Figure 10.7

Variation in ocean salinity. The map shows global variation in salinity at the ocean surface. PSU is a measure of salinity based on the electrical conductivity of seawater. The graphs show variation in salinity with depth. The halocline is the transitional zone of salinity change between the ocean surface and the deep sea. At a depth of about 3,500 m (11,500 ft), salinity is about 3.5% at all latitudes.