Antarctica (43 page)

The next day, I took my skidoo off to see the crevasse that had caused all the trouble with the Hercules. The rescuers from Mactown had half filled it with snow to retrieve their plane. You could walk down a snow slope into it, touch the sides and wonder. Inside it was cold, much colder than the surface, and my eyelashes quickly frosted over. Close to the entrance the walls were decorated with frost fronds the size of dinner plates, sticking out from the ice like corals. But as I climbed farther in the sides became sheer, and glowed faintly with a cold, hard blue. They grew closer together until I could barely fit in the gap between. I tried to imagine what it would be like to fall and be wedged in, and shivered. Nobody knew why there was a crevasse here in the inner part of the ice stream, far away from the margins where the ice was supposed to run smooth. But perhaps there was some kind of bobble in the bed beneath, just enough to make the ice rear up a little and split. It wasn't a trap so much as a reminder that Antarctica was not built with humans in mind. We could occupy it, and study it, but it was still barely tolerating us.

That evening the light was lovely. I borrowed some skis and went out a few kilometres beyond the camp. Apparently there hadn't been much wind lately; the sastrugi were smooth and low. This was a new variant of the familiar ‘flat white' of the East Antarctic plateau. Though the air here was 5°F and dry enough to scrape the skin, it was still noticeably damper than the dry desert of the east. There was moisture enough in the air to coat guy ropes with hoar frost. And the crystals on the surface were big and bold and flashy. They glinted in the slanting sunshine, as if someone had scattered handfuls of diamonds over the snow.

There was something liberating about being able to go where I pleased, with no tracks or roads to direct me. Earlier in the day, when one of the team had offered to let me drive one of the snow cats back to the camp, I had asked him nervously ‘what if I crash into something?' He had turned slowly on his heels in a full circle, peering in exaggerated fashion at the flat white landscape. ‘Into what?' he had said.

I had been assured that there were no hazards as long as I stayed away from the only crevasse in the neighbourhood, took a radio and kept within sight of the camp. But still I felt oddly nervous. Suddenly I felt myself falling with a mighty ‘whump!'. Almost before I could register the sensation, I hit solid ground again and gasped with relief. It was a ‘firn quake', in which an area of ice weakened by the attentions of the sun suddenly drops a few centimetres. Steve had warned me about them a few days ago, though I'd forgotten. ‘It's shocking at first,' he had said. ‘You fall three inches to your death.'

Apart from freezing to death, crevasses are the most prevalent—and romantic—danger in Antarctica. The great Antarctic heroes marched resolutely over the ice, knowing the risks, that at any moment they could plunge through a thin bridge of snow and find themselves dangling helplessly in their harnesses over a gigantic blue crack that descended all the way to oblivion. And yet although my heart was now racing from the firn quake, I still couldn't understand how it would feel to be faced with an apparently innocent landscape that was riddled with dangers. I still didn't really know crevasses at all.

Next morning, the team decided to pack up. They had done as much as they could and there was a plane coming soon to take out the first load of equipment. In eight days they had drilled six holes. They were exuberant, deservedly so. Now the people shovelling snow into the melter were preparing a hot tub, while the rest took a banana sledge and tobogganed down the snow pile, which they had unofficially christened ‘The Mountain'. Wheeeee! ‘Look at that,' Barclay said. ‘It's the only mountain on the West Antarctic Ice Sheet.'

Barclay's work at Upstream D confirmed what he had seen before and what he, and others, would see again. Some combination of water and mud lay beneath all of the ice streams, both here on the Siple Coast feeding the Ross Ice Shelf and the ones on the other side of the continent, which were feeding the Ronne Ice Shelf.

