An unexpected, thriving ecosystem

A diverse group of creatures beneath an Antarctic ice shelf could give pause to researchers who infer past ecological conditions from fossils found in such sediments.

In December 2003, researchers drilled a hole through the 480-meter-thick Amery ice shelf in Antarctica to get a look at the ocean bottom. At the drill site, 100 kilometers from open ocean, they expected to see a barren seafloor. How wrong they were.

Video of the ocean bottom at a depth of about 775 m revealed a wealth of creatures, says Martin J. Riddle, a marine biologist at the Australian Government Antarctic Division in Kingston, Tasmania. On the 2-square-meter patch of seafloor within camera range, the team identified more than two dozen familiar-looking species of invertebrates, including sponges, mollusks, sea urchins, and a sea snail.

Most of the creatures typically filter food and nutrients from the water or scavenge the ocean bottom. Scientists hadn’t expected currents to bring much food to the site under the ice shelf, says Riddle. However, the team reports in the January Paleoceanography that instruments on the probe measured currents strong enough to bring in microplankton that form the base of the site’s food chain.

The researchers warn that if paleontologists were to find the remains of such a complex community of organisms in ancient sediments, they’d probably assume that the site hadn’t been covered by ice. While that would seem a reasonable assumption, says Riddle, “it’s obviously wrong. … These creatures are no different from those that live in open water at that depth.”