| Summary: | Mercury (Hg) is a naturally occurring metalloid element and an environmental contaminant of global concern. It can be emitted to the environment from anthropogenic activities, such as fossil fuel combustion, as well as through natural emissions, such as volcanic activity. While anthropogenic Hg emissions have been fairly well constrained and are projected to decline with recent emission reduction efforts, there remain major uncertainties in the amount of Hg emitted from volcanoes due to a scarcity of field measurements, methodological uncertainties, and the diversity of Earth’s volcanism over space and time. This is an important knowledge gap because evaluating the effectiveness of Hg emission regulations such as the Minamata Convention on Mercury requires sufficient knowledge of both anthropogenic and natural inputs to the global Hg cycle. This thesis reports the results of four field campaigns from 2019 to 2022 on the highly active volcanic island country of Iceland. During the 2021 and 2022 effusive eruptions of the Fagradalsfjall volcanic system, Hg was measured in the volcanic plume by drone directly above the active vent (a first for volcanic Hg research) as well as at more distant downwind locations, with a relatively low time-averaged Hg flux of 84 ± 62 kg a–1 for these eruptions. To assess the role of geothermal degassing in Iceland’s natural Hg emissions, we measured soil gaseous elemental mercury (GEM) concentrations at six geothermal fields and used an adapted gradient method to estimate soil–air fluxes. These yielded similarly low GEM emission figures: an estimated Icelandic geothermal flux of 1.8 kg a–1 and a total Icelandic flux (including non-geothermal areas) of ~18 kg a–1. Despite the minor geothermal flux, soil gas GEM concentrations at 10 cm depth were often hundreds and in some cases thousands of times higher than surface air concentrations, and geothermal soils showed major enrichments in total Hg (THg). This thesis shows that Icelandic geothermal activity can generate extreme gas and soil ...
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