PBS高端访谈:科学家根据阿拉斯加冰雪层的状况监测气候变化

 　　GWEN IFILL: Finally tonight: how climate change may be affecting life in Alaska as we know it and the captivating images we see there, from ice to Marine 1 life.

　　NewsHour science correspondent Miles O'Brien went there to see for himself.
　　MILES O'BRIEN: Alaska may seem like a place where things don't change very quickly, the natural beauty is set in stone and is as predictable as the caribou 2 beside the road.
　　But make no mistake, things are changing here quickly, and not for the better. Alaska is at the frontier of climate change. Scientists are scrambling 3 to try and understand it.
　　KARL KREUTZ, University of Maine: We know that the Arctic is warming more rapidly than most other places on Earth.
　　MILES O'BRIEN: To catch up with University of Maine paleoclimatologist Karl Kreutz and his team, we hopped 4 on a plane rigged with skis that landed right on the Ruth Glacier 5 in the heart of the Denali National Park.
　　KARL KREUTZ: Most glaciers 6 in Alaska are retreating. We'd like to be able to predict with better accuracy of what will happen, but it's hard to imagine a scenario 7 there where glaciers will not continue to lose mass in this area. The question is how fast.
　　MILES O'BRIEN: But the answer is unknowable if they don't know how much ice is here right now.
　　SETH CAMPBELL, U.S. Army Corps 8 of Engineers: To goal of this specific study is to come up with ice depth measurement across the glacier.
　　MILES O'BRIEN: Kreutz's colleague Seth Campbell is a research geophysicist for the U.S. Army Corps of Engineers. He and University of Maine undergrad Abby Bradford spent long, strenuous 9 days on skis towing a ground-penetrating radar 10 up, down and across the glacier.
　　SETH CAMPBELL: The transfer sends a pulse through the cable. The pulse gets sent down through the ice, reflects off the bedrock, returns back to the surface. And it returns and is recorded by this receiver cable.
　　We know how fast a radio wave travels through the ice, so based on how long it takes it for the signal to be transmitted and received, we can calculate how deep the ice is.
　　All right, so sample two should come from a depth of 50 centimeters, please.
　　MILES O'BRIEN: To have complete confidence in the radar data, they dug this pit 11.5-feet deep and had Abby repel 11 down to take readings.
　　MAN: This is great. SEAL Team Six time. Let's go, baby!
　　MILES O'BRIEN: Dutiful reporter that I am, I went in.
　　ABIGAIL BRADFORD, University of Maine: So what we're in, this is just one layer, one annual layer. This is this year's snowfall. And then right what we're standing 12 on, where this probe stops — it's a bit covered with snow now, but there's an ice layer right there.
　　MILES O'BRIEN: And you know that's the previous season?
　　ABIGAIL BRADFORD: That's the previous season, yes.
　　MILES O'BRIEN: She weighs a fixed 13 volume of snow at various depths to determine its density 14. The hope is the layering they see in the pit matches the radar returns.
　　ABIGAIL BRADFORD: There's thousands of glaciers in Alaska, and very few have had data gathered on them. So we're hoping to piece that puzzle together.
　　MILES O'BRIEN: Getting back to the surface might have been easy for her, but, for me, well, let's just say I didn't score any style points.
　　Later in camp, Karl Kreutz dug me a shallower pit.
　　KARL KREUTZ: But, of course, as we're going deeper in this — on this wall, we're going back in time.
　　MILES O'BRIEN: A thin wall backlit by the sun. The key is the layers of snow and most importantly ice, proof of a melt.
　　KARL KREUTZ: These layers in the snowpack are very analogous 15 to tree rings. All of these, as we go down and go through the layers are going back in time on the glacier, and we get deeper and deeper.
　　MILES O'BRIEN: Last season, they went much deeper, drilling out this long ice core a few miles away. It is nature's ancient history book for this glacier.
