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.
From "Ocean Talk" by Naval Meteorology and Oceanography
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).