SEMESTER- II CC-III
INTRODUCTION TO OCEANOGRAPHY
CODE: 18K2G03
Unit III: Distribution of Temperature and Salinity: Vertical and Horizontal distribution of Sea
water temperature – Salinity: Factors controlling salinity and distribution – Density of Sea water.
Temperature Distribution of Oceans
The study of the temperature of the oceans is important for determining the
1. movement of large volumes of water (vertical and horizontal ocean currents),
2. type and distribution of marine organisms at various depths of oceans,
3. climate of coastal lands, etc.
Source of Heat in Oceans
The sun is the principal source of energy (Insolation).
The ocean is also heated by the inner heat of the ocean itself (earth’s interior is hot. At the
sea surface, the crust is only about 5 to 30 km thick). But this heat is negligible compared to that
received from sun.
VERTICAL AND HORIZONTAL DISTRIBUTION OF OCEAN TEMPERATURE
The distributional pattern of temperature of ocean water is studied in two ways viz.
Horizontal distribution (temperature of surface water) and
Vertical distribution (from surface water to the bottom).
Since the ocean has three-dimensional shape, the depth of oceans, besides latitudes, is also
taken into account in the study of temperature distribution. The following factors affect the
distribution of temperature of ocean water.
Latitudes
The temperature of surface water decreases from equator toward the poles because the
sun’s rays become more and more slanting and thus the amount of insolation decreases pole
ward 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 40°Latitude and the poles in
both the hemispheres.
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 northern hemisphere and water in the southern
hemisphere. As far as surface temperature is concerned, it has the following implications:
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 northern hemisphere than the
southern hemisphere.
The isotherms are not regular and do not follow latitudes in the northern hemisphere
because of the existence of both warm and cold landmasses 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 whereas it is 37.8°C in the Red Sea and 34.4°C (94°F) in
the Persian Gulf.
Prevailing wind
Wind direction largely affects the distribution of temperature of ocean water. The winds
blowing from the land towards the oceans and seas (i.e. 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.
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.
Other factors
Other factors include the following:
Submarine ridges
Local weather conditions such as storms, cyclones, hurricanes, fog, cloudiness,
evaporation and condensation
Location and Shape of area: The enclosed seas in the low latitudes record relatively
higher temperature than the open seas whereas the enclosed seas have lower temperature
than the open seas in the high latitudes.
Horizontal Distribution of Temperature Average temperature of surface water of the oceans
is 26.7°C and the temperature gradually decreases from equator towards the poles. The rate of
decrease of temperature with increasing latitudes is generally 0.5°C per latitude. The average
temperatures become 22°C at 20° N and S latitudes, 14°C at 40° N and S latitude, and 0°C
near the poles. I have already mentioned above that the oceans in the northern hemisphere
record relatively higher average temperature than in the southern hemisphere. Please note that
the highest temperature is not recorded at the equator rather it is a bit north of it. Also we should
note that the average annual temperature of all the oceans is 17.2°C. The average annual
temperatures for the northern and southern hemispheres are 19.4°C and 16.1°C respectively.
The variation of temperatures in the northern and southern hemispheres is because of unequal
distribution of land and water as Northern hemisphere is made up of more land, while the
southern hemisphere is made up of more oceans.
INTRODUCTION TO OCEANOGRAPHY
CODE: 18K2G03
Unit III: Distribution of Temperature and Salinity: Vertical and Horizontal distribution of Sea
water temperature – Salinity: Factors controlling salinity and distribution – Density of Sea water.
Temperature Distribution of Oceans
The study of the temperature of the oceans is important for determining the
1. movement of large volumes of water (vertical and horizontal ocean currents),
2. type and distribution of marine organisms at various depths of oceans,
3. climate of coastal lands, etc.
Source of Heat in Oceans
The sun is the principal source of energy (Insolation).
The ocean is also heated by the inner heat of the ocean itself (earth’s interior is hot. At the
sea surface, the crust is only about 5 to 30 km thick). But this heat is negligible compared to that
received from sun.
VERTICAL AND HORIZONTAL DISTRIBUTION OF OCEAN TEMPERATURE
The distributional pattern of temperature of ocean water is studied in two ways viz.
Horizontal distribution (temperature of surface water) and
Vertical distribution (from surface water to the bottom).
Since the ocean has three-dimensional shape, the depth of oceans, besides latitudes, is also
taken into account in the study of temperature distribution. The following factors affect the
distribution of temperature of ocean water.
Latitudes
The temperature of surface water decreases from equator toward the poles because the
sun’s rays become more and more slanting and thus the amount of insolation decreases pole
ward 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 40°Latitude and the poles in
both the hemispheres.
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 northern hemisphere and water in the southern
hemisphere. As far as surface temperature is concerned, it has the following implications:
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 northern hemisphere than the
southern hemisphere.
The isotherms are not regular and do not follow latitudes in the northern hemisphere
because of the existence of both warm and cold landmasses 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 whereas it is 37.8°C in the Red Sea and 34.4°C (94°F) in
the Persian Gulf.
Prevailing wind
Wind direction largely affects the distribution of temperature of ocean water. The winds
blowing from the land towards the oceans and seas (i.e. 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.
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.
Other factors
Other factors include the following:
Submarine ridges
Local weather conditions such as storms, cyclones, hurricanes, fog, cloudiness,
evaporation and condensation
Location and Shape of area: The enclosed seas in the low latitudes record relatively
higher temperature than the open seas whereas the enclosed seas have lower temperature
than the open seas in the high latitudes.
Horizontal Distribution of Temperature Average temperature of surface water of the oceans
is 26.7°C and the temperature gradually decreases from equator towards the poles. The rate of
decrease of temperature with increasing latitudes is generally 0.5°C per latitude. The average
temperatures become 22°C at 20° N and S latitudes, 14°C at 40° N and S latitude, and 0°C
near the poles. I have already mentioned above that the oceans in the northern hemisphere
record relatively higher average temperature than in the southern hemisphere. Please note that
the highest temperature is not recorded at the equator rather it is a bit north of it. Also we should
note that the average annual temperature of all the oceans is 17.2°C. The average annual
temperatures for the northern and southern hemispheres are 19.4°C and 16.1°C respectively.
The variation of temperatures in the northern and southern hemispheres is because of unequal
distribution of land and water as Northern hemisphere is made up of more land, while the
southern hemisphere is made up of more oceans.
