Carbon dynamics control comtemporary mercury burial in Arctic Ocean sediments

Carbon dynamics control comtemporary mercury burial in Arctic Ocean sediments | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Carbon dynamics control comtemporary mercury burial in Arctic Ocean sediments Charles Gobeil, Sophia Johannessen, Miguel Goñi, Zou Zou Kuzyk, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6457403/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Dec, 2025 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Abstract Mercury (Hg) contamination is a familiar concern in the Arctic. However, this study shows that variations of Hg concentration in 30 sediment cores collected across the North American Arctic Margin (NAAM) and in the deep central Arctic Ocean (AO) can be entirely explained by carbon sources and cycling. An apparent enrichment in Hg toward the sediment surface results from remineralization of organic carbon in the sediments, not from increased Hg flux. Hg values in AO sediments can be predicted with a high degree of confidence, based on three carbon sources with distinct Hg contents. Terrigenous organic carbon (OCTERR) dominates Hg delivery (80-95%) in the western NAAM, whereas inorganic carbon is the predominant carrier of Hg at many eastern NAAM sites (50-70%). Marine organic carbon (OCMAR) contributes <20% of the total Hg concentrations. The sedimentary Hg:OCTERR and Hg:OCMAR endmembers are higher in the deep AO than in the NAAM, likely due to greater organic matter remineralization during transit through the system. We conclude that the interplay among sedimentary carbon sources governs the scavenging, transportation and sequestration of Hg, and that Hg variations with depth in the sediments result mainly from diagenesis, not from changes in the modern Hg flux. Earth and environmental sciences/Biogeochemistry/Element cycles Earth and environmental sciences/Ocean sciences/Marine chemistry Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Mercury (Hg) is of persistent concern in the Arctic Ocean (AO), because higher-trophic level Arctic marine organisms contain elevated concentrations of this bioaccumulative, neurotoxic element 1-3 . Despite multiple research initiatives motivated by this finding, the modern Hg cycle in the AO nevertheless remains ill-defined, particularly as regards (i) its processing and burial in bottom sediments and (ii) the imprint that long-range atmospheric and oceanic transport of anthropogenic Hg might have on this cycle 4-6 . There is a widespread pattern of increasing Hg concentration toward the surface of AO sediments 6-10 , but it is unclear whether this trend emerges from an increase in the flux of Hg into the ocean or to diagenetic mechanisms within the sediment. Furthermore, Hg is thought to be transferred to AO sediments mainly in association with settling particles of marine ( autochthonous ) organic carbon (OC MAR ) 4,5 , as is the case in other oceans 11-16 . However, terrigenous ( allochthonous ) organic carbon (OC TERR ) predominates in marginal and deep basin sediments of the AO 17 , and Hg that enters the AO from continental sources is largely bound to OC TERR 18-22 . In addition, even though inorganic carbon (IC) is abundant in certain Arctic marine areas 23-24 , the role of IC in Arctic Hg cycling, as that of OC TERR , has not been examined. Here, we investigate what controls Hg surface enrichment in Arctic Ocean sediments, including the roles of carbon sources and organic carbon (OC) remineralization in the water column and sediments. We use a set of 24 sediment box-cores that spans a range of productivity and terrigenous flux across the North American Arctic Margin (NAAM), as well as six basin cores previously analyzed for Hg and other elements 10 (Fig. 1, Table S1). Results Vertical profiles of Hg and OC and regional variations in the Hg:OC ratio Mercury concentrations vary by more than an order of magnitude in NAAM sediments (2–98 ng Hg g SED −1 dry weight, n = 514). Both Hg and OC tend to decline exponentially below the sediment–water interface (Fig. 2 ). The Hg:OC ratio varies little (13 ± 9%) and exhibits no systematic trend with depth in the cores, except in five of the Bering and Chukchi Seas cores, where it increases slightly, between the sediment surface and 5–10 cm depth (Fig. S1 ). In contrast to the profiles of Hg and OC, reduced sulphur (i.e., acid volatile sulphide + chromium reducible sulphur), which reveals sulphate reduction under anoxic conditions 25 , is low in surface sediment and increases with depth (Fig. S2). Cores with low reduced sulphur inventories (e.g., the Canadian Archipelago cores) tend to have well-defined Fe oxyhydroxide surface enrichments (Fig. S3), which are indicative of anaerobic organic matter oxidation by ferri-reducing bacteria. In the cores from the Bering and Chukchi Seas, where reduced sulphur inventories are the most elevated, the absence of such surface enrichments testifies to the very limited O 2 penetration depth (< 0.5 cm) in the sediments at these locations 26 – 27 . Moreover, while Hg covaries positively (p < 0.01) with OC, the slope of the linear regression varies regionally (Fig. 3 ). In the NAAM, the shallowest slope (lowest Hg:OC ratio) is observed in the Bering and Chukchi Seas (1.2 µg Hg g OC −1 ), whereas the steepest slope (5.3 µg Hg g OC −1 ) is found in the Beaufort Sea (cores CG2 and CG3). Steeper slopes have been previously calculated for sediments of the deep central AO (2265–4230 m) 10 , where they reach 9.5 µg Hg g OC −1 in both the Amerasian and Eurasian Basins (Fig. 3 ). Although all regional linear relationships between Hg and OC have non-zero y-intercepts (i.e., for OC = 0 mg g − 1 ), these deviations are not statistically different from zero ( p < 0.01 ), with the exception of those characterizing the sediments of the Bering and Chukchi Seas and the Canadian Archipelago (see Table S2 for details). Relationship between the Hg:OC ratio and OC composition The stable isotope composition of OC (ẟ 13 C) was determined in samples from all the cores, except Lancaster Sound core CAA2. Overall, the ẟ 13 C values range between − 25.2‰ and − 20.1‰, with the lowest values in Beaufort Sea (–24.2 ± 0.3‰, n = 18) and Barrow Canyon (–23.7 ± 0.8‰, n = 52), and higher values in Lancaster Sound and Baffin Bay (–22.0 ± 0.2‰, n = 42), the Canadian Archipelago (–21.6 ± 0.6‰, n = 43), the Chukchi and Bering Shelves (–21.5 ± 0.4‰, n = 36), and Davis Strait (–20.7 ± 0.7‰, n = 16). Without considering the results for the five cores from the interior of the Canadian Archipelago (VS1, FS1, BE2, PS2 and PS1), in which IC concentrations are particularly elevated (30–60 mg g − 1 , Fig. S4), the Hg:OC ratios in NAAM sediments are negatively correlated (p < 0.01) with increasing ẟ 13 C values (Fig. S5). In the IC-enriched Canadian Archipelago cores, Hg:OC ratios do not follow the same trend (Fig. S5); they are higher than those of sediments from other regions having similar ẟ 13 C values (Lancaster Sound, Davis Strait, Bering and Chukchi Shelves) (Fig. S4). Discussion Diagenetic control of sedimentary Hg profiles The linearity of the regional Hg–OC relationships in NAAM sediments, and the fact that Hg concentrations tend to zero as OC concentrations also approach zero, reveal that particulate OC is the major Hg-binding phase. Furthermore, the nearly invariant Hg:OC ratio with depth in most cores indicates that the Hg profiles are not determined by a modification in Hg flux, but by OC dynamics within the sediment. If the Hg enrichment in surface sediment were the result of increasing anthropogenic flux, the Hg:OC ratio would also be higher toward the surface, which is not the case. The relatively stable Hg:OC ratio with depth in most cores implies that Hg released during early OC oxidation does not promptly precipitate or form solid-phase complexes, either with remaining organic matter or via adsorption to or coprecipitation with authigenic oxyhydroxide or sulphide minerals. If that were the case, the