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Fitzsimmons JN, Conway TM. Novel Insights into Marine Iron Biogeochemistry from Iron Isotopes. ANNUAL REVIEW OF MARINE SCIENCE 2023; 15:383-406. [PMID: 36100217 DOI: 10.1146/annurev-marine-032822-103431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The micronutrient iron plays a major role in setting the magnitude and distribution of primary production across the global ocean. As such, an understanding of the sources, sinks, and internal cycling processes that drive the oceanic distribution of iron is key to unlocking iron's role in the global carbon cycle and climate, both today and in the geologic past. Iron isotopic analyses of seawater have emerged as a transformative tool for diagnosing iron sources to the ocean and tracing biogeochemical processes. In this review, we summarize the end-member isotope signatures of different iron source fluxes and highlight the novel insights into iron provenance gained using this tracer. We also review ways in which iron isotope fractionation might be used to understand internal oceanic cycling of iron, including speciation changes, biological uptake, and particle scavenging. We conclude with an overview of future research needed to expand the utilization of this cutting-edge tracer.
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Affiliation(s)
| | - Tim M Conway
- College of Marine Science, University of South Florida, St. Petersburg, Florida, USA;
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2
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König D, Conway TM, Hamilton DS, Tagliabue A. Surface Ocean Biogeochemistry Regulates the Impact of Anthropogenic Aerosol Fe Deposition on the Cycling of Iron and Iron Isotopes in the North Pacific. GEOPHYSICAL RESEARCH LETTERS 2022; 49:e2022GL098016. [PMID: 36245954 PMCID: PMC9539696 DOI: 10.1029/2022gl098016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 06/09/2022] [Accepted: 06/20/2022] [Indexed: 06/16/2023]
Abstract
Distinctively-light isotopic signatures associated with Fe released from anthropogenic activity have been used to trace basin-scale impacts. However, this approach is complicated by the way Fe cycle processes modulate oceanic dissolved Fe (dFe) signatures (δ56Fediss) post deposition. Here we include dust, wildfire, and anthropogenic aerosol Fe deposition in a global ocean biogeochemical model with active Fe isotope cycling, to quantify how anthropogenic Fe impacts surface ocean dFe and δ56Fediss. Using the North Pacific as a natural laboratory, the response of dFe, δ56Fediss, and primary productivity are spatially and seasonally variable and do not simply follow the footprint of atmospheric deposition. Instead, the effect of anthropogenic Fe is regulated by the biogeochemical regime, specifically the degree of Fe limitation and rates of primary production. Overall, we find that while δ56Fediss does trace anthropogenic input, the response is muted by fractionation during phytoplankton uptake, but amplified by other isotopically-light Fe sources.
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Affiliation(s)
- D. König
- School of Environmental SciencesUniversity of LiverpoolLiverpoolUK
| | - T. M. Conway
- College of Marine ScienceUniversity of South FloridaSt PetersburgFLUSA
| | - D. S. Hamilton
- Department of Earth and Atmospheric ScienceCornell UniversityIthacaNYUSA
| | - A. Tagliabue
- School of Environmental SciencesUniversity of LiverpoolLiverpoolUK
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König D, Conway TM, Ellwood MJ, Homoky WB, Tagliabue A. Constraints on the Cycling of Iron Isotopes From a Global Ocean Model. GLOBAL BIOGEOCHEMICAL CYCLES 2021; 35:e2021GB006968. [PMID: 35860342 PMCID: PMC9285799 DOI: 10.1029/2021gb006968] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 08/05/2021] [Accepted: 08/11/2021] [Indexed: 06/15/2023]
Abstract
