Four fifths of our planet is covered by ocean. While wind is the primary driver of surface currents, deep ocean currents are driven by density differences. They create a “Global Conveyor Belt” which moves vast quantities of heat around the surface of the planet, within the oceans. They also transport nutrients around the world and are vital for life as we know it on Earth. The global conveyor belt may move slower than air currents but can transport more heat and is absolutely critical to our understanding of the forces that drive climate change.
- For more information about the GCB read this article.
- Explore this animated video.
global conveyor belt (https://sealevel.jpl.nasa.gov/images/ostm/newsroom/features/images/201004-1a.jpg, accessed on 9/4/2020)
The differences in density which drive the currents are caused by salinity and temperature changes - we call this thermohaline circulation. (thermo = temperature, haline = salty).
For experiments you can do at home to investigate how temperature and salinity difference can induce circulation watch this video.
Or try these activities.
In the experiment investigating temperature difference the cold water should sink. This is because in the cold water the particles are closer together, this makes it more dense. The hot water is less dense and so floats above the cold water.
Temperature as a driver of the global conveyor belt
When warm water from the equator moves to the poles it begins to cool, particularly when it meets ice. This makes it sink downwards and warmer water moves in to replace it, which also then cools and sinks. This creates a conveyor belt. When the water approaches the equator again it is warmed and will rise upwards.
If you conduct the experiment in our video investigating salinity difference you should see that the saltwater sinks downwards. This is because it is more dense.
saline water sinking
When seawater freezes at the poles freshwater ice is formed, and the remaining seawater becomes more saline. This makes it denser and it sinks, adding to the downward pull.
salinity as driver of the global conveyor belt
This current initiated at the poles moves millions of cubic metres of water, moving heat around our planet. It is estimated to take hundreds to thousands of years to complete its circuit. Scientists are currently researching if climate change is causing the speed of circulation to change and forecasting the impact(s) this may have.
- To find out more on the possible effects caused by changes in the global conveyor belt read this article