The correct option is 1 and 3 only.
Explanation
The vertical distribution of salinity in the oceans is determined by the interaction of surface processes (such as evaporation and precipitation) and the density differences that drive water stratification. While surface salinity varies significantly by latitude, deep ocean salinity remains relatively uniform.
Statement-wise Analysis:
- Statement 1 is Correct. Salinity at the surface is directly influenced by the hydrological cycle. Processes that remove fresh water from the ocean, such as evaporation and the formation of sea ice (freezing), leave salts behind, thereby increasing the salinity of the remaining surface water. Conversely, precipitation and ice melting decrease salinity.
- Statement 2 is Incorrect. Salinity at depth is very fixed and stable, not highly variable. Once water sinks from the surface, it is isolated from the atmospheric processes (evaporation, precipitation) that alter salinity. Consequently, there is no mechanism to frequently add or lose salt in the deep ocean zones.
- Statement 3 is Correct. The vertical profile of the ocean typically exhibits a distinct zone called the halocline, where salinity changes sharply with depth. In general terms regarding density stratification, this zone is often characterized by a sharp increase in salinity, which contributes to the increasing density of water with depth.
Key Takeaway:
The halocline is the transition zone of rapid salinity change between the variable surface waters and the stable deep waters. While surface salinity fluctuates due to evaporation and precipitation, deep ocean salinity is largely constant.