrounding areas removal of parts of the sea floor will result in disturbances to the benthic layer, increased toxicity of the water column .

Consequences of Ocean Pollution -

1. Effect of Toxic Wastes on Marine Animals: Oil spill is dangerous to marine life in several ways. The oil spilled in the ocean could get on to the gills and feathers of marine animals, which makes it difficult for them to move or fly properly or feed their children. The long-term effect on marine life can include cancer, failure in the reproductive system, behavioural changes, and even death.

2. Disruption to the Cycle of Coral Reefs: Oil spill floats on the surface of water and prevents sunlight from reaching to marine plants and affects in the process of photosynthesis. Skin irritation, eye irritation, lung and liver problems can impact marine life over long period of time.

3: Depletes Oxygen Content in Water: Most of the debris in the ocean does not decompose and remain in the ocean for years. It uses oxygen as it degrades. As a result of this, oxygen levels go down. When oxygen levels go down, the chances of survival of marine animals like whales, turtles, sharks, dolphins, penguins for long time also go down.

4: Failure in the Reproductive System of Sea Animals: Industrial and agricultural wastes include various poisonous chemicals that are considered hazardous for marine life. Chemicals from pesticides can accumulate in the fatty tissue of animals, leading to failure in their reproductive system.

5: Effect on Food Chain: Chemicals used in industries and agriculture get washed into the rivers and from there are carried into the oceans. These chemicals do not get dissolved and sink at the bottom of the ocean. Small animals ingest these chemicals and are later eaten by large animals, which then affects the whole food chain.

6. Affects Human Health: Animals from impacted food chain are then eaten by humans which affects their health as toxins from these contaminated animals gets deposited in the tissues of people and can lead to cancer, birth defects or long term health problems.

 

United Nation Convention on Law of Seas (UNCLOS)

UNCLOS replaces the older 'freedom of the seas' concept, dating from the 17th century: national rights were limited to a specified belt of water extending from a nation's coastlines .

The issue of varying claims of territorial waters was raised in the UN in 1967 and in 1973 the Third United Nations Conference on the Law of the Sea was convened in New York. In an attempt to reduce the possibility of groups of nation-states dominating the negotiations, the conference used a consensus process rather than majority vote. With more than 160 nations participating, the conference lasted until 1982. The resulting convention came into force in 1994 . The convention introduced a number of provisions. The most significant issues covered were setting limits, navigation, archipelagic status and transit regimes, exclusive economic zones (EEZs), continental shelf jurisdiction, deep seabed mining, the exploitation regime, protection of the marine environment, scientific research, and settlement of disputes.

Internal waters

Covers all water and waterways on the landward side of the baseline . The coastal state is free to set laws, regulate use, and use any resource. Foreign vessels have no right of passage within internal waters.

Territorial waters

Out to 12 nautical miles (22 kilometres; 14 miles) from the baseline, the coastal state is free to set laws, regulate use, and use any resource. Vessels were given the right of innocent passage through any territorial waters .Fishing, polluting, weapons practice, and spying are not "innocent", and submarines and other underwater vehicles are required to navigate on the surface and to show their flag. Nations can also temporarily suspend innocent passage in specific areas of their territorial seas, if doing so is essential for the protection of its security.

Contiguous zone

Beyond the 12-nautical-mile (22 km) limit, there is a further 12 nautical miles (22 km) from the territorial sea baseline limit, the contiguous zone, in which a state can continue to enforce laws in four specific areas: customs, taxation, immigration and pollution, if the infringement started within the state's territory or territorial waters, or if this infringement is about to occur within the state's territory or territorial waters . This makes the contiguous zone a hot pursuit area.

Exclusive economic zones (EEZs)

These extend from the edge of the territorial sea out to 200 nautical miles (370 kilometres; 230 miles) from the baseline. Within this area, the coastal nation has sole exploitation rights over all natural resources. In casual use, the term may include the territorial sea and even the continental shelf. The EEZs were introduced to halt the increasingly heated clashes over fishing rights, although oil was also becoming important. The success of an offshore oil platform in the Gulf of Mexico in 1947 was soon repeated elsewhere in the world, and by 1970 it was technically feasible to operate in waters 4,000 metres deep. Foreign nations have the freedom of navigation and overflight, subject to the regulation of the coastal states. Foreign states may also lay submarine pipes and cables.

High Sea :

The Oceans beyond the limit of continental shelf . All countries have equal rights of navigation , aviation , flying , mining , research and exploration .

Aside from its provisions defining ocean boundaries the convention establishes general obligation for safeguarding the marine environment and protecting the freedom of scientific research on the high seas and also creates a legal regime for controlling mineral resources exploration in deep sea bed areas through an International Sea Bed Authority  , ISA , and “the common heritage of mankind” principle .

Lakes

In simplest terms lakes can be defined as the hollows on the earth surface in which water accumulates. They vary a great deal in their shapes, sizes, depth and the mode of formation.

