The module has been written with the following objectives:

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Environmental Sciences

Environmental Geology Oceanography

Paper No: 04 Environmental Geology Module: 31 Oceanography

Development Team

Principal Investigator

&

Co- Principal Investigator

Prof. R.K. Kohli

Prof. V.K. Garg & Prof. Ashok Dhawan Central University of Punjab, Bathinda

Paper Coordinator Prof. R. Baskar, , Guru Jambheshwar University of Science and Technology, Hisar

Content Writer

Onkar S. Chauhan

Indian Science Congresses Association, Goa

Content Reviewer Dr. Sushmitha Baskar, SOITS, IGNOU, New Delhi

Anchor Institute Central University of Punjab

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Description of Module

Subject Name Environmental Sciences

Paper Name Environmental Geology

Module Name/Title

Oceanography

Module Id EVS/EG-IV/31

Pre-requisites

Objectives

The module has been written with the following objectives:

(i) Describe sub-division of ocean;

(2) Physical processes in the ocean;

(3) Chemical properties of ocean;

(4) Factor controlling movement of ocean water;

(5) Biological nature of ocean;

(6) Role of Ocean as climate regulator;

Keywords

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Module 31: Oceanography

The module has been written with the following objectives:

(i) Describe sub-division of ocean;

(2) Physical processes in the ocean;

(3) Chemical properties of ocean;

(4) Factor controlling movement of ocean water;

(5) Biological nature of ocean;

(6) Role of Ocean as climate regulator;

1. Introduction

The ocean occupies about 71 per cent of the area of the globe and it contains ~97 per cent of water present on the globe. The ocean water is denser than the water on the continents and it stores an immense amount of latent heat the advection of which leads to warming of the poler region. Ocean also regulates the precipitation and snowfall on the land, and it is a keeper of innumerable mineral wealth, and oil and natural gas. Mankind has been dependent on ocean for food, navigation, recreation since time immemorial

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Ocean is an unconventional pool of water that has a horizontal extent of several hundred km, though its vertical extent is found to be a few km (average depth 3.7km). This pool covers about 71 per cent area of the globe and it contains 97 per cent of water present on the earth. Ocean is the biggest storehouse of dissolved elements, and it is believed that the chemical composition of sea water has not changed significantly for long. For the sake of convenience, the pool of saline water has been subdivided into five oceans, i.e., the Indian Ocean, the Pacific Ocean, the Atlantic Ocean, the Arctic and the Antarctic Ocean. The Pacific Ocean is the biggest ocean, while the salinity fluctuations are optimum in the Arctic and the Antarctic Oceans.

The geographical distribution and the spatial extent of the ocean have varied in the past. It is because the upper layer of the earth (crust) moves over its mantle and that leads to rearrangement of the continents consuming the continent and ocean. The spreading centre (in which the plates of crust move apart) are different from the convergence boundary as at these places new oceanic crust forms by thermal plumes emanating from the mantle. The subduction zones consume the land as well as ocean plates. These processes have expanded or shrank the past oceans and seas. For example, the Indian Ocean has been formed due to the breakup of a massive landmass known as Gondwana. The fractionation of the Gondwana Land with multi-directional drifting of the India, the Australia, the Africa and the American plates had led to the opening of the Atlantic, the Pacific, and the Indian Ocean. Southward drifting and rearrangement of a section of the Gondwana Land have brought the Antarctica to its present position over the Southern Pole and that has led to the formation of Antarctic Sea.

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Fig. 1. The subdivision of the ocean margin.

