The Iron Biogeochemical Cycle Past and Present

Raiswell, R.; Canfield, Donald E.

doi:10.7185/geochempersp.1.1

Cited by 567 publications

(468 citation statements)

References 257 publications

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“…Riverine phosphorus fluxes have also increased by 50-300% over preindustrial levels and are expected to track future global population increases, unless declining mineral phosphorus reserves offset such changes 80 . Fluvial dissolved iron inputs are at present small relative to atmospheric inputs 81 . Any change in the estuarine trapping efficiency of the much larger fluvial particulate iron fluxes could, however, have a significant but uncertain impact on the supply of terrestrial iron to the open ocean 82 .…”

Section: Nature Geoscience Doi: 101038/ngeo1765mentioning

confidence: 96%

“…Cumulative anthropogenic inputs over century timescales are thus potentially equivalent in magnitude to 100%, 1-2% and <0.5% of the oceanic iron, nitrogen and phosphorus inventories, respectively. Owing to uncertainty over the bioavailability of particulate iron 81,82,96 , we primarily consider dissolved inputs. For all glacial flows we assume no change in water flows, which in reality are likely to increase with future warming.…”

Section: Implications For the Carbon Cyclementioning

confidence: 99%

“…Total (reactive particulate and dissolved) inputs are much higher, but most of the fluvial particulate iron input of around 627 Gmol yr -1 is probably trapped on the shelf 82 , although much of the glacial reactive particulate Fe supply of 140 Gmol yr -1 may reach the ocean 96 . We do not attempt to estimate the magnitude of potential changes in other dissolved iron inputs to the water column 81 , including increases in the important sedimentary source as a result of decreasing oxygen levels 66,75 . Iceberg-associated fluxes are also an important contributor, particularly in the Southern Ocean 81 .…”

Section: Implications For the Carbon Cyclementioning

confidence: 99%

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Processes and patterns of oceanic nutrient limitation

et al. 2013

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Microbial activity is a fundamental component of oceanic nutrient cycles. Photosynthetic microbes, collectively termed phytoplankton, are responsible for the vast majority of primary production in marine waters. The availability of nutrients in the upper ocean frequently limits the activity and abundance of these organisms. Experimental data have revealed two broad regimes of phytoplankton nutrient limitation in the modern upper ocean. Nitrogen availability tends to limit productivity throughout much of the surface low-latitude ocean, where the supply of nutrients from the subsurface is relatively slow. In contrast, iron often limits productivity where subsurface nutrient supply is enhanced, including within the main oceanic upwelling regions of the Southern Ocean and the eastern equatorial Pacific. Phosphorus, vitamins and micronutrients other than iron may also (co-)limit marine phytoplankton. The spatial patterns and importance of co-limitation, however, remain unclear. Variability in the stoichiometries of nutrient supply and biological demand are key determinants of oceanic nutrient limitation. Deciphering the mechanisms that underpin this variability, and the consequences for marine microbes, will be a challenge. But such knowledge will be crucial for accurately predicting the consequences of ongoing anthropogenic perturbations to oceanic nutrient biogeochemistry

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Section: Nature Geoscience Doi: 101038/ngeo1765mentioning

confidence: 96%

Section: Implications For the Carbon Cyclementioning

confidence: 99%

Section: Implications For the Carbon Cyclementioning

confidence: 99%

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Processes and patterns of oceanic nutrient limitation

et al. 2013

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“…As the Fe(II) in the proposed organic ligands is oxidised, it may remain associated with the ligand complex, converting to Fe(III)-L complexes, which may be much stronger than Fe(II)-L complexes. Alternatively, Fe(II) precipitation to Fe(III)-oxyhydroxide nanoparticles may constitute a colloidal fraction of dFe with or without organic complexes (e.g., Raiswell and Canfield 2012).…”

Section: Fe(ii) Oxidation Kinetics In Core-top and Water Column Seawatermentioning

confidence: 99%

“…However, this element and its redox cycling have major impacts on the cycling of other elements (e.g., P) in terrestrial waters and during diagenesis in sediments (Raiswell and Canfield 2012). Iron is also an essential micro-nutrient for marine primary producers and limits their growth in *25% of the open ocean (Boyd and Ellwood 2010), due to its low availability.…”

