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  • Elsevier  (2)
  • AAAS (American Association for the Advancement of Science)  (1)
  • 1
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    Deconvolving the saturation state and temperature controls on benthic foraminiferal Li/Ca, based on downcore paired B/Ca measurements and coretop compilation (2018)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 236 . pp. 297-314.
    Details
    Publication Date: 2021-02-08
    Description: Li/Ca in calcitic benthic foraminiferal tests has been suggested to co-vary with both temperature and carbonate chemistry, but these two influences have been difficult to disentangle. We use several new downcore records of Li/Ca in Cibicidoides wuellerstorfi and Uvigerina, paired with the carbonate proxy B/Ca, to further elucidate this behavior. We also combine the downcore measurements with a compilation of coretop Li/Ca data. Uvigerina B/Ca presumably records pore water saturation with respect to calcite (ΔCO32−), though downcore data show that it partially reflects bottom water ΔCO32− (inferred from C. wuellerstorfi B/Ca), with a relationship that is consistent with a previous global coretop calibration. Downcore Li/Ca is significantly correlated to B/Ca in both taxa, implying a positive relationship between Li/Ca and carbonate chemistry. This connection breaks down in the coretop compilation however, likely due to the confounding influence of temperature on Li/Ca. We attempt to isolate the temperature influence using a negative exponential equation previously derived from abiotic calcite precipitation experiments, and introduce a new quantity ΔLi/Ca, which is the observed departure from the temperature-based prediction. This transformation brings the downcore and coretop Li/Ca measurements into alignment, with up to 90% of the ΔLi/Ca variance explained by ΔCO32−. Finally, we perform preliminary tests of Li/Ca as a paleo-proxy for both ΔCO32− and temperature.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.gca.2018.02.029
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    13C-18O isotope signatures and ‘clumped isotope’ thermometry in foraminifera and coccoliths (2010)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 74 . pp. 5697-5717.
    Details
    Publication Date: 2017-09-27
    Description: Accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes. Most proxies for temperature are not thermodynamically based, appear to be subject to biological processes, require regional calibrations, and/or are influenced by fluid composition. As a result, their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated. Independent proxies for past temperature could provide an important means of testing and/or expanding on existing reconstructions. Here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths, relate those abundances to independently estimated growth temperatures, and discuss the possible scope of equilibrium and kinetic isotope effects. The proportions of 13C–18O bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonatecontaining minerals (apatite from fish, reptile, and mammal teeth; calcitic brachiopods and molluscs; aragonitic coral and mollusks). Most species that exhibit non-equilibrium 18O/16O (d18O) and 13C/12C (δ13C) ratios are characterized by 13C–18O bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium, with possible exceptions among benthic foraminiferal samples from the Arctic Ocean where temperatures are near-freezing. Observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: text
    DOI: 10.1016/j.gca.2010.07.006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Toward a Cenozoic history of atmospheric CO 2 (2023)
    AAAS (American Association for the Advancement of Science)
    Details
    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
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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