The correct option is 1, 2, 3 and 4.
Explanation
Ocean salinity refers to the total content of dissolved salts in seawater. It is not uniform across the oceans and is primarily determined by the balance between the addition of fresh water (precipitation, river inflow, ice melt) and the removal of fresh water (evaporation, ice formation), as well as the mixing caused by winds and currents.
Statement-wise Analysis:
- 1. Evaporation and precipitation (Correct): These are the most dominant factors affecting surface salinity. High evaporation (removal of water) increases salinity, while high precipitation (addition of fresh water) decreases salinity. For example, equatorial regions have lower salinity due to heavy rainfall despite high temperatures.
- 2. Fresh water flow from rivers (Correct): The influx of river water adds fresh water to the ocean, significantly reducing salinity in coastal areas and estuaries (e.g., the mouth of the Amazon or Ganges).
- 3. Freezing and thawing of ice (Correct): In polar regions, this is a crucial factor. When seawater freezes, salt is rejected (brine rejection), increasing the salinity of the remaining water. Conversely, when ice thaws, fresh water is released, diluting the seawater and lowering salinity.
- 4. Atmospheric pressure (Correct): Atmospheric pressure plays a significant role in determining salinity zones. High-pressure belts (subtropical highs) are associated with stable air, clear skies, and high evaporation, leading to high salinity. Low-pressure belts are associated with unstable air and high precipitation, leading to lower salinity. Additionally, pressure differences drive winds, which redistribute surface water and salinity.
Key Takeaway:
The salinity of ocean water is dynamic and is controlled by the water budget (evaporation vs. precipitation/inflow) and atmospheric conditions (pressure and wind) that regulate these processes.