On an average, the temperature of surface water of the oceans is 26.7°C (80°F) and the temperature gradually decreases from equator towards the poles.
The rate of decrease of temperature with increasing latitudes is generally 0.5°F per latitude.
The average temperatures become 22°C (73°F) at 20° latitude, 14°C (57°F) at 40° latitude, and 0°C (32°F) near the poles.
The oceans in the northern hemisphere record relatively higher average temperature than in the southern hemisphere.
The highest temperature is not recorded at the equator rather it is a bit north of it. The average annual temperature of all the oceans is 17.2°C (63°F).
The average annual temperatures for the northern and southern hemispheres are 19.4°C (67°F) and 16.1°C (61°F) respectively.
The variation of temperatures in the northern and southern hemispheres is because of unequal distribution of land and ocean water.
The decrease of temperature with increasing latitudes in the northern Atlantic Ocean (figs. below) is very low because of warm ocean currents.
The average temperature between 50°-70°N latitudes is recorded as 5°C (41°F). The decrease of temperature with increasing latitudes is more pronounced in the southern Atlantic Ocean.
The highest temperature of surface water of the oceans is at 5°N latitude whereas the lowest temperature is recorded between 80°N and the north pole and between 75°S and the south pole.
The average annual temperature of the Pacific Ocean is slightly higher than the Atlantic Ocean (16.91 °C or 60°F) and the Indian Ocean (17°C or 60.6°F).
The lowest (3.3°C or 35.94°F) and the highest (32.2°C or 89.96°F) temperatures of the oceans are recorded near New Scotland and in the western Pacific Ocean respectively.
The highest temperature of the Indian ocean (25°C or 82.4°F) is recorded in the Arabian Sea and Bay of Bengal but the enclosed seas of the Indian Ocean record still higher temperatures (Red Sea = 32.2°C or 90°F and Persian Gulf = 34.4°C or 94°F).
The average seasonal temperatures (February and August) of surface water of the oceans have been represented through isotherms .
The temperature of the surface water of the oceans is higher than the air temperature above the ocean surface which means ocean surface gives off heat to the atmosphere.
This phenomenon influences the generation of oceanic circulation mainly sea waves and ocean currents.
It has been observed that the air temperature at the height of 8m from the sea surface between 20°N and 55°S latitudes in the Atlantic Ocean is cooler by 0.80°C than the sea surface.
There is a lot of variation in the heat emitted from the oceans to the atmosphere during winter and summer and this phenomenon causes differences of air temperature over the oceans and the continents mainly during winter season.
The temperature for January is 22.2°C higher over the oceans between 20° and 80°N, while in July it is 4.8°C lower.
The mean annual temperature is 7°C higher over the water meridian’.
The difference between air and sea surface temperatures causes fogs over the seas and the oceans.
This happens when warm air passes over a cold sea surface having the temperature below dew point of the air.
Consequently the air over the sea surface is cooled from below and sea fog occurs.
Generally, sea fogs are frequently formed during spring and early summer because air coming from over the land is warmer while the sea surface is still cold.
Sea fogs are very common in the high latitudes but are generally absent in the tropics.
