The study of the temperature of the oceans is important for determining the movement of large volumes of water (vertical and horizontal ocean currents),,type and distribution of marine organisms at various depths of oceans,
climate of coastal lands, etc.
Temperature Distribution of Oceans
The uppermost 10 percent of the oceans contain more heat than the entire atmosphere. The temperature of the oceans is not uniform. It differs from latitude to latitude and from the surface to the bottom. The major determinants of ocean temperature are:
- Latitude: The surface temperature of the oceans declines from the equator towards the poles as the Sun’s rays are vertical on the equator and become slanting as one move towards the poles
- Prevailing Winds: Direction of the prevailing winds such as the Trade Winds, Westerlies etc., determines the surface temperature of ocean waters at a point. For instance, eastern edges of the ocean along the trade wind belt have cooler waters due to the pushing of the warm waters by the trade winds away from the coast causing the upwelling of bottom waters.
- Unequal distribution of Land and Water: The Northern Hemisphere has more land area than that of the Southern Hemisphere. Consequently, the oceans of the Northern are warmer than that of the Southern Oceans.
- Evaporation Rate: The volume of water that evaporates from the ocean surface is around 350,000 cubic kilometres per annum. However, the rate of evaporation is not uniform across different latitudes. Warmer tropical ocean waters have higher evaporation rate than the cooler temperate ocean waters.
- The density of water: The density of ocean water is mostly a function of its temperature and salinity. The density of waters also varies from latitude to latitude. In the areas of high salinity, the ocean waters are of a relatively higher temperature and vice versa.
- Ocean Currents: Surface temperature of oceans is also controlled by cold and warm currents. The presence of warm water increases the temperature and consequently the rate of evaporation. Consequently, the region records more rainfall, while the cold current reduces the temperature of the moisture-laden wind. The coast along which a cold water current flows records more fog, but less precipitation.
- Local Factors: Submarine ridges, local weather conditions like storms, cyclones, winds, fogs, cloudiness, the rate of evaporation, lapse rate, condensation, and precipitation also affect the distribution of temperature of the oceans
Factors Affecting Temperature Distribution of Oceans
- Insolation: The average daily duration of insolation and its intensity.
- Heat loss: The loss of energy by reflection, scattering, evaporation and radiation.
- Albedo: The albedo of the sea (depending on the angle of sun rays).
- The physical characteristics of the sea surface: Boiling point of the sea water is increased in the case of higher salinity and vice versa [Salinity increased == Boiling point increased == Evaporation decreased].
- The presence of submarine ridges and sills [Marginal Seas]: Temperature is affected due to lesser mixing of waters on the opposite sides of the ridges or sills.
- The shape of the ocean: The latitudinally extensive seas in low latitude regions have warmer surface water than longitudinally extensive sea [Mediterranean Sea records higher temperature than the longitudinally extensive Gulf of California].
- The enclosed seas (Marginal Seas – Gulf, Bay etc.) in the low latitudes record relatively higher temperature than the open seas; whereas the enclosed seas in the high latitudes have lower temperature than the open seas.
- Local weather conditions such as cyclones.
- Unequal distribution of land and water: The oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
Horizontal Distribution of Temperature:
In general, the temperature of the surface water in the lower latitudes is about 26 degrees Celsius which decreases towards poles. The oceans of the Northern Hemisphere record an average temperature of 19.4 degrees Celsius. However, the average temperature recorded at various latitudes also varies with 22 degrees Celsius recorded at 20 degrees latitude, and 14 degrees Celsius recorded at 40 degrees latitude in the Northern Hemisphere. At the poles, the temperature drops to 0 degrees Celsius.
Vertical Distribution of Temperature:
Both energy and sunlight decrease with depth in the oceans. Only about 45 percent of light energy striking the ocean surface reaches a depth of about one meter, and only 16 percent reaches a depth of 10 meters.