Lead isotopes and concentrations in snow and ice: A global review (Supplementary Data)

This literature review accompanies chapter 3 of H. L. Brooks' dissertation: Determining Sources of Volcanic Deposits and Anthropogenic Emissions Recorded in the North Pacific. It serves as a supplementary dataset, submitted in partial fulfillment of the requirements for the degree of doctor of philosophy (in Earth and Climate Sciences) at the University of Maine. <strong>To construct the dataset:</strong> An initial comprehensive literature search for the topic “Lead (Pb) isotopes and concentration in surface snow, snow pits and ice cores” was performed using all the databases available in the Web of Science Collection in September 2020. This search yielded 5475 records which were evaluated for relevance using the title and abstract. Removal of clearly off-topic papers (<em>e.g.,</em> the chemistry of penguin feces) gathered in the search due to the dual meaning of “lead” reduced the paper count to 326 titles. Full text of these 326 publications was evaluated for inclusion based on the following criteria: Only studies examining long-traveled background atmospheric lead signals were considered. All point source pollution studies examining the localized effects of traffic, road salt, mines, industry, power plants, human activity at base camp stations, etc were excluded. An exception was made for samples which were taken at sufficient depths in the analyzed record to predate the pollution source or where wind trajectory did not transport pollution to the collection site regardless of close geographic proximity. Only studies of natural, undisturbed snowpacks and ice cores were examined. Studies which sampled snow from urban structures were excluded. Additionally, studies examining the volcanic signal in snow following major modern eruptions were excluded, as this was classified as disturbed snow. Records of ²¹⁰Pb in snow and ice were excluded. While ²¹⁰Pb is useful for establishing chronology in young snow and ice due to its small half life (~ 22.3 years), it is not useful for consideration of old records and the source constraint of ²¹⁰Pb into the atmosphere is poorly constraint over time (Nijampurkar &amp; Clausen, 1990). Therefore, it cannot be considered in conjunction with Pb isotopes and concentrations. Pb isotopes and concentrations taken from cryoconites (soil-like composites of dust, industrial soot, and microbial mats of photosynthetic bacteria) were excluded from this literature review. While cryoconites are important to glacial systems as they alter the albedo of the glacier surface and therefore affect the glacier melt rate (Fountain et al., 2004), they must be considered separately from surface snow, snow pits, and ice cores due to the drastic differences in formation and biologic nature. The publication must be available to the author (<em>e.g.,</em> through the University Library, from collaborators) To ensure that the literature search conducted in the Web of Science was robust and complete, each publication was read carefully for references to previous studies. When a previous study was referenced in text, the citation was checked to ensure inclusion in the literature search results, and included when missing. Publications were indexed into the attached tables. Following the completion of publication indexing, these tables were evaluated against the 19 known glacial regions (Zemp et al., 2019) in order to identify areas/papers that may have been missed in the initial search. Areas with few or no results were searched again using Google Scholar and Web of Science.