The Arctic Ocean is one of the most inaccessible oceans in the world. This is because for much of the year it is covered in ice, and very few ships are capable of crossing it. Unlike, at the South Pole in the Antarctic, there is no land at the North Pole, only several metres of ice to stand on. In the very deepest parts, the seafloor can be over 4 km below the icy surface.
Water is actually quite heavy, so anything living at the sea floor experiences an enormous amount of pressure. We send our instrumentation down to these depths to measure the temperature and salinity (salt content) of the water and the amount of oxygen it contains, but we are very careful to design our equipment to withstand the high pressures. To demonstrate the effect that pressure can have on everyday objects we sent a polystyrene cup to 2500 m depth. Before its trip to the Arctic seafloor the cup was 11 cm high (and had a diameter of 8 cm). When we got it back onto the ship it was just 4.5 cm (3.5 cm diameter) – it had shrunk to 40% of its original size.
The cup also got very cold. The temperature at the bottom was a chilly –1 °C. Freshwater at this temperature would have frozen, but the high salt content of seawater (equivalent to putting 1.5 teaspoons of salt in your cup of tea) lowers its freezing point. Also, high pressures at the ocean floor helps lower the freezing point.
…We asked pupils from Mission Grove Primary school and Alloa Academy to decorate cups that we could send down to the deepest depths of the Arctic, look at the results!
They started off this size:
And then shrunk to this size:
…can anyone identify their cup?
Mission Grove primary school
…All cups will be returned to their owners soon. Thanks for doing such a good job decorating them!