The distributional pattern of temperature of ocean water is studied in two ways viz.:
(i) Vertical distribution (from surface water to the bottom)
(ii) Horizontal distribution (temperature of surface water)
Since the ocean has three dimensional shapes, the depth of oceans, besides latitudes, is also taken into account in the study of temperature distribution.
Factors that affect the distribution of temperature of ocean water:
- 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.
- The temperature of surface water between 40°N and 40°S is lower than air temperature but it becomes higher than air temperature between 40th latitude and the poles in both the hemispheres.
(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 Shio 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.
- Warm currents raise the temperature more in the northern hemisphere than in the southern hemisphere which is apparent from the fact that the 5°C isotherm reaches 70° latitude in the northern Atlantic Ocean whereas it is extended up to only 50° latitude in the southern Atlantic Ocean.
- This is because of more dominant effects of the warm Brazil current in the southern Atlantic Ocean.
(5) Minor Factors:
Minor factors include:
(i) Submarine ridges
(ii) Local weather conditions like storms, cyclones, hurricanes, fog, cloudiness, evaporation and condensation, and
(iii) Location and shape of the sea.