Avatar plumbs new depths

In the grim grey light before sunrise on January 23 1960 a stick of TNT exploded beneath the waves in the western Pacific and shot a plume of white water high into the sky with a shuddering ker-ump.

The crew of USS Lewis, a navy destroyer, had lobbed more than 800 charges overboard, using the blasts to sound the depths. The echo from the last detonation took a full 14 seconds to bounce off the seabed and back to the ship. The vessel was 320km off the coast of Guam and directly above the deepest chasm in the world’s deepest ocean.

As daylight broke, American sailors tossed buoyant flares into the water to mark the spot where Captain Don Walsh, a US navy submariner, and Jacques Piccard, a Swiss engineer, would descend into Challenger Deep, the deepest fissure in the Pacific’s Mariana Trench.

Inside their steel submersible, the Trieste, the two men, sitting on two stools, descended for five hours into the gloom, unsure of what they would find and of whether they would return.

A small bulb cast enough light to read the depth gauge, a thermometer and dials that monitored the water currents, but the powerful mercury vapour lamps on the submarine’s hull were switched off most of the time.

Walsh and Piccard’s descent is all the more nerve-racking for the 50-year-old technology they relied on. Despite great leaps in underwater exploration, no one has since attempted a repeat. But that is about to change.

‘Returning to the Mariana Trench’
Film director James Cameron—the man behind Avatar, Alien and, aptly, The Abyss—has gathered a team of engineers to build a submersible capable of returning to the Mariana Trench.

Cameron, who has filmed on the wreck of the Titanic, plans to use his new submersible to gather footage for a sequel to Avatar. The vessel is being assembled in Australia and tests on the hull are already complete.

The prospect of a return to the Mariana Trench comes as scientists are beginning to understand the importance of the deepest ocean. These are habitats with extraordinary and unique life forms; places that behave like deepwater stores for the carbon locked up in marine life when it dies and drifts downwards.

Cameron’s engineers will have pored over the details of Walsh and Piccard’s descent in the hope of avoiding the heart-stopping moments of their mission.

Less than an hour into the descent, at a depth of 1 280m, a dribble of water appeared and meandered down the wall of the vessel. It soon stopped. At 5 400m the vessel sprang another leak that also resealed itself.

At 9 800m, deeper than Mount Everest is high, there was a dull crack and the Trieste‘s cabin shook hard. For a few minutes, Walsh and Piccard stopped everything on board that made a noise. Tiny cracking sounds came from all around, but the submersible held.

The echo sounder used to locate the ocean bed revealed nothing but more water beneath. “Let’s go on,” said Piccard. At 12.56pm, the echo sounder quivered and scrawled its first trace as the ocean floor came within reach. Walsh and Piccard switched on the Trieste‘s lamps and peered into what turned out to be crystal-clear water.

Setting a record
The traces on the echo sounder got stronger and stronger, until at 13.06pm, the Trieste landed. The depth was 10 900m, as deep as a transatlantic airliner flies high. The water pressure on the cabin was 200 000 tonnes.

Walsh and Piccard spent only 20 minutes on the ocean floor—enough time to eat a chocolate bar and test their experimental acoustic telephone system—but their descent set a record for man’s deepest dive.

Jacques Piccard died in November 2008; but Walsh, now 79 and living in Oregon in the United States, advises a company called Deep Ocean Expeditions, which arranges trips in submersibles to iconic wrecks, including the Titanic. He explains the Trieste mission with characteristic understatement: “I had to get away from my desk job. “

The crack that made the vessel shake turned out to be a Plexiglas window fracturing, not from pressure but from cold. The cracks sealed themselves as the Trieste rose into warmer waters and broke through the waves.

“By the time all our kit was inside, there wasn’t much room for us,” says Walsh. “It was about as much room as inside a large household refrigerator. And about the same temperature.”

Walsh and Piccard agreed that someone would do the same descent within a year or two. But the Trieste‘s mission turned out to be like Nasa’s Apollo project to the moon—no one went back.

