R.V. LANCE, 82.6 Degrees North—Curious polar bears, venturing too close to working scientists, have had to be scared off with flares shot from a gun. Temperatures plunging 40 degrees below zero have snapped cables and crippled electronic instruments. But after six weeks of total darkness, the faintest daylight is finally reaching the frozen Arctic Ocean, where a Norwegian research vessel has been drifting through the polar night, tethered to a block of sea ice.

Going with the floe is the whole idea. To better understand how sea ice behaves in the Arctic, scientists aboard the R.V. Lance have embarked on a six-month study, sponsored by the Norwegian Polar Institute (NPI), to closely monitor sea ice across its entire seasonal life cycle—from the time when the new ice forms in winter until it melts in early summer.

Although Norwegians have a long history of polar exploration—in the coming months the Lance should cross the path of the illustrious Fram, the ship on which Fridtjof Nansen and his crew allowed themselves to be locked in the ice in 1893—this is still an unprecedented scientific expedition. (Read about the voyage of the Fram.)

"Most scientific cruises to the Arctic are conducted in summer, and this is where we have the most data," says Gunnar Spreen, an NPI sea-ice physicist on board the Lance. "The continuous changes that occur from winter into spring is a huge gap in our understanding, for example, the way the Arctic ecosystem wakes up in the spring or how melt ponds form on top of sea ice."

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Departing in early January from Spitsbergen, an island in the Svalbard archipelago, a Norwegian Coast Guard vessel broke a path for the Lance north through the growing winter sea ice to the 83rd parallel, where it began its wayward drift. Buoys, oceanographic instruments, ice-coring drills, air-particle sensors, a weather mast—a full laboratory—were deployed across a kilometer-wide (0.6 mile) floe, its sectors given cheeky nicknames like "no walk land" and "end of the world."

Last week photographer Nick Cobbing and I reached the Lance by Coast Guard ship and then helicopter from Longyearbyen, the world's northernmost town. We joined a second shift of scientists—hailing from Norway, Russia, Korea, Japan, Portugal, Germany, France, Denmark, and the United States—who will continue the study. In a series of dispatches over the next four weeks, we'll be capturing some of the action unfolding here at the top of the globe.

A Cap That Cools

View Images Preparing to abandon the floe, scientists retrieve rods they'd used to mark transects across the ice. Their unprecedented six-month study is looking at sea ice from the time it forms until it melts. Photograph by Nick Cobbing, National Geographic

For thousands of years, this vast blanket of bright white ice floating on the surface of the Arctic has cooled the planet by reflecting sunlight back into space. Though the ice cap has always expanded and contracted with the seasons, reaching its maximum extent in March and its minimum in September, over the past two decades it's been shrinking dramatically.

In September 2012, according to the National Snow and Ice Data Center, the ice cover was the smallest ever documented—just 52 percent of the average for the period 1981 to 2010. The ice is getting thinner as well. In September 2012 its total volume was only about 40 percent of the long-term average. What was once mostly a layer of thick ice floes that lingered for years has given way to large tracts of thin ice that forms and melts during a single year.

The loss of ice accelerates Arctic warming. Scientists have found that first-year ice reflects about 10 percent less solar energy than multiyear ice. That means it melts faster—it loses about five inches (13 centimeters) a month more in thickness than does multiyear ice, according to NPI data. As ice melts and exposes darker ocean water, more solar energy is absorbed by the water, producing clouds and escalating temperatures.

Indeed, data show that the temperatures in the Arctic have been warming twice as fast as the global average. "The results come out strongly in model outputs," explains Kim Holmén, NPI's international director. "The Arctic warms first, most, and fastest." All climate models are now in agreement: Coverage of summer sea ice will continue to decline. Later in this century it will be possible to sail across the open ocean to the North Pole.

This will of course have disastrous consequences for the entire ecosystem that depends on sea ice, from polar bears to the minuscule phytoplankton at the opposite end of the food chain. The loss of Arctic ice will likely affect weather patterns across the entire Northern Hemisphere as well. Some scientists already see a link to the polar vortex that's been bringing deep cold again to the eastern United States.

Arctic Data Dive

View Images The K.V. Svalbard, a Norwegian icebreaker, heads back to the Lance to guide it deeper into the growing ice pack and deliver a second crew of researchers. Photograph by Nick Cobbing, National Geographic

Over the course of NPI's six-month-long study (January 9 to June 27), scientists will plunge into nitty-gritty measurements of how sea ice behaves and all the factors that affect it, from the warmth and turbulence of the ocean below to the snow and clouds above it. They'll study the underside of the ice, and the algae that bloom below it, with autonomous and remotely operated vehicles.

"Every effort to enable a better description of how ice behaves is important for making our climate models better," says Holmén. For other scientists working with data collected by satellites or airplanes, the area around the Lance will become a unique ground-truth reference point.

For now, though, the crew and science team are recovering from a small setback. Back in January a Norwegian Coast Guard icebreaker, the K.V. Svalbard, had escorted the Lance to a position that was thought to be securely within the growing ice pack. But strong winds over the past six weeks pushed the vessel south, too close to the crackled edge of the ice. The day before Cobbing and I arrived from Spitsbergen with the new crop of scientists, the floe under study splintered into shards.

For three days and nights, in temperatures well below zero, the scientists scrambled to salvage their instruments, with mixed results. "It's the Arctic that's controlling our expedition, and the Arctic is unpredictable," said Amelie Meyer, an oceanographer with NPI. "We're going to break instruments, we're not going to be where we think we're going to be, and we don't know what the weather will bring us. This is really extreme science."

As I write, on Sunday, February 22, the K.V. Svalbard is cutting a new path for us, leading the Lance farther north and east, deeper into the ice. Within a few days we hope to begin drifting again.

That's the plan, anyway. Stay tuned.