Ocean currents may be driving mercury pollution in Arctic, says study

A new study reports that mercury keeps building up in the Arctic even though international efforts have reduced emissions of the metal. It names ocean currents as the main reason. The authors write that currents holding large stocks of older mercury may be the leading route for the mercury taken up in Arctic marine and coastal areas.

An international team of scientists examined peat in Greenland, and animals including fish, seals and polar bears. They measured mercury levels and chemical signatures in the samples. Tracking isotopes let the team work out where the mercury came from and how it moved through the environment.

The UN Minamata Convention came into force in 2017 and aimed to cut human-caused mercury releases into the atmosphere. Its measures include a ban on new mercury mines and a reduction or phase-out of mercury in different products and activities. According to the paper, mercury deposition from the atmosphere has generally fallen across the Arctic in recent decades, because global human emissions have dropped. Yet mercury is mostly trending upward in many biological materials, such as marine mammals and fish from salt and fresh water. The paper says this mismatch leaves gaps in knowledge about mercury sources and pathways.

The scientists found that ocean currents appear to carry what they call legacy mercury into the Arctic. The term means mercury that stays in the environment after the original source has been removed. The paper says this explains why deposition is falling while many Arctic species show no response or rising mercury loads, and that it matters for judging the Minamata Convention. Levels also differed within Greenland. The west, influenced by the Atlantic, had less total mercury but more of one isotope than the east and north, where currents from the Arctic Ocean dominate.

The researchers said more studies should be done in Alaska, Arctic Canada and Svalbard, to build a fuller picture of how mercury travels north. They added that ocean transport of legacy mercury should be examined in other regions, to help assess how mercury rules work and to meet the UN Sustainable Development Goals.