Temperature, Salinity and Density in the Oceans
Temperature, Salinity, Density defined
The earth's surface is composed of 70 percent water and most of it is oceans in different parts of the world. The ocean is a body of water that is of vital importance to humans as it proves to be relevant in man's livelihood and transportation. Thus, it is essential to know the different characteristics of the ocean such as temperature, salinity, and density. To understand temperature, one should first define heat as it is related to temperature. An object produces heat when molecules of the object become excited and moves rapidly. Heat is a determinant of the quantity of the molecules moving inside an object. In addition, heat also determines how rapid the movement of the molecules inside an object is. On the other hand, temperature is the reaction of an object to any changes in heat (Garisson 156). For example, the molecules of freezing water are stationary, which produces less or no heat at all and molecules of boiling water are very excited and move very rapidly, which produces heat. The measure of the change in the heat between freezing and boiling water is called temperature.
Salinity is generally defined to be the amount of dissolved materials in a kilogram of sea water. The general definition of salinity in practice is impossible as different dissolved materials that exist in sea water are immeasurable such as volatile gases. The International Council for Exploration of the sea developed a more complete definition of salinity. The council developed a committee recommending that salinity be defined as the amount of dissolved solid materials in a kilogram of sea water provided that all carbonate are converted to oxide and all bromine and iodine are replaced by chlorine (Garisson p. 187). Density, on the other hand, is simply defined as the ratio of mass to volume of materials. Thus, density is the measure of the amount of a certain material per volume of the material (Garisson 157).
How Salinity and Temperature affects Density
The density of oceans or sea water depends on different variables such as salinity and temperature. An increase in salinity yields to an increase in sea water density. This is because when salts are added in the water, there is an increase in the mass of water. The effect of temperature in density is slightly complicated. There is an increase in temperature and a decrease in density when salinity is greater. This is because salts are lighter when they are warmer. Cold sea water is denser than warm sea water with equal salinity because salts are heavier when they are cold (Reddy 137).
When salinity is over 24.7, the water freezes at the temperature of maximum density. Thus, when there is a higher salinity, the sea water freezes before the theoretical temperature of maximum density is reached. The water becomes denser as sea water comes close to the freezing point. However, when the salinity of sea water is less than 24.7 and with an increase in sea water temperature, the density also increases. This is mainly because the warming up and cooling off of sea water with less than 24.7 salinity makes it behave almost like fresh water (Reddy 138).
How Temperature and Salinity can be used to define Water Masses
A water mass is a part of water with its own distinct traits such as temperature, salinity, and density. In the ocean, water mass is determined through the "observation that water renewal in the deep ocean is the result of water mass formation in contact with the atmosphere, spreading from the formation region without atmospheric contact, and decay through mixing with other water masses." Through the analysis of the distribution of temperature and salinity, water mass can be determined. Temperature and salinity are plotted against each other in the temperature-salinity diagram, which is the basic tool for water mass analysis. This is where temperature and salinity are classified and analyzed. In the temperature-salinity diagram, homogenous water with almost consistent salinity and temperature will show up as a single plot (Tomczak n. p.).
A water mass as a body of water could mean that it takes up space and has mass in the ocean. Outside the regions where water mass is formed, water masses mix and share parts of the ocean. However, it is only in theory that water masses can be separated into little parts. Thus, each sub-volume of water mass occupies its own space. However, in theory, water masses are like physical manifestations which can occupy definitive volumes (Tomczak n. p.).
How Water Masses affect the Vertical Stratification (Density Zones) and General Circulation of the World's Oceans
The vertical movement of large volumes of water from the surface to deep parts and vice versa is only possible when the surface-water density and deep-water density are similar. The difference in temperature and density in great depths and surface of the ocean make the water very stable and prevents the exchange of deep and surface water. Despite the fact that the tropical ocean is constantly in horizontal motion, mixed, and stirred by tropical cyclones and currents, the stability of the sea water is still maintained. Vertical stratification is affected largely by the salinity difference between surface water and water at great depths. Heavier salinity will cause imbalance in the water and yield to limited vertical stratification and general circulation of the world's oceans (Garrison 170).
Garrison, Tom. Oceanography: An Invitation to Marine Science. Belmont, CA: Thomson Higher Education, 2007.
Reddy, M.P.M. Descriptive Physical Oceanography. India: A.A. Balkema, 2001.
Tomczak, M. "Water Masses in Shallow Seas." 2000. Web. 23 Oct. 2010.