Antarctic ice melt drives record mercury levels into marine food chain: Study

Antarctic glaciers are releasing increasing amounts of mercury into the surrounding ocean as climate change accelerates ice melt, potentially exposing marine organisms to a toxic pollutant that can accumulate through the food chain, according to a new study.

Published in the Proceedings of the National Academy of Sciences, the study examined 16 sediment cores collected from the continental shelf off the Antarctic Peninsula to investigate how mercury has accumulated there over the past 200 years.

The researchers found that nearly all the sediment cores showed a significant increase in mercury accumulation since industrialisation, which began in the mid-18th century. On average, mercury accumulation in the region increased by 160%, with the rate accelerating particularly rapidly from the 1950s.

The study also found that the amount of mercury released by Antarctic glaciers into the ocean has increased by 550% since industrialisation.

“Climate change acts as an amplifier of mercury cycling,” Maodian Liu, an environmental scientist at Peking University and co-author of the study, wrote in an email. “Global mercury pollution and climate change are not independent environmental problems.”

How mercury reaches Antarctica

Mercury has historically accumulated in Antarctica because the continent’s cold environment traps pollutants carried through the atmosphere and ocean.

Previous research has shown that mercury reaches Antarctica through atmospheric transport from sources including coal-fired power plants and mining operations. It can then settle on Antarctic ice and the Southern Ocean.

The new study sought to distinguish this atmospheric deposition from another source: mercury that had already been trapped in Antarctic ice and sediments and is now being released as glaciers melt.

The researchers used chemical analyses of the sediment cores to determine the amount and likely sources of mercury deposited over the past two centuries. Their analysis estimated that about 56% of the mercury detected in the Antarctic Peninsula seafloor cores originated from the atmosphere. The remainder likely came from glacier melt, weathering and erosion of Antarctic ice and sediment.

“Climate change is not only increasing the amount of glacial meltwater but is also releasing legacy mercury that was previously stored on the Antarctic Peninsula,” Liu wrote.

Why mercury release matters

Mercury is a toxic heavy metal that can become particularly concerning when it is converted into methylmercury, a more toxic form that can accumulate in living organisms.

Methylmercury can enter the Antarctic food web through plankton and move upwards through krill, fish, seabirds and marine mammals. At sufficiently high doses, it can affect animals’ neurological systems, behaviour, growth and reproduction.

The potential impact also extends beyond Antarctica’s wildlife. Some Antarctic krill and fish enter commercial fisheries, meaning mercury contamination could eventually have implications for human health.

Charles Driscoll, an environmental engineer at Syracuse University who was not involved in the study, said more research was needed to establish how much mercury in the cold waters of the Antarctic shelf could be converted into methylmercury. The conversion process typically occurs faster in warmer temperatures.

The study also adds to evidence that climate change is altering the global mercury cycle. Similar processes have been observed elsewhere, including the release of trapped mercury as Arctic permafrost thaws and the mobilisation of mercury through increased erosion and storms.

Mercury may continue to be released

The researchers said the findings suggest that reducing new mercury emissions alone may not immediately reverse the increase in environmental mercury.

Even if emissions from coal combustion, mining and other human activities decline, mercury stored in Antarctic ice could continue to enter the ocean as the ice melts. Liu wrote that “environmental mercury burdens are unlikely to decline immediately in step with emission reductions”.

The researchers said further studies are needed to determine whether the trends observed around the Antarctic Peninsula are representative of Antarctica as a whole.