B-15 was, at the time of its birth, the largest moving object on the Earth, easily seen with the naked eye from space.

The Antarctic sun glowed red on the horizon at 1 a.m. A mile and a half from the deck of Braveheart an iceberg the size of six city blocks the iceberg to which we'd been tethered just hours before ¿ heaved upwards, one end pausing high in the air like the bow of a foundering ship.

When it crashed back down, waves swept through the waters of Cape Hallett. As the boat slapped against the bumpy sea, the iceberg rose again and the upper end exploded. Shards of ice rained down, covering two square miles like shattered crystal.

As we stood on deck, we watched a part of our world come apart. Expedition co-leader Wes Skiles and I were below decks eating a meal when someone yelled to come up on deck ¿ quickly! We raced through the companionways, up the stairs, bumping our heads and grabbing cameras on the way. Almost too stunned to take pictures, we watched, mute, as the giant piece of ice vanished.

We were possibly the only people to record an iceberg exploding and live to tell about it. As we stood on deck, watching the seemingly solid block of ice disintegrate before our eyes, we once again realised just the very real dangers surrounding us in the world of ice we had come to study.

Our ultimate quarry was cruising the Ross Sea some 125 miles from Cape Halletat. Its name was B-15B, a 1,900-square-mile chunk of the original B-15, which, when it calved from the Ross Ice Shelf in March 2000, had an upper surface area of about 4,500 square miles (170 miles by 26 miles). B-15 was comparable in size to Connecticut or Jamaica, and contained enough fresh water, in the form of a thousand cubic miles of ice, to supply the United States for five years.

Doug MacAyeal from the University of Chicago tracked B-15, nicknaming it "Godzilla", and posted locations on his web site. After calving, B-15 drifted west, bumping and smashing along the edge of the Ross Ice Shelf and eventually breaking up into smaller, but still gigantic, pieces named B-15A, B-15B and B-15C, etc.

A berg with the dimensions of B-15 comes along once or maybe twice in a lifetime. The US National Ice Centre in Suitland, Maryland, which has been tracking Antarctic icebergs for 25 years, had never recorded a berg as big. For nine years, satellite images recorded cracks in the Ross Ice Shelf as they spread and set B-15 loose, making it the largest "fast" moving object on the planet and sending it on its journey that would eventually lead to us.

A month after B-15 was born, photographer and filmmaker Wes Skiles and I decided to launch an expedition to study and explore B-15 and other large icebergs of Antarctica.

On the day Wes called me, I was diving in Bermuda with Teddy Tucker on a coral reef project. Under a tropical sun, it was easy for me to jump at this ambitious proposal, but later, sliding across the ice-covered deck and wedged into my bunk in the towering seas, I would question my sanity. It had been 13 years since I had dived into Antarctica's clear, frozen waters, and I had often dreamed of returning. I could not wait to get back to the most exhilarating diving I had ever done.

It took a few hundred phone calls, numerous meetings at The National Geographic Society, a winter training session in the Colorado Rockies, and ambitious fund-raising efforts, but we were able to pull the expedition together in just seven months.

We were especially thrilled to have backing from National Geographic, for which Wes filmed and photographed the expedition and I wrote an article.

The mission of the expedition was scientific. As a marine biologist, I was interested in the ecology of large icebergs, which are really floating ice-islands. There is little information on how large icebergs affect the ocean and the distribution of animals around them. And, since ice is melting globally in more places and at higher rates than ever recorded, I wanted to dive into and sample these melting giants. Any information we gleaned about these icebergs would help us understand the effects of global warming.

We decided to head for B-15B, the second-largest chunk of B15 and the one farthest north in the Ross Sea. At the time, it measured approximately 60 miles by 25 miles.

Once I had decided to co-lead an Antarctic expedition, I became passionately interested in the early explorers. The smallest details of their journeys fascinated me, as I planned a trip to one of the most desolate places on earth hoping to avoid some of their mistakes. Our trip would have more in common with the early explorers of the Ross Sea than any contemporary "Antarcticans."

Among these early explorers were Sir James Clark Ross, Sir Douglas Mawson, Sir Ernest Shackleton, Roald Amundsen and Captain Robert Falcon Scott. They were the ones who discovered and lived in the region aboard ships like the Erebus, Terror,Discovery, Fram, Nimrod, Terra Nova and Aurora, ships roughly the same size class as ours.

What motivated these men, how did they get there, what happened to them, what could I learn from them and what might we expect on our journey? Reading the accounts of their expeditions late into the night, my eyes gritty with sleep, I was filled with admiration for these irrepressible explorers, their hardiness, determination and resourcefulness. At other times, reading these same accounts filled the pit of my stomach with terror.

My previous trips to the Antarctic had been to the other side of Antarctica, the Peninsula region, a much easier place to get to and work. People call it the "banana belt" of Antarctica for its relatively mild summer weather. But we were going to the Ross Sea, a completely different kind of trip: colder, a 14-day voyage, gale-force winds, much higher risk overall, but closer to the heart of Antarctica in every way.

More than 12,000 people travel to Antarctica each year, but most either go in aeroplanes to modern research bases or in larger ships to a few tourist areas in the relative comfort of the Antarctic Peninsula summer climate. Our expedition would take a relatively small ship and go to the more southerly, rarely visited offshore waters of the Ross Sea.

We were going to explore parts of Antartica, the fifth largest continent, about the size of North America, which covers ten per cent of the world's total land area. It contains most of the fresh water on the planet in the form of an ice sheet, which is really a series of massive glaciers that cover 99.5 per cent of the land area and tower more than two miles above the continent's soil.

This tremendous ice sheet began to form more than ten million years ago, but because most of the ice continually flows outward and off the continent into the ocean, the ice that occurs there today is usually no more than 100,000 years old, formed from snow accumulation. This ancient icy world makes the continent what some have called a Pleistocene relic. Winters are six months of nearly complete darkness, with temperatures and winds fiercer than any other place on Earth. B-15 was originally part of this ice sheet.

Though there are no land mammals in Antarctica, there are more marine mammals seals and whales than anywhere else. Antarctica is home to 33 million seals and more than 500,000 whales, but the diversity is not high: only six seal species and nine whale species inhabit its waters, including the largest animal to ever inhabit the earth, the blue whale (Balaenoptera musculus). For sheer numbers and size of individuals, Antarctica is a place of mammals.

On our expedition, we learned a great deal about the ecology of large icebergs. We determined that the large tabular icebergs of Antarctica are biological engines, bringing and perhaps enhancing the rich biology found along the edges of ice shelves with them as they move offshore. Throughout the oceans, the biological action is usually found along edges of currents, islands, continents and large objects. These edges help concentrate and mix nutrients required for fertilisation of the oceans and the growth of tiny single-celled marine plants called diatoms, the basis of marine food chains. Icebergs, too, act as edges.

As they drift and melt, large icebergs create powerful currents that leave physical and biological wakes in the ocean around them. These wakes may encourage the concentration of krill, fish, sea jellies, whales and seals. These bergs also create habitat for the icefish living inside and under the berg, for penguins and seals climbing up on ice ledges, and for seabirds nesting on them.