differences in the water. Water movements driven by differences in density are also known asthermohaline circulation because
water density depends on its temperature (thermo) and salinity (haline).
refers to an object's mass per unit volume, or how compact it is. A heavy, compact bowling ball is obviously going to be
denser than an air-filled beach ball. With water, colder and saltier equals denser.
At the earth's poles, when water freezes, the salt doesn't necessarily freeze with it, so a large volume of dense cold, salt water is
left behind. When this dense water sinks to the ocean floor, more water moves in to replace it, creating a current. The new water
also gets cold and sinks, continuing the cycle. Incredibly, this process drives a current of water around the globe.
The global conveyor belt
The global conveyor belt begins with the cold water near the North Pole and heads south between South America and Africa
toward Antarctica, partly directed by the landmasses it encounters. In Antarctica, it gets recharged with more cold water and then
splits in two directions -- one section heads to the Indian Ocean and the other to the Pacific Ocean. As the two sections near the
equator, they warm up and rise to the surface in what you may remember as upwelling. When they can't go any farther, the two
sections loop back to the South Atlantic Ocean and finally back to the North Atlantic Ocean, where the cycle starts again.
The global conveyor belt moves much more slowly than surface currents -- a few centimeters per second, compared to tens or
hundreds of centimeters per second. Scientists estimate that it takes one section of the belt 1,000 years to complete one full
circuit of the globe. However slow it is, though, it moves a vast amount of water -- more than 100 times the flow of the Amazon
River. [source: NOAA: "Currents"].
Cinching Our Belt?
Many scientists fear that global warming could affect the global conveyor belt. If global warming leads to increased rain, as some
believe it might, the added fresh water could decrease the salinity levels at the poles. Melting ice, another possibility of global
warming, would also decrease salinity levels. Regardless of the means, the end scenario is the same: Warmer, less dense water
won't be dense enough to sink, and the global conveyor belt could stop -- having far-reaching and devastating consequences
[source: NOAA: "Currents"].
The global conveyor belt is crucial to the base of the world's food chain. As it transports water around the globe, it enriches carbon