The deep, unexplored waters surrounding Antarctica have always been “a black spot on the map,” says marine biologist Angelika Brandt of the Hamburg Zoological Museum, who recently conducted the world’s first biological survey of the Southern Ocean floor. No more. Brandt led a small army of scientists on three expeditions to the Weddell Sea in Antarctica, where they collected bottom-dwelling organisms at 40 different locations, some in waters nearly four miles deep. She expected to find deep-sea biodiversity paralleling that of the Northern Hemisphere—rich near the equator but thin near the poles.

Instead, the researchers hauled up a startling variety—including bristly polychaete worms, isopod and amphipod crustaceans, mollusks, gastropods, sea urchins, brittle stars, nematode roundworms, and carnivorous sponges. “Before we went,” Brandt says, “we expected interesting results, but nothing like the tremendous diversity we documented.”

All in all, Brandt found more than 750 species that had never been seen before. She plans to return to the Southern Ocean later this year to study interactions between the sea and the atmosphere and to figure out how some of those newly discovered species get by. “We have no idea what they do there, what they feed on, who feeds on them, or what their ecological roles are,” says Brandt.

But she has no doubts that her next expedition will be equally surprising: “In the deep sea,” she says, “you can always find something unexpected.”