Ocean Salinity

The seawater is salty due to the presence of the chemical in it. Most of them are carried by the rivers containing chemicals dissolved from the rocks and the soil. sodium chloride is the main source of salt in the seawater

• 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

Here are some of the examples of the highest salinity in the water bodies

1. Lake Van in Turkey – salinity of seawater is 330.
2. Dead sea – ocean salinity is 238.
3. The Great Salt Lake – ocean salinity is 220.

The major composition of the different salts in the sea is

(i) Sodium chloride: 77.7%

(ii) Magnesium Chloride: 10.9%

(iii) Magnesium Sulphate: 4.7%

(iv) Calcium Sulphate: 3.6%

(V) Potassium Sulphate: 2.5%

Factors affecting Ocean Salinity

• At surface level, the salinity can depend on evaporation, the addition of freshwater, and precipitation
• Thawing ice, freezing, freshwater flow influence the surface salinity
• Wind transfers the water from one place to another. It influences ocean salinity
• The ocean’s current can vary the salinity.
• The salinity of the ocean can also be influenced by salinity, temperature, and density

Measurement of 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.

Properties of Saltwater

• The presence of salt in the seawater makes it denser than freshwater
• Saltwater takes a longer time to freeze than freshwater. Because it starts freezing after the saltwater gets cold

Places with High Salinity

High salinity takes places where there is hardly any rainfall. Warm and dry temperatures can cause more evaporation which leads to the deposition of salt.

• The Atlantic has high ocean salinity as it has very little rainfall and has strong winds
• The Mediterranean sea also has high salinity in the range of 38 ppt or more. It is close to the main sea, more evaporation, less rainfall, and no extra freshwater is added
• Ocean salinity can be balanced by removing water by evaporation and the addition of freshwater by the rain and river
• 34 to 36 ppt is the range of ocean salinity

Places with Low Salinity

In some places, the rainfall is more, so more freshwater is added to the ocean. So it reduces salinity.

• The seawater near the land surface is less saline. It is because of the influx of freshwater from the land surface
• The ocean near Antarctica is less saline. It is because the ocean salinity is less than 34 ppt
• The ocean near the arctic is less saline. It is because the ocean salinity is less than 30 ppt
• Icebergs are formed by the sheets of ice formed from the land surface, which hardly contains salt
• Icebergs add fresh water to the sea. The freezing of seawater turns into ice floes. Salt came to be removed by freezing
• The Baltic sea has less salinity of fewer than 10 ppt. It is located near northern Europe and Scandinavia. The less salinity is due to the influx of freshwater from the hundreds of rivers

Horizontal distribution of Salinity

• The average salinity for the open sea is 33 to 37

High salinity regions

• Landlocked Red sea has a high ocean salinity of 41
• When the evaporation is high, salinity can be reached up to 70 in hot and dry regions

Comparatively Low Salinity regions

• In the enclosed mouth of a river where fresh and saline water gets mixed(estuaries) and in the Arctic, the salinity varies. It varies from 0- 35. This variation is due to the addition of fresh water from the ice caps

Pacific Ocean

• There is a variation of salinity in the pacific oceans. This variation is due to shape and large areal extent

Atlantic Ocean

• The salinity of the Atlantic oceans varies between 36 to 37
• The salinity near the equator of the Atlantic ocean is 35. It is due to heavy rainfall near the equator
• The low salinity near the equator is due to high relative humidity, cloudiness and the air of the doldrums
• The salinity near the polar regions is between 20 to 32. It is due to less evaporation and more freshwater being received by the melting of ice
• Between 20 N and 30 N and 20 W- 60W maximum salinity of 37 is observed. And the Salinity is decreased towards the north

Indian Ocean

• The salinity of the Indian ocean is 35
• The low salinity is observed near the Bay of Bengal. It is due to the influx of water from the Ganga river
• Due to high evaporation and less addition of freshwater, the Arabian Sea has high salinity

Marginal Sea

• Irrespective of higher latitudes, the North sea has high salinity. It is due to the addition of saline water from the North Atlantic drift
• The Baltic sea has less salinity of fewer than 10 ppt. It is located near northern Europe and Scandinavia. The less salinity is due to the influx of freshwater from the hundreds of rivers
• Due to high evaporation, the Mediterranean sea has high salinity
• Due to the enormous influx of freshwater from the river, the Black sea has low salinity

Inland Seas and Lakes

• The salinity of the inland sea and lakes is very high. It is due to the addition of salt by the rivers
• And it is also progressively saline due to high evaporation
• As time passes, the ocean and the salt lakes are becoming more and more salter. It is due to high evaporation, and the river adds saline water into it

Cold and Warm Water Mixing Zones

• In the western part of the northern hemisphere, the salinity decreases from 35 to 31. It is due to the addition of freshwater from the Arctic region

Sub-surface Salinity

Variation in depth is responsible for salinity. Variation in latitudes also matters. Salinity is also decreased due to the variation of cold and warm currents.

1. In high latitudes – salinity increase with the increase in depth.
2. In middle latitudes- salinity increases up to 35 meters and gradually decreases.
3.   At equator – low ocean salinity.

Vertical Distribution of Salinity

• Through salinity changes with the variation in depths, it also varies depending on the location of the sea
• At the surface, the vertical distribution of salinity in the ocean is high due to high evaporations, and salinity is also low by the addition of freshwater
• Salinity at depth is fixed, As there is no way of adding or reducing water. But there is a major difference between the surface zone and the deep zone of the ocean
• High dense salinity water is always below the low salinity water
• At the halocline, the salinity will sharply increase
• As the vertical salinity distribution increases, the density of the seawater is also increased. So, high salinity water is present below the low salinity water. This will lead to stratification by salinity

Conclusion

In ocean salinity we have learned about the vertical distribution, and horizontal distribution of salinity. Salinity can be calculated as the amount of salt in a gram dissolved in 1000 grams or 1 kg of seawater. There is variation in salinity in different oceans due to their geographical location and the associated features.