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© NOC Southampton25 leagues under the sea
Captain Nemo had it easy. When robotic submarines are sent 6000 metres to the bottom of an ocean-ridge rift in March, they will face furiously hot temperatures, pressure that gives oil the consistency of treacle, and rugged cliffs that plunge into the abyss. The pay-off, for an international collaboration of researchers called InterRidge, should be an insight into an unexplored world.

The Cayman trough is a 100-kilometre-long rift in the seabed between Jamaica and the Cayman Islands where the ocean floor is slowly pulling apart and new lava seeps up to fill the gap - a so-called ocean ridge. Such ridges are home to hydrothermal vents, and while vents at 3800 metres below the surface have been explored before, InterRidge plans to visit some of the world's deepest, which lie around 6000 metres down. At this depth, water doesn't boil until it reaches 500 °C.

High temperatures, extreme pressures and the relative isolation of the Cayman trough make it likely that new species of chemosynthetic bacteria and other bizarre organisms will be discovered. Missions to other hydrothermal vents have identified 2-metre-long tube worms, giant clams and "bacterial snow" apparently raining down around the chimneys. Expect dramatic images of weird life forms to start being beamed back by the end of March. Before then, InterRidge vessels will be the first to visit the vent communities of the Southern Ocean, diving to the East Scotia ridge off South Georgia.

The Cayman trough might be more like 25 leagues under the sea than 20,000, but that won't make it any easier. It is an extremely slow-spreading ocean ridge, and the terrain is expected to be more rugged than at previously explored ridges. This means vast boulders and sheer cliffs that will make navigation for submarines like AutoSub6000 difficult. Landing on top of the furnace-like heat of an undersea chimney could also wreak havoc with their circuitry. As Bramley Murton of InterRidge told New Scientist: "Anything we get back will be a bonus."