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  • AAAS (American Association for the Advancement of Science)  (2)
  • GSA, Geological Society of America
  • 1
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    GSA, Geological Society of America
    In:  Geology, 36 (9). pp. 747-750.
    Publication Date: 2016-04-18
    Description: Geochemical, biomarker, and isotopic evidence suggests that the end-Permian was characterized by extreme oceanic anoxia that may have led to hydrogen sulfide buildup and mass extinction. We use an earth system model to quantify the biogeochemical and physical conditions necessary for widespread oceanic euxinia and hydrogen sulfide release to the atmosphere. Greater than threefold increases in ocean nutrient content combined with nutrient-trapping ocean circulation cause surface-water H2S accumulation in the paleo–Tethys Ocean and in areas of strong upwelling. Accounting for the presence of sulfide-oxidizing phototrophs in the model suppresses but does not prevent widespread release of H2S to the atmosphere. Evidence from the geologic record is consistent with modeled geochemical distributions of widespread nutrient-induced euxinia during the end-Permian, suggesting H2S toxicity and hypercapnia may have provided the kill mechanism for extinction.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2024-02-07
    Description: Changes in the concentration and isotopic composition of the major constituents in seawater reflect changes in their sources and sinks. Because many of the processes controlling these sources and sinks are tied to the cycling of carbon, such records can provide insights into what drives past changes in atmospheric carbon dioxide and climate. Here, we present a stable strontium (Sr) isotope record derived from pelagic marine barite. Our δ 88/86 Sr record exhibits a complex pattern, first declining between 35 and 15 million years ago (Ma), then increasing from 15 to 5 Ma, before declining again from ~5 Ma to the present. Numerical modeling reveals that the associated fluctuations in seawater Sr concentrations are about ±25% relative to present-day seawater. We interpret the δ 88/86 Sr data as reflecting changes in the mineralogy and burial location of biogenic carbonates.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2024-02-23
    Description: The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO 2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO 2 thresholds in biological and cryosphere evolution. Editor’s summary The concentration of atmospheric carbon dioxide is a fundamental driver of climate, but its value is difficult to determine for times older than the roughly 800,000 years for which ice core records are available. The Cenozoic Carbon dioxide Proxy Integration Project (CenCO2PIP) Consortium assessed a comprehensive collection of proxy determinations to define the atmospheric carbon dioxide record for the past 66 million years. This synthesis provides the most complete record yet available and will help to better establish the role of carbon dioxide in climate, biological, and cryosphere evolution. — H. Jesse Smith
    Type: Article , PeerReviewed
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