Northern Hemisphere icebergs like The Iceberg melt quickly once they drift down into the Atlantic, with its warming Gulf Stream. Almost certainly, within a few weeks of shaking up the world, The Iceberg had disappeared. Its ephemerality has only increased its fame; solid matter for just a few historic moments, it continues indefinitely in imaginary realms—for example, as a spooky cameo in the top-grossing movie of all time. The message of The Iceberg, common wisdom has it, concerns the inscrutability of our fate and the vanity of human pride. But when I meditate on ice and icebergs, I wonder if The Iceberg's message might have been simpler than that. Maybe the news The Iceberg bore was more ancient, powerful, planetary, and climatic. Maybe The Iceberg's real message wasn't about us, but about ice.

ICEBERGS ARE PIECES of freshwater ice of a certain size floating in the ocean or (rarely) a lake. They come from glaciers and other ice masses. Because of the physics of ice when it piles up on land, it spreads and flows, and as it does its advancing edge often meets a body of water. When the ice continues to flow out over the water, chunks of it break off, in a process called calving. Some of the faster-moving glaciers in Greenland calve an average of two or three times a day during the warmer months. Icebergs are not the same as sea ice. Sea ice is frozen salt water, and when natural forces break it into pieces, the larger ones are called not icebergs but ice floes. Icebergs are denser and harder than sea ice. When icebergs are driven by wind or current, sea ice parts before them like turkey before an electric carving knife. In former times, sailing ships that got stuck in sea ice sometimes used to tie themselves to an iceberg and let it pull them through.
A piece of floating freshwater ice must be at least 50 feet long to qualify as an iceberg, according to authorities on the subject. If it's smaller—say, about the size of a grand piano—it's called a growler. If it's about the size of a cottage, it's a bergy bit. Crushed-up pieces of ice that result when parts of melting icebergs disintegrate and come falling down are called "slob ice" by mariners. Students of icebergs have divided them by shape into six categories: blocky, wedge, tabular, dome, pinnacle, and drydock. The last of these refers to icebergs with columnar sections flanking a water-level area in the middle, like high-rise apartment buildings around a swimming pool.

At the edges of Antarctica, where plains of ice spread across the ocean and float on it before breaking off, most of the icebergs are tabular—flat on top, horizontal in configuration. In the Northern Hemisphere, because of the thickness of glacial ice and the way it calves, most icebergs are of the more dramatically shaped kinds. Tabular icebergs tend to be stable in the water and scientists sometimes land in helicopters on the bigger ones to study them. Northern Hemisphere icebergs, with their smaller size and gothic, irregular shapes, often grow frozen seawater on the bottom, lose above-water ice structure to melting, and suddenly capsize and roll. Venturing onto such icebergs is a terrible idea.

Antarctica has about 90 percent of all the ice in the world; most of the rest of it is in Greenland. Those two places produce most of the world's icebergs—about 100,000 a year from the first, about 10,000 to 15,000 from the other. Glaciers in Norway, Russia, and Alaska produce icebergs, too. The Exxon Valdez went aground in Alaska's Prince William Sound partly because it had changed course to avoid icebergs. Scientists have not been observing icebergs long enough to say if there are substantially more of them today. They know that the total mass of ice in Greenland has decreased at an accelerated rate in recent years. In Antarctica, because of its size and other factors, scientists still don't know whether the continent as a whole is losing ice or not.

SOME PEOPLE HAVE jobs that involve thinking about ice and icebergs all day long. A while ago I went to the National Ice Center in Suitland, Maryland, and met a few of them. The Ice Center is affiliated with the National Oceanic and Atmospheric Administration, the Coast Guard, and the Navy. The offices of the Ice Center are in one of the many long, three-story government buildings with extra-large satellite dishes on their roofs in a fenced-in, campuslike setting just across the Potomac from Washington. Antennae poking up from behind clumps of trees add to the spy-thriller atmosphere. The Ice Center's supervisor, a lieutenant commander in the Navy—many of the people who work at the Center are military personnel—introduced me to Judy Shaffier, ice analyst. She is a slim woman in her mid-thirties with a shaped haircut and avid dark eyes accustomed to spotting almost invisible details. An ice analyst looks at satellite images of ocean ice on a computer screen, compares the images to other weather information, and figures out what they mean. "It's a great job, really neat to tell people about at a party or something," Shaffier said. "But it takes explaining. When I say I analyze ice, sometimes people don't get that I mean ice. They think it must be one of those government-agency acronyms."

Much of the Ice Center is closed to visitors. That's the part where it pursues its main purpose, which is to provide classified information on ice conditions to the military. For example, a nuclear submarine can break through ice three feet thick or less; the Center can tell a submarine how close to surfaceable ice it is. Many countries—Japan, Denmark, Great Britain, Russia, France, Sweden—have ice-watching agencies similar to the Ice Center. Any country involved in global ocean shipping needs ice information sometimes. Providing it to merchant ships, scientific expeditions, and the general public is the nonclassified part of the Center's job.
Shaffier led me into a room with darkened windows and computers all along the walls. The glow of screens in the dimness lit the faces of ice analysts tapping on keyboards, summoning up satellite pictures of ice-covered oceans and seas. "I was trained as a meteorologist originally," Shaffier said. "I started analyzing ice in '94. Mostly what we do here is sea ice. Each of us has areas we concentrate on. Mine are the Yellow Sea, the Sea of Okhotsk, the Ross Sea, and the Sea of Japan. I feel like I really know the ice in those seas. Tracking icebergs is kind of secondary. We do it to keep everyone informed about possible dangers in the shipping lanes—in the Southern Hemisphere only, because another agency handles North Atlantic bergs. Also, I guess we do it for scientific and geographic reasons, or because icebergs are just interesting.

"For us to track an iceberg it must be at least ten nautical miles long," she continued. "We label each one according to the quadrant of Antarctica where it broke off. The quadrants are A through D, and after the letter we add a number that's based on how many other bergs from that quadrant we've tracked since we started doing this back in 1976. The A quadrant, between 90 west longitude and zero, has shelves that calve big icebergs all the time, and we've tracked a lot of bergs from there. A-38 was a recent one. And if a berg breaks up into pieces, any piece that's bigger than ten nautical miles gets its own label, like A-38A, A-38B, and so on."

The subject turned to giant "celebrity" icebergs, and whether she had a favorite.