1.1 Physiographic subdivision of Ocean

The margin of the ocean may be subdivided into two distinct categories i.e. continental and ocean margin. The continental margin is the portion of the continent that is now submerged into the sea, and it comprises of three main zones. These are (i) continental shelf, (ii) slope and (iii) the continental

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rise (Fig. 1). Oceanward from the shore, the submerged shallow flat region of the continent is termed as shelf region. This region generally has a slope of 1:1000, depth of 120-140 m, and it has several bathymetric perturbations (known as seamounts) of low height resulted from the biogenic or volcanogenic processes. It also has buried channels of the rivers. The continental slope is the region that slopes towards an oceanic plate and connects continental shelf with that of the base of the slope in the deeper region of the ocean (Fig. 1). Located at the base of the slope, a bathymetric high region is termed as continental rise. This region is the boundary between an ocean and a continental plate.

Normally, it receives the material through slumping from the continental shelf and the accumulation of such sediments gives it a positive bathymetry. The oceanic plate generally occurs > 2500 m depth.

It is veneered with a very thin cover of sediment and it has a very low gradient (1:10000). The region has a chain of hills of varying height formed by the volcanogenic processes. Some of these features are several km tall and give rise to a chain of islands in the ocean. Hawaii is one of the examples of such features. Laccadive Islands of India are another example. The deepest region of the ocean is found in the trench region, a negative bathymetry formed due to subduction of the oceanic plate. The Mariana Trench is the deepest region of the world and it has a depth of about 11km.

2 Physical Characteristics of seawater

The water in the ocean/sea is heavier than the water on the continents. It has a density of 103 g per cm^-3. Basically, the amount of salt (salinity) and temperature of seawater regulate its density. The density of sea water has been found to be rather variable in the different oceans (1.02 to 1.50 g per cm³). The fresh water supply through the fluvial fluxes and the melting of the continental and the sea ice are some of the reasons that influence the density of local waters. For example, during the rainy season (during June - September) a large fluvial discharge from the rivers debouching into the Bay of Bengal reduces the density of sea water in the bay at a regional scale. Evapotranspiration is also found to be the main cause that influences density. A higher rate of evaporation leads to loss of water in the form of vapour and that increases salinity as well as the density of sea water. The sea temperature is another parameter that regulates the density and salinity. Colder water is denser than the warm water. Warmed by the sunlight- that has very limited penetration into the ocean waters, the upper layer of the ocean (known as mixed-layer) is the warmest surface of the sea. Under the mixed-

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layer, the temperature of the ocean drops, and this layer has been named as thermocline (Fig. 2).

Associated with a low temperature, below the thermocline, the sea water has high density, and this leads to floating of warm waters of upper surface over deeper waters. Also, the water is cold in the proximity of the poles due to prevailing climate. This water also has a higher density. The ocean, therefore, has a layered structure as shown in Fig. 2.

Fig. 2. Typical vertical profiles of temperature, salinity, and density in the ocean.

3. Chemical composition of the seawater

The seawater has a thermal conductivity of 0.6 W/mK at 25⁰ C at a salinity of 35 g/kg. The pH of the sea water ranges from 7.5 to 8.4. Sea water contains almost all the elements. The major constituents of the sea water are: Oxygen (85.84%), Hydrogen (10.82%) Chloride (1.94%), Sodium (1.08%), Magnesium (0.1292%), Calcium (0.04%), Potassium (0.04%), Sulphur (0.091), and Carbon (0.0028).

Sodium, chloride, magnesium, sulphate and calcium are the most abundant dissolved ions. The salinity of sea water varies between 31-36 parts per million. The salinity is not uniform. The highest saline region of the world is the Red Sea. A large influx of fresh water from the rivers and from the melting of the ice into the sea reduces its salinity. Sir Edmond Halley was the first researcher to

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propose the reason for the salinity variations of the sea. He postulated that the proceeds of the continental weathering transported by the rivers contribute salt into the sea. The evapotranspiration of sea also increases the salt contents in the sea (similar to one found in enclosed lakes or inland water bodies such as the Caspian Sea). However, recent studies have shown that contribution of salts specifically that of sodium, through volcanogenic and hydrothermal activities is also the process that contributes to a salinity enhancement. The solubility of salts also depends on the temperature and pressure. In the ocean, the atmospheric pressure increases with the depth (the increases for every 10 m is 1013.25 hP), and deeper waters dissolve higher amount of salts. Because the temperature of the ocean at the deeper level is low, it also increases the dissolution of gases and salts and alters their physical and chemical properties. The residence time of various salts in the sea is highly variable.

