The correct answer is option 4: 1, 2 and 3.

Statement 1 states that the ocean salinity depends on evaporation and precipitation, which is correct. When water evaporates from the ocean, it leaves the salts behind, increasing the salinity. Conversely, when precipitation occurs, it adds freshwater to the ocean, reducing the salinity.

Statement 2 states that any change in temperature or density influences the salinity, which is also correct. Temperature and salinity are directly related, with higher temperatures leading to increased evaporation and higher salinity levels. Density, which is determined by salinity and temperature, affects the vertical movement of ocean water and can impact salinity distribution.

Statement 3 states that the major source of sea salinity is terrestrial discharge by rivers, which is true. The continental runoff from rivers carries dissolved and suspended salts into the ocean, contributing to its salinity.

Therefore, all three statements are correct, making option 4 the correct answer.