Oceanic euxinia in Earth history: Causes and consequences

Annual Review of Earth and Planetary Sciences (Impact Factor: 8.83). 01/2008; 36:251-88. DOI: 10.1146/

ABSTRACT Euxinic ocean conditions accompanied significant events in Earth history, including several Phanerozoic biotic crises. By critically ex-amining modern and ancient euxinic environments and the range of hypotheses for these sulfidic episodes, we elucidate the primary factors that influenced the generation of euxinia. We conclude that periods of global warmth promoted anoxia because of reduced sol-ubility of oxygen, not because of ocean stagnation. Anoxia led to phosphate release from sediments, and continental configurations with expansive nutrient-trapping regions focused nutrient recycling and increased regional nutrient buildup. This great nutrient supply would have fueled high biological productivity and oxygen demand, enhancing oxygen depletion and sulfide buildup via sulfate reduc-tion. As long as warm conditions prevailed, these positive feedbacks sustained euxinic conditions. In rare, extreme cases, euxinia led to biotic crises, a hypothesis best supported by evidence from the end-Permian mass extinction.

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    ABSTRACT: Of the two nanocrystal (magnetosome) compositions biosynthesized by magnetotactic bacteria (MTB), the magnetic properties of magnetite magnetosomes have been extensively studied using widely available cultures, while those of greigite magnetosomes remain poorly known. Here we have collected uncultivated magnetite- and greigite-producing MTB to determine their magnetic coercivity distribution and ferromagnetic resonance (FMR) spectra and to assess the MTB-associated iron flux. We find that compared with magnetite-producing MTB cultures, FMR spectra of uncultivated MTB are characterized by a wider empirical parameter range, thus complicating the use of FMR for fossilized magnetosome (magnetofossil) detection. Furthermore, in stark contrast to putative Neogene greigite magnetofossil records, the coercivity distributions for greigite-producing MTB are fundamentally left-skewed with a lower median. Lastly, a comparison between the MTB-associated iron flux in the investigated estuary and the pyritic-Fe flux in the Black Sea suggests MTB play an important, but heretofore overlooked role in euxinic marine system iron cycle.
    Nature Communications 01/2014; 5:4797. · 10.74 Impact Factor
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