Life below zero

Life continues to amaze. Hundreds of metres below Antarctic ice, in complete darkness and temperatures below zero, scientists have discovered a community of animals that expands knowledge about survival in frosty conditions.

They found the lifeforms, which consist of various sponges and other potentially unknown species, living on rock 260 kilometres in from the front of the ice shelf and up to 1500 kilometres upstream from the closest source of photosynthesis.

“This discovery is one of those fortunate accidents that pushes ideas in a different direction and shows us that Antarctic marine life is incredibly special and amazingly adapted to a frozen world,” says Huw Griffiths from the British Antarctic Survey. 

Griffiths is lead author of a paper titled “Breaking all the rules: The first recorded hard substrate sessile benthic community far beneath an Antarctic ice shelf,” published in the journal Frontiers in Marine Science.

The authors explain that current theories suggest the diversity of sessile lifeforms (stationary beings that include mussels, barnacles and coral) diminishes as you move further away from the ice shelf front, sunlight and nutrient availability. What’s left are small nomadic scavengers and predators that have previously been observed, such as fish, worms, krill and jellyfish.

The geologists were drilling through 900 metres of ice in the Filchner-Ronne Ice Shelf on the South Eastern Weddell Sea to collect sediment samples from the ocean floor. They were surprised to strike rock instead, and even more so by remote video footage that revealed a metre-long boulder covered in an assortment of marine fauna.

Such filter-feeding communities typically thrive on an abundance of plankton from above, which grow in response to summer melt and uninterrupted daylight. Underneath the ice, it was thought sessile feeders were restricted to food sources close to the shelf front, and they say none were previously found this far out.

“These observations challenge our understanding of what types of organisms can survive so far from daylight,” write Griffiths and colleagues, “and have wider implications with regards to the evolution of Earth’s first complex organisms on Earth, in particular through the ‘Snowball Earth‘ period, astrobiology and the survival of polar organisms during more recent glacial maxima.”

Similar types of fauna have been found under ice shelves before, notes Jonathan Stark from the Australian Antarctic Division, who wasn’t involved in the study. He points to filter feeders listed in the article such as bryozoans, ascidians, holothurians and sponges also found long distances from open water – albeit on sediments.

“While this study confirms that these organisms can be found on the rare bit of solid bottom – boulders or rock – under ice shelves,” he says, “it’s not really surprising given the very small area investigated to date.”

There is much to learn. As the study team notes: “Given that our combined knowledge of in-situ under-ice-shelf habitats (more than 1.5 million square kilometres) is drawn from 10 discrete observations covering an area comparable to that of a tennis court, it should not come as a surprise that we are still discovering previously unseen types of sub-ice-shelf communities far from open water.”

Do these communities have unknown connections to the outside world or have they developed special extreme adaptations? Such findings raise a flurry of questions such as how and when the creatures got there, what they eat, whether they are new species and how many there are. 

It also raises concerns about the fate of the ecosystems as climate change collapses the ice, putting pressure on polar scientists to learn more before they disappear – no small task at such a remote site, which calls for new and innovative approaches, according to Griffiths.

“To answer our questions we will have to find a way of getting up close with these animals and their environment.”