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.

At its most extreme, the water pressure rises to 1 tonne per square centimetre and the temperature drops to 1 degree C. Despite the challenging conditions, some animals survive and thrive in the trenches. Because the technical challenges to operating there are so high, we are only now just learning what is down there and how creatures adapt to life in the extremes.

Based at the University of Aberdeen in Scotland, deep sea ecologist Alan Jamieson is one of the premier explorers of life in the Hadal zone. In the programme, he talks through some of the latest video footage he has from the depths of the Kermadec Trench in New Zealand - not by visiting in person but by dropping cameras on a deep sea probe called a hadal lander to the distant sea floor. The images were gathered on an expedition in April and May. They revealed new habits of hadal creatures.

Rebecca does talk to two people who have ventured in person to the far limit of the Hadal zone: US Navy Lieutenant Don Walsh who went down to the bottom of Challenger Deep in the Mariana Trench in 1960, and Hollywood director James Cameron who, 52 years later, repeated Walsh's voyage to 11,000 metres.

(Photo: Supergiant amphipod at 6200 metres. Credit: Oceanlab, University of Aberdeen)