Hg:OC ratio would decrease or increase with depth in the sediments (depending on whether Hg reacted with oxyhydroxides or sulphides) because the total amount of Hg would remain the same, while the OC declined with depth, as hypothesized for other environments 28 – 32 . Rather, our results imply that Hg which is mobilized from the solid phase as a consequence of OC metabolism in the benthic boundary layer is lost from the sediments. As argued in other works 33 , 34 , a plausible mechanism might be that Hg migrates out of the sediments following its methylation by Fe-oxyhydroxides and sulphate-reducing bacteria and the subsequent transformation of the resulting monomethylmercury into volatile Hg species (Hg 0 , Hg(CH 3 ) 2 ) 35 , 36 . Although our dataset does not confirm unequivocally that these reactions occur in AO sediments, the vertical profiles of Fe oxyhydroxides and reduced sulphur (Figs. S3 and S2) in our cores show that the necessary redox conditions are fulfilled. We conclude that the Hg decline with depth in the cores is due to post-depositional release and evasion as OC is oxidized in the suboxic zone of the sediment. The only exception to this inference is for the cores from the Bering and Chukchi Seas, where the Hg:OC ratio increases with core depth over the top 5–10 cm of sediment (Fig. S1 ). These marine areas are characterized by high primary productivity and a shallow water column (Fig. 1 ), meaning that a high flux of labile OC reaches the sediment 27 . The oxygenated sediment surface layer at these sites is consequently shallow (< 0.5 cm), and there is a relatively high reduced sulphur concentration near the sediment surface (Fig. S2) 26 , 27 . These observations suggest that, as Hg is released from its association with labile OC, it is captured through surface complexation reactions with iron sulphide minerals or as a precipitate of HgS 28 , 29 . This pattern is not observed at other NAAM sites, where the OC is less labile, O 2 is less rapidly consumed, and reduced sulphur is not produced so close to the sediment surface. Role of carbon source composition in sedimentary Hg concentrations The trend of decreasing Hg:OC ratio with increasing ẟ 13 C values in NAAM sediments (Fig. S5) indicates that the relative proportions of marine and terrigenous OC are likely the major causal factor for the regional differences in the Hg:OC ratio. Assuming previously identified ẟ 13 C endmember values for OC TERR (–26.5‰) and OC MAR (–19.5‰) in our study area 23 , 37 – 39 , it can be seen that sediments with the highest OC TERR content have higher Hg:OC ratios (Fig. 3 ). The significant, positive intercept of the Hg:OC relationship observed in the Bering and Chukchi Seas and Canadian Archipelago sediments (Table S2) likely results from the presence of a Hg fraction associated to inorganic material, including reduced sulphur, as discussed above, but also carbonate and aluminosilicate minerals. Previous studies have reported Hg concentrations (~ 30 ng Hg g SED −1 ) in sedimentary calcareous rock samples from a variety of regions 24 , 40 , 41 , including limestones from eastern Canada and a high Arctic Archipelago watershed, from which a Hg:IC ratio of the order of 0.35 µg Hg g IC −1 can be derived. Presuming that carbonate minerals (calcite and dolomite) from detrital sources accumulating in NAAM sediments 23 , 24 are characterized by a similar endmember Hg:IC ratio, the supply of Hg to the sediments from this material can be assessed on the basis of the IC concentrations (Fig. S4). This contribution would be very low (< 1 ng Hg g SED −1 ) in the Bering and Chukchi Seas and moderate (1–7 ng Hg g SED −1 ) in the Barrow Canyon and Beaufort Sea. In the interior of the Canadian Archipelago and at a few other sites of the eastern NAAM the contribution of Hg from the IC sources could be as high as 20 ng Hg g SED −1 , thus representing 50–60% of measured Hg concentrations at many locations. Mercury from aluminosilicate rocks also contributes to the Hg contents of NAAM sediments, but its contribution is very small. Considering the Al concentrations in our sediment samples 27 and a Hg:Al ratio of 30 ng Hg g Al −1 42 , the Hg contribution from aluminosilicates in NAAM sediments is estimated to be on the order of 1.7 ± 0.4 ng Hg g SED −1 . To quantify the relative importance of the contributions of Hg from OC MAR and OC TERR sources to NAAM sediments, we need to estimate their Hg:OC endmember ratios. The fraction of OC from terrigenous source (F TERR ) and concentrations of OC MAR and OC TERR were determined using a simple, two-source mixing model, with measured concentrations and isotopic compositions of OC and previously-reported endmember values for OC TERR (–26.5‰) and OC MAR (–19.5‰) 23,37–39 . After subtracting the portions of Hg associated with carbonates and aluminosilicates, solving the Hg:OC vs F TERR regression for F TERR = 0 and F TERR = 1 gives endmembers of Hg:OC MAR = 0.39 µg Hg g OCMAR −1 and Hg:OC TERR = 7.2 µg Hg g OCTERR −1 (see inset of Fig. 4 ). Multiplying these values by the OC MAR and OC TERR concentrations, respectively, indicates that OC TERR dominates Hg delivery (75–95%) to western NAAM sediments and is also a key Hg carrier at many of the eastern NAAM sites (20–70%). OC MAR never represents more than 20% of the measured Hg concentrations (Fig. S6). The comparison shown in Fig. 4 of the measured Hg concentrations with the summation of the modelled Hg contributions from aluminosilicates and from each individual carbon source confirms that our measurements are internally consistent; that endmember values for the different Hg sources are well characterized; and that we have accounted for all significant sources. The predictive power of the mixing model convincingly demonstrates that carbon composition is the most important factor determining the Hg content of AO sediments. It further shows that the endmember values for each of the individual carbon sources do not vary much across the NAAM. The Hg:OC TERR ratio (7.2µg Hg g OCTERR −1 ) is about 20 times higher than the Hg:OC MAR (0.39 µg Hg g MAR −1 ) and Hg:IC (0.35 µg Hg g IC −1 ) ratios. Terrigenous OC is clearly the main source of Hg to NAAM sediments but, due to its elevated concentrations in the eastern NAAM, IC also represents an important Hg contributor in that region. There are fewer data available from which to test the mixing model in the deep Arctic basins. However, assuming that OC TERR represents 80% of the total sedimentary OC content in the central AO sediments 17 , 39 and that already given Hg:IC and Hg:Al endmember values also apply to basin sediments, the measured OC, IC and Al concentrations permit the inference of the sedimentary Hg:OC TERR and Hg:OC MAR endmembers at our deep basin coring sites. At these locations, the best fit between the measured and simulated Hg concentrations is obtained with terrigenous and marine endmembers of 11.2 µg Hg g OCTERR −1 and 0.80 µg Hg g OCMAR −1 , respectively (Fig. S8). Both of these OC endmembers for the deep basins are substantially higher than at the shallower sites. The higher Hg:OC ratios likely relate to the greater water depth and longer transit time over the basin than the continental margin, which results in greater OC remineralization in the water column, as discussed below. Role of OC remineralization on sedimentary Hg concentrations The isotopic signature of Hg in Arctic Ocean sediments shows that Hg is mainly from terrigenous sources, primarily permafrost 6 . The Hg:OC ratio in permafrost is 0.63 µg Hg g OC −1 43, 44 . The Hg:OC ratio in the Mackenzie River, which is the largest Arctic river in terms of sediment discharge 47 , is also on the order of 0.6 µg Hg g OC −1 45–47 . However, the terrigenous endmember Hg:OC ratio in AO sediments is much higher: 7.2 µg Hg g OC −1 on the NAAM, and 11.2 µg Hg g OC −1 in the deep central AO basins. The higher Hg:OC ratios in bottom sediment than in the source material is likely due to regenerative scavenging 15 , a process allowing Hg