Seawater Is About 3.5 Percent Salt

Everyone knows the sea is salty, but the amount can be stated exactly. NOAA’s National Ocean Service gives the average salinity of the ocean as about 35 parts per thousand. Stated another way, about 3.5 percent of the weight of seawater comes from the dissolved salts. NOAA also explains where the salt comes from. Ocean salt primarily comes from rocks on land and from openings in the seafloor. The figure of 3.5 percent is an average, and the sea is not equally salty everywhere. According to NOAA, salinity is generally low at the equator and at the poles, and high at mid-latitudes. So how salty a sample of seawater is depends partly on where in the world it was collected.