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Behavior of iron isotopes in hydrothermal systems: Beebe and Von Damm vent fields on the Mid-Cayman ultraslow-spreading ridge

Behavior of iron isotopes in hydrothermal systems: Beebe and Von Damm vent fields on the Mid-Cayman ultraslow-spreading ridge
Behavior of iron isotopes in hydrothermal systems: Beebe and Von Damm vent fields on the Mid-Cayman ultraslow-spreading ridge
It is now clear that, in some parts of the ocean, inputs of hydrothermal iron (Fe) can make a more significant contribution to the Fe inventory than previously thought. While the Fe isotopic signature of seawater has proved useful for distinguishing between inputs of Fe from atmospheric deposition and seafloor sediments, the Fe isotope signature of hydrothermal vent fluids may change during mixing of vent fluids and seawater. To better constrain the processes leading to these changes, the Fe isotopic compositions (δ56Fe) of dissolved and total dissolvable Fe have been determined in high temperature vent fluids and the buoyant hydrothermal plumes at the Beebe and the Von Damm vent fields, which are located along the ultraslow Mid-Cayman spreading center in the Caribbean Sea.
Our results show that the δ56Fe value of dissolved Fe in the earliest stages of buoyant plume formation was lower (as low as −4.08‰) than measured in a high temperature, low-Mg, vent fluid sample (−0.28‰). This indicates that the iron isotopic signature of dissolved Fe is principally controlled by oxidation of Fe(II) and precipitation of Fe-(oxyhydr)oxides that preferentially incorporate heavy Fe isotopes. In support of this, the δ56Fe value of labile particulate Fe was higher than the δ56Fe value of dissolved Fe. Nevertheless, at Beebe, the δ56Fe value of total dissolvable Fe increased as the proportion of Fe predicted to have been lost from the plume increased, consistent with preferential fall-out of Fe-sulfides that are enriched in light Fe isotopes. The very low δ56Fe values of dissolved Fe in the Beebe buoyant plume are consistent with (i) the high Fe/H2S ratio of the vent fluids, and (ii) high Fe(II) oxidation rates, relative to other vent sites.
Beebe, Von Damm, hydrothermal plumes, iron isotopes, vent fluids
0012-821X
Wang, Wenhao
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Lough, Alastair
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Lohan, Maeve
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Connelly, Douglas
d49131bb-af38-4768-9953-7ae0b43e33c8
Cooper, Matthew
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Milton, J. Andy
b9b65fba-a6fe-4eb3-afc7-641a98ac6383
Chavagnac, Valérie
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Castillo, Alain
527a5a5f-f364-4e00-8e46-29c3ee7fdd3f
James, Rachael
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Wang, Wenhao
b68f5405-54ec-4ff1-b600-044fabaa8909
Lough, Alastair
322ad339-e43e-455f-9140-47e7d9638ed5
Lohan, Maeve
6ca10597-2d0f-40e8-8e4f-7619dfac5088
Connelly, Douglas
d49131bb-af38-4768-9953-7ae0b43e33c8
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Milton, J. Andy
b9b65fba-a6fe-4eb3-afc7-641a98ac6383
Chavagnac, Valérie
2beb897f-660c-4a91-a57e-16a05a638dc8
Castillo, Alain
527a5a5f-f364-4e00-8e46-29c3ee7fdd3f
James, Rachael
79aa1d5c-675d-4ba3-85be-fb20798c02f4

Wang, Wenhao, Lough, Alastair, Lohan, Maeve, Connelly, Douglas, Cooper, Matthew, Milton, J. Andy, Chavagnac, Valérie, Castillo, Alain and James, Rachael (2021) Behavior of iron isotopes in hydrothermal systems: Beebe and Von Damm vent fields on the Mid-Cayman ultraslow-spreading ridge. Earth and Planetary Science Letters, 575, [117200]. (doi:10.1016/j.epsl.2021.117200).

Record type: Article

Abstract

It is now clear that, in some parts of the ocean, inputs of hydrothermal iron (Fe) can make a more significant contribution to the Fe inventory than previously thought. While the Fe isotopic signature of seawater has proved useful for distinguishing between inputs of Fe from atmospheric deposition and seafloor sediments, the Fe isotope signature of hydrothermal vent fluids may change during mixing of vent fluids and seawater. To better constrain the processes leading to these changes, the Fe isotopic compositions (δ56Fe) of dissolved and total dissolvable Fe have been determined in high temperature vent fluids and the buoyant hydrothermal plumes at the Beebe and the Von Damm vent fields, which are located along the ultraslow Mid-Cayman spreading center in the Caribbean Sea.
Our results show that the δ56Fe value of dissolved Fe in the earliest stages of buoyant plume formation was lower (as low as −4.08‰) than measured in a high temperature, low-Mg, vent fluid sample (−0.28‰). This indicates that the iron isotopic signature of dissolved Fe is principally controlled by oxidation of Fe(II) and precipitation of Fe-(oxyhydr)oxides that preferentially incorporate heavy Fe isotopes. In support of this, the δ56Fe value of labile particulate Fe was higher than the δ56Fe value of dissolved Fe. Nevertheless, at Beebe, the δ56Fe value of total dissolvable Fe increased as the proportion of Fe predicted to have been lost from the plume increased, consistent with preferential fall-out of Fe-sulfides that are enriched in light Fe isotopes. The very low δ56Fe values of dissolved Fe in the Beebe buoyant plume are consistent with (i) the high Fe/H2S ratio of the vent fluids, and (ii) high Fe(II) oxidation rates, relative to other vent sites.

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Accepted/In Press date: 5 September 2021
e-pub ahead of print date: 23 September 2021
Keywords: Beebe, Von Damm, hydrothermal plumes, iron isotopes, vent fluids

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Local EPrints ID: 451439
URI: http://eprints.soton.ac.uk/id/eprint/451439
ISSN: 0012-821X
PURE UUID: e373c13b-7d69-477c-b62b-0cd5928c8054
ORCID for Wenhao Wang: ORCID iD orcid.org/0000-0003-4198-6681
ORCID for Maeve Lohan: ORCID iD orcid.org/0000-0002-5340-3108
ORCID for Matthew Cooper: ORCID iD orcid.org/0000-0002-2130-2759
ORCID for Rachael James: ORCID iD orcid.org/0000-0001-7402-2315

Catalogue record

Date deposited: 27 Sep 2021 16:33
Last modified: 26 Nov 2021 03:00

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Contributors

Author: Wenhao Wang ORCID iD
Author: Alastair Lough
Author: Maeve Lohan ORCID iD
Author: Douglas Connelly
Author: Matthew Cooper ORCID iD
Author: J. Andy Milton
Author: Valérie Chavagnac
Author: Alain Castillo
Author: Rachael James ORCID iD

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