OCEANOGRAPHY Dr. Sunil Kumar Singh A Dept. of Geography G.D College, Begusarai OCEANOGRAPHY Oceanography is the study of the physical, chemical and biological features of the ocean, including the ocean’s ancient history, its current condition, and its future. OCEANS The ocean comprises 70.8% of the earths surface. Pacific Ocean – 35.4% Atlantic Ocean – 18.4% Indian Ocean – 14.5% And the Lands – 29.2% OCEANS The oceans are mainly dominated in the southern Hemisphere. Land and sea are generally antipodally arranged. About 2/3 of the land is in the Northern Hemisphere. Only 1.5% of the earths surface has land antipode to land. The centre of the ocean hemisphere lies near New Zealand, 89% which is ocean 11% land. The average depth of sea is 3790m. The oceanic crust is approximately 5km thick and have an average density of 3.0 g/cm3. BOTTOM TOPOGRAPHY OF OCEANS Continental Shelf Continental slope Continental rise Oceanic ridge and rise Oceanic trenches Island arcs Marginal Ocean Basins Ocean Basin Sea Mounds and Guyots Plateau BOTTOM TOPOGRAPHY OF OCEANS CONTINENTAL SHELF These are not the part of oceanic crust and are composed of continental crust. They can be called as submerged part of the shield or stable platform. The average with is 78 km and depth is 133 m. It is generally wide along low lying lead and narrow along mountainous coasts. These are smooth and flat sometimes low hills and shallow basins or valleys are present. Wide and shallow continental shelves are rich ground for the growth of plankton. CONTINENTAL SHELF CONTINENTAL SLOPE Continental slope descends from the outer edge of the continental shelf as a long continuous slope to the ocean basin. They mark the boundary between continental and oceanic crust. Average slope is 4.30 . The continental slope is steep where mountain ranges border the coasts (4-60) and it is gentle opposite major deltas and stable coasts (2-3.50) Numerous submarine canyons and furrow are present in the slope region. CONTINENTAL SHELF CONTINENTAL RISE At the base of the continental slope, the slope decreases to 10 or less continuing into the abyssal hills or plains to form continental rise. OCEANIC BASIN The oceanic basin are composed of abyssal floor, tectonically inactive rise and sea mounds. Broad, relatively smooth surface are know as abyssal floor, it consists of two sections namely abyssal plain and abyssal hills. Sea mounds and guyots, which are isolated submarine volcanic features 2- 100 km wide and more than 1000m high whose surface lies less than 2000m below sea level. Sea mounds are sharply pointed but those which have flat topped are called Guyots. Guyots have steep sides 12-35 0 and are considered to be leveled platform submerged largely by sea floor subsidence. Guyots are commonly capped by coral growth in the tropics. OCEANIC RIDGES Oceanic ridges are the most prominent features on the Earth covering nearly 23% of the Earth’s Surface. It is broad, transversely fractured linear swell, lying mostly near the centers of ocean . The mid Atlantic ridge is the largest and the best known ridge which height extends well above the sea level to form Azores, Ascension islands. OCEANIC RIDGES The other ridges are Carlsberg ridge in the Indian Ocean, East Pacific Ridge in the Pacific, Lomonosov Ridge in the Arctic Ocean etc. The main difference between ridge and rise is that the ridges are steep sided while rise are gentle sloping . Important rise are : Galpagos rise, Rio rise, the Hawaiian and Austral Marshall Gilbert Chain. OCEANIC TRENCH Along some coast, the continental shelf drops steeply into trenches forming the deepest part of oceans. They are 30-100km wide and 3000-5000 km long. Their side slope to (4-80) and then (10-16 0) to depth of more than 10,000m. Examples of trenches are Mariana Trench of the Philippines (11 km depth), the Tonga Trench (10 .8 km), Java trench (7.5km), Pureto Rico Trench (8.6 km) etc. MARIANA TRENCH ISLAND ARCS They are the chain of volcanic islands, generally convex towards the open sea and run parallel to oceanic trenches and mountain chains. They range in size from less than 1 km to the size of Guinea, Luzon or Hokkaido . They are seismically active and topographically and structurally continuous with continental belts of young fold mountains. Eg. Malaya, Kamchatka, Alaska. Island arcs may be submerged eg. Ryuku islands between Japan and Taiwan or it may be topographically and structurally fixed with the inner arc,eg. Japan. ISLAND ARCS TROUGHS Troughs are simply depressions on the deep sea floor. Eg. Barlett Trough, ayman Trough MARGINAL SEAS BASINS Marginal sea basins lie either between island arcs and the continent like Philippine sea or between continent masses. They are 500-1000 km wide and may include abyssal plain extending down to more than 5km below sea level. PLATEAU They are submarine elevations of considerable extent with relatively flat tops. Eg. The Seychelles Plateau in the Indian Ocean and the Azores plateau in the North