World’s Physical Geography

#INTRODUCTION-

Salinity is the amount or degree of dissolved salts in the ocean. It is basically calculated as part per thousands (‰). The oceanic salinity affects marine organism, plant community as well as the physical property of oceanic water such as temperature, density, pressure, waves, currents etc.

FACTORS DETERMINING OCEANIC SALINITY–

1. ADDITION OF FRESH WATER:

♦ Precipitation- It is inversely proportional to salinity (higher the rainfall, lower the salinity and vice versa). The volume of water in the oceans is increased due to heavy rainfall and thus the ratio of salt to total volume of water is reduced.

♦Melting of glacier- It is more zonal in nature. It is more confine to the polar to sub polar region as the number  of glaciers are more there. Due to melting, freshwater is added to oceanic water which lower the salinity of surrounding area.

♦Discharge by rivers- Big and voluminous river pour down immense volume of water into the ocean and thus the salinity is reduced at their mouths. The influx of river water is more pronounced in enclosed sea as it further reduces the salinity.

2. EXTRACTION OF WATER:

♦Evaporation-  There is direct relation between evaporation and salinity as greater the evaporation greater the salinity and vice versa. evaporation with high temperature and low humidity increases concentration of salt. It is totally depend on temperature, wind velocity, relative humidity.

3. MIXING:

♦Warm current- Due to high temperature near warm current the salinity will be  higher.

♦Cold current- If the temperature is low than the salinity will be low.

♦Partially Enclosed sea- Here one can register extremes.

4. ATMOSPHERIC CIRCULATION-

♦Anticyclonic condition with stable air and high temperature increase salinity of surface water of the ocean.

♦ Area of upwelling of water less saline water moves up from below whereas the areas where water is piled up the salinity is increased.

SPATIAL DISTRIBUTION ACROSS WORLD-

◊ HORIZONTAL DISTRIBUTION:

•Equator– There is less salinity near equator at least from 5 to 5 degree north and south hemisphere. reasons for less salinity involves more or convectional rainfall and less evaporation(due to high relative humidity, more cloudiness so less insolation)

•Polar-sub-polar– Due to more addition of fresh water as compared to subtraction(evaporation). reasons involved glacial melt and high rainfall due to frontogenesis in that region

• Tropics– Here the salinity is very high due to less precipitation and high evaporation.

◊ HEMISPHERICAL CONTRAST-

•Southern hemisphere has  greater salinity then northern hemisphere because-

1.Greater extraction of fresh water than addition due to higher wind velocity & presence of greater volume of water.

2.Size of southern hemisphere ocean is larger than northern hemisphere hence less effected by precipitation.

3.Greater continentality in northern hemisphere.

◊VERTICAL DISTRIBUTION-

•There is no definite trend of salinity vertically. some characteristics as follows-

Salinity increases with increasing depth in higher latitude due to presence of dense water below.

In middle latitudes, increase in salinity with increasing depth confine to 200 fathom beyond which it decreases with increasing depth.

In equator, salinity is low at surface due to rainfall and oceanic currents but beyond some meters it become high again

Thermocline zone between 300-1000 meter is characterize by rapid change in density of water below which a low salinity and above it high salinity can be detected.

FIG– this figure explain latitudinal distribution of salinity.