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

Abstract

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.

Anthropogenic Influence on Tropospheric Reactive Bromine Since the Pre‐industrial: Implications for Arctic Ice‐Core Bromine Trends

“…(2023), ozone dry deposition velocity onto snow and ice is updated to 0.01 cm s −1 , consistent with observations (Simpson, Carlson, et al., 2007, Simpson, von Glasow, et al., 2007). Snowpack bromine emissions (Swanson et al., 2022; Zhai et al., 2023) are not included in the model. The magnitude of the snowpack emission source is estimated to be 278 Gg Br/yr during spring in the AN source regions, based on model simulations from Swanson et al.…”

“…Following Zhai et al. (2023), ozone dry deposition velocity onto snow and ice is updated to 0.01 cm s −1 , consistent with observations (Simpson, Carlson, et al., 2007, Simpson, von Glasow, et al., 2007). Snowpack bromine emissions (Swanson et al., 2022; Zhai et al., 2023) are not included in the model.…”

“…According to the updated age model, the ice core covers an estimated time range of year 200 BCE‒1999 CE (McConnell et al., 2019), but we only present records since CE 1750. This ice core was chosen because it is expected to preserve an atmospheric signal of bromine due to its high snow accumulation rate and high‐latitude location, both of which limit photochemical loss of bromine from the snowpack (Zhai et al., 2023).…”

“…GEOS-Chem is open software and available for download (Yantosca et al, 2021). GEOS-Chem historical simulations output is archived in the Dryad Data Repository (Zhai & Alexander, 2023).…”

“…Here, we use a global model to quantify the impact of anthropogenic emissions on tropospheric reactive bromine abundances since the pre‐industrial. Since previous work suggests that the Russian Arctic AN ice‐core preserves an atmospheric signal while Greenland ice cores may not (Zhai et al., 2023), we compare the model to AN ice‐core bromine observations. We use the model‐ice core comparison to examine implications of anthropogenic emissions for tropospheric Br y abundance and interpretation of Arctic ice‐core bromine records.…”