Icebergs in the Arctic. Credit: David Schultz/ Mint Images / Getty Images

A model, supported by ice-core analyses in Greenland, shows that climate warming after the end of the last ice age triggered drastic environmental changes and a concomitant threefold rise in mercury levels in the Arctic1.

Mercury, a pollutant, is transported to the Arctic via the atmosphere, oceans and rivers. It accumulates in land and water, and eventually affects the health of people who rely on marine animals as a food source. Natural processes and human activities have been shown to alter mercury flux in this region.

How Arctic mercury levels varied in response to past climate changes has not previously been studied. To find out, an international research team, led by Delia Segato, studied the Arctic’s mercury variability during the transition from the last ice age to the warmer Holocene epoch, between 15,000 and 9,000 years ago.

The team, which included researchers at the Institute of Polar Sciences in Venice-Mestre, Italy, and the Indian Institute of Tropical Meteorology in Pune, found that perennial sea ice melted, creating a large area of ice-free ocean.

This allowed sunlight to penetrate deeper into the sea, triggering a proliferation of tiny sea-surface organisms that reduced mercury to its volatile form. This process, known as mercury evasion, led to greater mercury release from the ocean, contributing to 75% mercury variability in the Arctic.

In the early Holocene, higher bromine levels converted elemental mercury into gaseous oxidized mercury that contributed to a 25% change in Arctic mercury levels.

Current climate warming and the resulting loss of sea ice may potentially increase mercury release from the Arctic Ocean in the near future, the researchers say.