Unprecedented levels of molecular chlorine have been found in the Arctic atmosphere about Barrow, Alaska, according to a new study. The chlorine — which is being released by melting sea ice — could be a contributing factor in climate change. It could also be speeding the deposit of toxic mercury into the Arctic ecosystem.

"No one expected there to be this level of chlorine in Barrow or in polar regions," Greg Huey, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in Atlanta, said in a news release.

Huey is a co-author of a new paper about the discovery, which was published this week in the journal Nature Geoscience. The lead author on the paper was one of Huey's graduate students, Jin Liao, who is currently a postdoc at the National Oceanic and Atmospheric Administration.

The study — which was conducted over several years starting in 2009 — found levels of molecular chlorine as high as 400 parts per trillion. At first their results seemed atypically high, so they kept testing, using chemical ionization mass spectrometry to verify the results, which were not a good sign.

"Molecular chlorine is so reactive that it's going to have a very strong influence on atmospheric chemistry," Huey explained. Molecular chlorine reacts with and oxidizes atmospheric constituents such as methane, a powerful greenhouse gas, and mercury, which can then enter the food chain and also serves to break down ozone. Mercury mostly comes to the region through the burning of coal in electric plants around the world.

The research team found that molecular chlorine levels varied throughout the day. It would peak in early morning and late afternoon, possibly as a result of the presence of sunlight and ozone. Chlorine levels would fall to almost nothing during the night.

Although the chlorine is said to have originated in the sodium chloride of sea salt, which is present in sea ice and Arctic snow pack, the exact mechanism of how the sea ice transformed into molecular chlorine remains unknown at this time. What is obvious, however, is that the region currently has less sea ice than it did in previous years due to climate change. This is likely to get worse in the future, Huey said, although exactly what this means remains unknown. "Sea ice is changing dramatically, so we're in a time where we have absolutely no predictive power over what's going to happen to this chemistry. We're really in the dark about the chlorine."

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