Though it makes the ice streams both quick and dynamic, this could still be good news. Some of the mechanisms that researchers have since found to explain the dynamism of the ice streams also suggest that they may be making the ice sheet more stable, not less.
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If they sped up, for instance, the ice would get thinner, which would mean less weight pressing down, which meant less friction, so less water, so they would slow down again. If they ate back into a region where there was no sediment, they would probably stop. And radar evidence from planes crisscrossing the Siple Coast suggests that it is not losing ice; in fact it may be thickening slightly.
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On the other side of the continent, the streams feeding the Ronne Ice Shelf look, if anything, even safer. They are thicker, but they run in grooves, so it is hard for them to widen or writhe, and one of the largest—the Rutford Ice Stream—is pegged on a high rise that keeps it in check.
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So several decades of work on the ice streams feeding the Ross Ice Shelf on one side of the continent, and those feeding the Ronne Ice Shelf on the other, have produced this reassuring message: for the foreseeable future, it looks as though these two-thirds of the West Antarctic Ice Sheet are fairly stable. Even as temperatures warm over the next few centuries, the shifting, snaking ice streams are very unlikely to speed up enough to send the ice sheet sliding into the sea.

But, of course, there's a twist. Because while all these scientists were spending all this time and trouble tramping around the front and back doors of the West Antarctic Ice Sheet, nobody was checking the side door. The Amundsen Sea Embayment is the third section of the West Antarctic Ice Sheet, the one that spills out into the South Pacific, the one that's hardest to get to, that's farthest from anyone's field of operation and has the foulest weather. The one that nobody was watching. And it turns out that this missing piece, this final third of the West Antarctic jigsaw puzzle, is the one where all the action is.

 

It wasn't entirely unexpected. Certain glaciologists have been worried about the Amundsen Sea Embayment for decades. First, there was the lack of ice shelves. Unlike the other two exit points for West Antarctic ice, which flow into the Ross and Ronne ice shelves, the glaciers pouring into the Amundsen Sea have no massive shelf of floating ice to buttress them. Instead, each has its own miniature ice shelf that runs for just twenty miles before it hits open water. That puts the glaciers perilously close to the ocean, with very little to hold them back.

On top of that, there were signs from expeditions made back in the 1950s that the ground deep beneath these Amundsen Sea glaciers seemed to have an unusual shape: from the coast going inland, it sloped downwards like the inside of a bowl.

This combination of warm seawater lapping up close to the glacier front, and underlying ground sloping downwards as it went inland, could be devastating. The point where the land ice goes offshore and starts to float acts like a hinge; the floating part moves up and down with the tides (and any other changes in sea level). If this hinge line started to retreat inwards, the seawater would follow it, flowing in and down the sides of the bowl beneath the land ice. This would reduce the resistance for the flowing land ice, so it would slide faster, so the hinge line would retreat further, moving inwards towards that central basin in what could be an unstoppable feedback. Back in the early 1980s, the Amundsen Sea Embayment was already being called the ‘weak underbelly of Antarctica'.

And yet, there was no way to know for sure. This whole region of West Antarctica is appallingly hard to study. For one thing, it's perfectly positioned to evade scientific scrutiny. Although the Amundsen Sea Embayment is not much more than 1,000 km from the main British base on the Peninsula, that puts it just beyond the comfortable range of the British Antarctic Survey's Twin Otter aircraft. The Americans could reach that far with their ski-equipped Hercules planes, but McMurdo is further away, again just far enough to put it out of reach.

And even if it were closer to one or other of these major research centres, reaching it would still be challenging. The region's speeding glaciers—called Thwaites, Pine Island and Smith—fill the bay with icebergs and help choke it up with sea ice for eleven months of the year, deterring all but the bravest of captains from entering by ship. And the heavy snowfall that feeds these glaciers comes from clouds that sock the place in for most of the year, discouraging planes and fogging the vision of satellites that might otherwise have been able to take stock from space.

This mysterious third of the West Antarctic Ice Sheet couldn't have done a better job of keeping out of the scientific limelight if it had tried.

But then, in the 1990s, the European Space Agency launched the European Research Satellites (ERS-1 and -2). Unlike previous satellites, these carried radar instruments capable of firing radio waves through the clouds to reflect off the ice beneath. They also made two passes over the same piece of surface, about a month apart. By comparing the measurements from one pass to the next, researchers could derive a very accurate measurement not just of the height of the ice, but of changes in that height. If the ice were thinning, or if the hinge line were moving, the new satellites should be able to tell.

