Implications of Snowpack Reactive Bromine Production for Arctic Ice Core Bromine Preservation

• Published in: Journal of geophysical research. Atmospheres 2023-10, Vol.128 (20)
• Main Authors: Zhai, Shuting, Swanson, William, McConnell, Joseph R., Chellman, Nathan, Opel, Thomas, Sigl, Michael, Meyer, Hanno, Wang, Xuan, Jaeglé, Lyatt, Stutz, Jochen, Dibb, Jack E., Fujita, Koji, Alexander, Becky
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Arctic ice; Arctic snow; Atmospheric models; Bromides; Bromine; Chemical reactions; Chemical speciation; Chemical transport; Cores; Depletion; Emissions; Euphotic zone; Geophysics; Halogens; Human influences; Ice cores; Latitude; Locations (working); Modelling; Ozone; Ozone depletion; Photochemicals; Preservation; Records; Sea ice; Snow; Snow accumulation; Snow and ice; Snowpack; Trend analysis; Trends
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2023JD039257

Snowpack emissions are recognized as an important source of gas‐phase reactive bromine in the Arctic and are necessary to explain ozone depletion events in spring caused by the catalytic destruction of ozone by halogen radicals. Quantifying bromine emissions from snowpack is essential for interpretation of ice‐core bromine. We present ice‐core bromine records since the pre‐industrial (1750 CE) from six Arctic locations and examine potential post‐depositional loss of snowpack bromine using a global chemical transport model. Trend analysis of the ice‐core records shows that only the high‐latitude coastal Akademii Nauk (AN) ice core from the Russian Arctic preserves significant trends since pre‐industrial times that are consistent with trends in sea ice extent and anthropogenic emissions from source regions. Model simulations suggest that recycling of reactive bromine on the snow skin layer (top 1 mm) results in 9–17% loss of deposited bromine across all six ice‐core locations. Reactive bromine production from below the snow skin layer and within the snow photic zone is potentially more important, but the magnitude of this source is uncertain. Model simulations suggest that the AN core is most likely to preserve an atmospheric signal compared to five Greenland ice cores due to its high latitude location combined with a relatively high snow accumulation rate. Understanding the sources and amount of photochemically reactive snow bromide in the snow photic zone throughout the sunlit period in the high Arctic is essential for interpreting ice‐core bromine, and warrants further lab studies and field observations at inland locations. Bromine is a reactive chemical species emitted from natural and anthropogenic sources and can be reemitted from Arctic snowpack after its deposition on snow. This leads to ozone depletion and alters the record of bromine preserved in ice cores. Here, we studied ice‐core records of bromine from six Arctic locations to quantify the extent of bromine loss from the snowpack since the pre‐industrial era. We found that only one location had significant trends of bromine over time, consistent with trends in bromine sources from both nature and human activities. An atmospheric model including chemical reaction processes suggested that this Russian Arctic location favored preservation of bromine compared to the five Greenland ice cores. Understanding bromine preservation in Arctic snow and ice is important for interpreting ice‐core records. Ice