To the bottom of the ocean
A week before I started the long journey to the Antarctica, I visited the Costessy Infant School and had a wonderful morning with the three reception classes. My friend the albatross and I enjoyed it a lot. We talked a lot about the habitat Southern Ocean and its animals, and how all life down here depends on krill – one of our main research objectives down here.
And that is what we did for the last two weeks. We took water samples, measured temperature and salinity of the krill habitat and even monitored swarms of krill by sound. We used underwater gliders and the ship to sample all these – while the gliders are carefully ballasted and cannot carry additional items, the instrument we do lower with a cable from the ship to the ocean floor and back can. This large heavy instrument is called CTD, which is an abbreviation for Conductivity – Temperature – Depth, which are the main measurements it does with high accuracy.
In this image you can see the CTD just before it is lowered into the water.
The CTD does further more serve as a platform for many other instruments. These are attached to the CTD and sample other chemical, biological or physical properties of the ocean water, parameters, as we call them. For example our CTD did sample how far light travels through the water, how much oxygen there is for the fish and other animals to breath and how much algae are in the water.
The good thing about the CTD, next to all the scientifically interesting measurements, is that it is a very heavy instrument, thus other objects can be tied to and lowered to the ocean floor. Knowing this, Albatross and I took many foam cups with us to the school, which were then coloured by everyone with waterproof markers. The foam cups then came all the way with me down to the Antarctica.
Unpacking them on my desk on board – did fill the whole desk! I really enjoyed all the artistic colouring, drawings and names written onto the cups done by the kids and so did all the other people on board.
We did fill the cup with a small piece of paper towel, so they do better keep their shape and don’t break that easily and then put them into a fine mesh. This mesh bag was tied to the CTD.
As you probably all know, foam cups are squashed or deformed easily and they break if you squash them to hard, but in case you apply the same pressure from both sides to a foam cup it just gets flattened at the location of your fingers – and exactly that happens in the water if you lower the foam cups to the ocean floor. At the bottom of the ocean floor, in 3000m depth, a pressure of around 300bar is pressing against the cups from all sides at the same strength. Around 1 bar is the pressure we have at the surface of the earth, 300 times that pressure we have in 3000m, about 2 mile depth; pressure strong enough to make steel cylinders with air in them implode, a pressure that would crush most submarines apart from specific designed scientific ones.
The same pressure is acting onto the cups, but since they are open, it is the same pressure from the inside and the outside, it is just that every little foam cell that is filled with air gets squeezed. They do not break due to the same reason the foam cup does not break if you squeeze the wall with two fingers, from the inside and outside at the same location at once. And when you bring the foam cups back to the surface, they are miniaturized – all the air is pressed out of the foam.
The foam cups are now back in my luggage and will travel with me back to Norwich. And to be honest, not only the three reception classes of Costessy Infant School had fun colouring the foam cups, many scientists and crew of the RRS James Clark Ross had a lot of fun colouring as well.
Overall more than 100 foam cups got pressurized on the bottom of the Antarctic Ocean.
Back to the journals.