And they did. In the late 1990s NASA scientist Eric Rignot from the Jet Propulsion Laboratory in California put together images of the front end of Pine Island Glacier from 1992 to 1996. By looking for the places where the floating ice moved up and down with the tides, he managed to track the hinge line, the place where the glacier started to float. And he discovered that in just four years its hinge line had retreated inwards at more than a half mile per year.
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His paper, published in July 1998, caused a sensation. Other scientists pored over the satellite results, hastily publishing a blizzard of papers in all the best journals. And they all pointed to massive change in the Amundsen Sea Embayment: Pine Island Glacier's floating hinge line was indeed moving inland, and the grounded glacier itself was shrinking, losing nearly six feet of height per year. And it was moving faster every year. Thwaites Glacier's hinge line was also moving inland. And it was thinning, too. In fact, all the glaciers flowing into the Amundsen Sea were thinning. And Thwaites was getting steadily wider. And every year, more and more of the West Antarctic Ice Sheet was rushing out through that unwatched side door and tipping into the Amundsen Sea.
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If only one of the glaciers had been affected, it could have been something local—a particularly soft bed to slide on, or extra heat coming from below. But this synchronised thinning needed something more general, something from the outside. Eric suspected the oceans. He teamed up with two British scientists, Andy Shepherd and Duncan Wingham, to look at the satellite data from those small floating ice shelves just off shore.
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They found that all three shelves in the bay showed that they had been getting thinner, by an impressive eighteen feet per decade.
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Marine geologist Stan Jacobs thought he knew why. Most of the seawater around Antarctica is very cold. The freezing air sucks warmth out of the surface waters, taking it close to 28°F, the point at which salty seawater can freeze. But deeper down is a band of warmer water, protected from that cold air, that hovers at a relatively toasty 34°F.

This warm deep water doesn't usually get a chance to approach the ice too closely. It is held back by a gigantic underwater shelf that skirts the entire continent. But in the Amundsen Sea there were a few weak points in this natural defence, channels gouged out in the sea floor in the past, when the ice sheet was bigger and the glaciers stretched out much farther than they do today. Back in 1994, Stan had managed to battle his way into Pine Island Bay by ship, and get up to the front of the Pine Island floating shelf. There he found that warm water had crept up through these channels and was lapping right up against the shelf, where it had no right to be.

Perhaps, then, it was this unusually warm water that was doing the damage. Still, the data from the 1994 cruise gave just one snapshot in time. In January 2009 Stan decided to go back, in the National Science Foundation's icebreaker, the
Nathaniel B. Palmer.
This time, he found the water near the shelf was warmer still, and the shelf was melting even more dramatically. Stan calculated that the melting rate had increased by 50 per cent in just fifteen years. But why?

With him on the ship was Adrian Jenkins from the British Antarctic Survey, who had already tried several times to get into Pine Island Bay. He was desperate to look underneath the ice with a specially designed autonomous submarine, Autosub3. This clever beast is twenty feet long, does not need to be tethered, and can go for more than thirty hours before having to return to the ship. It sends out sound waves to scan the ice above and the sea floor below. It can look into the darkest, murkiest, most inaccessible corners of the ocean beneath the ice, see things that no other instrument can see, and still come back when called. It is the hunting dog of the submarine world. And although nobody actually lives in it, it is also pleasingly yellow.

Dealing in autonomous subs is risky. They are unattached and beyond a couple of miles you have no way of speaking to them. The Autosub engineers had already lost a previous prototype under a small ice shelf.

But if you want a true picture of what's going on under these ice shelves, you have to take the risk. The technicians from the National Oceanography Centre in Southampton, UK, who had lovingly designed and built this and the previous machines, could only give it instructions, release it from the ship—and hope.

At first the missions went well. The little yellow submarine sank below the waves, headed off to the Pine Island Ice Shelf, and chose a careful path underneath the ice, mapping the sea floor on the way out and the ice's underbelly on the way back. Three times it went, each time penetrating twenty miles—which was halfway along the shelf.