Although iron (Fe) is a key regulator of primary production over much of the ocean, many components of the marine iron cycle are poorly constrained, which undermines our understanding of climate change impacts. In recent years, a growing number of studies (often part of GEOTRACES) have used Fe isotopic signatures (δ56Fe) to disentangle different aspects of the marine Fe cycle. Characteristic δ56Fe endmembers of external sources and assumed isotopic fractionation during biological Fe uptake or recycling have been used to estimate relative source contributions and investigate internal transformations, respectively. However, different external sources and fractionation processes often overlap and act simultaneously, complicating the interpretation of oceanic Fe isotope observations. Here we investigate the driving forces behind the marine dissolved Fe isotopic signature (δ56Fediss) distribution by incorporating Fe isotopes into the global ocean biogeochemical model PISCES. We find that distinct external source endmembers acting alongside fractionation during organic complexation and phytoplankton uptake are required to reproduce δ56Fediss observations along GEOTRACES transects. δ56Fediss distributions through the water column result from regional imbalances of remineralization and abiotic removal processes. They modify δ56Fediss directly and transfer surface ocean signals to the interior with opposing effects. Although attributing crustal compositions to sedimentary Fe sources in regions with low organic carbon fluxes improves our isotope model, δ56Fediss signals from hydrothermal or sediment sources cannot be reproduced accurately by simply adjusting δ56Fe endmember values. This highlights that additional processes must govern the exchange and/or speciation of Fe supplied by these sources to the ocean.
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Affiliation(s)
- D. König
- School of Environmental SciencesUniversity of LiverpoolLiverpoolUK
| | - T. M. Conway
- College of Marine ScienceUniversity of South FloridaSt PetersburgFLUSA
| | - M. J. Ellwood
- Research School of Earth SciencesAustralian National UniversityCanberraACTAustralia
| | - W. B. Homoky
- School of Earth and EnvironmentUniversity of LeedsLeedsUK
| | - A. Tagliabue
- School of Environmental SciencesUniversity of LiverpoolLiverpoolUK
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4
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Abstract
Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a "rusty source") that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.
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Laufer-Meiser K, Michaud AB, Maisch M, Byrne JM, Kappler A, Patterson MO, Røy H, Jørgensen BB. Potentially bioavailable iron produced through benthic cycling in glaciated Arctic fjords of Svalbard. Nat Commun 2021; 12:1349. [PMID: 33649339 PMCID: PMC7921405 DOI: 10.1038/s41467-021-21558-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 01/28/2021] [Indexed: 01/31/2023] Open
Abstract
The Arctic has the highest warming rates on Earth. Glaciated fjord ecosystems, which are hotspots of carbon cycling and burial, are extremely sensitive to this warming. Glaciers are important for the transport of iron from land to sea and supply this essential nutrient to phytoplankton in high-latitude marine ecosystems. However, up to 95% of the glacially-sourced iron settles to sediments close to the glacial source. Our data show that while 0.6-12% of the total glacially-sourced iron is potentially bioavailable, biogeochemical cycling in Arctic fjord sediments converts the glacially-derived iron into more labile phases, generating up to a 9-fold increase in the amount of potentially bioavailable iron. Arctic fjord sediments are thus an important source of potentially bioavailable iron. However, our data suggests that as glaciers retreat onto land the flux of iron to the sediment-water interface may be reduced. Glacial retreat therefore likely impacts iron cycling in coastal marine ecosystems.