associated to organic particles sinking in oxygenated water columns to be preferentially retained relative to carbon during remineralization 14 , 48 (Fig. 5 ). As a result of this process, the Hg:OC ratio in settling particles increases with depth in the water column 14 , 15 , 49 , so that sediments from deepest marine environments tend to have greater Hg:OC ratios than sediments from shallow coastal zones. In the Arctic continental margin, about 94% of marine OC is remineralized before it reaches the sediments, and this is even more in the deep central AO 17 . In comparison, terrigenous OC degradation is smaller than that of marine OC, but represents nevertheless about 35% of its total inputs 17 , 50 . There is greater remineralization of OC in water column and higher Hg:OC ratios in the central basins than in the continental margin, because of the greater transit time. Although anthropogenic activities have resulted in significant Hg contamination in the AO 1 , 4 , the data presented here show that, once Hg reaches this ocean, its transport, distribution and fate are determined by the cycling of OC, in which terrigenous OC plays a more important role than in other oceans. Whereas remineralization of OC in the water column causes the Hg:OC ratio to increase with transit duration through the system, remineralization in suboxic sediment causes the Hg:OC ratio to remain constant, because Hg is released, likely through methylation and reductive demethylation (Fig. 5 ). The sedimentary record consequently fails to reveal anthropogenic Hg imprint. The strong connection between Hg and OC implies that any future change in organic carbon pathways could have strong effects on the transport and burial of Hg in this ocean. Online Methods Study area. The cores analyzed for this study are from sub-regions of the NAAM where the water depth, primary production and proportions of terrestrial and marine OC in the sediments exhibit pronounced differences. Our spatial coverage encompasses the North Bering and Chukchi Seas, the Barrow Canyon, the Beaufort Sea margin, the Canadian Archipelago and Lancaster Sound, and the Davis Strait in Southern Baffin Bay (Fig. 1). The Bering and Chukchi Shelves receive nutrient-rich Pacific water and are highly productive environments, where the proportion of marine OC in the sediment is higher than that of terrestrial OC 37,51 . At the eastern edge of the Chukchi Sea, the Barrow Canyon includes a regional hotspot of high productivity in its upper portion 52 and accumulates bottom sediments with a high concentration of terrestrial OC 27, 53 . Primary production in the Beaufort Sea is as much as five times lower than that of the Chukchi Shelf 54,55 . A large amount of terrestrial OC from the Mackenzie River is deposited in this region 23,38 . Further to the East, the Canadian Arctic Archipelago and Lancaster Sound, which form together a complex shelf consisting of multiple channels, and the Davis Strait at the southern entrance of Baffin Bay, are also characterized by much lower rates of biological productivity 55-57 than that of the Chukchi Shelf, although autochthonous OC predominates in the sediments 23 . Sampling. As part of the Canadian research program of the International Polar Year, sediment box-cores were collected in the NAAM, from the Canadian Coast Guard Ships (CCGS) Sir Wilfrid Laurier and Louis S. St-Laurent in 2007 and 2008, respectively 58 . The geographical coordinates of the sampling locations and water depth at each site are reported in Table S2. Each core was sub-sampled on board in 0.5-cm intervals for the first 2 cm, 1-cm intervals from 2 to 10 cm depth, and then in progressively thicker layers of 2 and 3 cm down to the bottom of the cores, to a maximum depth of 45 cm. The outermost 2-3 cm of the 600 cm 2 sediment layers in contact with the core liner was discarded, and the sediment samples were stored in double plastic bags and kept frozen for subsequent analyses. Analysis. The concentration of Hg in freeze-dried sediment samples was determined by gold amalgamation-atomic absorption spectroscopy, using a semi-automatic mercury analyzer (Milestone, DMA-80) and the US EPA standard protocol No. 7473 as a guide. Our analytical precision, appraised from replicate measurements (n=16) of the reference material MESS-3 (certified Hg concentration 91±9 ng g -1 ), was 8.5%, and the accuracy, expressed as recovery rate, 109%. For a 100-mg sediment aliquot the detection limit was ca. 1 ng g -1 . We report the Hg concentrations on a dry weight basis, after correction for the salt content of the sediment approximated from the measured porosity of each sample and the salinity of the bottom water (~34 on the Practical Salinity Scale). Our cores from NAAM had also been previously analyzed for other elements and isotopes through proven methodologies. The radioisotopes 210 Pb and 226 Ra were measured by non-destructive gamma spectroscopy 53 . Measurements of OC were performed by high temperature combustion of pre-acidified samples, using an NC2500 Thermo Quest Elemental Analyzer, and OC isotopes (ẟ 13 C) by high temperature combustion, followed by isotope ratio mass spectrometry using a Carlo Erba 1500 Elemental Analyzer coupled to a ThermoQuest Delta Plus XP Mass Spectrometer 23 . Iron associated with poorly and well-crystallized oxyhydroxides (Fe OX ), was determined through extraction with a sodium dithionite solution at pH ~4.7 and ICP-OES measurements 26 . Reduced sulphur (S RED ), defined as the total sulphur contained in authigenic iron monosulfide (FeS) and pyrite (FeS 2 ), was also operationally determined through successive leaching of sediment samples with HCl and Cr(II) solutions and subsequent colorimetric analysis 27 . The occurrence of S RED in the sedimentary column indicates an anoxic condition under which sulphate reduction has been an active reaction. References Naidu, A.S. et al. The continental margin of the North Bering Chukchi Seas : concentrations, sources, fluxes, accumulation and burial rates of organic carbon. Chap. 7.3 in The Organic Carbon Cycle in the Arctic Ocean (eds Stein, R. & Macdonald, R.W.), 193-203 (Springer 2004). Grebmeier, J.M., Cooper, L.W., Feder, H.M. & Sirenko, B.I. Ecosystem dynamics of the Pacific-influenced Northern Bering and Chukchi Seas in the Amerasian Arctic. Prog. Oceanogr . 71 , 331-361 (2006). Kuzyk, Z. 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Nitrogen and carbon isotopic composition of marine and terrestrial organic matter in Arctic Ocean in sediments: implications for nutrient utilization and organic matter composition. Deep-Sea Res. 46 , 789-810 (2001). Semkin, R.G., Mierle, G. & Neureuther, R.J. Hydrochemistry and mercury cycling in a High Arctic watershed. Sci. Tot. Environ. 342 , 199-221 (2005). Jonasson, I.R. & Boyle, R.W. Geochemistry of mercury and origins of natural contamination of the environments. Can. Min. Metall. Bull. 65 , 32-39 (1972). Canil, D., Crockford, P.W., Rossin, R. & Telmer, K. Mercury in some arc crustal and mantle peridotites and relevance to the moderately volatile element budget of the Earth. Chem. Geol. 396 , 134-142 (2015). Lim, A.G. et al. A revised pan-Arctic permafrost soil Hg pool based on Western Siberian peat Hg and carbon observations. Biogeosciences 17 , 3083-3097 (2020). Schuster, P.F. et al. Permafrost stores a globally significant amount of mercury. Geophys. Res. Lett . 45 , 1463-1471 (2018). Rachold, V. et al. Modern terrigenous organic carbon input to the Artic Ocean. Chap.2 in The Organic Carbon Cycle in the Arctic Ocean (eds Stein, R. & Macdonald, R.W.), 33-55 (Springer 2004). Zolkos, S. et al. Mercury export from Arctic great rivers. Environ. Sci. Technol. 54 , 4140-4148 (2020). Leitch, D.R. et al. The delivery of mercury to the Beaufort Sea of the Arctic Ocean by the Mackenzie River. Sci. Tot. Environ. 373 , 178-195 (2007). Qu, Y., Zhong, H., Liu, X., Zhang, W. & Chen, T. Coupling and decoupling between sedimentary mercury and organic carbon preservation in the oxygenated marine environment. Geochem. Geophys. 