Release of tephra-hosted iron during early diagenesis fingerprinted by iron isotopes
Release of tephra-hosted iron during early diagenesis fingerprinted by iron isotopes
The micronutrient iron (Fe) plays a fundamental role controlling primary productivity in the upper ocean, with volcanic eruptions and deposition of airborne volcanic material (termed tephra) a potential source of Fe. Here, we investigate the geochemical and Fe isotopic (δ 56Fe) composition of tephra layers, sediments, and mixed tephra-sediment samples from the Integrated Ocean Drilling Program (IODP) Hole 1396C, located offshore the volcanically active island of Montserrat in the Lesser Antilles, Caribbean Sea. We find that buried tephras, which have experienced diagenesis, exhibit lighter δ 56Fe (relative to standard IRMM-524a) compositions (down to −0.26 ± 0.04‰, 2SD) than fresh tephra deposited in Montserrat (δ 56Fe = 0.02 ± 0.02‰, 2SD). Such negative values suggest that isotopically heavier Fe has been lost from the originally deposited material. Using multivariate statistical modelling and mass balance constraints, we identify the outward Fe flux (with calculated δ 56Fe of 0.21 ± 0.31‰, 2SD, n = 12) during non-reductive dissolution of tephra as the likely cause of the retention of these light δ 56Fe compositions. Due to the widespread nature of tephra deposition, tephra diagenesis may provide an important source of isotopically heavy dissolved Fe (dFe) to the oceans. This process contrasts with more commonly considered reductive dissolution processes, which provide a source of dFe enriched in light isotopes to the oceans.
Fe cycle, Fe isotopes, biogeochemistry, tephra, volcanism
Longman, Jack
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Dunlea, Ann G.
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Böning, Philipp
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Palmer, Martin R.
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Gernon, Thomas M.
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McManus, James
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Manners, Hayley R.
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Homoky, William B.
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Pahnke, Katharina
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1 March 2023
Longman, Jack
84e3d567-8575-477e-8d2f-5b21a1c709e4
Dunlea, Ann G.
70cc69ca-ffb9-414e-a6ea-749008949c01
Böning, Philipp
06f11a20-b185-4c67-ae35-f2c50d2a36d1
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Gernon, Thomas M.
658041a0-fdd1-4516-85f4-98895a39235e
McManus, James
2eefd888-eea8-46df-bf71-202bf70b49f8
Manners, Hayley R.
98c78033-549b-4c25-922c-bb080651240c
Homoky, William B.
f47c433a-bd13-4a11-88eb-96fa1a798ca3
Pahnke, Katharina
7745025d-b534-4731-bfa6-d4d45300d0ff
Longman, Jack, Dunlea, Ann G., Böning, Philipp, Palmer, Martin R., Gernon, Thomas M., McManus, James, Manners, Hayley R., Homoky, William B. and Pahnke, Katharina
(2023)
Release of tephra-hosted iron during early diagenesis fingerprinted by iron isotopes.
Earth and Planetary Science Letters, 605, [118016].
(doi:10.1016/j.epsl.2023.118016).
Abstract
The micronutrient iron (Fe) plays a fundamental role controlling primary productivity in the upper ocean, with volcanic eruptions and deposition of airborne volcanic material (termed tephra) a potential source of Fe. Here, we investigate the geochemical and Fe isotopic (δ 56Fe) composition of tephra layers, sediments, and mixed tephra-sediment samples from the Integrated Ocean Drilling Program (IODP) Hole 1396C, located offshore the volcanically active island of Montserrat in the Lesser Antilles, Caribbean Sea. We find that buried tephras, which have experienced diagenesis, exhibit lighter δ 56Fe (relative to standard IRMM-524a) compositions (down to −0.26 ± 0.04‰, 2SD) than fresh tephra deposited in Montserrat (δ 56Fe = 0.02 ± 0.02‰, 2SD). Such negative values suggest that isotopically heavier Fe has been lost from the originally deposited material. Using multivariate statistical modelling and mass balance constraints, we identify the outward Fe flux (with calculated δ 56Fe of 0.21 ± 0.31‰, 2SD, n = 12) during non-reductive dissolution of tephra as the likely cause of the retention of these light δ 56Fe compositions. Due to the widespread nature of tephra deposition, tephra diagenesis may provide an important source of isotopically heavy dissolved Fe (dFe) to the oceans. This process contrasts with more commonly considered reductive dissolution processes, which provide a source of dFe enriched in light isotopes to the oceans.
Text
Longman 2023
- Accepted Manuscript
More information
Accepted/In Press date: 16 January 2023
e-pub ahead of print date: 6 February 2023
Published date: 1 March 2023
Additional Information:
Funding Information:
This manuscript used samples provided by the Integrated Ocean Drilling Program (IODP) from Expedition 340. IODP is sponsored by the U.S. National Science Foundation (NSF). The authors are grateful to the co-chief scientists A. Le Friant and O. Ishizuka of Expedition 340 as well as all the participants in the expedition for their contributions to the sea-going effort. Appreciation is extended to Jesse Muratli at Oregon State University for his work in the laboratory. Financial support was provided by the United States Science Support Program (USSSP) and the US National Science Foundation to JM under grant Numbers 1360077 and 1715106 for shore-based analyses. MRP and TG acknowledge NERC grant NE/K00543X/1 .
Publisher Copyright:
© 2023 Elsevier B.V.
Keywords:
Fe cycle, Fe isotopes, biogeochemistry, tephra, volcanism
Identifiers
Local EPrints ID: 476565
URI: http://eprints.soton.ac.uk/id/eprint/476565
ISSN: 0012-821X
PURE UUID: b248446e-a071-4bf9-b5bc-ca07a8701767
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Date deposited: 09 May 2023 16:30
Last modified: 17 Mar 2024 03:21
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Contributors
Author:
Jack Longman
Author:
Ann G. Dunlea
Author:
Philipp Böning
Author:
James McManus
Author:
Hayley R. Manners
Author:
William B. Homoky
Author:
Katharina Pahnke
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