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WATER (OCEANS) 103 from the mouths of large rivers. The Hudson (iv) Ocean currents : warm ocean currents raise the temperature in cold areas while Canyon is the best known submarine canyon in the world. the cold currents decrease the temperature in warm ocean areas. Gulf Guyots stream (warm current) raises the temperature near the eastern coast of It is a flat topped seamount. They show North America and the West Coast of evidences of gradual subsidence through stages to become flat topped submerged Europe while the Labrador current (cold mountains. It is estimated that more than current) lowers the temperature near the north-east coast of North America. 10,000 seamounts and guyots exist in the All these factors influence the temperature Pacific Ocean alone. oftheoceancurrentslocally.Theenclosedseas Atoll in the low latitudes record relatively higher temperature than the open seas; whereas the These are low islands found in the tropical enclosed seas in the high latitudes have lower oceans consisting of coral reefs surrounding temperature than the open seas. a central depression. It may be a part of the sea (lagoon), or sometimes form enclosing a Horizontal and Vertical Distribution body of fresh, brackish, or highly saline water.of Temperature T EMPERATURE OF O CEAN W ATERS The temperature-depth profile for the ocean water shows how the temperature decreases This section deals with the spatial and verticalwith the increasing depth. The profile shows a variations of temperature in various oceans. boundary region between the surface waters Ocean waters get heated up by the solar energy of the ocean and the deeper layers. The justasland.Theprocessofheatingandcooling boundary usually begins around 100 - 400 m of the oceanic water is slower than land. below the sea surface and extends several hundred of metres downward (Figure 12.3). Factors Affecting Temperature Distribution This boundary region, from where there is a The factors which affect the distribution of rapid decrease of temperature, is called the temperature of ocean water are : thermocline. About 90 per cent of the total (i) Latitude: thetemperatureofsurfacewater volume of water is found below the thermocline decreases from the equator towards the in the deep ocean. In this zone, temperatures approach 0° C. poles because the amount of insolation decreases poleward. The temperature structure of oceans over (ii) Unequal distribution of land and water : middle and low latitudes can be described as the oceans in the northern hemisphere athree-layersystemfromsurfacetothebottom. receive more heat due to their contact The first layer represents the top layer of warm oceanic water and it is about 500m with larger extent of land than the oceans in the southern hemisphere. thick with temperatures ranging between 20° (iii) Prevailing wind : the winds blowing from and 25° C. This layer, within the tropical the land towards the oceans drive warm region, is present throughout the year but in surface water away form the coast mid latitudes it develops only during summer. The second layer called the thermocline resulting in the upwelling of cold water from below. It results into the longitudinalayerliesbelowthefirstlayerandischaracterised variation in the temperature. Contrary to byrapiddecreaseintemperaturewithincreasing this, the onshore winds pile up warm depth. The thermocline is 500 -1,000 m thick. water near the coast and this raises the The third layer is very cold and extends upto the deep ocean floor. In the Arctic and temperature. Reprint 2026-27