Sodium and chloride have much longer residence time compared to calcium. Over the time, the average salinity of the sea has remained same. This has been attributed to three processes:

1. The input of the anion and cation deemed to be equal because there is continuous precipitation of salt by chemical as well as biogeochemical processes.

2. Sodium chlorite and calcium sulphate precipitate in the warm or arid region of the marginal seas when sea water advects inland by the tidal forcing or during storm surges. The Rann of Kachchh is one such example where a large amount of sea salt is precipitated due to the cyclic influx of sea water and prevailing warm climate.

3. The precipitation associated with super-saturation of salt in the sea. Gypsum and carbonates are the salts that generally precipitate in the shallow seas. In addition silica and carbon are also extracted from sea water by biogenic processes, specifically by phytoplankton, the microorganism that fixes these in the presence of sunlight through photosynthesis. Corals, sponges, lobster and several other living animals including fish continuously extracts skeletons containing CaCO3, phosphate and several other metals from sea water through primary and secondary productivity.

4. 0 Sea level

The level of the pool of the water on the globe is dynamic and it changes continuously in response to several factors. Associated with hydrological cycle, the most dynamic changes in the sea level are

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induced by the melting/freezing of water on the globe. Any change in the temperature of the globe induces a change in its hydrological cycles, which is comprised of moisture/water/ice in the ocean, atmosphere, and at the land. A higher rate of evaporation increases moisture in the atmosphere and that may induce more intense rains over the land. An enhanced evaporation may reduce the global sea level, but the higher rainfall associated with it may increase the riverine discharge that ultimately returns to the sea. The residence time of water in each of the components of the hydrological cycle, viz at land (lakes, glaciers, underground subsurface-water etc.) in the atmosphere and in the ocean is, therefore, crucial for the determination of the global sea level. Among all, the melting of ice on land as well as at the sea is deemed to be the most important parameters that have brought a large change in global sea level. For example, melting of ice since 18 Ka had increased the sea level by about 120- 130 m globally (Fig. 3).

Fig. 3. The global sea level rise during past 24 Ka (source https://en.wikipedia.org/wiki/Sea_level_rise)

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Local sea level to a large extent depends upon eustatic and isostatic processes. Eustatic processes regulate the amount of water in the sea and that increases the global sea level. Isostatic process is a local tectonic process that subsides or uplifts the landmass. This process either accelerates or retards the influence of eustatic sea level. Besides, sea surface temperature also increases sea level by virtue of thermal expansion. In the prevailing scenario of global warming, the Intergovernmental Panel on Climate Change (IPCC) has stated that it is very likely human-induced (anthropogenic) warming that has contributed to the sea level rise observed in the latter half of the 20th century (Fig. 4). The IPCC report (AR5) had concluded: "there is high confidence that the rate of sea level rise has increased during the last two centuries, and it is likely that GMSL (Global Mean Sea Level) has accelerated since the early 1900" ("Sea Level Change - Chapter 13" IPCC. 2013 ). In these evaluations, the expected rate of sea level rise is 1-3 mm y^-1 and that may get further accelerated with thermal expansion of ocean due to an increase in the sea surface temperature. It is mooted that the rise by 2100 is expected to be 0.52 to 0.98 m with a rate of 8 to 16 mm y^–1during 2081–2100. The local sea level also gets influenced by tides, cyclonic surges, physiographic amplification of water level, and atmospheric pressure. The millennium-scale changes in the sea level, however, take place due to plate tectonics that leads to the reorganisation of continental as well as oceanic plates.

