Distribution Of Salinity in the Water of the Ocean

Salinity refers to the total content of dissolved materials in water bodies. It means the amount of salt dissolved in seawater. It is calculated as the amount of solid material (in gm) dissolved in 1,000 gm (1 kg) of seawater and it is generally denoted as parts per thousand(‰) or ppt.

Ocean Salinity is affected by several factors.
These are evaporation, rainfall, river water influx, ocean currents, atmospheric pressure, wind direction, and global warming.
The average salinity of oceans and seas is 35‰.
Oceans and seas experience spatial and temporal variations in the distribution of salinity, although it is not equally distributes.
This variation is both horizontal and vertical; horizontal distribution means the variation of salinity at the surface level of the ocean and vertical distribution refers to salinity changes with the depth of the ocean.

Surface seawater salinities largely reflect the local balance between evaporation and precipitation.

Low salinities occur near the equator due to rain from rising atmospheric circulation.
High salinities are typical of the hot dry gyres flanking the equator (20-30 degrees latitude) where atmospheric circulation cells descend.
Salinity can also be affected by sea ice formation/melting (e.g. around Antarctica)
The surface N. Atlantic is saltier than the surface N. Pacific, making surface water denser in the N. Atlantic at the same temperature and leading to down-welling of water in this region this difference is because on average N. Atlantic is warmer (10.0 C) than N. Pacific (6.7 C).
This is mostly because of the greater local heating effect of the Gulf Stream, as compared to the Kuroshio Current. Warmer water evaporates more rapidly, creating a higher residual salt content.
The surface North Atlantic is saltier than the surface North Pacific, making surface water denser in the North Atlantic at the same temperature and leading to the down-welling of water in this region.
This difference is due to the fact that the North Atlantic is warmer (10.0 C) on average than the North Pacific (6.7 C).
The influence of surface salinity fluctuations due to evaporation and precipitation changes is generally small below 1000 m, where salinities are mostly between 34.5 and 35.0 at all latitudes.
Typically, at low and mid-latitudes, between the mixed surface layer and the deep ocean, we find zones where salinity decreases with depth.
These are referred to as haloclines.
Two approaches are use to investigate the spatial distribution of salinity across oceans
- Horizontal Distribution of Salinity &
- Vertical Distribution of Salinity

Ques 1. How is salinity distributed in the water of the ocean?

Ans. Salinity in the water of the ocean is distributed unevenly across different regions. Various factors, such as evaporation, precipitation, freshwater inputs from rivers, melting ice, and ocean currents, influence the distribution of salinity in the ocean. As a result, salinity can vary from one area to another, creating distinct zones with different salinity levels.

Ques 2. What are the main factors that affect the distribution of salinity in the ocean?

Ans. Several factors influence the distribution of salinity in the ocean. Evaporation plays a significant role, as areas with high evaporation rates tend to have higher salinity. Precipitation, on the other hand, dilutes the seawater, reducing salinity. Freshwater inputs from rivers and melting ice can introduce lower salinity water into specific regions. Ocean currents also contribute to the distribution of salinity, transporting water masses with different salinity levels across the ocean.

Ques 3. What are the major zones of salinity distribution in the ocean?

Ans.The ocean divides into several zones of salinity based on its latitudinal distribution. The equatorial zones generally have comparatively low salinity due to high precipitation. The tropical zones have the maximum salinity, influenced by high evaporation rates. The temperate zones exhibit lower salinity, while the sub-polar and polar zones have the minimum salinity due to freshwater inputs from melting ice and low evaporation rates.