Under the ice

It’s like turning over a big rock in the garden and seeing all the creepy-crawlies scatter. When an iceberg the size of Nashville broke away from Antarctica’s Brunt Ice Shelf in late February, scientists raced to the Weddell Sea to investigate what had been living under the massive formation.

Researchers aboard the German research vessel Polarstern arrived first on the scene southeast of Argentina. Gale-force winds kept the ship from steaming directly into the growing rift between the A74 iceberg and the rest of the Brunt Ice Shelf. But by March 13, the German team managed to navigate into position.

Towing a camera platform attached to the ship via cable, the researchers collected video of the ocean floor that just weeks before had been obscured by the 500-feet-thick slab of ice. “The first images from the seafloor reveal an amazing level of biodiversity in a region that was covered by thick ice for decades,” the team said in a statement.

First, they saw barnacles clutching onto rocks on the seafloor that had been pushed out to sea by glacial ice. With more time, they discovered mollusks, sea stars, sea cucumbers, two kinds of squid, and at least five species of fish living in the once-darkened area.

An international team of researchers made similar findings after investigating the nearby Filchner-Ronne Ice Shelf. In research published in February, scientists cut a hole through the Antarctic ice using hot water and inserted a camera. They discovered colonies of filter-feeding sea sponges clutching rocks and waiting for phytoplankton to come to them. That’s an unusual spot to find filter feeders, since phytoplankton requires sunlight to grow.

Scientists theorize that phytoplankton living near the edge of ice get carried under the shelves by the Weddell Sea’s prevailing currents before dropping to the filter feeders below. The Polarstern crew’s discovery demonstrates that the currents carry phytoplankton at least 18 miles toward Antarctica from the sunlit edges to the spot where the A74 iceberg broke free from the rest of the Brunt Ice Shelf.