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Unexpectedly high levels of molecular chlorine in the air has been found in the atmosphere above the Alaskan city of Barrow, according to a new study. Researchers were analyzing the atmosphere when they found the change in the chemistry of the ice due to global warming.

According to researchers, the substance comes from sea salt released when the ice in the region melts. It then interacts with sunlight to create highly reactive chlorine atoms.

These atoms can turn elemental mercury into more toxic forms through oxidization. These can also participate in a chemical reaction that can increase the degradation speed of methane.

“No one expected there to be this level of chlorine in Barrow or in polar regions,” Greg Huey, one of the study authors and a professor at the Georgia Institute of Technology School of Earth and Atmospheric Sciences, said in a press release. “Molecular chlorine is so reactive that it’s going to have a very strong influence on atmospheric chemistry."

Investigators observed that the chlorine concentration mostly peaked during the early morning and late afternoon hours. At night time, the concentration even plummeted to zero levels.

“Previous Arctic studies have documented high levels of oxidized mercury in Barrow and other polar regions,” he added. “The major source of elemental mercury in the Arctic regions is coal-burning plants around the world. In the spring in Barrow, ozone and elemental mercury are often depleted from the atmosphere when halogens – chlorine and bromine – are released into the air from melting sea ice.”

The study has been published in the Sunday’s edition of the journal Nature Geoscience.