Atlantic. TEMPERATURE OF THE OCEANS Average temperature of Ocean Waters is 26.7 0 C. There are three different layers of the ocean from top to bottom in the tropics. Epilimnion – First Layer (Extends up to 500 m, having temperature of 20-25 0 C. Mixing occurs in this layer due to wind action and currents. Thermocline layer – below the first layer, here temperature decreases with depth. Hyplomnion – third layer is characterized by a uniform temperature but is cooler than the other layers. DISTRIBUTION OF TEMPERATURE Latitude - Temperature decreases from the equator towards the poles. Unequal distribution of land and water – Temperature is higher in the Northern Hemisphere than the southern hemisphere due to the dominance of land in the Northern Hemisphere. Prevailing Winds Ocean Currents : Warm and cold currents Minor Factors : Storm, cloudiness, fog, evaporation, condensation etc… VERTICAL DISTRIBUTION OF TEMPERATURE Temperature decreases from the ocean surface with increasing depth but the rate of decrease of temperature with increasing depth is not uniform everywhere. SALINITY OF THE OCEAN Salinity is defined as ‘the total amount of solid material in grams contained in one kilogram of sea water and is expressed as part per thousand. The average salinity of ocean water is 35 .2 ‰. Sodium chloride (77.8%) followed by Magnesium chloride (10.9%), Magnesium sulphate (4.7%) dominate the salt composition. In addition to these Calcium and Potassium Phosphate, calcium carbonate, Bromide, iodine,….gold, silver and radium are found in sea water. SOURCE OF SALT IN OCEAN River Volcanic ashes Marie organism CONTROLLING FACTORS OF SALT IN OCEAN Evaporation – Greater the evaporation, higher the salinity and vice versa. Maximum evaporation is seen in the tropics than the equator. Precipitation – Higher the precipitation lower the salinity and vice versa . Influx of river water- River water brings down the salinity of the ocean water and it is more pronounced in the closed seas. CONTINUED… Atmospheric pressure and wind direction – anti-cyclonic condition with stable air and high temperature increases the salinity of the surface water of the ocean. Winds also helps in the re distribution of salinity in the ocean . Salinity increases in the area where water is piled up by the winds. Thus the easterlies and westerly play an important role in salinity balance. CONTINUED… Circulation of Ocean Water – Ocean current affect the spatial distribution of salinity by mixing sea waters. DISTRIBUTION OF SALINITY Latitudinal distribution – Salinity generally decreases from the equator towards the poles, though the highest salinity is recorded between 20-40 degree latitudes. Regional distribution : According to Jankins ; Seas having salinity above normal: Red sea, Persian gulf, Mediterranean sea Seas having normal salinity: Caribbean sea and gulf of Mexico Seas having salinity below normal: Arctic Ocean, Bearing Sea, North Australian Sea. VERTICAL DISTRIBUTION OF SALINITY No definite trend of distribution of salinity with depth can be spelt out because both trends of increase and decrease of salinity with increasing death has been observed. OCEAN DEPOSITS The unconsolidated sediments derived from various sources, deposited at the sea floor are included in the ocean deposit. The main sources are Terrigenous materials, Volcanic eruptions and marine plants and animals . TERRIGENOUS DEPOSITS Continental in origin which are bought by the river. Gravel, Sand, Silt, Clay and Mud (Blue mud- rich in iron sulphide, Red mud- rich in iron oxide, Green mud- green silicates of potassium and gluconite ) VOLCANIC MATERIAL Volcanic eruption on the Land Volcanic eruption on the oceans and seas ORGANIC MATERIAL Comprises of dead skeleton of animals and plants. These are divided into Neretic and Pelagic matters. Neretic – includes skeleton of marine animals and plant remains. Pelagic- consists of remains of different types of algae. PELAGIC DEPOSITS These are derived from algae and are in the form of liquid mud, generally known as Ooze. They are divided into tow groups on the basis of Silica and lime content. Calcareous Ooze : pteroped Ooze and globigerina Ooze . Silicious Ooze: Radiolaria Ooze and Diatoms OOze INORGANIC MATEIRAL Red clay – Silicate of alumina and oxides of iron are the chief constituents of red clay. WAVES Wave phenomena transmits energy through various states of matter by setting up patterns of oscillation motion in particle that make up the matter. Most of the waves observed at sea are progressive wind waves, i.e., they are generated by winds. DIFFERENT TYPES OF WAVES Shallow water wave, deep water wave, gravity wave, constructive and destructive wave, Rogue wave, Tsunami or sesmic wave. DEEP AND SHALLOW WAVES CONSTRUCTIVE & DESTRUCTIVE WAVES TSUNAMI WAVES CURRENTS The general movement of a mass of oceanic water in a definite direction is called currents which are more or less similar to water streams flowing on the land surface of the earth.