A French diver begins an unprecedented 28-day expedition in the Mediterranean on Monday in the hope of learning more about little-known species of marine life.
During three decades of diving, Laurent Ballesta has often descended 120 metres below the surface, but only for a few minutes, followed by a slow, careful ascent in stages to avoid the bends.
The pressure at 120m is 13 times greater than at the surface, and only 1 per cent of sunlight gets through.
Mr Ballesta, 45, is now employing a system inspired by the saturation diving techniques used in the oil industry to allow him and three other divers to spend eight hours at a depth of 120m every day for a month.
They will travel along the coast between Marseille and Monaco in small, pressurised capsules, in which the pressure is the same as that at 120m.