Temperature of oceans is of great significance as it supports all life forms, their types and distribution at various depths in the oceans. Temperature controls the movement of large volume of ocean water. Sun is the major source of temperature of ocean water. It heats up the ocean through the process of insolation (shortwave electromagnetic radiation emanated from the sun is received at the ocean surface).
However, The process of heating and cooling of the oceanic water is slower than land. Heating of ocean water also occurs due to a number of processes apart from insolation. Heat is also received from the interior of earth near the ocean bottom which is distributed through convection currents to the upper layers of ocean.
FACTORS AFFECTING THE TEMPERATURE DISTRIBUTION
- Latitude: Amount of insolation decreases from equator towards poles. Hence, temperature of surface water decreases from equator towards poles.
- Location: Oceans in northern hemisphere receive more heat due to their contact with huge land masses compared to oceans located in southern hemisphere where there is dominance of water with greater uniformity.
- Prevailing winds: Onshore winds pile up warm water near coast while offshore winds drive warm surface water from the coast resulting into upwelling of cold water from below. Trade winds blowing along western coastal regions are offshore and hence reduce the temperature long the adjoining coasts while trade winds blowing along eastern coastal areas are onshore and hence, they raise the temperature of those coastal regions.
- Ocean currents: Warm Ocean currents raise temperature of adjoining coastal area and cold ocean currents reduces the temperature in major oceans of the world. Ex. Gulf stream (warm current) raises temperature near eastern coast of North America and West Coast of Europe while Labrador current (cold current) lowers the temperature near north-east coast of North America.
HORIZONTAL DISTRIBUTION OF TEMPERATURE
Average temperature of surface water of oceans is 26.7° C. Temperature of ocean water is not uniform and several factors like insolation, prevailing winds, ocean currents, affect its distribution.
- There is a gradual decrease of temperature from equator towards poles and the rate of decrease of temperature is generally of the order 0.5° per latitude.
- Highest value of surface temperature is found to slightly north of equator because maximum amount of radiation is received a little north of equator.
- The oceans in northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
- In Atlantic Ocean, decrease of temperature with increasing latitude is relatively low because of the presence of warm ocean currents.
- Average annual temperature of Pacific Ocean is higher than Atlantic Ocean (16.91° C) because the isotherms run parallel to the latitudes. (Isotherm is a line on the map which joins the places that have same temperature at a particular time)
- Enclosed seas like Red Sea records high average temperature i.e., 30° C compared to open oceans.
- Average temperature of surface water at 20° latitude is about 22° C, 14° C at 40° latitude and 0° C near poles.
VERTICAL DISTRIBUTION OF TEMPERATURE
As the ocean surface receives direct insolation from the sun, so the temperature of surface water is higher than the temperature of water increasing depths from the ocean surface. However, this rate of decrease of temperature of the oceans is not uniform.
- The temperature depth profile for the ocean water can be described as a three-layer system from surface to the bottom.
- The first layer represents the top layer and it about 500m thick. This layer present throughout the year in tropical region. The temperature in this region ranges between 20° to 25° C.
- The second layer is called Thermocline. It is a boundary region, where there is a rapid decrease of temperature is observed. It is 500m – 1000m thick. About 90% of the total volume of water is found below the thermocline in the deep ocean. In this zone, temperatures approach 0° C.
- The third layer which extends from 1000m-1500m to the deep ocean floor is very cold and only one layer of cold water exists here.
- The heat is transmitted to the lower sections of the oceans through the process of convection.
