Pressure test: Diving 1,000m below sea level
Four teams are diving to the deepest part of the ocean, the Mariana Trench, which lies 11km (seven miles) down in the western Pacific.
To find out more about the challenges of working in the deep, science reporter Rebecca Morelle went to the University of Aberdeen.
With the help of some polystyrene heads and a pressure vessel, she was able to see the effects that increasing pressure has at various depths.
Here, she looks at what happens 1,000m (3,000ft) below sea level.