Among all liquids, water has nearly the greatest capacity to store heat while undergoing relatively small temperature changes. In fact, the upper 2 m (6.2 ft) of the ocean can store as much heat as the entire overlying atmosphere, which has much less mass and much less ability to store heat. The meteorologist-climatologist Carl Rossby and other scientists before him drew attention to the fact that the great mass of the world ocean not only could store large amounts of heat but also could remove this heat by direct contact with the atmosphere for long periods of time, from years to millennia. This could be accomplished through the downward movement of the water that is observed to occur in certain regions of the world ocean such as the Labrador Sea. Relatively dense surface water can sink and displace less dense subsurface water. Even if the temperature of the surface water is warmer than the subsurface water it displaces, the surface water can still be denser than the subsurface water if its salinity is greater than the subsurface water. At subsurface depths this heat can be transported via ocean currents over large distances in the horizontal as well as the vertical before returning to the sea surface in modified form due to mixing of water masses of different temperatures and salinities. This mechanism is called the thermohaline circulation (“thermo” refers to temperature and “haline” to salinity) and is known popularly as the ocean conveyor belt.