Oceanic Salinity and its effects.

Salinity is defined as the amount of salt dissolved in 1000 gms of sea water. it is usually expressed as parts per thousand or ppt. The salinity for normal open ocean ranges between 33o/oo and 37o/oo. Oceanic salinity varies significantly due to the free movement of ocean water and its distribution has two aspects: 

• Horizontal: The areas of highest salinity (about 37o/oo, in Atlantic Ocean) are found near the Tropics due to active evaporation owing to clear skies, high temperature and steady Trade winds. From the tropical areas, salinity decreases both towards the equator and towards the poles. Salinity is relatively low near the equator (about 35o/oo, in Atlantic Ocean) due to high rainfall, high relative humidity, cloudiness and calm air of the doldrums. In polar seas, salinity decreases (20-32o/oo) due to very little evaporation and due to melting ice yielding fresh water. 

• Vertical: Generally salinity decreases with increasing depth. Surface water is more saline due to loss of water from evaporation. This varies greatly with latitudes and is influenced by the cold and warm currents. In higher latitudes, salinity increases with depth and in middle latitudes it increases up to 35 meters and then decreases. 

The multidimensional effects of oceanic salinity are as follows:- 

• Salinity determines compressibility, thermal expansion, temperature, density, absorption of insolation, evaporation and humidity. 

• Salinity & Water Cycle: Water in liquid state dissolves rocks and sediments which creates a complex solution of mineral salts in ocean basins. Conversely, in other states such as vapor and ice, water and salt are incompatible and water vapor and ice are essentially salt free. By tracking ocean surface salinity we can directly monitor variations in the water cycle: land runoff, sea ice freezing and melting, and evaporation and precipitation over the oceans. 

• Salinity, Ocean Circulation & Climate: Ocean circulation in deep waters is primarily driven by changes in seawater density, which is determined by salinity and temperature. In the North Atlantic near Greenland, cooled high-salinity surface waters can become dense enough to sink to great depths. 

• Salinity & Climate Density: The ocean stores more heat in the uppermost three meters than the entire atmosphere. Thus density-controlled circulation is key to transporting heat in the ocean and maintaining Earth’s climate. Excess heat associated with the increase in global temperature during the last century is being absorbed and moved by the ocean. 

• Salinity also influences the distribution of fish and other marine resources. 

• NASA studies suggest that sea water is getting fresher in high latitudes while saltier in sub-tropical latitude. This will significantly impact not only ocean circulation but also the climate in which we live.