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Mercury stable isotopes constrain atmospheric sources to the ocean



Human exposure to toxic mercury (Hg) is dominated by the consumption of seafood1,2. Earth system models suggest that Hg in marine ecosystems is supplied by atmospheric wet and dry Hg(ii) deposition, with a three times smaller contribution from gaseous Hg(0) uptake3,4. Observations of marine Hg(ii) deposition and Hg(0) gas exchange are sparse, however5, leaving the suggested importance of Hg(ii) deposition6 ill-constrained. Here we present the first Hg stable isotope measurements of total Hg (tHg) in surface and deep Atlantic and Mediterranean seawater and use them to quantify atmospheric Hg deposition pathways. We observe overall similar tHg isotope compositions, with median Δ200Hg signatures of 0.02‰, lying in between atmospheric Hg(0) and Hg(ii) deposition end-members. We use a Δ200Hg isotope mass balance to estimate that seawater tHg can be explained by the mixing of 42% (median; interquartile range, 24–50%) atmospheric Hg(ii) gross deposition and 58% (50–76%) Hg(0) gross uptake. We measure and compile additional, global marine Hg isotope data including particulate Hg, sediments and biota and observe a latitudinal Δ200Hg gradient that indicates larger ocean Hg(0) uptake at high latitudes. Our findings suggest that global atmospheric Hg(0) uptake by the oceans is equal to Hg(ii) deposition, which has implications for our understanding of atmospheric Hg dispersal and marine ecosystem recovery.

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Fig. 1: Depth profiles of seawater Hg species concentrations and total and particulate Hg stable isotope composition at station K2 in the Mediterranean Sea and the North Atlantic.
Fig. 2: Hg stable isotope composition of atmospheric Hg deposition sources (gaseous Hg(0) and Hg(ii) in rainfall), and seawater (total (tHg) and particulate (pHg)).
Fig. 3: Hg stable isotope composition in different ocean basins for total Hg (tHg) and particulate Hg (pHg) in seawater, marine sediments and marine fish.
Fig. 4: Latitudinal variation in atmospheric Hg sources and deposition fluxes to the global ocean.

Data availability

Hg stable isotope and Hg speciation data that support the findings of this study are available from data are provided with this paper.


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This work was supported by research grants ANR-17-CE34-0010 MERTOX to D.P., FP7-IDEAS-ERC grant no. 258537, and H2020 ERA-PLANET grant no. 689443 via the iCUPE and iGOSP project to J.E.S., Chantier Arctique Francais funding via the Pollution in the Arctic System Project to J.E.S. and L.E.H.B., H2020 Marie Skłodowska-Curie grant no. 657195 and Swiss National Science Foundation grant PZ00P2_174101 to M.J., APOG DECOMAR, MISTRALS AT P&C and the AXA RF grants to L.E.H.B., and the French National Research Agency (ANR-13-BS06-0014, ANR-12-PDOC-0025-01), the French National Centre for Scientific Research (CNRS-LEFE-CYBER), the LabexMER (ANR-10-LABX-19), and Ifremer. We are grateful to G. Sarthou and P. Lherminier, chief scientists of the 2014 GEOVIDE cruise, and to H. Planquette for coordinating clean sampling. We thank M. Rutgers van der Loeff, T. Kanzow and the Alfred-Wegener-Institute for Polar and Marine Research for organizing the 2016 GRIFF cruise. We thank E. de Saint-Léger and F. Pérault of the technical division of INSU for support with operations at sea. We thank L. Laffont for laboratory management and O. Grosso and D. Malengros for technical assistance. We thank L. Metral from MARBEC and F. Ménard from MIO for providing tuna fish samples from the Mediterranean Sea. We thank J. Kuss and H. Horowitz for discussion on gas exchange model parameterization. We thank the captains, crew and sampling teams onboard the RV Antedon II, RV Pourquoi Pas? and FS Polarstern for their support at sea. Thanks also go to the shipboard participants, captain and crew of the N/O l’Atalante for obtaining sediment samples from the 2015 VESPA cruise. VESPA was funded by the French Ministry of Research and Higher Education, with support from the governments of New Zealand and New Caledonia.

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Authors and Affiliations



L.E.H.B., J.E.S., M.J. and D.P. conceived the study. L.E.H.B., M.J., D.P., M.P., M.V.P., M.M.D. and J.E.S. performed sampling. J.E.S., M.J. and L.E.H.B. developed and applied the tHg isotope pre-concentration methods. J.E.S., M.J., J.M. and J.C. performed isotope measurements. M.M.D., M.V.P., A.D., L.E.H.B., M.J., J.M., D.P. and M.T. performed additional laboratory work. M.J., J.E.S. and L.E.H.B. analysed the data. J.E.S. and M.J. wrote the draft paper, which was improved by contributions from L.E.H.B. and D.P., and commented on by all authors.

Corresponding authors

Correspondence to Martin Jiskra, Lars-Eric Heimbürger-Boavida or Jeroen E. Sonke.

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The authors declare no competing interests.

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Peer review information Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Summary of marine Hg(ii) deposition and Hg(0) air-sea exchange fluxes.