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Affiliation(s)
- Katja Laufer-Meiser
- grid.7048.b0000 0001 1956 2722Center for Geomicrobiology, Department of Biology, Aarhus University, Aarhus, Denmark ,grid.15649.3f0000 0000 9056 9663Present Address: GEOMAR, Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
| | - Alexander B. Michaud
- grid.7048.b0000 0001 1956 2722Center for Geomicrobiology, Department of Biology, Aarhus University, Aarhus, Denmark ,grid.296275.d0000 0000 9516 4913Present Address: Bigelow Laboratory for Ocean Sciences, Maine, USA
| | - Markus Maisch
- grid.10392.390000 0001 2190 1447Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
| | - James M. Byrne
- grid.10392.390000 0001 2190 1447Center for Applied Geosciences, University of Tübingen, Tübingen, Germany ,grid.5337.20000 0004 1936 7603Present Address: School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol, UK
| | - Andreas Kappler
- grid.10392.390000 0001 2190 1447Center for Applied Geosciences, University of Tübingen, Tübingen, Germany ,grid.15649.3f0000 0000 9056 9663Present Address: GEOMAR, Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
| | - Molly O. Patterson
- grid.264260.40000 0001 2164 4508Department of Geological Sciences and Environmental Studies, Binghamton University, New York, USA
| | - Hans Røy
- grid.7048.b0000 0001 1956 2722Center for Geomicrobiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Bo Barker Jørgensen
- grid.7048.b0000 0001 1956 2722Center for Geomicrobiology, Department of Biology, Aarhus University, Aarhus, Denmark
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Anderson RF. GEOTRACES: Accelerating Research on the Marine Biogeochemical Cycles of Trace Elements and Their Isotopes. ANNUAL REVIEW OF MARINE SCIENCE 2020; 12:49-85. [PMID: 31337253 DOI: 10.1146/annurev-marine-010318-095123] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The biogeochemical cycles of trace elements and their isotopes (TEIs) constitute an active area of oceanographic research due to their role as essential nutrients for marine organisms and their use as tracers of oceanographic processes. Selected TEIs also provide diagnostic information about the physical, geological, and chemical processes that supply or remove solutes in the ocean. Many of these same TEIs provide information about ocean conditions in the past, as their imprint on marine sediments can be interpreted to reflect changes in ocean circulation, biological productivity, the ocean carbon cycle, and more. Other TEIs have been introduced as the result of human activities and are considered contaminants. The development and implementation of contamination-free methods for collecting and analyzing samples for TEIs revolutionized marine chemistry, revealing trace element distributions with oceanographically consistent features and new insights about the processes regulating them. Despite these advances, the volume and geographic coverage of high-quality TEI data by the end of the twentieth century were insufficient to constrain their global biogeochemical cycles. To accelerate progress in this field of research, marine geochemists developed a coordinated international effort to systematically study the marine biogeochemical cycles of TEIs-the GEOTRACES program. Following a decade of planning and implementation, GEOTRACES launched its main field effort in 2010. This review, roughly midway through the field program, summarizes the steps involved in designing the program, its management structure, and selected findings.
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Affiliation(s)
- Robert F Anderson
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA;
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Jung J, Yoo KC, Rosenheim BE, Conway TM, Lee JI, Yoon HI, Hwang CY, Yang K, Subt C, Kim J. Microbial Fe(III) reduction as a potential iron source from Holocene sediments beneath Larsen Ice Shelf. Nat Commun 2019; 10:5786. [PMID: 31857591 PMCID: PMC6923428 DOI: 10.1038/s41467-019-13741-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 11/21/2019] [Indexed: 11/25/2022] Open
Abstract
Recent recession of the Larsen Ice Shelf C has revealed microbial alterations of illite in marine sediments, a process typically thought to occur during low-grade metamorphism. In situ breakdown of illite provides a previously-unobserved pathway for the release of dissolved Fe2+ to porewaters, thus enhancing clay-rich Antarctic sub-ice shelf sediments as an important source of Fe to Fe-limited surface Southern Ocean waters during ice shelf retreat after the Last Glacial Maximum. When sediments are underneath the ice shelf, Fe2+ from microbial reductive dissolution of illite/Fe-oxides may be exported to the water column. However, the initiation of an oxygenated, bioturbated sediment under receding ice shelves may oxidize Fe within surface porewaters, decreasing dissolved Fe2+ export to the ocean. Thus, we identify another ice-sheet feedback intimately tied to iron biogeochemistry during climate transitions. Further constraints on the geographical extent of this process will impact our understanding of iron-carbon feedbacks during major deglaciations. Recent recession of the Larsen Ice Shelf C has revealed that microbial alteration of illite can occur within marine sediments, a process previously thought to only occur abiotically during low-grade metamorphism. Here, the authors show that such microbial alteration of illite could provide a potential source of Fe release to Southern Ocean waters during Holocene glacial cycles.
