Ocean temperature at BATS changes both with time and depth.   In the winter, storms help mix deep, cold water (blues) to the surface (the white line shows the depth of winter mixing).  This water is then warmed by the sun, and forms a very "stable" warm water layer (yellows and reds) at the surface.  As you can see, the difference in temperature in the surface waters ranges from 18 to 29 degrees Celsius.