The connection between changes in the Arctic Ocean’s ice cover and chemical processes leading to changes in chemical pollutants lies in the interaction among the salt in sea ice, frigid temperatures, and sunlight. When these mix, the salty ice releases bromine atoms into the air and starts a cascade of chemical reactions called a "bromine explosion," which creates more and more molecules of bromine in the atmosphere. Bromine then reacts with a gaseous form of mercury, turning it into a pollutant that falls to Earth´s surface.
The study, which has been accepted for publication in the Journal of Geophysical Research – Atmospheres, was also undertaken to better understand the fundamental nature of bromine explosions. The team of scientists wanted to find where in the atmosphere they occur – whether it is in the troposphere, the lowest layer of the atmosphere and therefore the air we breathe, or in the stratosphere, the air layer above the troposphere. This question about bromine explosion, discovered first in the Canadian Arctic, has puzzled scientists over the past two decades. Bromine also reacts with and depletes ground level tropospheric ozone. Despite its beneficial role blocking harmful radiation in the stratosphere, ozone is a pollutant in the low troposphere.
The scientists used the topography of mountain ranges in Alaska and Canada as a "ruler" to measure the altitude at which bromine explosions were taking place. In spring of 2008, satellites detected increased concentrations of bromine 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.
Sea ice continues to be dominated by younger saltier ice, and extreme cold spells occur more often in the Arctic due to climate change, bromine explosions are likely to increase in the future. Still there are uncertainties, as Professor Lars Kaleschke from the University of Hamburg and Professor John Burrows form the University of Bremen point out: "On the other hand, climate change could lead to a decrease in bromine explosions and therefore to an increase in ground-level ozone concentration".
While this study made a connection between changes in Arctic sea ice and mercury input to ocean and land, the amount of mercury is entering the environment due to bromine explosions is an area for further investigation.
To provide new insights into the bromine explosions phenomenon and assess its impacts, a new Arctic field campaign will be conducted in March 2012 (BROMEX), with international contributions by more than 20 institutions and agencies. Organizations participating in this study also include the University of Bremen and Hamburg.