Vertical Distribution Of Salinity in The Ocean

The term used to define the total content of dissolved salt in the seawater is called Salinity. The salinity can be calculated as the amount of salt in a gram dissolved in 1000 grams or 1 kg of seawater. Ocean salinity can be expressed as parts per thousand or ppt. If the salinity of seawater is 24.7, it is considered as the upper limit. If the salt content in the ocean is 24.7, then the water is known as brackish water.

Role of Ocean Salinity

Salinity determines compressibility, humidity, and absorption. It also determines thermal expansion, temperature, and density.
The distribution of the fishes and the other marine resources are being affected by the ocean salinity. The salinity also influences the composition and the movement of the sea.

Vertical Distribution Of Salinity

Salinity changes with depth, but the way it changes depends upon the location of the sea.
Salinity at the surface increases by the loss of water to ice or evaporation or decreased by the input of freshwaters, such as from the rivers.
Salinity at depth is very much fixed because there is no way that water is ‘lost’, or the salt is ‘added.’ There is a marked difference in the salinity between the surface zones and the deep zones of the oceans.
The lower salinity water rests above the higher salinity dense water.
Salinity, generally, increases with depth and there is a distinct zone called the halocline (compare this with thermocline), where salinity increases sharply.
Other factors being constant, increasing the salinity of seawater causes its density to increase. High salinity seawater, generally, sinks below the lower salinity water. This leads to stratification by salinity.

Salt Budget

It is also known as the salt cycle. It involves all the processes through which salt moves from the ocean into the lithosphere, to a certain extent into the atmosphere, and back into the oceans.

Moving water, including groundwater, leaches minerals from the rocks through the process of surface erosion. The mineral-laced water joins the rivers and streams which finally reach the oceans. These minerals add to the salinity levels of the ocean waters.
Some of the salts in the ocean waters accumulate at the ocean bottom through the process of sedimentation turning into mineralized rocks. Over a period of millions of years, some of these rocks get raised above the ocean surface due to plate tectonics, or due to volcanic activity. This brings the salt back to the lithosphere in the form of minerals (rocks).
Salt from the oceans also gets sprayed into the atmosphere due to the action of wind. This salt returns to the lithosphere mixed with precipitation. However, this constitutes a tiny fraction of salt moving from the land to the sea and vice versa.
Salt cycle operates over a very long period of time.

Every year, around 3 billion tons of salt get added to the oceans from the land. A tiny fraction of this salt is extracted by humans for daily consumption.

FAQs related with Vertical Distribution Of Salinity

Ques 1.How does salinity change with depth in the ocean?

Ans. The vertical distribution of salinity in the ocean varies with depth. Generally, salinity tends to increase with depth due to factors such as evaporation, formation of sea ice, and the sinking of denser water masses. However, there are regions where salinity decreases with depth, such as in areas influenced by freshwater inputs from rivers or melting ice.

Ques 2. What are the main factors influencing the vertical distribution of salinity?

Ans. Several factors contribute to the vertical distribution of salinity in the ocean. These include processes like evaporation and precipitation, which can alter the balance of salt and water. Other factors include the mixing of different water masses, the influence of ocean currents, and the input of freshwater from sources such as rivers, melting ice, or rainfall.

Ques 3. How does the vertical distribution of salinity affect ocean circulation?

Ans. The vertical distribution of salinity plays a crucial role in ocean circulation patterns. Variations in salinity influence the density of seawater, which in turn affects its buoyancy and vertical movement. This can lead to the formation of density-driven currents, such as deep ocean currents and the global thermohaline circulation. Salinity gradients also contribute to the formation of ocean stratification, influencing the distribution of heat, nutrients, and dissolved gases throughout the ocean.