DEEP-SEA DIVERS

ore than 80 per cent of the world’s oceans remain unexplored, but several submersibles are working to bring that percentage down. The deep ocean is considered to start around 200 metres below the surface, where light begins to dim, also referred to as the euphotic zone. The deep ocean is further divided into descending zones, such as the twilight zone (down to 1,000 metres), midnight zone (down to 4,000 metres) and so on until the last defined zone, the hadal zone. The hadal zone, also known as the hadopelagic, sits between 6,000 and 11,000 metres below the ocean surface. The deepest dive any vehicle has ever made was achieved by the Deepsea Challenger, a 109-centimetre-wide manned submersible that reached the