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They’ll have it now

Gail Thomson, Associate Principal at Swanson School, and her students use resources from across the Hub to explore the effects of temperature and salinity on ocean currents and water density. Gail advocates the use of hands-on activities as a means of deepening science understanding.

To view the resources Gail used with her students, visit the Teaching and Learning Approaches collection in the Icy Ecosystems context.


We looked at cycles, we looked at the carbon cycle, we looked at the water cycle. They knew the water cycle, they didn’t know the carbon cycle, and so we looked at that quite extensively. We also looked at oceans. There was a video that I showed the children – it’s called the conveyor, the conveyor belts with the currents – and it showed very clearly how they move, and that’s where the hot and cold came in.

When both currents, when the hot and the cold currents meet, what’s happening?

The cold current sinks to the bottom because it’s more dense than the warm, and the warm water is above the cold because the molecules are acting faster than the cold water.

They thought that the Antarctic and Arctic, well the ice was actually made from seawater, and so we had to talk about that and why it wasn’t. And so then it was quite clear that we really had to do this sort of thing.

I will give you a sheet, a little sheet that you will work on, and it just asks you some questions about what is happening as you do this, OK? OK, another experiment that we’re gonna be looking at is looking at seawater and freshwater, and when they mix, what happens. OK, ordinarily you wouldn’t be able to see it because, you know, water is water. But we’ve got food colouring to show you the different colours, how they mix.

Half fill one of the 30 ml beakers with hot water and add some red food colouring, repeat with the other beaker adding icy water and blue food colouring. Gently add a few drops of red hot water to the room temperature water, then add some blue cold water.

So the cold, the cold water’s going under and the hot water’s up the top.

Blue is the normal water and green is saltwater,

And here’s the reaction.

The saltwater basically just, in freshwater sinks down to the bottom because it contains traces of salt, which is heavier than normal freshwater.

They’ll have it now, they’ll talk to the little ones tomorrow. They’ll have it again, it’ll be there. They’ll know about dense water, they’ll always know about dense water.