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Soluble iron conservation and colloidal iron dynamics in a hydrothermal plume

Soluble iron conservation and colloidal iron dynamics in a hydrothermal plume
Soluble iron conservation and colloidal iron dynamics in a hydrothermal plume
Iron (Fe) limits or co-limits primary productivity and nitrogen fixation in large regions of the world's oceans, and the supply of Fe from hydrothermal vents to the deep ocean is now known to be extensive. However, the mechanisms that control the amount of hydrothermal Fe that is stabilized in the deep ocean, and thus dictate the impact of hydrothermal Fe sources on surface ocean biogeochemistry, are unclear. To learn more, we have examined the dispersion of total dissolvable Fe (TDFe), dissolved Fe (dFe) and soluble Fe (sFe) in the buoyant and non-buoyant hydrothermal plume above the Beebe vent field, Caribbean Sea. We have also characterized plume particles using electron microscopy and synchrotron based spectromicroscopy.

We show that the majority of dFe in the Beebe hydrothermal plume was present as colloidal Fe (cFe = dFe − sFe). During ascent of the buoyant plume, a significant fraction of particulate Fe (pFe = TDFe − dFe) was lost to settling and exchange with colloids. Conversely, the opposite was observed in the non-buoyant plume, where pFe concentrations increased during non-buoyant plume dilution, cFe concentrations decreased apparently due to colloid aggregation. Elemental mapping of carbon, oxygen and iron in plume particles reveals their close association and indicates that exchanges of Fe between colloids and particles must include transformations of organic carbon and Fe oxyhydroxide minerals. Notably, sFe is largely conserved during plume dilution, and this is likely to be due to stabilization by organic ligands, in contrast to the more dynamic exchanges between pFe and cFe.

This study highlights that the size of the sFe stabilizing ligand pool, and the rate of iron-rich colloid aggregation will control the amount and physico-chemical composition of dFe supplied to the ocean interior from hydrothermal systems. Both the ligand pool, and the rate of cFe aggregation in hydrothermal plumes remain uncertain and determining these are important intermediate goals to more accurately assess the impact of hydrothermalism on the ocean's carbon cycle.

This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.
iron, colloids, nanoparticles, hydrothermal Beebe, Piccard
0009-2541
225-237
Lough, A.J.M.
64be5e9d-9ca2-438c-b566-cfee88ff1a37
Homoky, W.B.
39da18e9-28b8-42c4-8e17-2cb66af8ee4d
Connelly, D.P.
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Comer-Warner, S.A.
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Nakamura, K.
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Abyaneh, M.K.
d1a9900f-f558-4943-9af1-39c108441a51
Kaulich, B.
b71ae5fe-a6e0-43e1-8c58-9d9462f3fcb0
Mills, Rachel
a664f299-1a34-4b63-9988-1e599b756706
Lough, A.J.M.
64be5e9d-9ca2-438c-b566-cfee88ff1a37
Homoky, W.B.
39da18e9-28b8-42c4-8e17-2cb66af8ee4d
Connelly, D.P.
d49131bb-af38-4768-9953-7ae0b43e33c8
Comer-Warner, S.A.
0e0ab910-d429-4043-b480-28ba152480d2
Nakamura, K.
3788fb40-df62-428d-b81f-c46c4db0849d
Abyaneh, M.K.
d1a9900f-f558-4943-9af1-39c108441a51
Kaulich, B.
b71ae5fe-a6e0-43e1-8c58-9d9462f3fcb0
Mills, Rachel
a664f299-1a34-4b63-9988-1e599b756706

Lough, A.J.M., Homoky, W.B., Connelly, D.P., Comer-Warner, S.A., Nakamura, K., Abyaneh, M.K., Kaulich, B. and Mills, Rachel (2019) Soluble iron conservation and colloidal iron dynamics in a hydrothermal plume. Chemical Geology, 511, 225-237. (doi:10.1016/j.chemgeo.2019.01.001).

Record type: Article

Abstract

Iron (Fe) limits or co-limits primary productivity and nitrogen fixation in large regions of the world's oceans, and the supply of Fe from hydrothermal vents to the deep ocean is now known to be extensive. However, the mechanisms that control the amount of hydrothermal Fe that is stabilized in the deep ocean, and thus dictate the impact of hydrothermal Fe sources on surface ocean biogeochemistry, are unclear. To learn more, we have examined the dispersion of total dissolvable Fe (TDFe), dissolved Fe (dFe) and soluble Fe (sFe) in the buoyant and non-buoyant hydrothermal plume above the Beebe vent field, Caribbean Sea. We have also characterized plume particles using electron microscopy and synchrotron based spectromicroscopy.

We show that the majority of dFe in the Beebe hydrothermal plume was present as colloidal Fe (cFe = dFe − sFe). During ascent of the buoyant plume, a significant fraction of particulate Fe (pFe = TDFe − dFe) was lost to settling and exchange with colloids. Conversely, the opposite was observed in the non-buoyant plume, where pFe concentrations increased during non-buoyant plume dilution, cFe concentrations decreased apparently due to colloid aggregation. Elemental mapping of carbon, oxygen and iron in plume particles reveals their close association and indicates that exchanges of Fe between colloids and particles must include transformations of organic carbon and Fe oxyhydroxide minerals. Notably, sFe is largely conserved during plume dilution, and this is likely to be due to stabilization by organic ligands, in contrast to the more dynamic exchanges between pFe and cFe.

This study highlights that the size of the sFe stabilizing ligand pool, and the rate of iron-rich colloid aggregation will control the amount and physico-chemical composition of dFe supplied to the ocean interior from hydrothermal systems. Both the ligand pool, and the rate of cFe aggregation in hydrothermal plumes remain uncertain and determining these are important intermediate goals to more accurately assess the impact of hydrothermalism on the ocean's carbon cycle.

This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

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Soluble iron conservation and colloidal iron dynamics in a hydrothermal plume - Accepted Manuscript
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More information

Accepted/In Press date: 7 January 2019
e-pub ahead of print date: 10 January 2019
Published date: 20 April 2019
Keywords: iron, colloids, nanoparticles, hydrothermal Beebe, Piccard

Identifiers

Local EPrints ID: 427937
URI: http://eprints.soton.ac.uk/id/eprint/427937
ISSN: 0009-2541
PURE UUID: 6fdaddcb-ac80-478f-b01b-39cd76a5b88c
ORCID for Rachel Mills: ORCID iD orcid.org/0000-0002-9811-246X

Catalogue record

Date deposited: 05 Feb 2019 17:30
Last modified: 18 Feb 2021 16:42

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