A message In a bottle Oct 14, 2012 By Anita Ramachandran

A deep-water current having a force 16 times as strong as the world’s rivers combined, works at more depth. This current is known as the global conveyor belt and is driven by density difference in the water. The density differences are caused by temperature differences and salt content. Cold water is denser than warm water and saltier water is denser as well. Known as the thermohaline circulation, the water’s motion is dependent on its temperature (thermo) and salinity (haline).

The global conveyor belt begins in the North Pole and heads south between South America and Africa towards Antarctica. The landmasses affect the direction of the currents. In Antarctica, it gets recharged with more cold water and splits in two directions – one towards Indian Ocean and the other to the Pacific Ocean [follow the cold lines].

Near the equator, the two sections warm up and rise to the surface to cause upwelling. When they cant go any farther, they loop back to the South Atlantic Ocean and North Atlantic Ocean respectively [follow the warm lines], where the cycle starts again.

Very likely Jasmine’s bottle was picked up by the longshore currents. And while it bobbed along with the surface currents, the underlying Global Conveyor belt carried the bottle southward, then along the western shores of Africa, looping into the Southern Indian Ocean into the Largs Bay in Australia. Amazing, isn’t it?

1. 
   What causes surface currents in the oceans?
   

2. 
   What causes a thermohaline current? Hint: Think about the water at the North or South Pole vs. water at the equator
   

3. 
   What do they mean by the name ‘Global Conveyor Belt’?
   

4. 
   How do you think boat captains could use these currents to their advantage?
   

5. 
   How could these currents interact with pollution? Hint: We have items from the Japanese tsunami washing up on the shores of California.