Exploring the isotopic dimension of the global biogeochemical mercury cycle – MERCY
Mass-independent isotope fractionation (MIF) effects in natural terrestrial environments were discovered twice during the 20th century - for the elements oxygen and sulfur. Both discoveries have opened a broad variety of applications, including physical chemistry studies, atmospheric chemistry, palaeoclimatology, biologic primary productivity assessment, Solar System origin and evolution, planetary atmospheres (Mars), and the origin and evolution of life in Earth's earliest environment. Recently mercury (Hg) was added to this shortlist when isotopic anomalies were observed for Hg's two odd isotopes, 199Hg and 201Hg in biological tissues. The objective of the MERCY project is to take Hg MIF beyond the initial discovery, and use it to address major outstanding scientific questions of societal and philosophical interest. We propose to use mercury MIF to better understand global Hg dynamics at different time scales, from the early Earth to Pleistocene and modern times, and in a context of global environmental change. Three main themes will be investigated: 1.The modern Hg cycle focusing on: emissions from coal burning, recent atmospheric Hg deposition in the Arctic from lichens, moss and peat, and recent Arctic Ocean Hg records from archived biological tissues. 2.Post-glacial atmospheric Hg deposition from up to 14,500 yr ombrotrophic peat deposits from the Pyrenees and Jura mountains, and minerotrophic peat deposits from the Candadian and Greenland (sub-) Arctic. 3.Palaeo-Hg dynamics spanning the 2.45 Ga 'great oxidation event' and the 635 Ma snowball Earth glaciation. The MERCY project places strong emphasis on the Arctic environment, because despite long-standing scientific and political interest, the reason for the high Hg levels in the Arctic ecosystem remains unknown, and recently climate change has entered the debate. Our preliminary work on the atmospheric and marine Arctic Hg cycle suggests that Hg MIF can put powerful constraints on key Hg sources and processes, such as anthropogenic Hg emission fingerprinting or marine Hg photo-reduction under the influence of climate change. Another point of focus is on the isotopic traceability of Hg emissions from coal burning. Coal burning currently represents 67% of all anthropogenic emissions (41% from Asia alone), and is likely going to increase in coming centuries. Recent evidence of variable Hg MIF signatures in coal suggest that theses can be traced upon atmospheric dispersion. In addition to modern, recent, and Pleistocene Hg records, we propose a journey into deep time and the origins of life on Earth. We will probe mercury MIF anomalies in ancient marine sediments as a proxy of atmospheric Hg chemistry, notably the dynamics of the Great Oxidation Event (GEO), when free O2 first accumulated in the atmosphere, and the last snowball Earth events, which spawned another oxidation event and the early origin of animals. By studying ancient Hg MIF dynamics during the 635 Ma global glaciation, we may be able to better understand our modern Hg MIF ' climate observations and those proposed on recent and post-glacial time scales. It is highly likely that MIF will be discovered in natural environments for other elements, and the understanding we gain by investigating mercury will accelerate the future application of other MIF processes and open up new horizons and opportunities. By tapping information from the isotopic dimension of Hg cycling, including revolutionary mass-independent effects, we expect a maximum scientific impact while supporting a socially relevant and urgently needed investigation at the frontier of isotope geosciences.
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
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Beginning and duration of the scientific project: - 0 Months