Oceanography

Surface Salinity Distribution in the Oceans

In the open ocean, surface salinity varies generally between 33ppt and 37ppt. The distribution of surface salinity in the oceans is primarily zonal. Lower salinity values are found in the coastal areas where large rivers enter the oceans. The salinity values are lower in the polar regions of the oceans because of melting of ice. Higher values of salinity are observed in the ocean regions where evaporation is high. A comparison of the average surface salinities of the North Atlantic, South Atlantic, North Pacific and South Pacific oceans reveals that the North Atlantic is most saline (35.5) and the North Pacific is least saline (34.2). Similarly, a comparison of the average salinities of the three non-polar oceans, namely, the pacific, the Atlantic and the Indian Oceans shows that the Pacific oceans is the least saline (34.62), and the Atlantic oceans is the most saline (34.90), while the salinity of the Indian Ocean (34.76) lies between the salinities of the Atlantic and Pacific Ocenas.

The average surface salinity of the oceans as a whole is more in the southern hemisphere (35ppt) than in the northern hemisphere (34ppt). In the northern hemisphere, the proportion of land to water is 2:3, while in the southern hemisphere it is 1.4:7. So there is less sea water in the northern hemisphere to receive the fresh water of rainfall upon land and sea. As a result, the surface salinity of the oceans in the southern hemisphere is high. There are other certain areas in the oceans where the surface salinity is relatively high. The most important among these is the Sargasso Sea in the central part of the North Atlantic Where the salinity reaches a high value of 38. In the Indian oceans, there are two areas of high surface salinity as high as 36ppt. In the South Pacific Ocean, there is an area off the coast of Peru with high surface salinity of 36.5.