Deepest dive ever under Antarctica reveals a shockingly vibrant world

In the morning, when we arrive on foot from Dumont d’Urville, the French scientific base on the Adélie Coast of East Antarctica, we have to break up a thin layer of ice that has formed over the hole we drilled the day before. The hole goes right through the 10-foot-thick ice floe. It’s just wide enough for a man, and below it lies the sea. We’ve never tried to dive through such a small opening. I go first.

Pushing and pulling with hands, knees, heels, and the tips of my swim fins, I shimmy through the hole. As I plunge at last into the icy water, I look back—to a sickening sight. The hole has already begun to close behind me.

The bottom surface of the sea ice is a thick slurry of floating ice crystals, and my descent has set them in motion. They’re converging on the hole as if it were an upside-down drain. By the time I thrust one arm into the icy mush, it’s three feet thick. Grabbing the safety rope, I pull myself up inch by inch, but my shoulders get stuck. Suddenly I’m stunned by a sharp blow to the head: Cédric Gentil, one of my dive buddies, is trying to dig me out, and his shovel has struck my skull. Finally a hand grabs mine and hauls me into the air. Today’s dive is over—but it’s only one of 32.

I’ve come here with another photographer, Vincent Munier, at the invitation of filmmaker Luc Jacquet, who’s working on a sequel to his 2005 triumph, March of the Penguins. While Jacquet films emperor penguins and Munier photographs them, my team will document life under the sea ice. In the winter the ice reaches 60 miles out to sea here, but we’ve come in October 2015, at the beginning of spring. For 36 days, as the ice breaks up and retreats to within a few miles of the coast, we’ll dive through it, down as deep as 230 feet.

I’ve worked for decades as a deep-diving photographer, at first in the Mediterranean Sea, where I learned to dive 30 years ago. Later, a craving for new mysteries took me elsewhere. I’ve dived to 400 feet off South Africa to photograph rare coelacanths, and for 24 straight hours off Fakarava, in French Polynesia, to witness the mating of 17,000 groupers. But this expedition to Antarctica is unlike any other. Here we’ll be diving deeper than anyone has dived before under Antarctic ice—and the conditions will be beyond harsh.