What typically increases the salinity of seawater?

The increase in salinity of seawater is primarily associated with the evaporation of water. When seawater evaporates, it leaves behind salts and other dissolved minerals. This process concentrates the remaining salts in the water, leading to higher salinity levels. In areas with high temperatures and low humidity, such as tropical regions, evaporation can significantly elevate salinity because the rate of water loss exceeds the rate at which freshwater input can dilute the salts.

Conversely, processes like the absorption of freshwater, increased rainfall, or plant growth typically lead to a decrease in salinity. Freshwater input from rivers, rain, or melting ice dilutes the salts in seawater, thereby lowering salinity levels. Additionally, plant growth does not directly contribute to an increase in salinity; in some cases, it can enhance local water retention and result in less evaporation, influencing salinity indirectly. Therefore, evaporation stands out as the primary mechanism by which salinity in seawater is elevated.