Antarctic seabed creatures on the retreat | Polarjournal
Numerous invertebrates such as mussels, sea urchins, snake stars and sponges live under the ice of the coastal areas of Antarctica despite cold and ice. But in some places, conditions for these critters had been worse than usual until 2014. Photo: Steve Clabuesch, National Science Foundation

The Antarctic paradox stated that despite global warming, pack ice had expanded in Antarctica. These changes on the surface along the Antarctic coast also led to changes in the seabed. In particular, biomass of invertebrates and productivity declined massively between 1988 and 2014 in the eastern part of the Weddell Sea, a now published study showed.

However, the research group led by project leader Dr. Claudio Richter of the Alfred Wegener Institute for Polar and Marine Research (AWI) found not only the decline, but also an explanation for it: the increasing sea ice cover during this time span and the greater amounts of snow on the ice. “We always had suspected that sea ice could be the key,” explains Dr. Richter. “Sea ice has increased around most of Antarctica until recently. More snow-covered ice floes mean less light, which would support the growth of small algae at the water surface and thus less dead plankton that sink to the bottom.” This had deprived the basis for bottom-dwelling species and filtering species such as mussels or sponges which have been stripped of their food, according to the researchers. The result is lower biomass and productivity in this otherwise very rich habitat.

The decline in plankton means that filter-feeders lose their food base, but species that feed on deposits and stranded species (starfish at the back of the picture) can find more food. Photo: Andrew Tabor, AAD

But where there are losers, there are winners. Santiago Pineda-Metz, a student and first author of the study, found that the winners are mainly species that feed on deposits and the stranded organisms. These include, for example, sea cucumbers or starfish. Overall, the frequencies of the different types of diet shifted back and forth accordingly, but biomass, a measure of the state and productivity of the system, declined. The researcher attributed this mainly to the loss of glass sponges, which make up a large part of the bottom-dwelling organisms and form a habitat for many smaller organisms. These sponges actually live on “plankton rain”, dead micro-algae that fall down slowly in the water column and form bottom sediments when not filtered.

The samples, which had been taken over the course of 26 years at various locations near Neumayer III Station, were all obtained with the help of a multi-armed, 2 tonne multi-gripper. Photo: AWI

The samples are all from the Kapp Norvegia-Auståsen region near the German Neumayer III station on the east side of the Weddell Sea. Between 1988 and 2014, the AWI had collected a total of 59 samples from the seabed of the region with the Polarstern A specially developed device, the 2 ton Multi-gripper, was used, which had taken a total of 300 samples. More than 45 tons of sediment were sifted through and tens of thousands of organisms were identified. The analysis of the data then fell on Santiago Pineda-Metz as part of his doctoral thesis. He also examined the possible reasons for the decline, such as analyzing the influence of breaking ice shelf and icebergs smouldering across the ground as possible factors. But the negative influence of the snow layer and the sea ice remained. But from 2014, with the end of the data sampling, there was also a reversal of sea ice cover. Since then, Antarctic sea ice has suffered a massive loss and has fallen back to the amount of the 1980s. This could be good news for the benthic communities. Researchers want to start a new series of data sampling early next year, because the recovery of the system is also of climate-relevant importance. “The storage of carbon (called blue carbon) in the benthos is an important feedback for the climate system,” says Pineda-Metz. His postdoctoral work seems at least clear.

Source: Alfred Wegener Institute for Polar and Marine Research

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