Answer:
decrease; an increase
Explanation:
Density is a physical quantity which depends upon two factors mass and volume. Density has a direct relationship with mass while an indirect relationship with volume i.e. if mass will increase then density will also increase but if volume will increase then density will decrease.
The formula for density is mentioned as under:
Density = mass/volume.
Here, in this question the reason why density of sea water will increase if temperature decreases is because a decrease in temperature will result into less movement and therefore lesser space between water molecules and lesser space indicates less volume. Since, volume and density has inverse relationship so less volume will be responsible for increase in density.
When it comes to salinity, an increase in salinity will result into the higher density of sea water. When salts dissolve into the water they add to the mass/weight of the water i.e. mass of the water increases with increase in salinity. Since, mass and density have direct relationship, an increase in salinity will increase the density of water.