The study found that thick, perennial Arctic sea ice was being replaced by a thinner and saltier ice that releases bromine into the air when it interacts with sunlight and cold, said Son Nghiem, a NASA researcher at the Jet Propulsion Laboratory in Pasadena.

That in turn triggers a chemical reaction called a "bromine explosion" that turns gaseous mercury in the atmosphere into a toxic pollutant that falls on snow, land and ice and can accumulate in fish, said Nghiem, lead author of the study.

"Shrinking summer sea ice has drawn much attention to exploiting Arctic resources and improving maritime trading routes," Nghiem said.

"But the change in sea ice composition also has impacts on the environment," he said. "Changing conditions in the Arctic might increase bromine explosions in the future.

Nghiem said the released bromine can also remove ozone from the lowest level of the atmosphere, the troposphere.

Though much of the attention on Arctic sea ice has focused on summer sea ice cover, the NASA-led study, which has been accepted for publication in the Journal of Geophysical Research-Atmospheres, examined perennial sea ice during winter and the transition into spring.

Nghiem said scientists were still trying to determine why the Arctic had lost an estimated one million square kilometers of perennial sea ice over the last 10 years, saying it could be due to a change in wind patterns over that time period.

In March 2008, the extent of year-round perennial sea ice set a 50-year low, shrinking by an area the size of Texas and Arizona combined, according to NASA. It has been replaced by younger, seasonal sea ice that is saltier because it has not undergone the processes that wash out its salts.

The study was conducted by a team from the United States, Canada, Germany and the United Kingdom and combined data from six NASA, European Space Agency and Canadian Space Agency satellites as well as field observations and a model.

(Reporting by Dan Whitcomb; editing by Cynthia Johnston and Todd Eastham)

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