A review of colloidal iron partitioning and distribution in the open ocean

Heyden, Bjorn P. von der; Roychoudhury, Alakendra N.

doi:10.1016/j.marchem.2015.05.010

Cited by 26 publications

(26 citation statements)

References 87 publications

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“…Our study region covered a wide range of dissolved iron concentrations, with particularly elevated concentrations in the North Sea, as also observed previously (Gledhill et al, 1998). At such high iron concentrations, it is likely that some of the iron measured as dissolved iron, would be present in an inert, potentially colloidal fraction (Gledhill and Buck, 2012;Hawkes et al, 2013;Von Der Heyden and Roychoudhury, 2015). Figure 5 shows the impact of accounting for the presence of an inert phase that is in selective disequilibrium with HNN, for three titrations on samples 3, 10, and 14, which were determined to have very different dFe concentrations (0.9, 21, and 10.6 respectively).…”

Section: Selection Of Nica-donnan Parameterssupporting

confidence: 63%

Influence of Ocean Acidification on the Organic Complexation of Iron and Copper in Northwest European Shelf Seas; a Combined Observational and Model Study

et al. 2016

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The pH of aqueous solutions is known to impact the chemical speciation of trace metals. In this study we conducted titrations of coastal seawaters with iron and copper at pH 7.91, 7.37, and 6.99 (expressed on the total pH scale). Changes in the concentration of iron and copper that complexed with the added ligands 1-nitroso-2-napthol and salicylaldoxime respectively were determined by adsorptive cathodic stripping voltammetry-competitive ligand equilibrium (AdCSV-CLE). Interpretation of the results, assuming complexation by a low concentration of discrete ligands, showed that conditional stability constants for iron complexes increased relative to inorganic iron complexation as pH decreased by approximately 1 log unit per pH unit, whilst those for copper did not change. No trend was observed for concentrations of iron and copper complexing ligands over the pH range examined. We also interpreted our titration data by describing chemical binding and polyelectrolytic effects using non-ideal competitive adsorption in Donnan-like gels (NICA-Donnan model) in a proof of concept study. The NICA-Donnan approach allows for the development of a set of model parameters that are independent of ionic strength and pH, and thus calculation of metal speciation can be undertaken at ambient sample pH or the pH of a future, more acidic ocean. There is currently a lack of basic NICA-Donnan parameters applicable to marine dissolved organic matter (DOM) so we assumed that the measured marine dissolved organic carbon could be characterized as terrestrial fulvic acids. Generic NICA-Donnan parameters were applied within the framework of the software program visual MINTEQ and the metal-added ligand concentrations [MeAL] calculated for the AdCSV-CLE conditions. For copper, calculated [MeAL] using the NICA-Donnan model for DOM were consistent with measured [MeAL], but for iron an inert fraction with kinetically inhibited dissolution was required in addition to the NICA-Donnan model in order to approximate the trends observed in measured [MeAL]. We calculated iron and copper speciation in Northwest European shelf water samples at ambient alkalinity and projected increased pCO 2 concentrations as a demonstration of the potential of the approach.

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Section: Selection Of Nica-donnan Parameterssupporting

confidence: 63%

Influence of Ocean Acidification on the Organic Complexation of Iron and Copper in Northwest European Shelf Seas; a Combined Observational and Model Study

et al. 2016

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“…Higher organic ligand concentrations were generally observed along GP16 compared to the Atlantic Ocean; in particular, a plume of strong ligand L1 extended from the margin between 1000-3000 m to as far as 90°W (Buck et al in this issue). In addition, Fe can be transported over long distance as colloids, which may account for as much as half of the dissolved Fe pool in the deep ocean (Hunter and Boyd, 2007;von der Heyden and Roychoudhury, 2015), as long as they do not aggregate and sink (Fitzsimmons et al, 2014).…”