25 , e2023Gc011201 (2024) Cossa, D. et al. Mercury accumulation in the sediment of the Western Mediterranean abyssal plain: A reliable archive of the late Holocene. Geochim. Cosmochim. Acta. 309 , 1-15 (2021). Ittekkot, V. Global trends in the nature of organic matter in river suspension, Nature 322 , 436-438 (1988). Additional Declarations There is NO Competing Interest. Supplementary Files GobCArcticHgExtData15Ap25.pdf Data basis GobCArcticHgSupInf15Ap25.docx Supplementary Information Cite Share Download PDF Status: Published Journal Publication published 24 Dec, 2025 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6457403","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":444202123,"identity":"4739f9b0-7736-4058-8fbe-e0e202665e0f","order_by":0,"name":"Charles Gobeil","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYDACCSB+AGbxMDAkFNjwEKclAa7FII1ULQwGhwnr4J/d/OxDQkUdg7x778EHDwzOy5hLH3/A8KMGjyV3jhnPSDhzmMHwzLlkgwSD2zyWfTkGjD3HcGsxkEgwZkhsO8BgOCPHTAKkxeAMDwMzAxs+LemfGRL/1YG0mP9IMDgH1ML+gJnhHz4tOUBbGpgZ5CVyzIAhdgCohcGAmbENj19u5BQzJBw7zGPAcy4Z6LBkkMMMDvb24dbCPyN9M8OHmjo5+fbegx9/VNjZAx328MGPb7i1wACPwQEk3gEcqlCBfANRykbBKBgFo2AkAgAZI0vmUhOudAAAAABJRU5ErkJggg==","orcid":"","institution":"Institut National de la Recherche Scientifique","correspondingAuthor":true,"prefix":"","firstName":"Charles","middleName":"","lastName":"Gobeil","suffix":""},{"id":444202124,"identity":"a13475ce-c1b7-48f2-a975-37205a49b73a","order_by":1,"name":"Sophia Johannessen","email":"","orcid":"https://orcid.org/0000-0003-3788-2994","institution":"Fisheries and Oceans Canada","correspondingAuthor":false,"prefix":"","firstName":"Sophia","middleName":"","lastName":"Johannessen","suffix":""},{"id":444202125,"identity":"ba88c281-45af-40a7-924f-397294a4821b","order_by":2,"name":"Miguel Goñi","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Miguel","middleName":"","lastName":"Goñi","suffix":""},{"id":444202126,"identity":"d2ddae76-2aad-4b9d-9097-ffb2a65345a2","order_by":3,"name":"Zou Zou Kuzyk","email":"","orcid":"","institution":"University of Manitoba","correspondingAuthor":false,"prefix":"","firstName":"Zou","middleName":"Zou","lastName":"Kuzyk","suffix":""},{"id":444202129,"identity":"20fc3e9f-6287-4716-b56c-b163f6cd7b54","order_by":4,"name":"Daniel Cossa","email":"","orcid":"","institution":"Université Grenoble Alpes, ISTerre","correspondingAuthor":false,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Cossa","suffix":""}],"badges":[],"createdAt":"2025-04-15 18:40:51","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6457403/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6457403/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s43247-025-03058-7","type":"published","date":"2025-12-24T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81189805,"identity":"81bcf670-2c58-4ea1-81de-52c862945828","added_by":"auto","created_at":"2025-04-23 09:06:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":549826,"visible":true,"origin":"","legend":"\u003cp\u003eMap of the North American Arctic margin showing the coring sites, areas of high and low productivity, and the relative concentrations of marine and terrigenous organic carbon (OC) in different regions. Inset: locations of the sediment cores from the deep the central Arctic Ocean previously analyzed for Hg\u003csup\u003e\u003cstrong\u003e10\u003c/strong\u003e\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/f177178bb6137df9d30c33cc.png"},{"id":81188391,"identity":"4027fd9d-0971-421e-9653-2c1f6cdb8516","added_by":"auto","created_at":"2025-04-23 08:50:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":626809,"visible":true,"origin":"","legend":"\u003cp\u003eSediment core profiles of Hg and organic carbon (OC), grouped by region. Core locations are shown in Fig. 1. Note that the concentration scales vary among plots to better illustrate the shapes of the profiles.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/6bef4166688eb97feae74297.png"},{"id":81188390,"identity":"07e86c0f-5acf-41a3-86ae-8483926bbff4","added_by":"auto","created_at":"2025-04-23 08:50:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":442150,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between Hg and OC in (a) Western NAAM and Amerasian Basin and (b) Eastern NAAM and Eurasian Basin. The slope (Hg:OC ratio) is marked for each region, along with the average \u003csup\u003e13\u003c/sup\u003edC value for the region, which was used to determine the proportion of terrigenous material.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/045e25a75ea9eafa1ff1fcb7.png"},{"id":81189367,"identity":"4331319f-a985-43eb-8d7e-e2e95dc5f439","added_by":"auto","created_at":"2025-04-23 08:58:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":286225,"visible":true,"origin":"","legend":"\u003cp\u003eAgreement between modelled and measured Hg concentrations in North American Arctic Margin (NAAM) sediment. Inset: relationship between the fraction of terrigenous OC (F\u003csub\u003eTERR\u003c/sub\u003e) and the Hg:OC ratio determined after subtracting the portions of Hg associated with carbonates and aluminosilicates; regression line is calculated with the core average values (red squares).\u0026nbsp;\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/6eac74730c5b3c3928d52583.png"},{"id":81188397,"identity":"d198d92c-0ec2-4127-8943-4de433c072ff","added_by":"auto","created_at":"2025-04-23 08:50:15","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":314241,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic showing how OC dynamics affect Hg delivery to and burial in North American Arctic Margin sediments. Mercury is associated with both marine and terrigenous OC in surface water. As the particulate OC sinks, ~94% of OC\u003csub\u003eMAR\u003c/sub\u003e and ~35% of OC\u003csub\u003eTERR\u003c/sub\u003e is remineralized before reaching NAAM sediment. Within the sediment, as OC is remineralized, O\u003csub\u003e2\u003c/sub\u003e is consumed, and soluble reduced Hg is released. The Hg:OC ratio increases with depth in the water column but remains constant with depth in sediment. At many locations of the eastern NAAM, inorganic carbon is also an important carrier of Hg to the sediment. Numbers associated to green, brown and grey colored squares in the sediments and in the upper part of the water column represent the content of Hg (µg g\u003csup\u003e-1\u003c/sup\u003e) in OC\u003csub\u003eMAR\u003c/sub\u003e, OC\u003csub\u003eTERR\u003c/sub\u003e and IC, respectively.\u0026nbsp;\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/d5149037211f29fee7bc440d.png"},{"id":99935467,"identity":"503df3d3-f46b-4aa9-9d11-26583cfc9b5d","added_by":"auto","created_at":"2026-01-10 08:13:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3036254,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/53bd4d73-0d10-41de-9180-623202f4c8d6.pdf"},{"id":81188392,"identity":"9b4098ce-95ec-4042-8a42-a1e8660cd929","added_by":"auto","created_at":"2025-04-23 08:50:15","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":600784,"visible":true,"origin":"","legend":"Data basis","description":"","filename":"GobCArcticHgExtData15Ap25.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/7ff9af65c630b601ede16db9.pdf"},{"id":81189365,"identity":"01b59375-33fd-42e3-960b-50189463a542","added_by":"auto","created_at":"2025-04-23 08:58:15","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1063494,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"GobCArcticHgSupInf15Ap25.docx","url":"https://assets-eu.researchsquare.com/files/rs-6457403/v1/95befd3ee7fd0cac61151d52.