　　KARL KREUTZ: So, over the past 40 or 50 years, the number of ice layers that have formed each summer has been increasing. And so we interpret that as meaning that the summertime temperatures in this area have gradually been warming over the past couple decades.
　　MILES O'BRIEN: The vast majority of glacier ice on our planet lies in Greenland and Antarctica, and so it should come as no surprise that's where most of the attention and scientific effort is.
　　But the people who come here to the mountains and the glaciers say the ice here shouldn't be overlooked.
　　SETH CAMPBELL: The interesting thing about Alaska is, a lot of the glaciers sit right at a temperature — right at a zero degree temperature. So, small changes in atmospheric 16 air temperature can cause drastic changes in ice point.
　　MILES O'BRIEN: Five hundred and fifty miles north on the sea ice off Barrow, the notion that Alaska rocks at a tipple 17 point is not just academic. It's a matter of survival for a proud culture.
　　The 2005 film "The Eskimo and the Whale" tells the story of the Inupiat people trying to preserve their subsistence whale hunting tradition.
　　NELSON NUNGASAT, Inupiat Whaler: The ice is shrinking. We have a lot of cracks in the ice, so we have to watch them a lot more. When I was little, these — these ice piles here, they were — they were 10 times bigger.
　　MILES O'BRIEN: Nelson Nungasat is captain of a whale hunting team. They rely on stable, thick ice to harpoon 18 the 25 bowhead whales they're allowed to take each year for food.
　　Nelson works as a guide and polar bear sentinel for some scientists focused on the sea ice and the other end of the food chain, the tiny light-sensitive organisms that live in the ice.
　　CRAIG AUMACK, Columbia University: Temperatures effects up here and ice extent up here actually has profound effects on the marine community underneath 19 the ice.
　　MILES O'BRIEN: Marine ecologist Craig Aumack is with Columbia University's Lamont-Doherty Observatory 20. He and his team do a lot of coring as well to measure the temperature of the ice at 10-centimeter intervals 21. They drop cameras through the holes and take a peek 22 underneath.
　　What do you hope to see?
　　CRAIG AUMACK: Well, we kind of just look at the bottom to see. So that pigmentation, this is all algae 23.
　　MILES O'BRIEN: During the winter, the algae hibernates 24 in the ice, but, in the spring, it blooms and drops into the water. When and how fast that happens depends on how much light gets through the ice. And that is changing as the ice shrinks, gets thinner and is covered by less snow.
　　CRAIG AUMACK: So what we're really interested in is then finding out what role this material plays in the total diet of these organisms.
　　It's really hard to understand the impact of the loss of sea ice without actually understanding then what importance it has toward the underlying 25 marine systems.
　　MILES O'BRIEN: Algae is a so-called primary producer, meaning it is foundation for the entire food chain.
　　Craig's scientific collaborator 26 is marine biologist Andy Juhl.
　　ANDY JUHL, Columbia University: We know it starts out in the ice, it grows in the ice. Then it gets released from the ice. It ends up in the water. Some of it sinks to the bottom. And so the next question is, who's eating it?
　　MILES O'BRIEN: They analyze 27 all manner of small creatures to see what they're eating and, by analyzing 28 their tissue, what provides them the most nutrition. As they gather data, they are working their way up the chain. On this day, they netted a jellyfish.
　　MAN: Jelly.
　　MILES O'BRIEN: Cause enough for a science nerd happy dance on the ice. But beneath the surface here, there are grave concerns about what happens when the sea ice is dramatically diminished.
　　ANDY JUHL: Large marine animals, seals and beluga whales and bowhead whales, the polar bears, all of those organisms are here, because it is an incredibly productive environment and therefore can support those really big organisms, because there are a lot of algae at the base of the food chain here.
　　MILES O'BRIEN: The amount of snowfall, the depth of the ice supports a finely-honed balance that ultimately sustains the top of the food chain. Here, a single degree of change across the line between ice and water is changing everything.
　　Miles O'Brien, the "PBS NewsHour," Barrow, Alaska.