The largest migration of life on earth departs every night from the twilight zone, the kilometre-deep middle layer of open ocean in which the majority of living creatures can be found. As darkness falls, millions of tons of animals, ranging in size from the smallest arrow worms to the largest cetaceans, swim their way up to the photic zone to feed in relative safety, braving shallower waters under cover of night to gorge themselves on nutrients – and on one another – before plunging back into the gloomy depths as dawn begins to break. For a few short hours, the top thirty metres of the world’s great oceans teem like overstocked aquaria. The process, known as vertical migration, was discovered relatively recently, and as yet scant details of its natural history have been collected by marine zoologists, for whom many of the goings-on in the ocean’s deeper regions remain just as mysterious and out of reach as they were when ocean science began in earnest in the mid-19th century. ‘The great depths of the ocean are entirely unknown to us,’ Jules Verne declared in 1869, in the early pages of Twenty Thousand Leagues under the Sea. ‘What passes in those remote depths – what beings live, or can live, twelve or fifteen miles beneath the surface of the waters – what is the organisation of these animals, we can scarcely conjecture.’ Much the same could be said today, 140 years on from the voyage of the Nautilus, with less than 5 per cent of the world’s 320 million cubic miles of ocean having so far been explored, and an estimated 50 million unknown species thriving in its depths.
Like space exploration, a branch of science with which it is often compared, deep-sea oceanography is an extremely expensive and risky endeavour; in fact, more people have been sent into outer space than have ever journeyed into the dark zone, 2000 metres below the surface, and there are still only a handful of unmanned submersibles capable of reaching the deep-sea floor, six or seven kilometres down. What makes deep exploration so difficult and dangerous is the steady increase in hydrostatic pressure caused by the weight of water above. By 1000 metres down, the outside pressure has risen to 100 times that at the surface. By 5000 metres (just over three miles) down, the pressure will have increased to 500 atmospheres – some 3.5 tons per square inch – inducing levels of stress that few man-made objects can withstand. A popular trick among deep-sea divers is to strap a polystyrene coffee cup to the outside of their submersible, and, as they descend, watch it being slowly crushed to the size of a doll’s-house thimble – which is pretty much what would happen to their internal organs should the vessel spring a leak.
the full text of the article can be found here.
Later Posts/Вперёд
0 comments:
Post a Comment