Thursday 21 October, 4 PM CET
PROF. BRIDGET BERGQUIST
ABSTRACT: Mercury is a globally distributed metal that bioaccumulates in aquatic food webs leading to dangerous exposure to humans and wildlife. Despite decades of research, many knowledge gaps hinder our understanding of both the modern and past Hg cycle. These gaps make it challenging to predict how changes in emissions and climate will affect the Hg cycle. A rapidly growing tool to study Hg is Hg stable isotope geochemistry. Mercury is unique in that it exhibits many types of isotopic fractionation including conventional mass dependent fractionation (MDF) and at least three types of mass independent fractionation (MIF). Hg isotope geochemistry is already being used to successfully trace sources of Hg, quantify certain transformations of Hg in the environment, and challenge our understanding of Hg in the environment. Much like the traditional stable isotope systems (i.e. C, O), Hg MDF is ubiquitous in nature and occurs during redox, biological, speciation and phase changes. Unlike Hg MDF, large Hg MIF is thought only to occur in photochemical reactions, with different photochemical reactions displaying unique patterns of MIF for different isotopes of Hg, six of which are routinely measured. Because MIF signatures are only affected by a limited number of reactions, the extent and ratio of MIF from different isotopes is preserved and can be used as a reliable tracer of different sources if the sources have different MIF signatures. In this talk, applications of Hg isotopes to modern problems, such as tracing global pollution sources and understanding Hg cycling, along with using Hg isotopes to understand links between large scale volcanism and mass extinctions in the past will be discussed.