Which of the following is the most important influence on seawater density?

depth

salinity

temperature

none of the above

salinity

Explanation:

Depth and temperature have a minor influence in the density of liquid water.

Although the density of the liquid water depends on the temperature, the change is small. For instance, the density of water at 0ºC is 0.9998 g/cm³; at 4ºC it is 1.0000 g/cm³; at 30ºC 0.9957 g/cm³.

Most of liquids are incompressible, which means that their density does not change with the pressure; thus, the depth has almost not effect on the density.

On the other hand, salinity, the salt content, does change the density of water. The more the solute, salt, dissolved the higher the density of the seawater. This is so because the dissolved salt increases the mass in a greater proportion than it increases the volume.

An example of this is the high density of the water of Dead Sea, one of the saltiest natural waters of the planet, with a density of 1.24g/cm³. It is impossible not floating with this density.