Produced by human and volcanic activity or melting ice, mercury concentrations are increasing in Antarctic food chains, particularly in the Ross Sea, according to a study by Fanny Cusset and her colleagues.
A feather a little heavier than the others. Those of Adélie penguins in the Ross Sea are the most contaminated of the species by mercury. A study published in mid-October in Ecotoxicology reveals the distribution of concentrations of this heavy metal around the 7th continent.
The Ross Sea is particularly rich in biomass. Its shallower continental shelf is extensive. Ample marine circulation maintains thousands of small open areas in the ice. “These gyres bring nutrients to the upper layers of the ocean offshore, a boon for phytoplankton, which flourish and feed the entire Antarctic ecosystem,” describes Fanny Cusset, marine biologist and principal investigator of the study.
Marine predators have access to krill, fish, etc. Half of the orcas in the Southern Ocean and a third of the Adélie penguins live in the Ross Sea. If these animals are contaminated, it means that the whole food chain is contaminated too,” she points out.
Adélie penguins, which live both east and west of the continent, from the Antarctic Peninsula to Terre Adélie, are a good medium for studying the distribution of mercury. To measure this metal, we had to remove tissue without endangering the life of the animal,” explains the biologist. “By chemical affinity, almost 90% of the mercury accumulated in the penguin’s body goes into its feathers. A natural process to purify the body”.
The concentrations measured are a few micrograms per gram of feather. These values are below the toxicity threshold, but four to 20 times higher than those of krill and 50 times lower than those of albatrosses, which feed on different prey further north.
The researchers believe that the mercury in the Ross Sea was probably deposited by katabatic winds, the strong winds that blow down from the continent towards the ocean. But also by snow, rain and directly by the ocean.
“It’s difficult to discern the anthropogenic part from the natural part at the moment,” says the investigator. “We need to look at the snow and pack ice and study the whole metal cycle in Antarctica.”
Mercury comes from the combustion of fossil fuels, gold mining and the chemical industry, where it is used as a catalyst. It escapes into the atmosphere, rivers and major ocean currents and reaches Antarctica. In the Ross Sea, the volcanism of Mount Erebus and Mount Melbourne probably plays a role in the contamination. This initial survey of circumpolar mercury does not describe the impact of this metal. “We’ll have to go further to find out,” she adds.
“The advantage of feathers is that they are stable over time,” adds Fanny Cusset, who will now be looking at samples stored in certain natural history museums, such as those in Paris, London and Copenhagen. This work will make it possible to retrace time scale of contamination since the beginning of the industrial era.
Camille Lin, PolarJournal
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