| Summary: | Degree: Doctor of Philosophy Abstract: Human activities have profoundly altered the biogeochemical cycle of many elements including mercury (Hg). Since ~1850 AD, industrial processes are suggested to have led to a 3-fold increase in Hg deposition above natural, pre-industrial levels. Despite extensive historical evidence for pre-industrial Hg extraction, there has been little evidence for any pre-industrial Hg pollution. This dissertation contains five research papers which critically investigate our understanding of pre-industrial Hg cycling using the geochemical record preserved in lake sediments. Pre-industrial Hg pollution has long been hypothesized on the basis of historical records but has never been proven. Using lake sediment cores from three regions in the Peruvian and Bolivian Andes, I show that pre-industrial Hg pollution resulted from a multitude of mineral-extractive activities including: (i) Colonial (1532-1900 AD) and pre-Colonial (pre-1532 AD) cinnabar (HgS) extraction (chapter 2); (ii) Colonial Hg amalgamation (chapter 3), and; (iii) pre-Colonial smelting of argentiferous ores (chapter 4). All three of these activities resulted in atmospheric Hg emissions, and Hg speciation analyses demonstrate that at least some of these emissions were transported long distances. Chapter 5 explores how sediment core chronologies influence the calculation of pre-industrial Hg accumulation rates (fluxes), and suggests 14C dates are necessary if accurate Hg flux histories are sought. Relying on 210Pb chronologies alone overestimates pre-industrial Hg fluxes, resulting in an underestimation in the degree to which human activities have altered the natural biogeochemical cycle of Hg. The final paper presented here (chapter 6) places 20th-century Arctic Hg enrichment in an unparalleled long-term, multi-proxy perspective using two unique paleolimnological records, both of which are from Baffin Island, Canada. These records span the Holocene at high resolution but also include sediment from the last and penultimate ...
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