Acidity in Polar Ice Cores - North American Acid Rain History Recorded in the Greenland Ice Sheet and the Natural Patterns of Acid and Base Aerosols in Antarctica
AdvisorMcConnell, Joseph R
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pH is a master variable that controls many chemical reactions in nature due to the abundance of acids and bases in the Earth environment. A novel method for continuously measuring pH and acidity in ice cores is applied here to the analysis of ice core arrays from Greenland and Antarctica. The Greenland array documents the history of acidic deposition in a location that is downwind from the major air polluting regions of North America. Comparisons show that the ice core records closely track precipitation chemistry data from North America, available since 1979, thus enabling the ice cores to serve as a valid proxy for the history of acid deposition in North America since industrialization began in the mid-1800s. Ice core observations suggest that the natural background of sulfur acidity declined during the 20th century and this decline is attributed to decreased biogenic sulfur emissions associated with changing sea ice conditions in the North Atlantic Ocean.Acidity records from Antarctica are utilized in a comprehensive assessment of the primary acid-anions and base-cations, including nitrate, sulfate, ammonium, and chloride. Arrays from high and low snow accumulation regions are exploited for their strengths in providing subannual resolution and long duration records, respectively. Biomass burning is found to be the source of a significant portion of the nitrate and ammonium that reaches Antarctica based on high correlations with published methane isotopes and measured black carbon data, respectively. Chloride at the low accumulation sites is found to be a heavily diffused version of the original sea salt aerosol record, the latter of which is linked to cooler ocean temperatures, possibly through the sea ice mechanism for sea salt aerosol production.