Pictures: Mysterious Deep-Sea Life Below Antarctica

For nearly five hours at a time, divers documented plant and animal life up to 70 metres below the surface.

One of Antarctica’s 16 species of octopus sits on the bottom. All Antarctic octopuses have a specialised pigment in their blood, turning it blue, to help them survive subfreezing temperatures.

The most southerly breeding mammal in the world, a Weddell seal, swims beneath the ice. The seals stay near the coast, breathing air through holes in the ice.

A diver swims more than 65 metres below the surface, where the light is dim and temperatures drop below -1.5 degrees Celcius.

A young Weddell seal sits in an ice gap. The juvenile will be about 3 metres long and weigh half a tonne once it's fully grown.

The icy waters below Antarctica are also home to a variety of marine invertebrates.

A seal swims beneath sea ice near East Antarctica’s Dumont d’Urville Station.

A diver swims beneath several feet of Antarctic ice. The rope hanging nearby helps divers find their way back to the surface.

Tethered to the seafloor more than 65 metres down, syphoning in water to collect food, orange sea squirts, “look very simple, like sponges,” says marine biologist Pierre Chevaldonné. “Yet they’re quite evolved”—they’re invertebrates, but the larvae have spinal cords. Synoicum Adareanum

More than 30 metres below the ice, a feather star waves its frond-like arms, groping for food particles. It’s an animal, not a plant—a cousin of sea stars—and it can swim. Photographer Laurent Ballesta dived as deep as 75 metres to get these shots. Promachocrinus Kerguelensis

An octopus jets above a seabed packed with life. Antarctica has at least 16 species of octopuses. All have a specialised pigment in their blood called haemocyanin, which turns the blood blue and helps them survive subfreezing temperatures. Pareledone sp

A curious young Weddell seal, weeks old, comes in for a close-up. It may have been the pup's first swim, says marine biologist Pierre Chevaldonné, who has worked at Dumont d’Urville. Weddell seals are the most southerly breeding mammal in the world.

Body stowed inside the ice floe, an anemone lets its tentacles dangle in the dark water. Marine biologist Marymegan Daly says it’s the only anemone species known to live in ice. Scientists can’t say how it penetrates the ice—or survives there. Edwardsiella Andrillae

Tendrils of ice-covered brine, or brinicles, leak from sea ice near East Antarctica’s Dumont d’Urville Station. Ephemeral and seldom seen, they form when trapped, supercooled brine escapes from the ice and freezes less salty seawater.

An isopod looks like a pill bug—and rolls up when threatened— but is nearly 10cm long. Glyptonotus Antarcticus.

A wary icefish takes cover in a kelp grove. These bottom dwellers have antifreeze proteins in their blood that help them withstand temperatures below -1.5 degrees Celcius. There are at least 50 species of icefish in the freezing waters of Antarctica. Family Nototheniidae (icefish); Himantothallus Grandifolius (kelp)

A Weddell seal accompanies her pup on a swim beneath the ice. When the juvenile is fully grown, it will be its mother’s size, about 3 metres long and weighing half a tonne. These placid seals stay close to the coast, breathing air through holes in the ice. Leptonychotes Weddellii

Emperor penguins head for the open ocean in search of food. The brownish patches above them are microalgae that cling to the sea ice and start to photosynthesise in spring. The photographer’s day camp was on one of these floes. Aptenodytes Forsteri (penguins)

The sea star nestled up to a worm-ridden, treelike sponge? It’s more than 30cm across. Macroptychaster sp

At 6cm (3 inches) long, this icebound Antarctic scallop is probably decades old—growth is slow in the extreme cold. Adamussium Colbecki

Sea spiders are another example of mysterious 'polar gigantism'; they’re tiny in other places, but this one in Antarctica has legs that span seven inches. Colossendeis Megalonyx

A bioluminescent crown jellyfish, some 35cm wide, floats by at 40 metres deep, glowing and trailing a dozen stinging tentacles. These bell-shaped plankton-eaters avoid direct light, which can kill them.