Tropical ocean waters are more saline than colder waters because tropical waters

The answer is; are warmer

The amount of solute (this case salts) that a solvent (this case water) can dissolve is directly proportional to the temperatures of the solution. The higher the temperatures the more solute is dissolved before saturation is reached. Tropical waters are warm due to the angle and surface areas at which the water hit the waters, as compared to the polar regions.