Rebecca Morelle talks to explorers of deep ocean trenches, from film-maker James Cameron to biologists discovering dark realms of weird pink gelatinous fish and gigantic crustaceans.
The deepest regions of the ocean lie between 6,000 and 11,000 metres. Oceanographers term this the Hadal Zone. It exists where the floor of abyss plunges into long trough-like features, known as ocean trenches. The Hadal zone is the final frontier of exploration and ecological science on the planet.