According to a new NASA-led study Drastic reductions in Arctic sea ice in the last decade
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may be intensifying the chemical release of bromine into the atmosphere, resulting in ground-level ozone depletion and the deposit of toxic mercury in the Arctic. The connection between changes in the Arctic Ocean’s ice cover and bromine chemical processes is determined by the interaction between the salt in sea ice, frigid temperatures and sunlight. When these mix, the salty ice releases bromine into the air and starts a cascade of chemical reactions called a “bromine explosion.” These reactions rapidly create more molecules of bromine monoxide in the atmosphere. Bromine then reacts with a gaseous form of mercury, turning it into a pollutant that falls to Earth’s surface. Bromine also can remove ozone from the lowest layer of the atmosphere, the troposphere. Despite ozone’s beneficial role blocking harmful radiation in the stratosphere, ozone is a pollutant in the ground-level troposphere. The team combined data from six NASA, European Space Agency and Canadian Space Agency satellites, field observations and a model of how air moves in the atmosphere to link Arctic sea ice changes to bromine explosions over the Beaufort Sea, extending to the Amundsen Gulf in the Canadian Arctic. The study was undertaken to better understand the fundamental nature of bromine explosions, which first were observed in the Canadian Arctic more than two decades ago. The team of scientists wanted to find if the explosions occur in the troposphere or higher in the stratosphere. Nghiem’s team used the topography of mountain ranges in Alaska and Canada as a “ruler” to measure the altitude at which the explosions took place. In the spring of 2008, satellites detected increased concentrations of bromine, which were associated with a decrease of gaseous mercury and ozone. After the researchers verified the satellite observations with field measurements, they used an atmospheric model to study how the wind transported the bromine plumes across the Arctic. The model, together with satellite observations, showed the Alaskan Brooks Range and the Canadian Richardson and Mackenzie mountains stopped bromine from moving into Alaska’s interior. Since most of these mountains are lower than 6,560 feet (2,000 meters), the researchers determined the bromine explosion was confined to the lower troposphere. After the researchers found that bromine explosions occur in the lowest level of the atmosphere, they could relate their origin to sources on the surface. Their model, tracing air rising from the salty ice, tied the bromine releases to recent changes in Arctic sea ice that have led to a much saltier sea ice surface. According to scientists if sea ice continues to be dominated by younger saltier ice, and Arctic extreme cold spells occur more often, bromine explosions are likely to increase in the future.