Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 390, Issue -, Pages 253-263Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2014.01.001
Keywords
cobalt; trace element proxies; ocean redox; shale; iron formation; pyrite
Categories
Funding
- National Science Foundation (NSF) IRFP
- Deutsche Forschungsgemeinschaft [KA 1736/24-1]
- NSF EAR-PF
- NSF ELT program
- NSERC
- LabexMER
- CGS-M from NSERC
- Europole Mer
- IFREMER
- Gordon and Betty Moore Foundation
- NSF Chemical Oceanography program
- NASA Exobiology Program
- NASA's Astrobiology Institute Fund for International Cooperation
- University of Colorado Center for Astrobiology
- J.W. Fulbright Foundation
- University of Colorado's Office of the Vice Chancellor for Research
- Directorate For Geosciences
- Division Of Earth Sciences [1144317] Funding Source: National Science Foundation
- Directorate For Geosciences
- Division Of Ocean Sciences [1233261] Funding Source: National Science Foundation
- Office Of The Director
- Office Of Internatl Science &Engineering [1064391] Funding Source: National Science Foundation
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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 Earth's 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 Earth's 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 Earth's history. (C) 2014 Elsevier B.V. All rights reserved.
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