Temperature of ocean water

Introduction

The ocean water temperature is directly affected by the amount of radiation received from the sun on the ocean’s surface. Since the latitudes closer to the equator receive direct sunlight all year round, the ocean surface is relatively warmer in these regions. 

The ocean water temperature also differs in terms of depth and longitudes. There is an inverse correlation between the depth and the ocean’s temperature, i.e., the deeper the depth, the lower the temperature would be.

Since the latitudes closer to the equator receive more direct radiation from the sun than the latitudes closer to the polar region, the temperature of ocean water in both these regions can range between 30 degrees Celsius in the equator to -2 degrees Celsius at the pole. 

Horizontal distribution of the ocean temperature

• The average temperature of the ocean water is approximately 27 degrees Celcius near the equator, and it gradually decreases as the latitudes proceed closer to the poles
• The temperature of the ocean water decreases at the rate of 0.5 degrees per latitude. The isothermal lines are used to depict the horizontal temperature distribution of the ocean water
• The isothermal lines connect the areas of equal temperature. The isotherm is depicted in curves on a chart with two variables, i.e. volume and pressure, where the temperature remains constant

Vertical distribution of ocean temperature

• The vertical distribution of ocean water is measured from the ocean’s surface to the bottom of the ocean floor; with the gradual increase in the ocean’s depth, the temperature of the ocean water decreases
• This is because the ocean surface receives direct radiation from the sun, which heats the surface while the deeper depth remains relatively cooler
• The ocean water temperature experiences a rapid decline after a certain point where the temperature of the warmer surface interacts with the much cooler temperature of the deep oceanic waters, and this transition point is known as Thermocline
• The thermocline layer of the ocean is almost 500-1000 mts thick, and this region is known for the rapid decrease in temperature of the ocean water as compared to the surface
• The warmer surface temperature region is known as the Epipelagic zone, and the cooler temperature at a depth of the ocean is known as the Mesopelagic zone
• After the thermocline layer, the third layer of the ocean experiences much cooler temperatures which extends up to the deep oceanic floor. The temperature almost becomes stagnant or constant in this region

Unequal distribution of land and water

Ocean water in the Northern Hemisphere is relatively warmer than the temperature of the oceanic water of the Southern Hemisphere. This phenomenon is because the oceans in the Northern Hemisphere are exposed to more surface area of the land compared to the Southern Hemisphere.

This condition can be further explained as follows:

• The line of isotherms often fluctuates in the Northern Hemisphere due to the fact that the temperature of the landmass and the surface of the ocean is highly inconsistent. The condition in the Southern Hemisphere is the opposite
• In the Southern Hemisphere, since the distribution of landmass is relatively less than compared to the Northern Hemisphere, the ocean surface temperature remains relatively constant
• Also, the ocean waters in the lower latitudes that are closer to the equator are exposed to more landmass. Hence, the temperature of the ocean surface in this region is relatively higher than the oceans closer to the higher latitudes
• It has been estimated that the average annual temperature of the ocean surface near the equator is 26.7 degrees Celsius. The temperature of the ocean surface near the Persian Gulf and the Red Sea is approximately 37.4 degrees annually

Prevailing winds

The direction of wind from the land to the ocean and vice versa also affects the longitudinal temperature of the ocean surface. The wind blowing from the land to the ocean, also known as offshore winds, drives away the warm surface water from the coastline, making the cooler water from below the surface level move upwards. This process of vertical movement of the ocean water is known as upwelling.The exact opposite of this phenomenon occurs when the onshore winds blowing from the sea towards the land drive the warm oceanic waters towards the coastline, raising the temperature and causing downwelling. This whole process leads to the longitudinal difference in the temperature of ocean water.

Ocean current 

The horizontal movement of the ocean water controlled by gravity and other variables such as wind is known as an ocean current. The warm ocean currents raise the temperature of the ocean’s surface, whereas the cold ocean currents significantly lower the temperature.

Conclusion

A number of variables and factors control the temperature of ocean water. The reception of direct radiation from the sun is the most important factor affecting the ocean water’s surface temperature.The temperature of the oceanic water differs in terms of latitude and longitude. The oceans that are closer to the equator and the lower latitudes are warmer in terms of surface temperature than the oceans closer to the poles.Also, the oceans in the Northern Hemisphere are relatively warmer than the oceans in the Southern Hemisphere due to exposure of the ocean coastline to a greater landmass in the Northern Hemisphere.