Due South, by ship

With the wind in our favor, the sudden whiff of fish and a rumble of cavernous snorts announced that the quarry was within range. A few steps later, the mound of mottled boulders at the high tide line rolled and heaved, and a half-dozen dozen giant elephant seals came alive.

"Keep back, amigos," warned our guide and elephant seal researcher Mauricio Alvarez, 43, as the shutterbugs in our group opened their tripods and, ignoring his advice, pushed ahead. "These guys are pretty calm, muy calma, while they're molting, but they can move fast when they have to," he said, drawing a line in the sand. Reluctantly retreating to a safe distance, we sat down to wait and watch the animals grunt, stretch and jostle.

Like the elephant seals, which migrate to the Tierra del Fuego Archipelago to loll in the sun, Alvarez joins the cruise ship Stella Australis in summer as a naturalist and team leader, guiding the ship's passengers through the winding channels and deep fiords of Chile's Alberto de Agostini National Park, at South America's southern tip.

The 210-passenger Stella, sailing three and four-night itineraries between Punta Arenas, Chile, and Ushuaia, Argentina, is the newest of Cruceros Australis' three expedition-style ships, all based in Southern Patagonia. Prowling among gravelly islets and beneath towering ice-clad peaks, they follow a circuitous route from the Straits of Magellan to the hidden coves of Ainsworth Bay, and from Glacier Alley through the Beagle Channel.

For most of us onboard, the sobering subtext of the voyage was the imperceptible climate changes threatening this still-wild region: melting glaciers, warmer winters and vanishing marine life. The trip was the chance to catch the action up close, in person and with a trained naturalist, that had us bounding out of our very comfortable beds each morning and hustling into our rain-proof gear.

On a small luxury ship like the Stella, the ambience is casual, the decor is nautical simplicity and the appointments are state-of-the-art. Each cabin has a large outside window and twin beds.

Twice-a-day excursions get underway in 20 minutes, the time it takes for the passengers to climb into their assigned Zodiac and motor away from the ship. And the biologist-guides know where the animals are likely to be found.

On our first outing we encountered the elephant seals almost by accident. The next day we motored to the Tucker Islets to see some of the thousands of winsomely waddling Magellanic penguins that nest here in summer. The Zodiacs don't land -- "never would we disturb them, not for any reason," said Alvarez -- so we kept our seats and bobbed a few feet offshore in the surf, taking turns in the prow for a closer look.

The Tucker Islets aren't the penguins' only nesting grounds but they must be the loveliest. Fairy rock gardens, they are boxy sedimentary formations formed first by erosion then isolated when the seas rose around them. Terraced over time, they're a wonderland of green grasses, native flowers and lacy tree branches. The migrating penguins swim here in pairs, clump ashore, find a spot on the summit or in a cliff, and hollow out a burrow. Here, safe and out of sight, they incubate their eggs, raise the chicks, teach them to swim and march about together like wind-up toys.

The penguins and their kin, the whales and seals, occupy center stage here in the spiky peaks of Darwin Cordillera. But it's the mountainous setting, the "wallpaper" if you will, that creates the drama. At the tip-end of the Andes mountains, the range rises 6,500 feet straight up out of the ocean, ice clad, ghost-like and cerebral. But even this is changing.

"You see the Marinelli Glacier, two miles away in that valley?" asked Alvarez, as we stood on the beach watching the elephant seals sneeze and snort. "This island here is a terminal moraine from that glacier, the pile of dirt and rocks that it left behind when it stopped growing and started to shrink back. And it's still shrinking."

Later we cruised through the channel known as Glacier Alley to the constantly calving face of the massive Pia Glacier. Anchoring in deeper water, we went ashore to climb the adjacent rocky hill and to ponder the ice field's mass and ancient lineage. As the clouds moved away and the sun came out, we heard the voice of the ice: now rifle-shot cracks, now rumbling roars.

For some passengers, the highlight of the cruise was sailing around Cape Horn, the stony island marking the continent's end. A perilous passage and frequent widow-maker, the voyage around the Horn is something to dine out on, even if you've only done it on a cruise. Historians estimate that 800 ships sank or vanished around Cape Horn between the years 1600 and 2000, 100 of them in the five decades after 1850.

On a tranquil day the trip looks deceptively easy. But even captains of modern ships like the Stella Australis know better. They study the weather reports and gauge the wind before deciding to land for a tour. The sun shone and the breezes abated the morning we stepped off onto the shore, but fierce gusts made the mandatory climb to the summit and the Albatross Monument a chore.

With the world's most changeable weather -- "four seasons in a single day," as they say here in Southern Patagonia -- "layering" is the mantra. After a frustrating first attempt to don my expedition gear -- layering long underwear, jeans, a shirt, jacket, parka and waterproof pants -- dressing became second nature. And a good thing, too, Tierra del Fuego's summers, from October to April, are warm in the sun, cool in the shade and sometimes even chilly.

Our weather during the January shoulder season, early summer in the Southern Hemisphere, invariably included light winds, a brief rain shower and sunshine. My REI thermometer (clipped to my backpack) lingered between 55 and 68 degrees.

So why is the climate so cool when cities in similar latitudes, like Moscow and Edmonton, enjoy warm summers? The answer, said Paula Girauldi, a naturalist, is because most of the world's land lies in the Northern Hemisphere. In the predominantly oceanic Southern Hemisphere, a 586-mile band of open water girdles the globe between the tip of South America and the Antarctic.

For this year, and the next and the next, the Stella Australis will sail these waters. For most of us, imagining a time without the glaciers or the streams and waterfalls they replenish was a sobering thought. Will the penguins, the elephant seals and the ice be here in another 10 years? For the first time, no one is sure.