How Salty the Ocean

On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every kilogram (roughly one liter by volume) of seawater has approximately 35 grams of dissolved salts (predominantly sodium chloride. The average density of seawater at the ocean surface is 1.025 g/ml. Seawater is denser than both fresh water and pure water because the dissolved salts add mass without contributing significantly to the volume. The freezing point of seawater decreases as salt concentration increases. NASA's Aquarius satellite has successfully completed its commissioning phase and is now tasting the saltiness of Earth's ocean surface, making measurements from its perch in near-polar orbit. Aquarius will make NASA's first space observations of the salinity, or concentration of salt, at the ocean surface, a key variable in satellite studies of Earth. Variations in salinity influence the ocean's deep circulation, outline the path freshwater takes around our planet and help drive Earth's climate.