The primary factor influencing ocean salinity is the balance between freshwater input and evaporation. Regions with high evaporation rates, such as in hot climates, tend to have higher salinity levels due to the concentration of salts. Conversely, areas with significant freshwater influx from rivers or melting glaciers reduce salinity. Through processes like rain and melting, salinity can also be affected on larger scales, influencing marine life and ocean circulation patterns.