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. p. 118016. ISSN 0012-821X
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Tephra Fe isotopes_Longman_2022_Revised_vFinal2.pdf - Accepted Version Available under License Creative Commons Attribution Non-commercial No Derivatives 4.0. Download (629kB) | Preview |
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 (δ56Fe) 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 δ56Fe (relative to standard IRMM-524a) compositions (down to −0.26 ± 0.04‰, 2SD) than fresh tephra deposited in Montserrat (δ56Fe = 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 δ56Fe of 0.21 ± 0.31‰, 2SD, n = 12) during non-reductive dissolution of tephra as the likely cause of the retention of these light δ56Fe 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.
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| 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. |
| Uncontrolled Keywords: | biogeochemistry, Fe cycle, Fe isotopes, tephra, volcanism |
| Subjects: | F700 Ocean Sciences |
| Department: | Faculties > Engineering and Environment > Geography and Environmental Sciences |
| Depositing User: | John Coen |
| Date Deposited: | 15 Feb 2023 11:20 |
| Last Modified: | 06 Feb 2024 03:30 |
| URI: | https://nrl.northumbria.ac.uk/id/eprint/51408 |
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