Ice shelves are gigantic ice fields fed by Antarctic glaciers that reach far out into the ocean. While the surface of the ice shelves appear flat and empty, the underwater world beneath is barely explored. Especially the area where the shelves begin to float in the water column has hardly been seen by human eyes so far. But an international research team now has discovered by chance that beneath the hundreds of metres thick Filchner-Ronne ice shelf, there is a richer fauna than previously thought.
The team, led by lead author Dr Huw Griffiths of the British Antarctic Survey, concluded after examining the available material that the seafloor, particularly rocks, is home to a larger number of sessile species such as sponges and previously unidentified stalked species. “What we found was surprising because we hadn’t expected to discover these types of animals that filter their food from the water column, far from any food source or daylight,” explains Dr Huw Griffiths. The video and images were taken from the far western part of the Filchner-Ronne ice shelf, which extends far into the Weddell Sea. The drilling was carried out about 300 kilometres from the edge of the ice shelf, where the ice is almost 900 metres thick and the water column is another 470 metres deep. The results of the work were published today in the journal Frontiers of Marine Science.
The original aim of the drilling was to obtain cores from the sediment of the seabed. But after the drill hit a rock, the rock revealed an abundant number of different sessile organisms. The analysis of the images and video recordings made afterwards revealed sponges and unidentified stalked creatures. A total of 22 individuals from three different groups were recognized by the researchers, a previously unknown diversity of animals in this region, living far away from light and food sources, at depths of over 1,200 meters and at water temperatures of around -2.2°C. “The really exciting thing for me about our discovery is that it provides more questions than answers,” Dr Griffiths continues. “We have no idea what species they are. We don’t know how they cope with the extreme conditions.” More than half of the species could not be identified just from the recordings.
The prevailing conditions identified by the research team are in fact anything but favourable to life. In addition to the darkness, the pressure and the low temperature, the current speed of the water is also very high, as is the salinity. The finest particles are carried along with the current, which probably forms the food basis of the animal species. But how high the proportion of recyclable material is cannot yet be determined with certainty, as the team writes in their paper. Also important is the fact that the stone lies in the current in such a way that the current has already traveled almost 700 kilometers before the water hits the stone. Because that means food particles could be rather scarce. Furthermore, the animals need a hard substrate to attach themselves to. This is not possible in the surrounding soft sediment bottom and therefore the larvae of the animals need something like stones or rocks. These are transported by the glaciers from the continental mountains and drop out of the ice when it thaws. Since this probably doesn’t happen too often at the site, such permanent residences are also rarer.
The significance of the find is enormous. Because it topples previous assumptions about life beneath the ice shelves. Previously, sessile organisms had been found at the edges of ice shelves; from boreholes in the Ross Sea and Whillans Ice Stream, only mobile species such as fish and crabs had been discovered, or dead zoological material. The size of the areas investigated so far is also not very large. “Everything we know about these areas under the ice comes from a handful of holes that have been drilled into the ice by a number of people,” Dr Griffiths explains. “This means we don’t really know much. And the total area that has been looked at by humans so far is about the size of a tennis court.” That’s why the research team wants to conduct further studies using slightly gentler methods in the region. Because the ice shelves are in danger of breaking apart quickly. This would rapidly change conditions and endanger what may be highly specialized wildlife. And there are still too many unanswered questions that can shed light on the darkness beneath these ice shelfs.
Dr Michael Wenger, PolarJournal
Link to the study: Griffiths HJ, Anker P, Linse K, Maxwell J, Post AL, Stevens C, Tulaczyk S and Smith JA (2021) Breaking All the Rules: The First Recorded Hard Substrate Sessile Benthic Community Far Beneath an Antarctic Ice Shelf. Front. Mar. Sci. 8:642040. doi: 10.3389/fmars.2021.642040
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