Data to support: Implications of snowpack reactive bromine production for Arctic ice core bromine preservation

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 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 1mm) 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 Akademii Nauk 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.

积雪排放物被公认为北极地区气相活性溴的重要来源，亦是解释由卤族自由基催化破坏臭氧所引发的春季臭氧损耗事件的必要依据。量化积雪排放的溴，对于解析冰芯中的溴记录至关重要。本研究提供了6个北极点位自工业化前（公元1750年）以来的冰芯溴记录，并借助全球化学传输模型（global chemical transport model）分析了积雪溴的潜在沉积后损耗过程。对冰芯记录的趋势分析显示，唯有俄罗斯北极地区高纬度沿海的Akademii Nauk冰芯（Akademii Nauk ice core）保留了自工业化前以来的显著趋势，该趋势与海冰范围以及源区人为排放的变化趋势一致。模型模拟结果表明，在雪表皮层（雪层顶部1毫米）发生的活性溴循环过程，会导致全部6个冰芯点位的沉积溴出现9%至17%的损耗。雪表皮层下方以及积雪透光层内的活性溴生成过程，潜在影响更为显著，但该来源的强度仍存在不确定性。模型模拟结果显示，相较于格陵兰岛的5根冰芯，Akademii Nauk冰芯最有可能保留大气信号，这得益于其高纬度区位与相对较高的积雪沉积速率。明晰北极高纬度地区整个日照期内积雪透光层中光化学活性雪溴化物的来源与总量，对于解析冰芯溴记录至关重要，该方向亟需开展内陆点位的实验室研究与野外观测工作。