Mysterious Sponges Live on a Boulder Under 3,000 Feet of Antarctic Ice

When scientists aiming to collect a sediment sample were stopped by a boulder, they found unexpected life instead

A boulder underwater has thin sponges growing off of it
“There’s all sorts of reasons they shouldn’t be there,” says British Antarctic Survey biologist Huw Griffiths Dr Huw Griffiths/BAS

Researchers with the British Antarctic Survey (BAS) were hoping to gather a sample of the ocean floor from beneath the Filchner-Ronne ice shelf when they happened upon an unexpected, miniature ecosystem.

At first, each time they lowered the sediment-collecting instrument down into the borehole, waited an hour for it to sink and return to the surface, it came up empty, Matt Simon reports for Wired. Only when reviewing footage from a Go Pro did the scientists realize that they had drilled through the ice directly over a boulder.

“It’s like, bloody hell!” says BAS geologist James Smith to Wired. “It's just one big boulder in the middle of a relatively flat seafloor. It’s not as if the seafloor is littered with these things.”

Unfortunate placement for a geologist turned out to be a stroke of luck for BAS biologist Huw Griffiths, who reviewed the footage back in the United Kingdom. Sponges and other sedentary life forms, possibly barnacles or tube warms, studded the surface of the boulder. A study describing the discovery was published on Monday in the journal Frontiers in Marine Science.

“It’s slightly bonkers,” says Griffiths, to Ian Sample at the Guardian. “Never in a million years would we have thought about looking for this kind of life, because we didn’t think it would be there.”

When ice shelves travel over land, they sometimes pick up boulders that become embedded in the bottom of the ice. When that portion of ice reaches the ocean, it can carry the boulder far from shore until it drops and sinks to the sea floor, per the Guardian. The boulder sat below 3,000 feet of ice and about 160 miles from the nearest source sunlight.

“There’s all sorts of reasons they shouldn’t be there,” says Griffiths to New Scientists Adam Vaughan. Biologists had spotted mobile creatures, like small fish and crustaceans, deep under the ice before. But those critters can swim or scuttle to a new source of food if the pickings get slim. Sponges and barnacles, on the other hand, are firmly rooted in place.

“This is by far the furthest under an ice shelf that we’ve seen any of these filter-feeding animals,” says Griffiths to the Guardian. “These things are stuck on a rock and only get fed if something comes floating along.”

Ripples in the sediment around the sponge’s boulder suggest that a current is present, reports Wired. Analysis of the way that water flows under the ice shelf suggests that the nearest source of food—probably dead plankton—is between 370 and 930 miles away. The nutrient-carrying detritus would need to float along in the sideways-flowing current for hundreds of miles and pass through a sponge to get the energy it needs to survive.

The discovery raises many new research questions. The scientists didn’t have the equipment to gather samples from the boulder, so they were unable to identify the species of sponges and other animals living there, or their source of food. A future mission, with the help of a remotely-operated vehicle, might be able to gather DNA samples for further research. Researchers might also investigate how and when the sponges came to land on that particular boulder. Biologists also hope to determine whether these species are run-of-the-mill, open-ocean sponges or unique to the environment found under the ice.

“[If] the organisms evolved to live beneath ice shelves, they may provide us with a molecular clock that can be used to gauge past climate driven changes in Antarctic ice,” says Montana State University polar ecologist John Priscu to NBC News’ Tom Metcalfe. Some Antarctic glass sponges, for example, live for thousands of years.

The seafloor beneath Earth’s ice shelves is still full of mystery. Humans can only study the Antarctic seafloor by drilling boreholes in ice shelves, so scientists only have tiny snapshots of vast swaths of the region, making it one of the least-explored ecosystems on the planet. The Filchner-Ronne ice shelf covers more than 160,000 square miles, so even if you add every borehole ever drilled together, the total area accounts for a portion of seafloor about the size of a tennis court.

At the same time, climate change puts them at risk of being lost forever.

“There is a potential that some of these big ice shelves in the future could collapse, and we could lose a unique ecosystem," Griffiths tells Wired.

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