Comments on ‘Influence of measurement uncertainties on fractional solubility of iron in mineral aerosols over the oceans’ Aeolian Research 22, 85–92

Abstract

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. The main focus of their paper is the errors that occur during the determination of fractional solubility (using distilled water or DI leaches) due to the dissolution of <0.45 µm particles during storage of the leaches. We agree that such dissolution errors are important, but go further here in choosing to emphasise the fundamental role of mineralogy, which lies at the heart of the errors in this methodology. Our view is that DI leach errors need to be considered in relation to the forms of iron in dust samples and their mineralogical associations. Comments onThe DI technique leaches dust at pH 5.6 through a <0.45 µm filter in a flow through system (Buck et al., 2006;. This minimises Fe losses due to precipitation of Fe ( Mineralogy may also provide important insights into potential bioavailability (Raiswell et al., 2016). Most dFe is considered to be bioavailable because organically boundFe can be taken up by phytoplankton through several known pathways (Shaked and Lis, 2012;Meskhidze et al.,2016). However the iron dissolved by the DI leach is mainly inorganic (see above) and only the highly reactive and/or amorphous phases are likely to be bioavailable. For example there is experimental evidence to suggest that poorly crystalline or amorphous phases such as ferrihydrite can be used by plankton (Wells et al., 1983;Rich and Morel, 1990; Kuma and Matsunga, 1995;Nodwell and Price, 2001). By contrast the more crystalline phases may not be readily bioavailable unless modified by dissolution or grazing (Barbeau et al., 1996;Shaked and Lis, 2012). Thus using a technique that extracts only adsorbed or amorphous iron phases (such as ferrihydrite), and excludes contributions from crystalline phases would produce a closer correspondence between dFe and the DI leach.Iron mineralogy has often been peripheral to the dust research agenda although it plays a crucial role in atmospheric processes such as radiative forcing and ice nucleation (Mahowald, 2013). Unfortunately observations of dust iron minerals are scarce although models such as those presented by Scanza et al.(2015), Perlwitz et al.(2015) and Journet et al.(2014) are now trying explicitly to represent dust mineralogy and their impacts on the climate s...

Atmospheric Inputs of Iron and Manganese to Coastal Waters of the Southern California Current System: Seasonality, Santa Ana Winds, and Biogeochemical Implications

“…Although in the literature there are recent estimates of trace metals solubility from dust (e.g., Chance et al, ; López‐García et al, ; Mackey et al, ; Ravelo‐Pérez et al, ; Winton et al, ), solubility percentages are usually as variable as reported values of atmospheric dust deposition in the ocean. The reasons for such variability include the origin, load, and geochemical characteristics of dust (Baker et al, ; Jickells et al, ; Sholkovitz et al, ) as well as a lack of consensus among the methodologies used for its estimation (Meskhidze et al, ; Raiswell et al, ; Schulz et al, ). Thus, to calculate the atmospheric supply of soluble metals from the total fluxes of Fe and Mn, we selected as the most representative for our study, Fe and Mn solubility percentages reported for soils from the nearest semiarid region and dust samples from the coastal portion of the CCS.…”

“…its estimation (Meskhidze et al, 2016;Raiswell et al, 2017;Schulz et al, 2012). Thus, to calculate the atmospheric supply of soluble metals from the total fluxes of Fe and Mn, we selected as the most representative for our study, Fe and Mn solubility percentages reported for soils from the nearest semiarid region and dust samples from the coastal portion of the CCS.…”

Iron in Glacial Systems: Speciation, Reactivity, Freezing Behavior, and Alteration During Transport

“…The inorganic materials are minerals (or mineral aggregates) whose properties are modified by size and by the nature of the organic admixtures and/or complexes. There are a variety of techniques (Shi et al, 2012;Raiswell et al, 2017) available to study the CNFe fraction. These techniques include; scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectrometry (EDX) and selective area X-ray diffraction (SAED), all of which provide compositional, structural, and mineralogical information down to nanometre scales.…”

“…The particulate fraction is commonly defined in terms of fractional solubility which is the percentage of total Fe that passes through a 0.2, 0.4, or 0.45 µm filter after treatment with a specified extractant (Meskhidze et al, 2016;Raiswell et al, 2017). Unfortunately a wide variety of extraction techniques are commonly used such that fractional solubilities vary widely, e.g., the fractional solubility of aeolian dusts ranges from 0.001 to 80% (Jickells and Spokes, 2001;Baker and Croot, 2010).…”

Aerosol-Climate Interactions During the Last Glacial Maximum

“…Additional paleodata from marine sediment cores, as well as future improvements in ocean biogeochemistry models, also driven by data from initiatives such as GEOTRACES [191] or process-based field campaigns, are needed to better quantify iron solubility [192][193][194] and indirect effects of dust on the ocean carbon cycle. Recent developments in explicitly representing mineralogy and aging in dust models [195][196][197] will provide enhanced tools to derive dust-borne iron inputs to the ocean, especially if also used for paleoclimate experiments and notably for the LGM [99].…”