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Carbon dynamics control comtemporary mercury burial in Arctic Ocean sediments","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMercury (Hg) is of persistent concern in the Arctic Ocean (AO), because higher-trophic level Arctic marine organisms contain elevated concentrations of this bioaccumulative, neurotoxic element\u003cstrong\u003e\u003csup\u003e1-3\u003c/sup\u003e\u003c/strong\u003e. Despite multiple research initiatives motivated by this finding, the modern Hg cycle in the AO nevertheless remains ill-defined, particularly as regards (i) its processing and burial in bottom sediments and (ii) the imprint that long-range atmospheric and oceanic transport of anthropogenic Hg might have on this cycle\u003cstrong\u003e\u003csup\u003e4-6\u003c/sup\u003e\u003c/strong\u003e. There is a widespread pattern of increasing Hg concentration toward the surface of AO sediments\u003cstrong\u003e\u003csup\u003e6-10\u003c/sup\u003e\u003c/strong\u003e,\u003csup\u003e\u0026nbsp;\u003c/sup\u003ebut it is unclear whether this trend emerges from an increase in the flux of Hg into the ocean or to diagenetic mechanisms within the sediment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFurthermore, Hg is thought to be transferred to AO sediments mainly in association with settling particles of marine (\u003cem\u003eautochthonous\u003c/em\u003e) organic carbon (OC\u003csub\u003eMAR\u003c/sub\u003e)\u003cstrong\u003e\u003csup\u003e4,5\u003c/sup\u003e\u003c/strong\u003e, as is the case in other oceans\u003cstrong\u003e\u003csup\u003e11-16\u003c/sup\u003e\u003c/strong\u003e. However, terrigenous (\u003cem\u003eallochthonous\u003c/em\u003e) organic carbon (OC\u003csub\u003eTERR\u003c/sub\u003e) predominates in marginal and deep basin sediments of the AO\u003cstrong\u003e\u003csup\u003e17\u003c/sup\u003e\u003c/strong\u003e, and Hg that enters the AO from continental sources is largely bound to OC\u003csub\u003eTERR\u003c/sub\u003e\u003cstrong\u003e\u003csup\u003e18-22\u003c/sup\u003e\u003c/strong\u003e. In addition, even though inorganic carbon (IC) is abundant in certain Arctic marine areas\u003cstrong\u003e\u003csup\u003e23-24\u003c/sup\u003e\u003c/strong\u003e, the role of IC in Arctic Hg cycling, as that of OC\u003csub\u003eTERR\u003c/sub\u003e, has not been examined.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Here, we investigate what controls Hg surface enrichment in Arctic Ocean sediments, including the roles of carbon sources and organic carbon (OC) remineralization in the water column and sediments. We use a set of 24 sediment box-cores that spans a range of productivity and terrigenous flux across the North American Arctic Margin (NAAM), as well as six basin cores previously analyzed for Hg and other elements\u003cstrong\u003e\u003csup\u003e10\u003c/sup\u003e\u003c/strong\u003e (Fig. 1, Table S1).\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003eVertical profiles of Hg and OC and regional variations in the Hg:OC ratio\u003c/h2\u003e \u003cp\u003eMercury concentrations vary by more than an order of magnitude in NAAM sediments (2\u0026ndash;98 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eSED\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e dry weight, n\u0026thinsp;=\u0026thinsp;514). Both Hg and OC tend to decline exponentially below the sediment\u0026ndash;water interface (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The Hg:OC ratio varies little (13\u0026thinsp;\u0026plusmn;\u0026thinsp;9%) and exhibits no systematic trend with depth in the cores, except in five of the Bering and Chukchi Seas cores, where it increases slightly, between the sediment surface and 5\u0026ndash;10 cm depth (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). In contrast to the profiles of Hg and OC, reduced sulphur (i.e., acid volatile sulphide\u0026thinsp;+\u0026thinsp;chromium reducible sulphur), which reveals sulphate reduction under anoxic conditions\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, is low in surface sediment and increases with depth (Fig. S2). Cores with low reduced sulphur inventories (e.g., the Canadian Archipelago cores) tend to have well-defined Fe oxyhydroxide surface enrichments (Fig. S3), which are indicative of anaerobic organic matter oxidation by ferri-reducing bacteria. In the cores from the Bering and Chukchi Seas, where reduced sulphur inventories are the most elevated, the absence of such surface enrichments testifies to the very limited O\u003csub\u003e2\u003c/sub\u003e penetration depth (\u0026lt;\u0026thinsp;0.5 cm) in the sediments at these locations\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMoreover, while Hg covaries positively (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01) with OC, the slope of the linear regression varies regionally (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In the NAAM, the shallowest slope (lowest Hg:OC ratio) is observed in the Bering and Chukchi Seas (1.2 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e), whereas the steepest slope (5.3 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) is found in the Beaufort Sea (cores CG2 and CG3). Steeper slopes have been previously calculated for sediments of the deep central AO (2265\u0026ndash;4230 m)\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, where they reach 9.5 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e in both the Amerasian and Eurasian Basins (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Although all regional linear relationships between Hg and OC have non-zero y-intercepts (i.e., for OC\u0026thinsp;=\u0026thinsp;0 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), these deviations are not statistically different from zero (\u003cem\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/em\u003e), with the exception of those characterizing the sediments of the Bering and Chukchi Seas and the Canadian Archipelago (see Table S2 for details).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eRelationship between the Hg:OC ratio and OC composition\u003c/h2\u003e \u003cp\u003eThe stable isotope composition of OC (ẟ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC) was determined in samples from all the cores, except Lancaster Sound core CAA2. Overall, the ẟ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC values range between \u0026minus;\u0026thinsp;25.2\u0026permil; and \u0026minus;\u0026thinsp;20.1\u0026permil;, with the lowest values in Beaufort Sea (\u0026ndash;24.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u0026permil;, n\u0026thinsp;=\u0026thinsp;18) and Barrow Canyon (\u0026ndash;23.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u0026permil;, n\u0026thinsp;=\u0026thinsp;52), and higher values in Lancaster Sound and Baffin Bay (\u0026ndash;22.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u0026permil;, n\u0026thinsp;=\u0026thinsp;42), the Canadian Archipelago (\u0026ndash;21.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u0026permil;, n\u0026thinsp;=\u0026thinsp;43), the Chukchi and Bering Shelves (\u0026ndash;21.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u0026permil;, n\u0026thinsp;=\u0026thinsp;36), and Davis Strait (\u0026ndash;20.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u0026permil;, n\u0026thinsp;=\u0026thinsp;16). Without considering the results for the five cores from the interior of the Canadian Archipelago (VS1, FS1, BE2, PS2 and PS1), in which IC concentrations are particularly elevated (30\u0026ndash;60 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, Fig. S4), the Hg:OC ratios in NAAM sediments are negatively correlated (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01) with increasing ẟ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC values (Fig. S5). In the IC-enriched Canadian Archipelago cores, Hg:OC ratios do not follow the same trend (Fig. S5); they are higher than those of sediments from other regions having similar ẟ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC values (Lancaster Sound, Davis Strait, Bering and Chukchi Shelves) (Fig. S4).