The cycling of iron, zinc and cadmium in the North East Pacific Ocean – Insights from stable isotopes

Conway, Tim M.; John, Seth G.

doi:10.1016/j.gca.2015.05.023

Cited by 152 publications

(155 citation statements)

References 95 publications

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“…Although the concentrations of CH 3 Hg in our experiments exceed the concentrations found in marine waters, our ratio of CH 3 Hg to sulfide mineral surface area are similar to the ratio expected on particles or inside planktonic cells present in the ocean. For example, for the low oxygen waters in the North Atlantic, where observed concentration of particulate Cd has been assumed to mainly be composed of CdS (s) , calculated particulate CH 3 Hg:Cd is about 10 −3 (molar basis)3435. Furthermore, inside planktonic cells the molar CH 3 Hg:Fe ratio of 10 −3 to 10 −4 is typically found but the expected CH 3 Hg:FeS is lower given that not all intracelleular Fe would occur as FeS-clusters83637.…”

Section: Resultsmentioning

confidence: 99%

Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces

Jonsson

Mazrui

Mason

2016

Sci Rep

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Underlying formation pathways of dimethylmercury ((CH3)2Hg) in the ocean are unknown. Early work proposed reactions of inorganic Hg (HgII) with methyl cobalamin or of dissolved monomethylmercury (CH3Hg) with hydrogen sulfide as possible bacterial mediated or abiotic pathways. A significant fraction (up to 90%) of CH3Hg in natural waters is however adsorbed to reduced sulfur groups on mineral or organic surfaces. We show that binding of CH3Hg to such reactive sites facilitates the formation of (CH3)2Hg by degradation of the adsorbed CH3Hg. We demonstrate that the reaction can be mediated by different sulfide minerals, as well as by dithiols suggesting that e.g. reduced sulfur groups on mineral particles or on protein surfaces could mediate the reaction. The observed fraction of CH3Hg methylated on sulfide mineral surfaces exceeded previously observed methylation rates of CH3Hg to (CH3)2Hg in seawaters and we suggest the pathway demonstrated here could account for much of the (CH3)2Hg found in the ocean.

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Section: Resultsmentioning

confidence: 99%

Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces

Jonsson

Mazrui

Mason

2016

Sci Rep

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“…This is confirmed by Köbberich and Vance (), who found that extremely low Zn uptake rate could result in the enrichment of isotopically heavy Zn in diatom, but more rapid Zn uptake rate did not produce Zn isotope fractionation between diatom and the external free Zn pool. Recently, the GEOTRACES investigation demonstrated either invariant or decreasing δ 66 Zn values toward the surface in modern ocean (Conway & John, , ; Zhao et al, ), which may also suggest no net Zn isotope fractionation when Zn is fixed into a diatom opal (Archer et al, ; Zhao et al, ), or the adsorption of heavy Zn isotope on organic particle surface (John & Conway, ; Köbberich & Vance, ). Other experiments have suggested that lighter Zn isotopes are preferred in diatom cell (Δ 66 Zn cell‐solution = −0.80‰ to −0.2‰), but heavier Zn isotopes are preferred on cell or organic particle surface during adsorption (Gélabert et al, ; John et al, ; John & Conway, ).…”

Section: Discussionmentioning

confidence: 99%

“…It has a short residence time (11,000 years) and a total mass of 1.35 × 10 21 kg in global oceans (Little, Vance, et al, ). The surface seawater is characterized by depletion of dissolved Zn and strongly variable Zn isotope compositions (Conway & John, ; John & Conway, ; Samanta et al, ). These variations in δ 66 Zn values could be associated with complexation with organic ligands (Jouvin et al, ), biological uptake (John et al, ; Samanta et al, ), particle scavenging (John & Conway, ), and input from river and aerosols (John & Conway, ; Little, Sherman, et al, ).…”

Section: Introductionmentioning

confidence: 99%

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

et al. 2018

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During the early Ediacaran, there was a large influx of phosphorus into the oceans and a resultant high phosphorus concentration in seawater, where multicellular eukaryotes may have been the primary type of marine productivity. The eukaryotes could play a critical role in regulating Zn cycling and isotopes. To establish Zn geochemical cycling patterns in the phosphorus‐rich ocean, this study investigates Zn isotopic signatures of shallow water phosphorite that contains phosphatized microfossils (Weng'an biota) and deep‐water shale from the Doushantuo Formation. Our results indicate that phosphorite commonly preserves heavier Zn isotope composition, with an average of 0.80‰. The positive δ66Zn values in phosphorites may be ascribed to Zn isotope fractionation associated with the complexation of Zn with phosphate and the adsorption of isotopically heavy Zn onto Fe‐Mn oxides and organism's surfaces. We argue that phosphorite may represent an important sink of isotopically heavy Zn in a phosphorus‐rich ocean during Earth history. Meanwhile, deep‐water organic‐rich shale shows an enrichment of isotopically light Zn with an average of 0.23‰, which may be attributed to sulfide precipitation in mid‐depth environment. The organic‐rich shale may represent an isotopically light Zn sink. In addition, the highest δ66Zn value (0.45‰) in a euxinic black shale may indicate that Zn isotope signal of anoxic deep water is similar to that of modern deep seawater. If that is the case, it suggests that Zn geochemical cycling in the early Ediacaran oceans was similar to that of modern oceans.

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“…Given the interaction of Cd with the biological cycle, one may also look for relations of δ 114 Cd with the major nutrients in surface waters. For the same δ 114 Cd dataset these relationships are listed in (Conway and John, 2015b). Here it also would be interesting to look for nitrate deficits versus phosphate due to nitrate reduction, as an indicator of the reductive intensity of OMZ conditions (e.g.…”

Section: Interactions With Major Nutrientsmentioning

confidence: 99%

Interactions of dissolved CO2 with cadmium isotopes in the Southern Ocean

et al. 2017

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A B S T R A C THere we report the first ever observations of a strong correlation in ocean surface waters of the dissolved δ 114 Cd with dissolved CO 2 . This is observed in the Southern Ocean along the 0°W meridian in both and its conversion to CO 2 . For this the algae need more enzyme carbonic anhydrase that normally has Zn as its co-factor, but Cd may substitute for Zn and there also are Cd-specific carbonic anhydrases known for some phytoplankton species. Indeed in incubations of the local plankton communities it is shown that the phytoplankton have a very strong preferential uptake of CO 2 , such that the uptake ratio { seawater. Future research of local phytoplankton in unperturbed natural waters of the Southern Ocean is recommended to be able to verify the hypothesis of a function of Cd in carbonic anhydrase in Antarctic phytoplankton.

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The cycling of iron, zinc and cadmium in the North East Pacific Ocean – Insights from stable isotopes

Cited by 152 publications

References 95 publications

Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces

Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

Interactions of dissolved CO2 with cadmium isotopes in the Southern Ocean

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