A peat core Hg stable isotope reconstruction of Holocene atmospheric Hg deposition at Amsterdam Island (37.8°S)

• Main Authors: Li, Chuxian, Enrico, Maxime, Magand, Oliver, Araujo, Beatriz F., Le Roux, Gaël, Osterwalder, Stefan, Dommergue, Aurélien, Bertrand, Yann, Brioude, Jérôme, De Vleeschouwer, François, Sonke, Jeroen E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2023
• Subjects: Hg stable isotopes; Southern Hemisphere; Peat; Rain; Hg deposition; Amsterdam Island
• Online Access: https://hdl.handle.net/20.500.11850/583105; https://doi.org/10.3929/ethz-b-000583105

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 δ) and mass-independent fractionation (represented by Δ) 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, 37.8oS), and in modern rainfall and gaseous elemental Hg (Hg0) 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 (SWW). Modern AMS gaseous Hg0 and rainfall HgII isotope signatures are similar to those in the Northern Hemisphere (NH). Holocene peat Δ199Hg and Δ200Hg are significantly correlated (R2 = 0.67, P < 0.001, n = 58), consistently oscillating between the modern Hg0 and rainfall HgII end-members. Peat Δ200Hg and Δ199Hg provide evidence of plant uptake of Hg0 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 Δ199Hg, recent peat layers (post-1900CE) from AMS show the lowest Δ199Hg in the peat profile (-0.42 ± 0.27 ‰, 1σ, n = 8). This potentially reflects changes in the isotopic composition of the SH atmospheric Hg pool in response to industrial emissions, including associated changes in atmospheric Hg chemistry, and/or changes in peat soil Hg mobility. 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. ISSN:0016-7037 ISSN:1872-9533