\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eDiagenetic control of sedimentary Hg profiles\u003c/h2\u003e \u003cp\u003eThe linearity of the regional Hg\u0026ndash;OC relationships in NAAM sediments, and the fact that Hg concentrations tend to zero as OC concentrations also approach zero, reveal that particulate OC is the major Hg-binding phase. Furthermore, the nearly invariant Hg:OC ratio with depth in most cores indicates that the Hg profiles are not determined by a modification in Hg flux, but by OC dynamics within the sediment. If the Hg enrichment in surface sediment were the result of increasing anthropogenic flux, the Hg:OC ratio would also be higher toward the surface, which is not the case.\u003c/p\u003e \u003cp\u003eThe relatively stable Hg:OC ratio with depth in most cores implies that Hg released during early OC oxidation does not promptly precipitate or form solid-phase complexes, either with remaining organic matter or \u003cem\u003evia\u003c/em\u003e adsorption to or coprecipitation with authigenic oxyhydroxide or sulphide minerals. If that were the case, the Hg:OC ratio would decrease or increase with depth in the sediments (depending on whether Hg reacted with oxyhydroxides or sulphides) because the total amount of Hg would remain the same, while the OC declined with depth, as hypothesized for other environments\u003csup\u003e\u003cb\u003e\u003cspan additionalcitationids=\"CR29 CR30 CR31\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. Rather, our results imply that Hg which is mobilized from the solid phase as a consequence of OC metabolism in the benthic boundary layer is lost from the sediments. As argued in other works\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, a plausible mechanism might be that Hg migrates out of the sediments following its methylation by Fe-oxyhydroxides and sulphate-reducing bacteria and the subsequent transformation of the resulting monomethylmercury into volatile Hg species (Hg\u003csup\u003e0\u003c/sup\u003e, Hg(CH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e)\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. Although our dataset does not confirm unequivocally that these reactions occur in AO sediments, the vertical profiles of Fe oxyhydroxides and reduced sulphur (Figs. S3 and S2) in our cores show that the necessary redox conditions are fulfilled. We conclude that the Hg decline with depth in the cores is due to post-depositional release and evasion as OC is oxidized in the suboxic zone of the sediment.\u003c/p\u003e \u003cp\u003eThe only exception to this inference is for the cores from the Bering and Chukchi Seas, where the Hg:OC ratio increases with core depth over the top 5\u0026ndash;10 cm of sediment (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). These marine areas are characterized by high primary productivity and a shallow water column (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), meaning that a high flux of labile OC reaches the sediment\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. The oxygenated sediment surface layer at these sites is consequently shallow (\u0026lt;\u0026thinsp;0.5 cm), and there is a relatively high reduced sulphur concentration near the sediment surface (Fig. S2)\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. These observations suggest that, as Hg is released from its association with labile OC, it is captured through surface complexation reactions with iron sulphide minerals or as a precipitate of HgS\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. This pattern is not observed at other NAAM sites, where the OC is less labile, O\u003csub\u003e2\u003c/sub\u003e is less rapidly consumed, and reduced sulphur is not produced so close to the sediment surface.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eRole of carbon source composition in sedimentary Hg concentrations\u003c/h3\u003e\n\u003cp\u003eThe trend of decreasing Hg:OC ratio with increasing ẟ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC values in NAAM sediments (Fig. S5) indicates that the relative proportions of marine and terrigenous OC are likely the major causal factor for the regional differences in the Hg:OC ratio. Assuming previously identified ẟ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC endmember values for OC\u003csub\u003eTERR\u003c/sub\u003e (\u0026ndash;26.5\u0026permil;) and OC\u003csub\u003eMAR\u003c/sub\u003e (\u0026ndash;19.5\u0026permil;) in our study area\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, it can be seen that sediments with the highest OC\u003csub\u003eTERR\u003c/sub\u003e content have higher Hg:OC ratios (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The significant, positive intercept of the Hg:OC relationship observed in the Bering and Chukchi Seas and Canadian Archipelago sediments (Table S2) likely results from the presence of a Hg fraction associated to inorganic material, including reduced sulphur, as discussed above, but also carbonate and aluminosilicate minerals.\u003c/p\u003e \u003cp\u003ePrevious studies have reported Hg concentrations (~\u0026thinsp;30 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eSED\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) in sedimentary calcareous rock samples from a variety of regions\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, including limestones from eastern Canada and a high Arctic Archipelago watershed, from which a Hg:IC ratio of the order of 0.35 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eIC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e can be derived. Presuming that carbonate minerals (calcite and dolomite) from detrital sources accumulating in NAAM sediments\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e are characterized by a similar endmember Hg:IC ratio, the supply of Hg to the sediments from this material can be assessed on the basis of the IC concentrations (Fig. S4). This contribution would be very low (\u0026lt;\u0026thinsp;1 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eSED\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) in the Bering and Chukchi Seas and moderate (1\u0026ndash;7 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eSED\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) in the Barrow Canyon and Beaufort Sea. In the interior of the Canadian Archipelago and at a few other sites of the eastern NAAM the contribution of Hg from the IC sources could be as high as 20 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eSED\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, thus representing 50\u0026ndash;60% of measured Hg concentrations at many locations.\u003c/p\u003e \u003cp\u003eMercury from aluminosilicate rocks also contributes to the Hg contents of NAAM sediments, but its contribution is very small. Considering the Al concentrations in our sediment samples\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e and a Hg:Al ratio of 30 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eAl\u003c/sub\u003e\u003csup\u003e\u0026minus;1 \u003cb\u003e42\u003c/b\u003e\u003c/sup\u003e, the Hg contribution from aluminosilicates in NAAM sediments is estimated to be on the order of 1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 ng\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eSED\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo quantify the relative importance of the contributions of Hg from OC\u003csub\u003eMAR\u003c/sub\u003e and OC\u003csub\u003eTERR\u003c/sub\u003e sources to NAAM sediments, we need to estimate their Hg:OC endmember ratios. The fraction of OC from terrigenous source (F\u003csub\u003eTERR\u003c/sub\u003e) and concentrations of OC\u003csub\u003eMAR\u003c/sub\u003e and OC\u003csub\u003eTERR\u003c/sub\u003e were determined using a simple, two-source mixing model, with measured concentrations and isotopic compositions of OC and previously-reported endmember values for OC\u003csub\u003eTERR\u003c/sub\u003e (\u0026ndash;26.5\u0026permil;) and OC\u003csub\u003eMAR\u003c/sub\u003e (\u0026ndash;19.5\u0026permil;)\u003csup\u003e\u003cb\u003e23,37\u0026ndash;39\u003c/b\u003e\u003c/sup\u003e. After subtracting the portions of Hg associated with carbonates and aluminosilicates, solving the Hg:OC vs F\u003csub\u003eTERR\u003c/sub\u003e regression for F\u003csub\u003eTERR\u003c/sub\u003e = 0 and F\u003csub\u003eTERR\u003c/sub\u003e = 1 gives endmembers of Hg:OC\u003csub\u003eMAR\u003c/sub\u003e = 0.39 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOCMAR\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e and Hg:OC\u003csub\u003eTERR\u003c/sub\u003e = 7.2 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOCTERR\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e (see inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Multiplying these values by the OC\u003csub\u003eMAR\u003c/sub\u003e and OC\u003csub\u003eTERR\u003c/sub\u003e concentrations, respectively, indicates that OC\u003csub\u003eTERR\u003c/sub\u003e dominates Hg delivery (75\u0026ndash;95%) to western NAAM sediments and is also a key Hg carrier at many of the eastern NAAM sites (20\u0026ndash;70%). OC\u003csub\u003eMAR\u003c/sub\u003e never represents more than 20% of the measured Hg concentrations (Fig. S6).