Some lakes being consistently fed by fresh water streams or rivers and also having outlet streams are fresh water lakes. On the other hand lakes which form a part of Endorheic or Inland drainage basin are saline lakes. Also, lakes are only a temporary feature of earth’s crust as they will eventually be eliminated by the twin process of draining and silting up.

Types of lakes

Lakes can be of several types depending on their modes of formation.

There are tectonic lakes and rift valley lakes formed by tectonic movements beneath the earth’s crust that give rise to depressions on earth’s surface. The rift valley lakes like Tanganyika, Malawi etc. and tectonic depressions like Caspian sea, Titicaca lake are few examples.

Glaciation also produces lakes. The most common ones are cirque or corrie  lakes and the lakes formed in the drumlin depressions. Apart from these there are lakes formed by valleys being dammed by moraines carried by glaciers. Such lakes formed by glacial actions are very common in North and North West Europe.

Lakes can also be formed by volcanic activity. Crater or caldera lakes like Lake Toba in Sumatra are very common at the mouths of large volcanic cones. Similarly at times a stream of lava may solidify and block the flow of a river forming Lava Blocked Lakes like the Sea of Galilee.

Erosion of earth’s surface may also produce hollows which if occupied by water can form lakes. Depressions formed in the limestone regions by the solution of calcium carbonate by water are very common. Such depressions form lakes called poljes. Similarly wind deflated hollows in the arid regions may get transformed into salt lakes or oasis.

Lakes can also be formed by the deposition action of rivers, winds or ocean waves. Ox-bow lakes[3] are very common among the mature stages of a river. Similarly wave action may produce bars and spits that may cut off a bay to produce lagoons.

Apart from these there are lakes made by animals like the beaver lakes in USA and a series of man-made lakes made by human beings.

Role of lakes in human life

Lakes have immense significance for human beings as they satisfy a series of their needs.

• Lakes provide a wide range of foods and minerals.
• Lakes are a crucial source for regulating river flows. They absorb excess waters during heavy rains to prevent downstream flooding. Also lakes absorb excessive sediment load from rivers thereby enhancing their flow capacity.
• Large lakes like the Great Lakes have a moderating effect on the climate of the region.
• Lakes are used as a reservoir of water which then can be used for a variety of purposes like power generation, irrigation etc.
• Lakes, especially those connected to the large rivers are an effective means of transport and have acted as a main agent of economic development in several regions. The Great Lakes are the best example of this.

MAN MADE LAKES

WORLD’S GREATEST MAN MADE LAKES
Name of dam	Location	Million cubic metres	Year completed
Owen Falls	Uganda	204,800	1954
Kariba	Zimbabwe	181,592	1959
Bratsk	USSR (now CIS)	169,270	1964
High Aswan (Saddel Ali)	Egypt	168,000	1970
Akosombo	Ghana	148,000	1965
Daniel Johnson	Canada	141,851	1968
Guri (Raul Leoni)	Venezuela	136,000	1986
Krasnoyarsk	USSR (Now CIS)	73,300	1967
Bannet W.A.C.	Canada	70,309	1967
Zeya	USSR (Now CIS)	68,400	1978
Cabora Bassa	Mozambique	63,000	1974
La Grande 2	Canada	61,720	1982
La Grande 3	Canada	60,020	1982
Ust-illmsk	USSR (Now CIS)	59,300	1980
Volga-V.I. Lenin	USSR (Now CIS)	58,000	1955
Caniapiscau	Canada	53,790	1981
Pati (Chapeton)	Argentina	53,700	-
Upper Waingana	India	50,700	-
Sao Felix	Brazil	50,600	-
Bukhtarma	USSR (now CIS)	49,740	1960
Ataturk (Karababa)	Turkey	48,000	-
Cerros Colorados	Argentina	48,000	1973
Irkutsk	USSR (now CIS)	46,000	1956
Tucurul	Brazil	36,375	1984
Vilyuy	USSR (now CIS)	35,900	1967
Sanmenxia	China	35,400	1960
Hoover	Nevada / Arizona	35,154	1936
Sobridinho	Brazil	34,200	1981
Glen Canyon	Arizona	33,304	1964

Natural lakes

LARGE LAKES OF THE WORLDS
Name of location	Area in sq.km	Length sq.km	Max depth in mts.
Caspian Sea, CIS-Iran	394,299	1,199	946
Superior, USA-Canada	82,414	616	406
Victoria, Tanzania-Uganda	69,485	322	82
Aral, USSR (now CIS)	66,457	428	68
Huron, USA-Canada	59,596	397	229
Michigan, USA	58,016	517	281
Tanganyika, Tanzania- Zaire	32,893	676	1,435
Baikal, CIS	31,500	636	1,741
Great Bear, Canada	31,080	373	82
Nyasa, Malawi- Mozambique Tanzania	30,044	579	706