Temperature vs. Heat

Temperature measures the heat being released in a system or the average kinetic E.  Heat is the measure of the total quantity of kinetic E.

Water has a high specific heat

Specific heat is the heat - or total kinetic energy - needed to raise 1 gram of something 1 degree Celsius.  Water's specific heat is 1 calorie (that's high!).  Since water has a high specific heat, it takes a lot of heat to raise water's temperature a little bit; this also applies to the regulation of the human body temperature (remember we are 70% water).

Evaporative Cooling takes place in the human body to release heat by allowing water on the surface to vaporize and take the heat with the excited gaseous state.

Oceans are "heat sinks."  If the temperature of the ocean rises, the oean rises.

Water and Ice
Below 3.98 degrees Celsius water expands.  Prior to 3.98 is water's densest point.  At 0 degrees, water solidifies; when this happens it expands in to a rigid structure with every water molecule bonded to 4 other water molecules in a crystalline lattice.
Thus, in the winter, a layer of ice rises protecting the the water beneath from freezing with contact with the colder atmosphere.  In the spring, as the ice melts it sinks back down to the bottom of the body of water because it is the coldest (3.98) of the water present.  The latter is an example of convection.