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Arsenic-induced phosphate limitation under experimental Early Proterozoic oceanic conditions
Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences. Rutgers University, USA.
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Number of Authors: 5
2016 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 434, 52-63 p.Article in journal (Refereed) Published
Abstract [en]

Comparison of phosphorus concentrations associated with modern hydrothermal Fe(III)(oxyhydr)oxides and ancient Fe(III) oxide-rich iron formations, is used to estimate bioavailable Precambrian marine phosphorus (P) concentrations. This led to the proposition of a low dissolved P budget of similar to 10-25% of present-day levels, before similar to 1.9 billion years ago. Estimates incorporating ancient marine Si levels >= 0.67 mM instead suggested global dissolved P levels greater than today. Here we unite current experimental models that have considered NaCl solutions containing elevated dissolved Fe(II), Si, Ca2+ and Mg2+ ions in the incorporation of P in Precambrian marine Fe(III)(oxyhydr)oxides, in addition to arsenic as a hydrothermal proxy. We show that the coprecipitation of dissolved P and Fe(III)(oxyhydr)oxides from arsenic-rich marine waters produces an average P distribution coefficient of similar to 0.072 (+/- 0.01) mu M-1. This is comparable to the similar to 0.07 mu M-1 predicted for Fe(III)(oxyhydr)oxides in modern arsenic-rich, submarine hydrothermal settings, from which the lower Early Proterozoic dissolved marine P concentrations were predicted. As/P molar ratios below modern seawater ratios removed the negative feedback effect high Si impose on P scavenging by Fe(III)(oxyhydr)oxides. The binding of As(III) to Fe(III)(oxyhydr)oxides exhibits a lower competitive influence on P fixation. As(V) that likely became prominent in the surficially oxidized Early Proterozoic oceans induced dissolved P limitation because of preferential P sequestration at the expense of dissolved As(V) enrichment. The control of As on P scavenging by the precipitating Fe(III)(oxyhydr)oxides is strong regardless of common seawater cations (Mg2+ and Ca2+). The data suggest that the application of Si and Fe(III)(oxyhydr)oxides as an ancient seawater P proxy should consider chemical variability between depositional basins, taking into account the rather strong role hydrothermal arsenic has on the distribution of P in Fe(Ill)(oxyhydr)oxides. We propose that the generalized lower dissolved P budgets estimated from Early Proterozoic iron formations are consistent with oceans thought to be at least 3-4 times more hydrothermally active than at present.

Place, publisher, year, edition, pages
2016. Vol. 434, 52-63 p.
Keyword [en]
Fe(III)(oxyhydr)oxides, banded iron formations, primary productivity, atmospheric oxygenation
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-127377DOI: 10.1016/j.epsl.2015.11.009ISI: 000368870500006OAI: diva2:909463
Available from: 2016-03-07 Created: 2016-03-02 Last updated: 2016-03-07Bibliographically approved

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Fru, Ernest ChiHemmingsson, ChristofferHolm, Mikaela
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