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Arctic Ocean’s wintertime mercury concentrations limited by seasonal loss on the shelf

Abstract

High biota mercury levels are persisting in the Arctic, threatening ecosystem and human health. The Arctic Ocean receives large pulsed mercury inputs from rivers and the atmosphere. Yet the fate of those inputs and possible seasonal variability of mercury in the Arctic Ocean remain uncertain. Until now, seawater observations were possible only during summer and fall. Here we report polar night mercury seawater observations on a gradient from the shelf into the Arctic Ocean. We observed lower and less variable total mercury concentrations during the polar night (winter, 0.46 ± 0.07 pmol l−1) compared with summer (0.63 ± 0.19 pmol l−1) and no substantial changes in methylmercury concentrations (summer, 0.11 ± 0.03 pmol l−1 and winter, 0.12 ± 0.04 pmol l−1). Seasonal changes were estimated by calculating the difference in the integrated mercury pools. We estimate losses of inorganic mercury of 208 ± 41 pmol m−2 d−1 on the shelf driven by seasonal particle scavenging. Persistent methylmercury concentrations (−1 ± 16 pmol m−2 d−1) are probably driven by a lower affinity for particles and the presence of gaseous species. Our results update the current understanding of Arctic mercury cycling and require budgets and models to be reevaluated with a seasonal aspect.

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Fig. 1: Map of water-column Hg profiles in the Arctic Ocean.
Fig. 2: THg concentrations along the shelf–deep-basin gradient.
Fig. 3: ΔiHg and ΔMeHg at specified depth intervals for each station.
Fig. 4: Total MeHg concentrations along the shelf–deep-basin gradient.

Data availability

Temperature and salinity data from seasonal cruises are publicly available from the Norwegian Marine Data Centre (https://nmdc.no)54,55. Mercury and trace-element concentration data for all depths and stations are publicly available from the Norwegian Marine Data Centre (https://nmdc.no)56,57. Data shown in Fig. 3 and Extended Data Figs. 6 and 8 are included in Supplementary Tables 1 and 3.

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Acknowledgements

Financial support for this study was provided by the Norwegian University of Science and Technology (NTNU) (SGK) and the Research Council of Norway through the Nansen Legacy project, RCN#276730 (S.G.K., M.G.D., N.S. and M.V.A.). We thank the captain, crew, cruise leaders and fellow scientists onboard RV Kronprins Haakon on cruises Q3 and Q4. Additional thanks are to the entire Marine Biogeochemistry group at NTNU for their guidance and support. In addition, thanks to the Marseille Marine Mercury group and M.-M. Desgranges for her help with preparing the Hg samples for analysis.

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Authors

Contributions

S.G.K contributed to conceptualization, formal analysis, investigation, validation and visualization, and wrote the original draft. L.-E.H.-B. contributed to conceptualization, formal analysis, investigation, resources, writing, reviewing, editing and supervision. M.V.P. contributed to formal analysis, investigation, validation, resources, writing, reviewing, and editing. M.G.D. contributed to investigation, writing, reviewing and editing. N.S. contributed to formal analysis, investigation, writing, reviewing and editing. A.D. contributed to formal analysis, validation, reviewing and editing. A.S. contributed to formal analysis, validation, writing, reviewing and editing. K.N. contributed to conceptualization, writing, reviewing, editing and supervision. M.V.A. contributed to conceptualization, investigation, resources, writing, reviewing, editing, supervision and funding acquisition.

Corresponding authors

Correspondence to Stephen G. Kohler, Lars-Eric Heimbürger-Boavida or Murat V. Ardelan.

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Nature Geoscience thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editors: Xujia Jiang and Kyle Frischkorn, in collaboration with the Nature Geoscience team.

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Extended data

Extended Data Fig. 1 Conservative temperature (Θ) in degrees Celsius (°C) along the shelf-deep basin gradient.

Stations P1–P7, (Latitude) are on the x-axis for summer 2019 (top) and winter 2019 cruises (bottom). Data retrieved from the Norwegian Marine Data Centre54,55. Figure created using Ocean Data View51.

Extended Data Fig. 2 Salinity along the shelf-deep basin gradient.

Stations P1–P7, (Latitude) are on the x-axis for summer 2019 (top) and winter 2019 cruises (bottom). Data retrieved from the Norwegian Marine Data Centre54,55. Figure created using Ocean Data View51.

Extended Data Fig. 3 Dissolved manganese (DMn) concentrations (nmol L−1) along the shelf-deep basin gradient.

Stations P1–P7, (Latitude) are on the x-axis for summer 2019 (top) and winter 2019 cruises (bottom). Black contour lines for THg (pmol L−1) from each corresponding season are overlain. Concentrations greater than the presented range (7 nmol L−1) are plotted as the maximum. Figure created using Ocean Data View51.

Extended Data Fig. 4 Total acid-leachable manganese (TMn) concentrations (nmol L−1) along the shelf-deep basin gradient.

Stations P1–P7, (Latitude) are on the x-axis for summer 2019 (top) and winter 2019 cruises (bottom). Black contour lines for THg (pmol L−1) from each corresponding season are overlain. Concentrations greater than the presented range (10 nmol L−1) are plotted as the maximum. Figure created using Ocean Data View51.

Extended Data Fig. 5 Particulate manganese (PMn) concentrations (nmol L−1) along the shelf-deep basin gradient.

Stations P1–P7, (Latitude) are on the x-axis for summer 2019 (top) and winter 2019 cruises (bottom). Black contour lines for THg (pmol L−1) from each corresponding season are overlain. Concentrations greater than the presented range (10 nmol L−1) are plotted as the maximum. Figure created using Ocean Data View51.

Extended Data Fig. 6 ΔDMn (µmol m−2 d−1) at specified depth intervals for each station.

A positive Δ value indicates a temporal gain in the DMn pool while a negative Δ value indicates a temporal loss in the DMn pool. Δ values are reported with error bars as combined standard uncertainty (±1σ). *Stations P2 and P5 were integrated from 100 m to sample depth less than 200 m. Figure created using Microsoft Excel.

Extended Data Fig. 7 Total acid-leachable lead (TPb) concentrations (pmol L−1) along the shelf-deep basin gradient.

Stations P1–P7, (Latitude) are on the x-axis for summer 2019 (top) and winter 2019 cruises (bottom). Data points at or below the detection limit were assigned the value of the detection limit (1.08 pmol L−1) determined by the seaFAST-pico ICP-MS for plotting purposes. Black contour lines for THg (pmol L−1) from each corresponding season are overlain. Concentrations greater than the presented range (25 pmol L−1) are plotted as the maximum. Figure created using Ocean Data View51.

Extended Data Fig. 8 : ΔTPb (nmol m−2 d−1) at specified depth interval for each station.

A positive Δ value indicates a temporal gain in the TPb pool while a negative Δ value indicates a temporal loss in the TPb pool. Δ values are reported with error bars as combined standard uncertainty (±1σ). *Stations P2 and P5 were integrated from 100 m to sample depth less than 200 m. Figure created using Microsoft Excel.

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Supplementary Tables 1–4 and Discussion.

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Kohler, S.G., Heimbürger-Boavida, LE., Petrova, M.V. et al. Arctic Ocean’s wintertime mercury concentrations limited by seasonal loss on the shelf. Nat. Geosci. 15, 621–626 (2022). https://doi.org/10.1038/s41561-022-00986-3

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