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Fig.4. A trend of sea level rise associated with recent anthropogenic activities (source https://en.wikipedia.org/wiki/Sea_level_rise)

5. Dynamic Sea

The water of the oceans is never at a rest, but it is constantly dynamic. This stems from the several processes; the most important among these is the thermal gradient present on the globe. Though the earth cools at the poles, the ocean water is heated around the equator. This thermal gradient leads to the advection of warm waters from the equator to the poles by wind-induced currents along the boundary of the continents. The magnitude of these currents is highly variable. The other circulation

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found on the subsurface of the ocean is rather more complex. The cooling at poles produces denser water, and it sinks in the northern region of the Atlantic. This sunken water at the bottom of the sea migrates equatorward in the deeper part of the ocean. It overturns in the Pacific and in the Indian Ocean making it a conveyor circulation in all the Atlantic, Indian Ocean, and the Pacific Ocean as schematically shown in Figure 5. This current is found to be very slow and it remains enigmatic.

Fig. 5. Great conveyor belt

The water of the ocean also moves in response to the winds, gravity, coriolis force, pressure gradient and salinity gradient. The currents driven by these processes are regional in nature. Figure 6 shows generalised winds in the ocean. The surface currents are primarily driven by these winds. As the winds prevail over the globe, the wind stress curl induces movement of water mass (Fig. 7). The induced movement of water mass deflects to its right (left) in the northern (southern) hemisphere and is guided by the land mass of continent. These currents exist in the form of a gyre in the ocean, and these normally encompass the full basin (Fig. 7). The poleward advection of water masses is generally found in the western (eastern) margin of the globe along the regions that are north (south) of the equator. The western (eastern) boundary currents in the northern (southern) region are rapid and warm and these take heat from equator to the pole and keep the poler region much warmer. The wind- driven equatorward currents are generally found along the eastern (western) boundary in the northern (southern) hemisphere. These currents are sluggish, cold currents that advect at a slow speed. At the

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equator, the winds are generally easterly and the temperature gradient is rather absent. These winds generate equatorial currents and north and south equatorial counter currents that are warm (Fig. 7).

At the South Pole, around the Antarctica, a circumpolar cold current prevails, and that prevents the equatorward advection of cold water from the southern pole to the equator.

The winds also drive upwelling - a process that pumps the deeper, cold water to the surface.

The winds that prevailed at an inclined angle to shore induced shoreward advection of the surficial water. In the northern hemisphere, these get deflected to its right. This process leads to a rapid displacement of the surface waters reducing surface height leading to the upwelling of deeper, cold, nutrient-rich water to the surface. Upwelling is an important process that brings in the nutrients to the upper surface and aids in a higher primary productivity. The downwelling of the sea water also occurs.

This process is very prominent during the winter when the water cools over the surface and become denser compared to subsurface waters. The dense water then sinks. Winter convection sinking is very prominent in the northern Arabian Sea. This process enhances nutrient supply from the deeper layers into the upper surfaces and buttresses the primary productivity.

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Fig. 6. The generalised wind patterns over the globe. Please note northerly (southerly) winds along the western (eastern) boundary of the region north of the equator. (Source: http://www.climate- charts.com/World-Climate-Maps.html).

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Fig. 7. Circulation of oceanic currents. The polewards currents along the western (eastern) boundary in the northern (southern) hemisphere are the warm and rapid currents. The most prominent Gulf Stream is one the example of regional wind-driven currents

5. 1 Waves

The waves are primarily generated by the wind when it blows over a large fetch of the ocean. Even though occur at the upper surface, ocean waves oscillate within a fluid medium perturbed by the winds and restored by the gravity. When directly generated and affected by local winds, the wave system is called a wind sea. After the wind ceases to blow, and the wind waves have left the fetch, the waves have much-reduced roughness and a long wavelength. These waves are called swells. More generally, a swell consists of wind-generated waves that are not significantly affected by the local wind at that time. These waves propagate for several hundred km and become unstable only in the shallow region that has depth half of their wavelength. The wind waves may have a height ranging from small ripples to 10 m. Following factors influence the formation of the wind waves (Young, 1999):

1. Speed of the wind relative to wave speed; the speed of the wind shall exceed that of the wave

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2. The wind should blow over a large area (known as fetch) without significant change in its direction.

