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Evaluation of phosphate-uptake mechanisms by Fe(III) (oxyhydr)oxides in Early Proterozoic oceanic conditions
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Number of Authors: 32018 (English)In: Environmental Chemistry, ISSN 1448-2517, E-ISSN 1449-8979, Vol. 15, no 1-2, p. 18-28Article in journal (Refereed) Published
Abstract [en]

Banded iron formations (BIF) are proxies of global dissolved inorganic phosphate (DIP) content in Precambrian marine waters. Estimates of Precambrian DIP rely on constraining the mechanisms by which Fe(III) (oxyhydr)oxides scavenge DIP in NaCl solutions mimicking elevated Precambrian marine Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are (1) surface attachment on pre-formed Fe(III) (oxyhydr)oxides (adsorption), and (2) incorporation of P into actively growing Fe(III) (oxyhydr)oxides (coprecipitation) during the oxidation of Fe(II) to Fe(III) (oxyhydr)oxides in the presence of DIP. It has been suggested that elevated Si concentrations, such as those suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III) (oxyhydr)oxides; however, recent coprecipitation experiments show that DIP is scavenged by Fe(III) (oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In the present study, we show that the DIP uptake onto Fe(III) (oxyhydr)oxides by adsorption is less than 5 % of DIP uptake by coprecipitation. Differences in surface attachment and the possibility of structural capture within the Fe(III) (oxyhydr)oxides are inferred from the robust influence Si has on DIP binding during adsorption, meanwhile the influence of Si on DIP binding is inhibited during coprecipitation when As(III) and As(V) are present. In the Early Proterozoic open oceans, Fe(III) (oxyhydr)oxides precipitated when deep anoxic Fe(II)-rich waters rose and mixed with the first permanently oxygenated ocean surface waters. Our data imply that, DIP was removed from surface waters through coprecipitation with those Fe(III) (oxyhydr)oxides, rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III) (oxyhydr)oxides, and by the partial release of DIP into the anoxic bottom waters and buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters, both of which would have most likely decreased the productivity of cyanobacteria and O-2 production.

Place, publisher, year, edition, pages
2018. Vol. 15, no 1-2, p. 18-28
Keywords [en]
adsorption, coprecipitation, DIP, iron formations
National Category
Chemical Sciences Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-157756DOI: 10.1071/EN17124ISI: 000433340000003OAI: oai:DiVA.org:su-157756DiVA, id: diva2:1223462
Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2018-06-25Bibliographically approved

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Hemmingsson, ChristofferPitcairn, Iain K.
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