As some said the cold is literally the lack of heat but also the ocean plays a crucial role in determining climate because of its ability to absorb, store, and transport heat from the sun. Ocean water also affects atmospheric temperature and circulation around the world.
The ocean can warm or cool the air in a number of different ways. For example, when the air is at a lower temperature than seawater, the ocean transfers heat to the lower atmosphere, which becomes less dense as the heat causes molecules in the air to move farther apart. As a result, a low-pressure air mass forms over that part of the ocean. (Conversely, cool or cold waters lead to the formation of high-pressure air masses as air molecules move closer together.) Because air always flows from areas of higher pressure to those of lower pressure, winds are diverted toward the low-pressure area.
The ocean’s currents make it possible for weather effects to be widely distributed. Some currents carry warm water from tropical and subtropical regions toward the poles, while other currents move cool water in the opposite direction. The Gulf Stream is a current that transports warm water across the North Atlantic Ocean from Florida toward Europe. Before reaching Europe, the Gulf Stream breaks up into several other currents, one of which flows to the British Isles and Norway. The heat carried in this current warms the winds that blow over these regions, helping to keep winters there from becoming bitterly cold.
In this way, the ocean’s circulation compensates somewhat for the sun’s unequal heating of the Earth, in which the tropics receive more energy from the sun than the poles. Were it not for the moderating effects of ocean currents on air temperatures, the tropics would be much hotter than they are and the polar regions even colder.
I got this from http://science.howstuffworks.com/how-the-ocean-affects-climate-info1.htm