Volcanic Impact on Stratospheric Chlorine Chemistry and Perchlorate Formation: Evidence from Ice Cores

• Main Author: Kennedy, Joshua Andrew
• Format: Text
• Language: unknown
• Published: Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange 2020
• Subjects: Chlorine; Diffusion; Ice Core; Perchlorate; Stratosphere; Volcano; Atmospheric Sciences; Environmental Chemistry; Environmental Sciences; Arctic; Antarctic; The Antarctic; Greenland; South Pole; Antarc*; Greenland ice cores; ice core; South pole
• Online Access: https://openprairie.sdstate.edu/etd/3953; https://openprairie.sdstate.edu/context/etd/article/4980/viewcontent/Kennedy_Joshua_2020.pdf

Perchlorate, suspected to be chemically formed in both the troposphere and stratosphere, has been recently measured in Arctic snow and ice cores. These comprise both discontinuous snow and ice cores from the Canadian Arctic and a continuous record of perchlorate was compiled from an analysis of Greenland ice cores. While the background perchlorate concentration typically is very low, a few spikes in concentration coinciding with deposition of volcanic sulfate were observed in the Greenland record, suggesting that perchlorate levels in the atmosphere may be impacted by volcanic eruptions. As of yet, no work has been done to investigate the connection between volcanic eruptions and perchlorate formation. It was not known 1) whether the volcanic perchlorate response is limited to samples collected in Greenland, 2) if the volcanic perchlorate response is just limited to certain eruptions, 3) what factors influence the magnitude of the response, and 4) what chemistry drives the volcanic perchlorate response. In this work, detailed analysis and careful examination of the data collected from Antarctic, Alaskan, and Greenland ice cores show no seasonal oscillation during nonvolcanic periods prior to the 1980s, indicating a relatively small role for stratospheric photochemical production pathways in the Arctic during these times. The development of a strong seasonal oscillation in perchlorate concentration in snow since 1980 corresponds with a drastic increase in stratospheric organic chlorine throughout the late 20th century, indicating that the relative contribution of stratospheric photochemical processes to the perchlorate deposition in the Arctic has increased as a result of increased stratospheric organic chlorine. Correlation of annual perchlorate flux with mean annual ozone abundance in recent decades suggests that the abundance of both ozone and perchlorate are influenced by stratospheric chlorine. The analysis of ice cores from the South Pole containing the sulfate fallout from several large volcanoes revealed ...