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dc.contributor.authorJilbert, Tomen_UK
dc.contributor.authorAsmala, Eeroen_UK
dc.contributor.authorSchröder, Christianen_UK
dc.contributor.authorTiihonen, Rosaen_UK
dc.contributor.authorMyllykangas, Jukka-Pekkaen_UK
dc.contributor.authorVirtasalo, Joonas Jen_UK
dc.contributor.authorKotilainen, Aarnoen_UK
dc.contributor.authorPeltola, Pasien_UK
dc.contributor.authorEkholm, Päivien_UK
dc.contributor.authorHietanen, Susannaen_UK
dc.description.abstractIron (Fe) plays a key role in sedimentary diagenetic processes in coastal systems, participating in various redox reactions and influencing the burial of organic carbon. Large amounts of Fe enter the marine environment from boreal river catchments associated with dissolved organic matter (DOM) and as colloidal Fe oxyhydroxides, principally ferrihydrite. However, the fate of this Fe pool in estuarine sediments has not been extensively studied. Here we show that flocculation processes along a salinity gradient in an estuary of the northern Baltic Sea efficiently transfer Fe and OM from the dissolved phase into particulate material that accumulates in the sediments. Flocculation of Fe and OM is partially decoupled, likely due to the presence of discrete colloidal ferrihydrite in the freshwater Fe pool which responds differently from DOM to estuarine mixing. Further decoupling of Fe from OM occurs during sedimentation. While we observe a clear decline with distance offshore in the proportion of terrestrial material in the sedimentary particulate organic matter (POM) pool, the distribution of flocculated Fe in sediments is modulated by focusing effects. Labile Fe phases are most abundant at a deep site in the inner basin of the estuary, consistent with input from flocculation and subsequent focusing. The majority of the labile Fe pool is present as Fe (II), including both acid-volatile sulfur (AVS)-bound Fe and unsulfidized phases. The ubiquitous presence of unsulfidized Fe (II) throughout the sediment column suggests Fe (II)-OM complexes derived from reduction of flocculated Fe (III)-OM, while other Fe (II) phases are likely derived from the reduction of flocculated ferrihydrite. Depth-integrated rates of Fe (II) accumulation (AVS-Fe + unsulfidized Fe (II) + pyrite) for the period 1970–2015 are greater in the inner basin of the estuary with respect to a site further offshore, confirming higher rates of Fe reduction in near-shore areas. Mössbauer 57Fe spectroscopy shows that refractory Fe is composed largely of superparamagnetic Fe (III), high-spin Fe (II) in silicates, and, at one station, also oxide minerals derived from past industrial activities. Our results highlight that the cycling of Fe in boreal estuarine environments is complex, and that the partial decoupling of Fe from OM during flocculation and sedimentation is key to understanding the role of Fe in sedimentary diagenetic processes in coastal areas.en_UK
dc.publisherEuropean Geosciences Unionen_UK
dc.relationJilbert T, Asmala E, Schröder C, Tiihonen R, Myllykangas J, Virtasalo JJ, Kotilainen A, Peltola P, Ekholm P & Hietanen S (2018) Impacts of flocculation on the distribution and diagenesis of iron in boreal estuarine sediments. Biogeosciences, 15 (4), pp. 1243-1271.
dc.rights© Author(s) 2018. This work is distributed under the Creative Commons Attribution 3.0 License (
dc.titleImpacts of flocculation on the distribution and diagenesis of iron in boreal estuarine sedimentsen_UK
dc.typeJournal Articleen_UK
dc.type.statusVoR - Version of Recorden_UK
dc.contributor.funderThe Carnegie Trusten_UK
dc.contributor.funderScience & Technology Facilities Councilen_UK
dc.contributor.affiliationUniversity of Helsinkien_UK
dc.contributor.affiliationUniversity of Helsinkien_UK
dc.contributor.affiliationBiological and Environmental Sciencesen_UK
dc.contributor.affiliationUniversity of Helsinkien_UK
dc.contributor.affiliationUniversity of Helsinkien_UK
dc.contributor.affiliationGeological Survey of Finlanden_UK
dc.contributor.affiliationGeological Survey of Finlanden_UK
dc.contributor.affiliationBoliden Ronnskaren_UK
dc.contributor.affiliationUniversity of Helsinkien_UK
dc.contributor.affiliationUniversity of Helsinkien_UK
dc.relation.funderprojectA miniaturized Mössbauer spectrometer developed for Mars exploration applied to geological repositories for non-destructive and in situ analysesen_UK
dc.relation.funderprojectThe sedimentary iron cycle: A novel way to iron mineral characterization and separationen_UK
rioxxterms.apcnot requireden_UK
rioxxterms.typeJournal Article/Reviewen_UK
local.rioxx.authorJilbert, Tom|en_UK
local.rioxx.authorAsmala, Eero|en_UK
local.rioxx.authorSchröder, Christian|0000-0002-7935-6039en_UK
local.rioxx.authorTiihonen, Rosa|en_UK
local.rioxx.authorMyllykangas, Jukka-Pekka|en_UK
local.rioxx.authorVirtasalo, Joonas J|en_UK
local.rioxx.authorKotilainen, Aarno|en_UK
local.rioxx.authorPeltola, Pasi|en_UK
local.rioxx.authorEkholm, Päivi|en_UK
local.rioxx.authorHietanen, Susanna|en_UK
local.rioxx.projectNot Applicable|Science & Technology Facilities Council|en_UK
local.rioxx.projectNB|The Carnegie Trust|en_UK
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