The ocean in motion: learning about ocean currents

So far we have done a few blog posts about geophysics, but all of them are based on land phenomena. The next two blog posts will focus on the two elements of geophysics: oceans and atmosphere. In particular, in this blog post, we will be focusing on the oceans. Today we will talk about the ocean currents in our blog post.

Ocean currents are streams of water in the ocean that flow in a definite direction. They can be up to 200 kilometers wide, and they are driven by two different things: different density of water, which is responsible for moving them between surface and deep water, and also by the winds in the ocean, which make them move laterally. 

When these two effects combine, what we end up with is a phenomenon called circulation. Currents in the northern hemisphere circulate clockwise, and currents in the southern hemisphere circulate anticlockwise as you can see in the previous picture. The speed of circulation is faster in the surface and slower in the deep but generally very slow. 

The largest of these currents is called the Great Conveyor Belt. Since the speed of current is just a couple centimeters per second, and it would take a water drop about a whooping thousand years to do the whole loop. Also, you might be wondering how deep currents are. Some of these currents can affect up to 400 meters deep. 

The density of water is impacted by two different factors: temperature and salinity. Warm water is less dense and goes to the surface while cold water is denser and sinks. Likewise for salinity, the more salt the water carries, the denser it is which makes it sink. There are three factors that affect salinity: evaporation, rainfall, and melting of the ice.

This is why global warming is such a huge issue. Melting of the ice caps is interfering with the speed of ocean currents, making them weaker and slower. This would contribute to changing the climate of the planet and also would reduce the amount of nutrients available in the deep parts of the ocean. 

I've made an experiment that tried to replicate the impact of these two factors, temperature and salinity, on the density of the water. On one hand, I warmed up a little bit of water in a pot and added red food coloring. On the other hand, I put some water with a bit of ice, some salt dissolved, and a bit of blue food coloring.

As you can see in the previous image, it was amazing to see that they didn't mix. In the first attempt, though, I used a test tube and with a pipette and I tried to drop it carefully, but still the kinetic energy was enough to sink the water a bit and mix it. So, the result was some blue water at the bottom and then a purple gradient all the way to the surface. Once

I realized this, I decided to put a little sponge floating on top of the blue water and then pour the red water into the sponge to remove that kinetic energy. The result, as you can see, was a very clean separation of less dense hot water at the top and more dense salted cold water at the bottom.

The previous photo shows what it looked like after 48 hours. As you can see, if left undisturbed, they would still wouldn't mix.

I learnt a lot doing this blog. I hope you did too. In the next blog post, we will continue exploring the final part of geohysics we haven't covered yet: the atmosphere.