Adélie penguins have been breeding on Antarctica's Torgersen Island for thousands of years, but today the clacking and squawking of 20,000 birds hides a relatively new sound: camera shutters. A dozen tourists wander through the colony, having arrived by Zodiac rubber raft from their cruise ship.

"For me the noise of the penguin colonies is the real surprise," says Peter Vutz, stepping away from the wildlife paparazzi. "And the smell," adds his wife, Doris, swaddled in a bright parka.

In a few months Antarctic summer will begin, and these two 71-year-old Californians add to a surge in ship-based adventurers here that's doubled and redoubled in less than a decade: over 14,000 in the 1999-2000 season, up from 2,500 only ten years earlier. Millennium-related cruises accounted for some of the upsurge and numbers tapered after 9/11, but totals are expected to return to this rate in the 2003-2004 season.

Is this jump in tourism hurting Antarctica, or helping it?

In 1989 the Argentine navy resupply ship Bahia Paraiso stopped at the U.S. research base Palmer Station, near Torgersen, to allow tourists to visit. On departure the vessel struck an underwater rock. No one was seriously injured, but the ship later capsized, spreading an oil slick that fouled nearby penguin, cormorant, and seal colonies.

Incidents like that worry environmentalists, as do soaring visitation rates. "The sheer number of people can disrupt wildlife breeding and reduce populations," warns Beth Clark, director of the conservationist Antarctica Project.

One problem is that most tours land at the same points along the 800-mile-long (1,300-kilometer-long) Antarctic Peninsula, the continent's partly ice-free "banana belt." Cruise-ship passengers take in vistas of glaciated mountains and lichen-covered islands, stopping to visit penguin colonies, seal beaches, and abandoned whaling stations. Most tour operators try to ensure their passengers leave no garbage and don't walk on fragile areas, like moss beds that take a century to grow just a few inches.

"There can be ten ships down here at a time," says Mike Messick, an expedition leader on the Clipper Adventurer, a 330-foot (100-meter) converted Russian vessel. He recalls when only two cruise ships visited. "We have nightly radio contact with other ships to work around each other's schedules. There's a lot of room down here, so we don't need to be crowded."

Ice-hardened Russian vessels like Messick's now make up about half the tourist fleet. One, a former troopship called Marco Polo, carries more than 400 passengers and has to spend up to 12 hours shuttling visitors to and from breeding sites, exposing the animals to humans far longer than do smaller ships.

Even larger luxury liners sail along the peninsula. The 936-passenger Rotterdam started the trend in 2000 with a three-day "drive-by". Three other 1000-plus passenger ships made similar voyages from 2002 to 2003. More cruise ships regularly consider adding the route to their offered itineraries, and some of these big vessels send their passengers ashore. The danger: A large-ship accident in rough southern seas could be too isolated for rescue or environmental cleanup.

So far, though, much of the Antarctic tourism has remained environmentally benign, say scientists at Palmer Station. While some damage has occurred, an eight-year study by the National Science Foundation found no effect on the Adélie penguin population. The International Association of Antarctic Tour Operators (IAATO) has adopted voluntary standards to keep visitors from disturbing wildlife-by staying at least 15 feet (5 meters) from penguins and by not allowing their members with over 500 passengers to land, for instance. But enforcement depends on guides, and not all ships belong to IAATO.

A dozen tours a year visit Palmer Station to learn about marine biology, ozone depletion, and the effect of global warming on Antarctic ice and fauna. The hope, says environmental officer Joyce Jatko, is that "tourists will become ambassadors for Antarctica." Though the international community is not yet considering a limit on tourist numbers, she adds, "both the Antarctic Treaty nations and the tour operators agree that adopting some site specific guidelines is a good and necessary thing to do."

John Splettstoesser has been coming to Antarctica as a scientist and guide since 1960. "For now," he says, "this is still one of the few places where people can visit a pristine area of the globe without mucking things up." He looks out over the inlet toward a blue and white iceberg. Out past a cruising leopard seal, the distant Marr Glacier calves another berg, the boom echoing across the water. "Even for me, the glamour has never worn off."

David Helvarg's book, Blue Frontier: Saving America's Seas, was published in April 2001.