Fractionation of iron and chromium isotopes in hydrothermal plumes from the northern Mid-Atlantic Ridge
Fractionation of iron and chromium isotopes in hydrothermal plumes from the northern Mid-Atlantic Ridge
Hydrothermal venting impacts the global-scale biogeochemical cycles of many trace metals and their isotopes. Processes in hydrothermal plumes regulate the dispersal of vent-derived metals and may vary in response to differences in the geologic setting of vent fields and/or the geochemistry of the overlying ocean water. Here we present results of analyses of dissolved Fe and Cr concentrations, and dissolved Fe isotope (δ56Fe) and Cr isotope (δ53Cr) distributions, in seawater samples collected from above TAG and Rainbow vent sites on the Mid-Atlantic Ridge during the GEOTRACES GA13 cruise. We show that profiles of dissolved Fe and Cr isotopes through the near-field hydrothermal plumes are the mirror image of each other. Oxidation of Fe(II) and precipitation of Fe-(oxyhydr)oxides account for the low δ56Fe values of dissolved Fe, as low as −1.83‰ at TAG and −6.94‰ at Rainbow. Plume samples with low δ56Fe values are associated with elevated δ53Cr values of dissolved Cr compared to background seawater (by up to +0.14‰ and +0.69‰ at TAG and Rainbow, respectively), while particulate Cr is characterised by relatively low δ53Cr values (−1.02 to −1.22‰). This striking result suggests that seawater Cr(VI) is reduced to Cr(III) and precipitates on the surface of Fe(III) particles within the hydrothermal plume. Reduction of Cr(VI) and scavenging of Cr(III) by plume Fe-(oxyhydr)oxide particles mean that high-temperature hydrothermal systems are likely a net sink for seawater Cr at Rainbow (and also at TAG). As the removal flux of Cr is related to the flux of hydrothermal Fe(II) and the rate of Fe(II) oxidation in the hydrothermal plume, it may (i) vary across vent sites at a global scale and (ii) change over glacial-interglacial cycles.
Wang, Wenhao
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Lough, Alastair J.M.
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Goring-Harford, Heather
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Flanagan, Oli
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Gonzalez-Santana, David
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Resing, Joseph
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Connelly, Douglas
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Lohan, Maeve C.
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Tagliabue, Alessandro
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James, Rachael H.
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Wang, Wenhao
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Lough, Alastair J.M.
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Goring-Harford, Heather
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Flanagan, Oli
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Gonzalez-Santana, David
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Resing, Joseph
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Connelly, Douglas
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Lohan, Maeve C.
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Tagliabue, Alessandro
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James, Rachael H.
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Wang, Wenhao, Lough, Alastair J.M., Goring-Harford, Heather, Flanagan, Oli, Gonzalez-Santana, David, Resing, Joseph, Connelly, Douglas, Lohan, Maeve C., Tagliabue, Alessandro and James, Rachael H.
(2023)
Fractionation of iron and chromium isotopes in hydrothermal plumes from the northern Mid-Atlantic Ridge.
Earth and Planetary Science Letters.
(In Press)
Abstract
Hydrothermal venting impacts the global-scale biogeochemical cycles of many trace metals and their isotopes. Processes in hydrothermal plumes regulate the dispersal of vent-derived metals and may vary in response to differences in the geologic setting of vent fields and/or the geochemistry of the overlying ocean water. Here we present results of analyses of dissolved Fe and Cr concentrations, and dissolved Fe isotope (δ56Fe) and Cr isotope (δ53Cr) distributions, in seawater samples collected from above TAG and Rainbow vent sites on the Mid-Atlantic Ridge during the GEOTRACES GA13 cruise. We show that profiles of dissolved Fe and Cr isotopes through the near-field hydrothermal plumes are the mirror image of each other. Oxidation of Fe(II) and precipitation of Fe-(oxyhydr)oxides account for the low δ56Fe values of dissolved Fe, as low as −1.83‰ at TAG and −6.94‰ at Rainbow. Plume samples with low δ56Fe values are associated with elevated δ53Cr values of dissolved Cr compared to background seawater (by up to +0.14‰ and +0.69‰ at TAG and Rainbow, respectively), while particulate Cr is characterised by relatively low δ53Cr values (−1.02 to −1.22‰). This striking result suggests that seawater Cr(VI) is reduced to Cr(III) and precipitates on the surface of Fe(III) particles within the hydrothermal plume. Reduction of Cr(VI) and scavenging of Cr(III) by plume Fe-(oxyhydr)oxide particles mean that high-temperature hydrothermal systems are likely a net sink for seawater Cr at Rainbow (and also at TAG). As the removal flux of Cr is related to the flux of hydrothermal Fe(II) and the rate of Fe(II) oxidation in the hydrothermal plume, it may (i) vary across vent sites at a global scale and (ii) change over glacial-interglacial cycles.
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Wang et al Accepted
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More information
Accepted/In Press date: 27 October 2023
Additional Information:
OF was funded by a NERC-INSPIRE PhD award 538 (NE/S007210/1). DGS received funding from ISblue project, Interdisciplinary graduate school for 539 the blue planet (ANR-17-EURE-0015), and from the French government under the program
540 ‘Investissements d’Avenir’.
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Local EPrints ID: 483571
URI: http://eprints.soton.ac.uk/id/eprint/483571
ISSN: 0012-821X
PURE UUID: 364ec44d-889f-414a-a128-f8bae1dd938d
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Date deposited: 01 Nov 2023 18:02
Last modified: 18 Mar 2024 05:01
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Contributors
Author:
Wenhao Wang
Author:
Alastair J.M. Lough
Author:
Oli Flanagan
Author:
David Gonzalez-Santana
Author:
Joseph Resing
Author:
Douglas Connelly
Author:
Alessandro Tagliabue
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