Speaking scars
The Mariana Trench is not a small crack in the ocean floor. Research vessels have mapped it at close to 2 500km long and 70km wide. The huge scar speaks of the violence of plate tectonics—this is where the vast Pacific plate bends steeply beneath the Philippine plate, leaving a huge groove in the Earth’s crust.

The deepest part of the trench, named Challenger Deep after the Royal Navy’s HMS Challenger II vessel that surveyed the region in 1951, may be a tear in the Pacific plate.

Challenger Deep is beyond what oceanographers call the abyssal zone. Go deeper than 6km and you enter the Hadal zone, named after Hades, the Greek god of the underworld.

Deep ocean trenches do not teem with the diverse life of shallower waters. As sunshine cannot penetrate this deep, many organisms generate their own light through bioluminescence. There is little seaweed or kelp.

The trench’s towering walls are bare and rocky in places, but are overwhelmingly covered with sediment—dead plankton, glass skeletons from algae called diatoms and the excrement of marine life swimming above.

Some of the sediments are so soft that oceanographers try to ensure that equipment they send down does not trigger vast avalanches.

The Trieste was designed by Jacques Piccard’s father, Auguste, a physicist and hot-air balloon enthusiast. In the 1930s, Piccard senior flew a series of air balloons with pressurised gondolas capable of soaring to record altitudes. He then realised that he could adapt the principle for the ocean depths.

Inside a bowl of milk
The Trieste was kept buoyant by 130 000 litres of lighter-than-water gasoline, and sank with a ballast of iron pellets. To ascend, the pellets were jettisoned by cutting the power to an electromagnet that held them.

Walsh and Piccard came back without pictures of the bottom of the Mariana Trench. The cloud they kicked up as they touched down obscured the view—“It was like being in a bowl of milk,” says Walsh.

But shortly before reaching the bottom, Piccard saw what he believed was a flat fish, resembling a sole, on the seafloor. Many marine biologists doubted that a flatfish would venture so deep.

But in the 50 years since, oceanographers have developed sophisticated underwater robots that bring back stills and video from deep trenches such as the Mariana. Robotic “landers” have filmed fish at a record-breaking depth of nearly 8km. Hordes of ghostly white snailfish, which resemble foot-long tadpoles with suckers on their bellies, appeared when one lander released bait in front of its camera.

“The startling thing is that we see so many,” says Monty Priede, director of Aberdeen University’s Oceanlab. “These fishes are deep-sea specialists. In each trench we explore, there seems to be a different species of snailfish.”

For scientists, this poses a tough question: How did the deepest parts of the oceans, isolated from one another, become home to subtly different versions of the same peculiar creatures?

Shrimps abound at extreme depths, feeding on the dead marine life and other organic matter that funnels down the steep walls of trenches into the deepest crevices. “This is the end of the world. This is where all the rubbish from above ends up, and all these shrimp wait for it,” says Priede.

One oceanographer explained that humans are like party balloons—at great depths they are crushed to nothing. But deep-sea fish are like flat balloons—at the bottom of the ocean the pressure has little effect. Intense pressure causes nerves to stop working, but deep-sea life has evolved a more robust physiology at the molecular level.

The deep ocean has a direct bearing on global warming. Last month scientist Ronnie Glud returned from an expedition to send a robotic lander to the bottom of the Mariana Trench as part of a project to map carbon in the world’s seabeds.

The lander confirmed Glud’s suspicion that deep ocean trenches store a disproportionate amount of carbon, making them a major but unrecognised element of the planet’s carbon cycle.

“Every time people look they make new discoveries about these deep regions of the oceans,” said Andrew Bowen, director of the National Deep Submergence Facility at Woods Hole. “Think of the Earth as a puzzle.

Only through exploration can we begin to understand the shapes of the pieces and fit them together into a coherent view of the world.”—Guardian News & Media 2011

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