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Affiliation(s)
- Jaewoo Jung
- Department of Earth System Sciences, Yonsei University, Seoul, 03722, Korea
| | - Kyu-Cheul Yoo
- Korea Polar Research Institute, Incheon, 21990, Korea
| | - Brad E Rosenheim
- College of Marine Science, University of South Florida, Tampa, FL, USA
| | - Tim M Conway
- College of Marine Science, University of South Florida, Tampa, FL, USA.,School of Geosciences, University of South Florida, Tampa, FL, USA
| | - Jae Il Lee
- Korea Polar Research Institute, Incheon, 21990, Korea
| | - Ho Il Yoon
- Korea Polar Research Institute, Incheon, 21990, Korea
| | | | - Kiho Yang
- Department of Earth System Sciences, Yonsei University, Seoul, 03722, Korea
| | - Christina Subt
- College of Marine Science, University of South Florida, Tampa, FL, USA
| | - Jinwook Kim
- Department of Earth System Sciences, Yonsei University, Seoul, 03722, Korea.
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Birchill AJ, Hartner NT, Kunde K, Siemering B, Daniels C, González-Santana D, Milne A, Ussher SJ, Worsfold PJ, Leopold K, Painter SC, Lohan MC. The eastern extent of seasonal iron limitation in the high latitude North Atlantic Ocean. Sci Rep 2019; 9:1435. [PMID: 30723260 PMCID: PMC6363741 DOI: 10.1038/s41598-018-37436-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 11/25/2018] [Indexed: 11/29/2022] Open
Abstract
The availability of iron (Fe) can seasonally limit phytoplankton growth in the High Latitude North Atlantic (HLNA), greatly reducing the efficiency of the biological carbon pump. However, the spatial extent of seasonal iron limitation is not yet known. We present autumn nutrient and dissolved Fe measurements, combined with microphytoplankton distribution, of waters overlying the Hebridean (Scottish) shelf break. A distinct biogeochemical divide was observed, with Fe deficient surface waters present beyond the shelf break, much further eastwards than previously recognised. Due to along and on-shelf circulation, the Hebridean shelf represents a much-localised source of Fe, which does not fertilise the wider HLNA. Shelf sediments are generally thought to supply large quantities of Fe to overlying waters. However, for this Fe to influence upper-ocean biogeochemical cycling, efficient off-shelf transport mechanisms are required. This work challenges the view that the oceanic surface waters in close proximity to continental margins are iron replete with respect to marine primary production demands.
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Affiliation(s)
- A J Birchill
- School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, United Kingdom.
- National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom.
| | - N T Hartner
- School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, United Kingdom
- Institute of Analytical and Bioanalytical Chemistry, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - K Kunde
- Ocean and Earth Sciences, University of Southampton, Waterfront Campus, National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom
| | - B Siemering
- Scottish Association for Marine Science, Scottish Marine Institute, Oban, Argyll, PA37 1QA, United Kingdom
- Marine Institute, Rinville, Oranmore, Co., Galway, H91 R673, Ireland
| | - C Daniels
- National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom
| | - D González-Santana
- Ocean and Earth Sciences, University of Southampton, Waterfront Campus, National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom
| | - A Milne
- School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, United Kingdom
| | - S J Ussher
- School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, United Kingdom
| | - P J Worsfold
- School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, United Kingdom
| | - K Leopold
- Institute of Analytical and Bioanalytical Chemistry, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany
| | - S C Painter
- National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom
| | - M C Lohan
- School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, United Kingdom
- Ocean and Earth Sciences, University of Southampton, Waterfront Campus, National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom
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