Immobile life has been found on a boulder embedded in the sea floor beneath 900 metres of Antarctic ice shelf, challenging our ideas of life in this harshest of environments.
The life, including stalked sponges, non-stalked sponges and other unidentified creatures, was found accidentally when scientists sunk a borehole through the Filchner-Ronne ice shelf hoping to obtain a sediment core sample from the seabed. Instead, they crashed into a boulder around the size of a washing machine. When they sent their GoPro down the hole to investigate they encountered an alien-like world that has shocked scientists.
Prior to this finding, scientists had theorised about what life may live under Antarctic ice shelves based on just eight boreholes drilled for geological and glaciological studies, giving a combined observed area comparable to a tennis court. This is despite the fact that almost a third of Antarctica’s immense 5 million km2 continental area is seafloor beneath ice shelves. Working with this limited data, mainly just from two of Antarctica’s many ice shelves, scientists had assumed that the diversity of sea life decreased when travelling from the open sea to further beneath the ice shelf, mainly because of the nutrient decrease caused by life under the ice shelf being unable to photosynthesise. Far from the ice shelf front it was predicted that only the occasional mobile organism, scavengers and predators, would be found.
Analysis of the GoPro footage by Huw Griffiths of the British Antarctic Survey published in the journal Frontiers in Marine Science suggests otherwise. Over 260km from the nearest open water, the organisms identified in the footage are immobile and feed on organic matter suspended in the cold, dark water. This is even more astounding when ocean currents are taken into account; the strong currents in the region mean their food, possibly dead plankton, must travel between 625km and 1500km before being eaten.
The boulder organisms could be formed from larvae which have travelled with ocean currents deep under the ice shelf or, more interestingly, specialist life could have evolved to exploit this specific ecological niche. Given the huge extent of this strange habitat, the latter is very much possible. Boulders become lodged in the ice shelf during its formation when ice from Antarctica’s interior flows over the land before settling on the sea to form a shelf. Boulders are lodged in the base of the ice before eventually falling down to the seafloor. These ‘drop-stones’ are eventually covered in sediment, raising the prospect that these organisms may ‘island hop’ from stone to stone, like the hydrothermal vent communities that ‘hop’ between active vents.
Next, researchers need to find out more about the dropstone organisms and their frequency beneath the ice shelves. Future studies might exploit the relatively new technique of environmental DNA (eDNA) sampling, which collects DNA that has been shed by organisms into the environment, into water and sediment samples. This could help researchers work out whether or not the species are newly discovered specialist organisms or known organisms that have strayed much further than expected.
Some sub-ice shelf life is believed to perform chemosynthesis, and such life could be another source of nutrients beneath the ice sheet. Chemosynthesis is, like it sounds, similar to photosynthesis, but with a vital difference: it uses the oxidation of inorganic compounds (such as hydrogen sulfide) as a source of energy rather than sunlight. Chemosynthetic bacteria are common in cold seeps, regions of the ocean floor where hydrogen sulfide, methane and other fluids seep out of fissures in the seafloor caused by tectonic activity.
Chemosynthesis has been proposed as a possible basis for life on other planets, but some chemosynthetic organisms already seem very alien. Tubeworms that grow near hydrothermal vents lack a digestive system but contain — in an organ called a trophosome — chemosynthetic bacteria. These bacteria produce amino acids (the building blocks of proteins) and release them to the tubeworm. If chemosynthesis is playing a role in the ecosystem of the drop-stone then this sub-ice shelf habitat could teach us lots about how life elsewhere in the universe devoid of sunlight, and even oxygen, might function.