3. Width of area affected by fetch

4. Duration for which the wind has blown over a given fetch 5. Water depth

Fig. 8. Schematic diagram of wind waves formation

A large fetch and a longer duration of strong winds generate higher sea waves (Fig. 8). Upon arrival in the shallow region, the disintegration of the sea-waves gives rise to littoral currents that carry detritus alongshore. A great majority of a large breaker (seen on a beach) forms from disintegration of distant waves. Waves are very important for coastal circulation because they regulate the quantum of littoral drift, which controls nourishment or destruction of a beach and the safety of the coastal

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structures. The wave characteristics, therefore, form an important ingredient that determines the stability of coastal structures.

5.3 Tsunami

Tsunami, "the waves of the harbour" is the most destructive waves. These waves have very low amplitude in the deeper region and are generally produced by an abrupt perturbation in the sea caused by a major earthquake or slumping of large debris or an eruption of a volcano on the ocean floor.

Tsunami are very large solitary waves that have a wavelength of > 10 km to several hundred km and a very long period (100-3000 sec). In the open ocean, the low amplitude of these waves does cannot touch the sea bottom and hence they do not disintegrate. Once such waves arrive in the coastal waters, the shallow depth of the sea disintegrates and enhances their wave height. The depth induced enormous amplification of wave height and speed of the particles in the wave leads to massive destruction and inundation of a large region of the coast. The occurrence of the tsunami is an episodic phenomenon that continues till the energy of these long waves dissipates. Considering a large destruction by these waves, Government of India has installed a Tsunami warning system.

5.2 Tides

Tides are semidiurnal to diurnal change in the sea level. Tidal waves are generated due to the gravitational pull of celestial bodies. Being closer to the earth, the moon exerts more force, and therefore it has more influence on the sea that bulges at the equator. This force of attraction generates a large wave with low amplitude in the deeper water. If the Earth were a perfect sphere without any continents, all areas on the planet would experience two equally proportioned high and low tides every lunar day. The existence of large continents on the planet, however, blocks the westward passage of the tidal bulges as the Earth rotates. Unable to move freely around the globe, tides establish complex patterns within each ocean basin (Sumich, 1996).

Upon the entry of the tidal waves into the shallow region of shelf, there is an amplification of level of tides accompanied with currents. The increase in the level of the tide is called the flood phase while the receding tide is known as the ebb phase. Generally, two flood tidal levels day^-1 are termed as the semidiurnal tide while one flood phase day^-1 in a region is termed as diurnal tides. Also, tides may be

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symmetrical or asymmetrical depending upon the difference in the flood and ebb tidal amplitude. If the amplitude is same, the tide is deemed to be symmetrical. Owing to the interaction of the forcing of the moon and the sun, the tidal amplitude also has bi-weekly changes. The highest tides during one cycle are known as the spring tide while the lowest of the tides is termed as the neap tide.

6. 0 Marine Life

The information about the marine life is rather scanty because a large section of the deeper region of the ocean remains virtually unexplored. On the land, the primary productivity to a large extent is light limiting, and there is a well-defined food web. On the contrary, in the ocean, only top 100 m of the water column is normally sunlit. Yet the entire ocean including the deeper, dark regions is found to have life. The primary producers in the ocean are of two types, i.e., photosynthetic (fixing carbon using sunlight) and chemosynthetic (the organism that produces their food by chemical processes).

The former are planktons, mostly algae and cyanobacteria (commonly called cyanophyta) that obtain their energy through photosynthesis. The chemosynthetic community lives in the deeper regions of the ocean that do not receive any sunlight and they derive their food through chemical reaction around thermal plumes emanating from the hydrothermal vents.