Section: Slope Tei Fluxesmentioning

confidence: 99%

Radium-228 as a tracer of dissolved trace element inputs from the Peruvian continental margin

et al. 2018

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Continental margins play a central role in the composition of seawater by being an important source of trace element essentials to the functioning of the ocean ecosystems. Here, we measured long-lived radium isotopes (226 Ra, 228 Ra) along a zonal transect at 12°S (US GEOTRACES GP16) in the eastern tropical South Pacific Ocean. We used 228 Ra to quantify the trace element and isotope (TEI) fluxes (DMn, DFe, and DCo) delivered from the Peruvian continental i) shelf and ii) slope. First, elevated 228 Ra activities were measured in surface water over the entire transect (~8500 km), evidence that the continental shelf is an important source of sediment-derived TEIs not only to coastal areas, but to central Pacific Ocean waters. Modeled 228 Ra shelf fluxes combined with water column dissolved TEI/ 228 Ra ratios were used to quantify the shelf-ocean input rates (normalized to shelf-area) for DMn (3.3 × 10 3 μmol m − 2 y − 1), DFe (1.5 × 10 3 μmol m − 2 y − 1), and DCo (1.0 × 10 2 μmol m − 2 y − 1). Second, co-occurring plumes of 228 Ra, DFe, and DMn extended over 1800 km from the margin at 1000-2500 m depth, indicative of a continental slope sediment TEI input to the intermediate water column. The 228 Ra gradient allowed us to derive an effective horizontal eddy diffusion coefficient (K h) of 46 m 2 s − 1 , which in turn permitted the calculation of slope sediment DMn (6.4 μmol m − 2 y − 1) and DFe (5.9 × 10 2 μmol m − 2 y − 1) fluxes based on their offshore concentration gradients. On the scale of the South Pacific continental margin between 0-20°S, the DMn shelf flux is approximately 2-3 orders of magnitude higher than the slope flux, while the DFe shelf/slope flux is~3:1. Both shelf and slope sediment derived DMn was transported over a significant distance towards the ocean interior, while DFe concentration gradients were steep, consistent with longer water column residence time for DMn as compared to DFe in marine systems. These findings highlight the importance of considering the continental slope-ocean boundary in the oceanic budgets of biologically-important trace elements.

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“…Wind driven aeolian dust, resuspended sediments, fluvial, and hydrothermal fluids are major sources of Fe to the ocean (Mahowald et al 2005;Moore and Braucher 2008;Boyd and Ellwood 2010;Tagliabue et al 2010). As a result, a significant fraction of Fe in the upper-ocean exists as colloidal (0.02-0.4 lm: Wu et al 2001;Boye et al 2010;Von Der Heyden and Roychoudhury 2015) and particulate forms (> 0.4 lm, Jickells et al 2005). Solid Fe is not directly available to most phytoplankton, which can internalize only soluble Fe (Rich and Morel 1990).…”

mentioning

confidence: 99%

Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria

Basu

Shaked

2018

Limnology & Oceanography

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The high iron (Fe) demands of Trichodesmium, a keystone nitrogen‐fixing cyanobacterium, are often met by dust deposition at the ocean surface. Following up on our findings of unique dust capturing and processing by Trichodesmium, we explored the ability of natural Trichodesmium colonies from the Gulf of Aqaba and Fe‐limited laboratory culture (IMS101) to obtain Fe from the mineral ferrihydrite and compete with their epibiotic bacteria for this Fe source. To study this complex system, we carefully optimized a radiotracer method ensuring complete removal of external ferrihydrite and efficient separation of bacteria from the colonies. Trichodesmium‐only uptake rates of natural colonies were 5–50 times faster than those of laboratory culture, suggesting that natural colonies acquire ferrihydrite at a greater efficiency. In some days, total uptake rates of natural colonies exceeded dissolved Fe release from ferrihydrite, indicating that the colonies enhance the mineral dissolution rate. Furthermore, uptake rates of bacteria associated with natural colonies were faster than those of bacteria associated with the culture, implying that the bacteria benefit from the Trichodesmium‐enhanced mineral dissolution. At the cellular level, surface area normalized uptake rates of bacteria always exceeded those of cultured Trichodesmium, but in natural populations, the dominance shifted between Trichodesmium and bacteria on different days. At the community level, when accounting for the total bacteria and Trichodesmium cells, Trichodesmium dominated Fe uptake in both cultured and natural colonies. Overall, our findings suggest that natural Trichodesmium colonies are exceptionally adapted for accessing mineral Fe and maintaining a sustainable relationship with their associated bacteria.

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A review of colloidal iron partitioning and distribution in the open ocean

Cited by 26 publications

References 87 publications

Influence of Ocean Acidification on the Organic Complexation of Iron and Copper in Northwest European Shelf Seas; a Combined Observational and Model Study

Influence of Ocean Acidification on the Organic Complexation of Iron and Copper in Northwest European Shelf Seas; a Combined Observational and Model Study

Radium-228 as a tracer of dissolved trace element inputs from the Peruvian continental margin

Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria

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