Which of the following is true concerning the concentration of salt in seawater?

The concentration of salt in seawater affects its physical properties, particularly freezing point. When salt (sodium chloride) is dissolved in water, it disrupts the formation of ice crystals, which results in a lower freezing point than that of pure water. This means that seawater, which contains a significant concentration of salt, needs to be at a lower temperature to freeze compared to freshwater. This phenomenon is essential for understanding oceanic conditions and how seawater behaves in varying temperatures, influencing marine ecosystems and climate patterns.

In contrast, the other statements do not accurately reflect the relationship between salt concentration and freezing point. The concentration of salt in seawater has not varied widely over the last 10,000 years, and while cold water can indeed hold more dissolved salts, this does not mean that colder water is inherently saltier than warm water since temperature can affect solubility differently. The principle of how freezing points are influenced by salt content is a fundamental aspect of oceanography and demonstrates the unique characteristics of seawater.