The tropic levels in the ocean are given in Figure 9. The autotrophic communities (primary producers) are generally unicellular planktonic species that drifts in the waters and produce their food through photosynthesis in the euphotic zone. It also comprises of some species of macroscopic algae termed as weeds. The depth of euphotic zone depends upon several factors, important among these is cloud cover and the turbidity of the sea waters. The waters with reduced turbidity are found to have a deeper euphotic zone. The depth of euphotic zone is also less off the mouth of the rivers. Despite a higher turbidity that attenuates deeper penetration of the sunlight, the primary productivity of these waters was found to be many folds higher due to enhanced supply of the nutrients from the land. The mangroves and beach grasses are the only plants that are found in the coastal region.

Zooplankton, the floating herbivorous consumer are heterotrophic and these occupy the next level in the tropic diagram (Fig. 9). These organisms vary in size from < 2 to 200 µm and mostly feed on eutrophic species. Over 1500 species of fungi are known from marine environments. These are parasitic on marine algae or animals, or are saprobes on algae, corals, protozoan cysts, sea grasses,

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wood and other substrate, and can also be found in sea foam. Spores of many species have special appendages which facilitate attachment to the substratum. A very diverse range of unusual secondary metabolites is produced by marine fungi. The carnivorous consumer of the higher order viz. fish, squid, and large mammals (e.g. whales and dolphin) occupy the top of the pyramid. Generally, at each level, only 10% of the energy from an organism is transferred to its consumer. The rest is lost as waste, movement energy, heat energy and so on. As a result, each higher tropic level supports a smaller number of organisms – in other words, it has less biomass. This means that a top-level consumer, such as a shark, is supported by millions of primary producers from the base of the tropic pyramid (http://sciencelearn.org.nz/Contexts/Life-in-the-Sea/Science-Ideas-and-Concepts/Marine- food-webs).

Unlike the land, there are diverse species that dwell in the bottom of the sea or float below the euphotic zone. The bottom dwellers are generally termed as benthic fauna, and most of these are heterotrophic, though a very small community may be the primary producer (chemosynthetic community). The life in the dark, deep ocean is sustained from the supply of organic matter from the primary production in euphotic surface via biological pump. The decomposers are active at each of the levels of the tropic and these play a vital role in dissolving organic matter and the nutrients from the remains of euphotic life. Despite (i) a high pressure, (ii) no primary producer, and (iii) a low temperature, life in the deeper layers of the ocean is sustained from the rains of dead skeletons, organic remains and dissolution of nutrients released from the decomposition of the biotic components.

The marine biodiversity is found to be related to climate, the supply of nutrients and that of the availability of sunlight. A higher supply of nutrient through land or through upwelling may lead to a high primary productivity and that enhances the supply of organic matter into the deeper subsurfaces.

Most of this organic matter is consumed by heterotrophs or bacteria. A high marine production leads to a large consumption of oxygen by sinking organic matter, which makes these waters suboxic or anoxic through the process of eutrophication. The oxygen depleted waters are hazardous for marine life, specifically for the heterotrophs in the higher tropic order. Marine habitats are broadly divided into two sections, i.e., coastal and Open Ocean. Coastal habitat extends from the coast to the edge of

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the continental shelf. The region beyond the shelf edge is termed as Open Ocean Habitat. The deep ocean fish is termed as pelagic whereas shallow water species are known as demersal (https://en.wikipedia.org/wiki/Marine_biology).

Fig. 9. Tropic levels in the ocean.