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe comparison shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e of the measured Hg concentrations with the summation of the modelled Hg contributions from aluminosilicates and from each individual carbon source confirms that our measurements are internally consistent; that endmember values for the different Hg sources are well characterized; and that we have accounted for all significant sources. The predictive power of the mixing model convincingly demonstrates that carbon composition is the most important factor determining the Hg content of AO sediments. It further shows that the endmember values for each of the individual carbon sources do not vary much across the NAAM. The Hg:OC\u003csub\u003eTERR\u003c/sub\u003e ratio (7.2\u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOCTERR\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) is about 20 times higher than the Hg:OC\u003csub\u003eMAR\u003c/sub\u003e (0.39 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eMAR\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) and Hg:IC (0.35 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eIC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e) ratios. Terrigenous OC is clearly the main source of Hg to NAAM sediments but, due to its elevated concentrations in the eastern NAAM, IC also represents an important Hg contributor in that region.\u003c/p\u003e \u003cp\u003eThere are fewer data available from which to test the mixing model in the deep Arctic basins. However, assuming that OC\u003csub\u003eTERR\u003c/sub\u003e represents 80% of the total sedimentary OC content in the central AO sediments\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e and that already given Hg:IC and Hg:Al endmember values also apply to basin sediments, the measured OC, IC and Al concentrations permit the inference of the sedimentary Hg:OC\u003csub\u003eTERR\u003c/sub\u003e and Hg:OC\u003csub\u003eMAR\u003c/sub\u003e endmembers at our deep basin coring sites. At these locations, the best fit between the measured and simulated Hg concentrations is obtained with terrigenous and marine endmembers of 11.2 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOCTERR\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 0.80 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOCMAR\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively (Fig. S8). Both of these OC endmembers for the deep basins are substantially higher than at the shallower sites. The higher Hg:OC ratios likely relate to the greater water depth and longer transit time over the basin than the continental margin, which results in greater OC remineralization in the water column, as discussed below.\u003c/p\u003e\n\u003ch3\u003eRole of OC remineralization on sedimentary Hg concentrations\u003c/h3\u003e\n\u003cp\u003eThe isotopic signature of Hg in Arctic Ocean sediments shows that Hg is mainly from terrigenous sources, primarily permafrost\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. The Hg:OC ratio in permafrost is 0.63 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1 \u003cb\u003e43,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. The Hg:OC ratio in the Mackenzie River, which is the largest Arctic river in terms of sediment discharge\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, is also on the order of 0.6 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1 \u003cb\u003e45\u0026ndash;47\u003c/b\u003e\u003c/sup\u003e. However, the terrigenous endmember Hg:OC ratio in AO sediments is much higher: 7.2 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e on the NAAM, and 11.2 \u0026micro;g\u003csub\u003eHg\u003c/sub\u003e g\u003csub\u003eOC\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e in the deep central AO basins.\u003c/p\u003e \u003cp\u003eThe higher Hg:OC ratios in bottom sediment than in the source material is likely due to regenerative scavenging\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, a process allowing Hg associated to organic particles sinking in oxygenated water columns to be preferentially retained relative to carbon during remineralization\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). As a result of this process, the Hg:OC ratio in settling particles increases with depth in the water column\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, so that sediments from deepest marine environments tend to have greater Hg:OC ratios than sediments from shallow coastal zones. In the Arctic continental margin, about 94% of marine OC is remineralized before it reaches the sediments, and this is even more in the deep central AO\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. In comparison, terrigenous OC degradation is smaller than that of marine OC, but represents nevertheless about 35% of its total inputs\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e. There is greater remineralization of OC in water column and higher Hg:OC ratios in the central basins than in the continental margin, because of the greater transit time.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAlthough anthropogenic activities have resulted in significant Hg contamination in the AO\u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, the data presented here show that, once Hg reaches this ocean, its transport, distribution and fate are determined by the cycling of OC, in which terrigenous OC plays a more important role than in other oceans. Whereas remineralization of OC in the water column causes the Hg:OC ratio to increase with transit duration through the system, remineralization in suboxic sediment causes the Hg:OC ratio to remain constant, because Hg is released, likely through methylation and reductive demethylation (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The sedimentary record consequently fails to reveal anthropogenic Hg imprint. The strong connection between Hg and OC implies that any future change in organic carbon pathways could have strong effects on the transport and burial of Hg in this ocean.\u003c/p\u003e"},{"header":"Online Methods","content":"\u003cp\u003e\u003cstrong\u003eStudy area.\u0026nbsp;\u003c/strong\u003eThe cores analyzed for this study are from sub-regions of the NAAM where the water depth, primary production and proportions of terrestrial and marine OC in the sediments exhibit pronounced differences. Our spatial coverage encompasses the North Bering and Chukchi Seas, the Barrow Canyon, the Beaufort Sea margin, the Canadian Archipelago and Lancaster Sound, and the Davis Strait in Southern Baffin Bay (Fig. 