Gross fluxes (solid arrows, Mg y−1) are based on published model estimates3. Hg(0) exchange is bidirectional, meaning that despite surface ocean Hg(0) supersaturation and large Hg(0) evasion, Hg(0) invasion is substantial. Marine Δ200Hg signatures of 0.04‰ indicate a relatively more important contribution of the atmospheric Hg(0) end-member to marine Hg than current 3D models suggest. This indicates that either 3D model Hg(ii) deposition is overestimated or that Hg(0) invasion is underestimated (black dotted arrows, indicating 2–3 times lower or 2–3 times higher fluxes, required to fit Δ200Hg data).

Extended Data Fig. 2 Maps of sampling locations for total and particulate Hg isotopes.

Top: sampling locations K2 in the Mediterranean Sea (purple), Atlantic Ocean (yellow) and Fram Strait (green). Bottom: magnification of the four Mediterranean locations, with main station K2 (large purple circle), and pHg station K1 and Julio (small purple circles), and Endoume pier in Marseille Bay (grey square). Maps were made with Ocean Data View (Schlitzer, Reiner, Ocean Data View,, 2021).

Extended Data Fig. 3 Latitudinal distribution of Hg(ii) wet deposition.

Annual mean Hg(ii) wet deposition (µg m−2 y−1) at oceanic locations in the northern and southern hemispheres (NH, SH), binned in 5° latitude. Mean values (± standard deviation, SD) were calculated when sufficient data was available per 5° latitude band, and interpolated using polynomial fitting when no data were available (in which case a mean observed SD of 30% was applied). MDN, mercury deposition network; GMOS, global mercury observation system; USA, CAN, PR, United States of America, Canada, Puerto Rico.

Source data

Extended Data Fig. 4 Latitudinal distribution of dissolved gaseous Hg (DGM) concentrations.

Mean (± standard deviation) DGM are binned in 5° latitude bands, and equal weight was given to each study. Polar studies, affected by sea ice show unusually high concentrations (mean 219 fM in the Arctic, mean 138 fM around Antarctica) for high latitude waters and were excluded in 5° latitude binning (replaced in calculations by ‘open water only’ DGM data at 55–60°S and 75–80°N).

Source data

Extended Data Fig. 5 Atmospheric deposition pathways of the zonal reference model.

a, Marine Hg(ii) gross deposition, Hg(0) gross invasion, Hg(0) gross evasion, and net Hg flux [Hg(ii) deposition + Hg(0) invasion – Hg(0) evasion]; all in µg m−2 y−1 with evasion shown as negative numbers. Hg(0) invasion is driven by observed atmospheric Hg(0) and wind speed. Hg(ii) deposition is dominated by Hg(ii) wet deposition. Hg(0) evasion is driven by DGM concentrations and wind speed. The net Hg evasion trends shows important net deposition in the northern hemisphere, and net evasion in the southern hemisphere. b, Reference model Hg gross deposition fluxes (µg m−2 y−1) as a function of latitude used in estimating marine Δ200Hg in Fig. 4a (main text). Hg(ii) wet deposition observations as in Extended Data Fig. 3; Hg(ii) dry deposition was fixed at 5 µg m−2 y−1, and constrained as 40% of total Hg(ii) deposition38, since no dry deposition observations over oceans exist. Hg(0) invasion (ocean uptake, same as in top panel) is calculated from the observed inter-hemispheric atmospheric gaseous Hg(0) gradient3, wind and sea surface temperature (Copernicus), and the latest Hg(0) air–sea gas exchange model (see Supplementary Information).

Source data

Extended Data Fig. 6 Estimated latitudinal variation in Δ200Hg of atmospheric Hg(ii) deposition.

The small variation is caused by the variable contributions (Extended Data Figure 5) of Hg(ii) wet deposition with Δ200Hg of 0.16‰, and Hg(ii) dry deposition with Δ200Hg of 0.10‰ (Extended Data Table 1). The dashed line represents the median and the shaded area the interquartile range (IQR).

Source data

Extended Data Fig. 7 Variation of Δ204Hg in marine samples.

a, Δ204Hg versus Δ200Hg. The dashed line represents the York regression using IsoplotR54 for all marine samples (Δ200Hg = −0.32(±0.06) Δ204Hg +  (0.03±0.004), (± se), MSWD = 0.213). b, Δ204Hg boxplot for 5° latitudinal intervals. Marine samples are shown in boxes, where the bold horizontal line represents the median, the boxes the interquartile range, the whiskers 1.5 times the IQR and outliers are represented by dots. The solid line represents the predicted Δ204Hg based on the observational relationship between Δ204Hg and Δ200Hg in terrestrial samples by Blum and Johnson, 201755. The dashed line represents the predicted Δ204Hg derived from the York regression shown in panel a. Δ204Hg data are available for 339 out of 791 marine samples. Note that for pHg and tHg samples presented here, Δ204Hg was not measured because of the low abundance of the 204Hg isotope, and unavailability of a second 1013 Ω amplifier.

Source data

Extended Data Table 1 Summary of Hg stable isotope data
Extended Data Table 2 Modelled contribution of Hg(ii) from wet and dry deposition

Supplementary information

Supplementary Information

Supplementary Methods, Figs. 1–3 and references.

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Jiskra, M., Heimbürger-Boavida, LE., Desgranges, MM. et al. Mercury stable isotopes constrain atmospheric sources to the ocean. Nature 597, 678–682 (2021).

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