7.0 Ocean as regulator of climate

The ocean is a reservoir of heat received from the sun, Because of the tilt of the axis of the earth; the equator region receives more solar energy round the year. Since water has more capacity to store heat than the atmosphere, oceans act as a reservoir of heat and the energy of the Sun. The polar regions receive solar energy during one season only, and these are the coldest regions on the earth. This thermal gradient between equatorial ocean and poles gives advection of heat by the winds and

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currents from the equator to the poles, which also carries latent heat and moisture. The condensation of the ocean moisture carried by the winds over the continents gives rise to the rains/snow fall. The Indian monsoon is a typical example of control of the ocean over the precipitation and climate over the Asian Continent. Due to differential cooling - heating of the Southern Ocean and the Asian Sub- continent, specifically the Himalayas, there is an advection of south-westerly winds from the Southern Ocean to the land that carries the moisture and latent heat over the Asia from the ocean. The precipitation magnitude during the monsoon over the India and other regions of the Asia is known to be regulated by the magnitude of the thermal gradient between land and Southern Ocean.

The role of heat in the ocean water is profoundly reflected in the process known as El Nino and Southern Oscillations. This phenomenon is known to have global influence over the climate. It refers to dynamics of an ocean warm pool in the equatorial region. The easterly winds in the equatorial region of the Pacific Ocean maintain an ocean warm pool in the western region in the proximity of Indonesia. This warm pool releases vapour by trans- evaporation and strengthens the precipitation in the Asia and India. During an El Nino event (that occurs for 2-7 years) the easterly winds weaken due to a low pressure over the eastern Pacific. The warm pool then spreads westwards into the coast of Peru and along the southern America. This modifies the normal weather conditions of the American Continents and reduces rainfall over the Asia. The influence of El Nino is schematically shown in Figure 10.

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Fig. 10. Schematic diagram of El Nino phenomenon in the Pacific Ocean (source:

http://kron4.com/2015/08/13/90-percent-chance-el-nino-hits-california/)

8. Mineral wealth from the Sea

Ocean is also a keeper of mineral wealth. There are an extensive surface and subsurface occurrence of the minerals and petroleum products that are capable of meeting the future requirement of the mankind. The mineral wealth is generated by (i) the concentration of abiotic components, (ii) biological production, and (iii) chemical precipitation. Placer mineral deposits are the concentration of heavy minerals (.> 2.8 specific gravity) due to repeated wave action. Monazite sand of Kerala and the diamond deposits of South Africa are few examples of placer deposits. The rock salt, phosphorite, and calcite precipitate from sea waters in the shallow shelf region. Oil and gas are found in the subsurfaces that are contributed from the biotic components. Bombay high is a major oil production region of the India, which is located on the continental shelf off the Mumbai. The deeper regions,

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specifically the abyssal plane and active ocean divergent margins, are known to contain hydrothermal sulphides deposits of iron, copper, and zinc. Deeper ocean deposits include ferromanganese nodules, the chemical precipitates that contain complex minerals of Fe, Mn, Ni, Co, Zn etc. and these are considered the future source of trace metals. India has carried out extensive surveys of the ocean floor to discover several locations of the occurrence of these at the ocean floor deeper than 3000 m, and it been awarded a deep ocean site for the mining of nodules in the Central Indian Ocean Basin.

Gas hydrates are a future source of energy to the mankind. These deposits occur in the deeper regions of the ocean in which frozen gas molecules are trapped in water molecules. A high biological production leads to deposition of organic matter over the sea bottom. Upon the decomposition, this produces gas molecules. These get trapped in the water molecules, and these are the important sources of extracting gases. The exploration to identify gas hydrates at the ocean bottom is currently a priority of developed as well as developing nations.

Conclusion:

 From the reading of this chapter we learn that ocean is comprise of land part and newly formed oceanic plate.

 The ocean water has vertical variation in the physical as well chemical property

 Owing to the abundant supply of the sunlight, the upper 100 m layer of the ocean is more productive.

 The ocean water is constantly in the movement due to wind, gravity and influence of celestial bodies.

 The ocean contains a huge amount of mineral wealth

The module has been written with the following objectives:

Development Team

Oceanography

Contents:

The module has been written with the following objectives:

.