Ocean Water: Temperature

The ocean has a wide range of temperatures from the almost 100°F (38°C) shallow coastal waters of the tropics to the nearly freezing waters of the poles.

The freezing point of seawater is about 28.4°F (-2°C), instead of the 32°F (0°C) freezing point of ordinary water. Why do you think the freezing points are different? Right, because seawater has salt in it! As seawater increases 5 ppt in salinity, the freezing point decreases by 0.5°F.

The ocean can be divided into three vertical zones, depending on temperature. The top layer is the surface layer, or mixed layer. This layer is the most easily influenced with solar energy (the sun's heat), wind and rain. The next layer is the thermocline. Here the water temperature drops as the depth increases. The last layer is the deep-water layer. Water temperature in this zone decreases slowly as depth increases. Water temperature in the deepest parts of the ocean is averages about 36°F (2°C).