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- Li, Chuxian
(författare)
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A peat core Hg stable isotope reconstruction of Holocene atmospheric Hg deposition at Amsterdam Island (37.8(o)S)
- 2023
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 0046-564X. ; 341, s. 62-74
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) stable isotopes have been broadly used to investigate the sources, transformation and deposition of atmospheric Hg during the industrial era thanks to the multiple isotope signatures deriving from mass-dependent (represented by delta Hg-202) and mass-independent fractionation (represented by AxxxHg) in the environment. Less is known about the impact of past climate change on atmospheric Hg deposition and cycling, and whether Hg isotopes covary with past climate. Here, we investigate Hg concentration and Hg isotope signatures in a 6600-year-old ombrotrophic peat record from Amsterdam Island (AMS, 37.8(o)S), and in modern AMS rainfall and gaseous elemental Hg (Hg-0) samples. Results show that Holocene atmospheric Hg deposition and plant Hg uptake covary with dust deposition, and are both lower under a high humidity regime associated with enhanced Southern Westerly Winds. Modern AMS gaseous Hg-0 and rainfall HgII isotope signatures are similar to those in the Northern Hemisphere (NH). Holocene peat delta Hg-199 and A200Hg are significantly correlated (R2 = 0.67, P < 0.001, n = 58), consistently oscillating between the modern Hg-0 and rainfall Hg-II end-members. Peat A200Hg and delta Hg-199 provide evidence of plant uptake of Hg-0 as the dominant pathway of Hg deposition to AMS peatland, with some exceptions during humid periods. In contrast to NH archives generally documenting a modern increase in delta Hg-199, recent peat layers (post-1900CE) from AMS show the lowest delta Hg-199 in the peat profile (-0.42 +/- 0.27 parts per thousand, 1cs, n = 8). This likely reflects a significant change in the post-depositional process on deposited anthropogenic Hg in 20th century (i.e. dark abiotic reduction), enabling more negative delta Hg-199 to be observed in AMS peat. We further find that the oscillations of Hg isotopes are consistent with established Holocene climate variability from dust proxies. We suggest peat Hg isotope records might be a valid rainfall indicator. (C) 2022 The Authors. Published by Elsevier Ltd.
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| 2. |
- Li, Chuxian, et al.
(författare)
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Mercury deposition and redox transformation processes in peatland constrained by mercury stable isotopes
- 2023
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Peatland vegetation takes up mercury (Hg) from the atmosphere, typically contributing to net production and export of neurotoxic methyl-Hg to downstream ecosystems. Chemical reduction processes can slow down methyl-Hg production by releasing Hg from peat back to the atmosphere. The extent of these processes remains, however, unclear. Here we present results from a comprehensive study covering concentrations and isotopic signatures of Hg in an open boreal peatland system to identify post-depositional Hg redox transformation processes. Isotope mass balances suggest photoreduction of HgII is the predominant process by which 30% of annually deposited Hg is emitted back to the atmosphere. Isotopic analyses indicate that above the water table, dark abiotic oxidation decreases peat soil gaseous Hg0 concentrations. Below the water table, supersaturation of gaseous Hg is likely created more by direct photoreduction of rainfall rather than by reduction and release of Hg from the peat soil. Identification and quantification of these light-driven and dark redox processes advance our understanding of the fate of Hg in peatlands, including the potential for mobilization and methylation of HgII.
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