Mercury (Hg) is an environmental concern in the Arctic, where high concentrations are found in top predators such as polar bears and toothed whales. Despite declining atmospheric Hg emissions since the 1970s, increasing trends are still observed in many Arctic animals today. The residence time of Hg in the ocean is very long (>300 years) compared to the atmosphere (~1 year), which means it may take a long time before the effects of regulation become visible. Credit: Rune Dietz. CC BY-NC-ND.

New Danish research reveals ocean currents as a major source of centuries-old mercury contamination in the Arctic.

Despite global reductions in mercury emissions, mercury concentrations in Arctic wildlife continue to rise.

A new study by researchers from Aarhus University and the University of Copenhagen reveals that ocean currents may be transporting legacy mercury pollution to the Arctic — posing a long-term threat to ecosystems and human health.

Professor Rune Dietz from Aarhus University said: “We’ve monitored mercury in Arctic animals for over 40 years.

“Despite declining global emissions since the 1970s, we see no corresponding decrease in Arctic concentrations — on the contrary.”

Mercury released into the atmosphere from sources like coal combustion and gold mining can remain airborne for about a year.

However, once it enters the ocean, it can persist for over 300 years.

This means that even with current emission reductions, the Arctic may continue to experience elevated mercury levels for centuries.

In the marine species, total Hg concentrations in muscle tissue are lowest in sculpin, ringed seal, and polar bear, followed by glaucous gull. Hg stable isotope signatures vary significantly between matrices. Peat has the lowest δ202Hg for Central West and Northeast Greenland. Credit: Søndergaard, Dietz, Elberling. CC BY-NC-ND.

Mercury’s fingerprint in Arctic wildlife

The researchers analysed over 700 environmental samples — including tissues from polar bears, seals, fish, and peat — from across Greenland collected over the past 40 years.

By examining the composition of six common mercury isotopes, they identified distinct regional differences that align with ocean current patterns.

Senior researcher Jens Søndergaard, from Aarhus University, said: “These isotope signatures act like fingerprints, revealing the sources and transport pathways of mercury.”

For example, central West Greenland is influenced by Atlantic inflow via the Irminger Current, while other regions are dominated by Arctic Ocean currents.

Implications for global mercury regulation

Mercury is a potent neurotoxin. In Arctic top predators like polar bears and toothed whales, concentrations are now 20 – 30 times higher than before industrialisation.

This poses serious health risks not only to wildlife but also to Indigenous communities that rely on marine mammals for food.

Aarhus University’s Professor Christian Sonne said: “Mercury affects the immune system, reproduction, and possibly sensory functions in animals, which can impact their survival.”

The findings have significant implications for the UN’s Minamata Convention on Mercury, which aims to reduce global mercury pollution.

The study offers a potential explanation for why mercury levels in Arctic biota remain high despite falling atmospheric emissions.

Dietz said: “Transport of mercury from major sources like China to Greenland via ocean currents can take up to 150 years. This helps explain the lack of decline in Arctic mercury levels.”

Looking ahead

The research team is continuing their work on mercury isotopes across the Arctic through the GreenPath project, funded by the Independent Research Fund Denmark.

The isotopic analyses also contribute to international projects such as WhaleAdapt and ArcSolutions.

The research is published in Nature Communications.