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;The Bering and Chukchi Shelves receive nutrient-rich Pacific water and are highly productive environments, where the proportion of marine OC in the sediment is higher than that of terrestrial OC\u003cstrong\u003e\u003csup\u003e37,51\u0026nbsp;\u003c/sup\u003e\u003c/strong\u003e. At the eastern edge of the Chukchi Sea, the Barrow Canyon includes a regional hotspot of high productivity in its upper portion\u003cstrong\u003e\u003csup\u003e52\u0026nbsp;\u003c/sup\u003e\u003c/strong\u003e and accumulates bottom sediments with a high concentration of terrestrial OC\u003cstrong\u003e\u003csup\u003e27, 53\u0026nbsp;\u003c/sup\u003e\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePrimary production in the Beaufort Sea is as much as five times lower than that of the Chukchi Shelf\u003cstrong\u003e\u003csup\u003e54,55\u003c/sup\u003e\u003c/strong\u003e. A large amount of terrestrial OC from the Mackenzie River is deposited in this region\u003csup\u003e23,38\u003c/sup\u003e. Further to the East, the Canadian Arctic Archipelago and Lancaster Sound, which form together a complex shelf consisting of multiple channels, and the Davis Strait at the southern entrance of Baffin Bay, are also characterized by much lower rates of biological productivity\u003cstrong\u003e\u003csup\u003e55-57\u003c/sup\u003e\u003c/strong\u003e than that of the Chukchi Shelf, although autochthonous OC predominates in the sediments\u003cstrong\u003e\u003csup\u003e23\u003c/sup\u003e\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSampling.\u0026nbsp;\u003c/strong\u003eAs part of the Canadian research program of the International Polar Year, sediment box-cores were collected in the NAAM, from the Canadian Coast Guard Ships (CCGS) \u003cem\u003eSir Wilfrid Laurier\u003c/em\u003e and \u003cem\u003eLouis S. St-Laurent\u003c/em\u003e in 2007 and 2008, respectively\u003cstrong\u003e\u003csup\u003e58\u003c/sup\u003e\u003c/strong\u003e.\u0026nbsp;The geographical coordinates of the sampling locations and water depth at each site are reported in Table S2. Each core was sub-sampled on board in 0.5-cm intervals for the first 2 cm, 1-cm intervals from 2 to 10 cm depth, and then in progressively thicker layers of 2 and 3 cm down to the bottom of the cores, to a maximum depth of 45 cm. The outermost 2-3 cm of the 600 cm\u003csup\u003e2\u003c/sup\u003e sediment layers in contact with the core liner was discarded, and the sediment samples were stored in double plastic bags and kept frozen for subsequent analyses.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis.\u0026nbsp;\u003c/strong\u003eThe concentration of Hg in freeze-dried sediment samples was determined by gold amalgamation-atomic absorption spectroscopy, using a semi-automatic mercury analyzer (Milestone, DMA-80) and the US EPA standard protocol No. 7473 as a guide. Our analytical precision, appraised from replicate measurements (n=16) of the reference material MESS-3 (certified Hg concentration 91\u0026plusmn;9 ng g\u003csup\u003e-1\u003c/sup\u003e), was 8.5%, and the accuracy, expressed as recovery rate, 109%. For a 100-mg sediment aliquot the detection limit was ca. 1 ng g\u003csup\u003e-1\u003c/sup\u003e. We report the Hg concentrations on a dry weight basis, after correction for the salt content of the sediment approximated from the measured porosity of each sample and the salinity of the bottom water (~34 on the Practical Salinity Scale).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Our cores from NAAM had also been previously analyzed for other elements and isotopes through proven methodologies. The radioisotopes \u003csup\u003e210\u003c/sup\u003ePb and \u003csup\u003e226\u003c/sup\u003eRa were measured by non-destructive gamma spectroscopy\u003cstrong\u003e\u003csup\u003e53\u003c/sup\u003e\u003c/strong\u003e. \u0026nbsp;Measurements of OC were performed by high temperature combustion of pre-acidified samples, using an NC2500 Thermo Quest Elemental Analyzer, and OC isotopes (ẟ\u003csup\u003e13\u003c/sup\u003eC) by high temperature combustion, followed by isotope ratio mass spectrometry using a Carlo Erba 1500 Elemental Analyzer coupled to a ThermoQuest Delta Plus XP Mass Spectrometer\u003cstrong\u003e\u003csup\u003e23\u003c/sup\u003e\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Iron associated with poorly and well-crystallized oxyhydroxides (Fe\u003csub\u003eOX\u003c/sub\u003e), was determined through extraction with a sodium dithionite solution at pH ~4.7 and ICP-OES measurements\u003cstrong\u003e\u003csup\u003e26\u003c/sup\u003e\u003c/strong\u003e. Reduced sulphur (S\u003csub\u003eRED\u003c/sub\u003e), defined as the total sulphur contained in authigenic iron monosulfide (FeS) and pyrite (FeS\u003csub\u003e2\u003c/sub\u003e), was also operationally determined through successive leaching of sediment samples with HCl and Cr(II) solutions and subsequent colorimetric analysis\u003cstrong\u003e\u003csup\u003e27\u003c/sup\u003e\u003c/strong\u003e. The occurrence of S\u003csub\u003eRED\u0026nbsp;\u003c/sub\u003ein the\u003csub\u003e\u0026nbsp;\u003c/sub\u003esedimentary column indicates an anoxic condition under which sulphate reduction has been an active reaction.\u0026nbsp;\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eReferences\u003c/strong\u003e\u003c/p\u003e\n\u003col start=\"51\"\u003e\n \u003cli\u003eNaidu, A.S. et al. The continental margin of the North Bering Chukchi Seas : concentrations, sources, fluxes, accumulation and burial rates of organic carbon. 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Global trends in the nature of organic matter in river suspension, \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e322\u003c/strong\u003e, 436-438 (1988).\u003c/li\u003e\n \u003c/ol\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6457403/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6457403/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Mercury (Hg) contamination is a familiar concern in the Arctic. However, this study shows that variations of Hg concentration in 30 sediment cores collected across the North American Arctic Margin (NAAM) and in the deep central Arctic Ocean (AO) can be entirely explained by carbon sources and cycling. An apparent enrichment in Hg toward the sediment surface results from remineralization of organic carbon in the sediments, not from increased Hg flux. Hg values in AO sediments can be predicted with a high degree of confidence, based on three carbon sources with distinct Hg contents. Terrigenous organic carbon (OCTERR) dominates Hg delivery (80-95%) in the western NAAM, whereas inorganic carbon is the predominant carrier of Hg at many eastern NAAM sites (50-70%). Marine organic carbon (OCMAR) contributes \u003c20% of the total Hg concentrations. The sedimentary Hg:OCTERR and Hg:OCMAR endmembers are higher in the deep AO than in the NAAM, likely due to greater organic matter remineralization during transit through the system. We conclude that the interplay among sedimentary carbon sources governs the scavenging, transportation and sequestration of Hg, and that Hg variations with depth in the sediments result mainly from diagenesis, not from changes in the modern Hg flux.","manuscriptTitle":"Carbon dynamics control comtemporary mercury burial in Arctic Ocean sediments","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-23 08:50:10","doi":"10.21203/rs.3.rs-6457403/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"02243bcb-de0b-4d39-882a-4b1fb507e505","owner":[],"postedDate":"April 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":47292340,"name":"Earth and environmental sciences/Biogeochemistry/Element cycles"},{"id":47292341,"name":"Earth and environmental sciences/Ocean sciences/Marine chemistry"}],"tags":[],"updatedAt":"2026-01-10T08:13:41+00:00","versionOfRecord":{"articleIdentity":"rs-6457403","link":"https://doi.org/10.1038/s43247-025-03058-7","journal":{"identity":"communications-earth-and-environment","isVorOnly":false,"title":"Communications Earth \u0026 Environment"},"publishedOn":"2025-12-24 05:00:00","publishedOnDateReadable":"December 24th, 2025"},"versionCreatedAt":"2025-04-23 08:50:10","video":"","vorDoi":"10.1038/s43247-025-03058-7","vorDoiUrl":"https://doi.org/10.1038/s43247-025-03058-7","workflowStages":[]},"version":"v1","identity":"rs-6457403","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6457403","identity":"rs-6457403","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}