Life Found Surprisingly Abundant in the Darkness Under an Antarctic Ice Shelf

 

There is nothing but darkness deep beneath the ice of Antarctica's Ekström Ice Shelf.

According to a new article by academics from the UK and Germany, full darkness and a functioning ecosystem have persisted for thousands of years.

"This discovery of so much life flourishing in such harsh conditions is a complete surprise and serves as a reminder of how rare and precious Antarctic marine life is," says lead author and British Antarctic Survey marine biologist David Barnes.

"It's incredible that we found evidence of so many different animal species, the majority of which feed on microalgae (phytoplankton), despite the fact that no plants or algae can survive in this environment. So, how do these animals survive and thrive in this environment?"

Back in 2018, the researchers used hot water to drill two boreholes on the comparatively modest Ekström Ice Shelf in East Antarctica. The first hole stretched down 192 metres (630 feet) of ice until it reached 58 metres of liquid water, while the second hole covered 190 metres of ice with 110 metres of water beneath it.

They discovered life in that dark, cold, and food-scarce environment beneath the ice, and plenty of it. The researchers discovered 77 species of bryozoans from 49 distinct genera, including Melicerita obliqua, a sabre-shaped worm, and Paralaeospira sicula, a serpulid worm.

All of these animals are suspension feeders, meaning they sit in one spot and pluck organic materials from the water as it flows around them with their feathery tentacles, implying that some form of food supply, such as sunlight-dependent algae, must be getting in under the ice sheet.

Given that the nearest open water source is 9.6 kilometres (6 miles) distant, this is somewhat remarkable. On larger ice sheets like the Ross and McMurdo Ice Shelves, earlier study has discovered life much further inland.

"Life has been observed even 700 km from ice shelf borders despite perpetual darkness for at least thousands of years," the researchers wrote in their report.

"The diversity and quantity of life beneath ice shelves was assumed to be in short supply. Even for open-marine Antarctic continental shelf samples, the biodiversity we discovered at both borehole sites would be considerable."

Fragments of four Cellarinella species even revealed development increments, comparable to tree rings, which the researchers noticed were similar to other sized growth increments seen in samples from around Antarctica.

The researchers didn't simply seek for today's filter feeders deep beneath the ice; they also looked for long-dead bits and carbon-dated them to figure out how old they were.

"Another surprise was learning how long people had lived here. The carbon dating of these bottom animals' dead fragments ranged from current to 5,800 years "Gerhard Kuhn, a geologist at the Alfred Wegener Institute for Polar and Marine Research, is one of the researchers.

"Despite living 3-9 kilometres from the nearest open water, an oasis of life may have flourished under the ice sheet for approximately 6,000 years. Only samples taken from the seabed beneath the floating ice shelf will reveal information about the ice shelf's past."

This raises another issue: how did these dark ecosystems survive past glacial cycles when most of the Antarctic shelf was covered in grounded ice (ice that reaches all the way to the sea floor)?

According to the new findings, the organisms resided in small, un-grounded areas, whereas open areas of water surrounded by sea ice would have allowed phytoplankton to bloom and then be consumed by critters living far beneath the ice. The plankton would have been pushed beneath the ice by the water's flow, where it would have been within reach of the hungry critters below.

Unfortunately, despite these ecosystems' unusually long lives thus far, the researchers are concerned about their future.

"In most areas, it may be cold, dark, and food-scarce," the team writes, "yet the least disturbed habitat on Earth could be the first habitat to become extinct if sub-ice shelf conditions disappear owing to global warming."