Section: Introductionmentioning

confidence: 99%

Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

et al. 2017

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Shelf sediments underlying temperate and oxic waters of the Celtic Sea (NW European Shelf) were found to have shallow oxygen penetrations depths from late spring to late summer (2.2-5.8 mm below seafloor) with the shallowest during/after the spring-bloom (mid-April to mid-May) when the organic carbon content was highest. Sediment porewater dissolved iron (dFe,\0.15 lm) mainly ([85%) consisted of Fe(II) and gradually increased from 0.4 to 15 lM at the sediment surface to *100-170 lM at about 6 cm depth. During the late spring this Fe(II) was found to be mainly present as soluble Fe(II) ([85% sFe, \0.02 lm). Sub-surface dFe(II) maxima were enriched in light isotopes (d 56 Fe -2.0 to -1.5%), which is attributed to dissimilatory iron reduction (DIR) during the bacterial decomposition of organic matter. As porewater Fe(II) was oxidised to insoluble Fe(III) in the surface sediment layer, residual Fe(II) was further enriched in light isotopes (down to -3.0%). Ferrozine-reactive Fe(II) was found in surface porewaters and in overlying core top waters, and was highest in the late spring period. Shipboard experiments showed that depletion of bottom water Responsible Editor: Martin Solan.Electronic supplementary material The online version of this article (doi:10.1007/s10533-017-0309-x) contains supplementary material, which is available to authorized users. 49-67 DOI 10.1007/s10533-017-0309-x oxygen in late spring can lead to a substantial release of Fe(II). Reoxygenation of bottom water caused this Fe(II) to be rapidly lost from solution, but residual dFe(II) and dFe(III) remained (12 and 33 nM) after [7 h. Iron(II) oxidation experiments in core top and bottom waters also showed removal from solution but at rates up to 5-times slower than predicted from theoretical reaction kinetics. These data imply the presence of ligands capable of complexing Fe(II) and supressing oxidation. The lower oxidation rate allows more time for the diffusion of Fe(II) from the sediments into the overlying water column. Modelling indicates significant diffusive fluxes of Fe(II) (on the order of 23-31 lmol m -2 day -1 ) are possible during late spring when oxygen penetration depths are shallow, and pore water Fe(II) concentrations are highest. In the water column this stabilised Fe(II) will gradually be oxidised and become part of the dFe(III) pool. Thus oxic continental shelves can supply dFe to the water column, which is enhanced during a small period of the year after phytoplankton bloom events when organic matter is transferred to the seafloor. This input is based on conservative assumptions for solute exchange (diffusion-reaction), whereas (bio)physical advection and resuspension events are likely to accelerate these solute exchanges in shelf-seas.

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The impact of changing surface ocean conditions on the dissolution of aerosol iron

Fishwick

Sedwick

Lohan

et al. 2014

Global Biogeochemical Cycles

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The proportion of aerosol iron (Fe) that dissolves in seawater varies greatly and is dependent on aerosol composition and the physicochemical conditions of seawater, which may change depending on location or be altered by global environmental change. Aerosol and surface seawater samples were collected in the Sargasso Sea and used to investigate the impact of these changing conditions on aerosol Fe dissolution in seawater. Our data show that seawater temperature, pH, and oxygen concentration, within the range of current and projected future values, had no significant effect on the dissolution of aerosol Fe. However, the source and composition of aerosols had the most significant effect on the aerosol Fe solubility, with the most anthropogenically influenced samples having the highest fractional solubility (up to 3.2%). The impact of ocean warming and acidification on aerosol Fe dissolution is therefore unlikely to be as important as changes in land usage and fossil fuel combustion. Our experimental results also reveal important changes in the size distribution of soluble aerosol Fe in solution, depending on the chemical conditions of seawater. Under typical conditions, the majority (77-100%) of Fe released from aerosols into ambient seawater existed in the colloidal (0.02-0.4 μm) size fraction. However, in the presence of a sufficient concentration of strong Fe-binding organic ligands (10 nM) most of the aerosol-derived colloidal Fe was converted to soluble Fe (<0.02 μm). This finding highlights the potential importance of organic ligands in retaining aerosol Fe in a biologically available form in the surface ocean.

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The Iron Biogeochemical Cycle Past and Present

Cited by 567 publications

References 257 publications

Processes and patterns of oceanic nutrient limitation

Processes and patterns of oceanic nutrient limitation

Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

The impact of changing surface ocean conditions on the dissolution of aerosol iron

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