Cobalt and marine redox evolution

Type Article
Date 2014-03
Language English
Author(s) Swanner Elizabeth D.1, Planavsky Noah J.2, Lalonde Stefan3, Robbins Leslie J.4, Bekker Andrey5, Rouxel OlivierORCID6, Saito Mak A.7, Kappler Andreas1, Mojzsis Stephen J.8, 9, 10, 11, Konhauser Kurt O.4
Affiliation(s) 1 : Univ Tubingen, Dept Geosci, D-72076 Tubingen, Germany.
2 : Yale Univ, Dept Geol & Geophys, New Haven, CT 06520 USA.
3 : European Inst Marine Studies, UMR Domaines Ocean 6538, F-29280 Plouzane, France.
4 : Univ Alberta, Dept Earth & Atmospher Sci, Edmonton, AB T6G 2E3, Canada.
5 : Univ Manitoba, Dept Geol Sci, Winnipeg, MB R3T 2N2, Canada.
6 : IFREMER, Ctr Brest, F-29280 Plouzane, France.
7 : Woods Hole Oceanog Inst, Marine Chem & Geochem Dept, Woods Hole, MA 02543 USA.
8 : Ecole Normale Super Lyon, Lab Geol Lyon, F-69622 Villeurbanne, France.
9 : Univ Lyon 1, CNRS, UMR 5276, F-69622 Villeurbanne, France.
10 : Hungarian Acad Sci, Inst Geol & Geochem Res, H-1112 Budapest, Hungary.
11 : Univ Colorado, Dept Geol Sci, Boulder, CO 80309 USA.
Source Earth And Planetary Science Letters (0012-821X) (Elsevier Science Bv), 2014-03 , Vol. 390 , P. 253-263
DOI 10.1016/j.epsl.2014.01.001
WOS© Times Cited 70
Keyword(s) cobalt, trace element proxies, ocean redox, shale, iron formation, pyrite
Abstract Cobalt (Co) is a bio-essential trace element and limiting nutrient in some regions of the modern oceans. It has been proposed that Co was more abundant in poorly ventilated Precambrian oceans based on the greater utilization of Co by anaerobic microbes relative to plants and animals. However, there are few empirical or theoretical constraints on the history of seawater Co concentrations. Herein, we present a survey of authigenic Co in marine sediments (iron formations, authigenic pyrite and bulk euxinic shales) with the goal of tracking changes in the marine Co reservoir throughout Earthʼs history. We further provide an overview of the modern marine Co cycle, which we use as a platform to evaluate how changes in the redox state of Earthʼs surface were likely to have affected marine Co concentrations. Based on sedimentary Co contents and our understanding of marine Co sources and sinks, we propose that from ca. 2.8 to 1.8 Ga the large volume of hydrothermal fluids circulating through abundant submarine ultramafic rocks along with a predominantly anoxic ocean with a low capacity for Co burial resulted in a large dissolved marine Co reservoir. We tentatively propose that there was a decrease in marine Co concentrations after ca. 1.8 Ga resulting from waning hydrothermal Co sources and the expansion of sulfide Co burial flux. Changes in the Co reservoir due to deep-water ventilation in the Neoproterozoic, if they occurred, are not resolvable with the current dataset. Rather, Co enrichments in Phanerozoic euxinic shales deposited during ocean anoxic events (OAE) indicate Co mobilization from expanded anoxic sediments and enhanced hydrothermal sources. A new record of marine Co concentrations provides a platform from which we can reevaluate the role that environmental Co concentrations played in shaping biological Co utilization throughout Earthʼs history.
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