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  • 1
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    Using boron isotopes to characterise past carbon cycle perturbations: the case of the MECO (2014)
    Società Geologica Italiana
    In:  Rendiconti online della Società Geologica Italiana, 31 . pp. 101-102.
    Details
    Publication Date: 2020-06-04
    Type: Article , PeerReviewed
    DOI: 10.3301/ROL.2014.67
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Size-dependent response of foraminiferal calcification to seawater carbonate chemistry (2017)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 14 (13). pp. 3287-3308.
    Details
    Publication Date: 2020-02-06
    Description: The response of the marine carbon cycle to changes in atmospheric CO2 concentrations will be determined, in part, by the relative response of calcifying and non-calcifying organisms to global change. Planktonic foraminifera are responsible for a quarter or more of global carbonate production, therefore understanding the sensitivity of calcification in these organisms to environmental change is critical. Despite this, there remains little consensus as to whether, or to what extent, chemical and physical factors affect foraminiferal calcification. To address this, we directly test the effect of multiple controls on calcification in culture experiments and core-top measurements of Globigerinoides ruber. We find that two factors, body size and the carbonate system, strongly influence calcification intensity in life, but that exposure to corrosive bottom waters can overprint this signal post mortem. Using a simple model for the addition of calcite through ontogeny, we show that variable body size between and within datasets could complicate studies that examine environmental controls on foraminiferal shell weight. In addition, we suggest that size could ultimately play a role in determining whether calcification will increase or decrease with acidification. Our models highlight that knowledge of the specific morphological and physiological mechanisms driving ontogenetic change in calcification in different species will be critical in predicting the response of foraminiferal calcification to future change in atmospheric pCO2.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
    DOI: 10.5194/bg-14-3287-2017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Reconstruction of Cenozoic δ11Bsw Using A Gaussian Process (2023)
    Details
    Publication Date: 2023-11-30
    Description: The boron isotope ratio of seawater (δ11Bsw) is a parameter which must be known to reconstruct palaeo pH and CO2 from boron isotope measurements of marine carbonates. Beyond a few million years ago, δ11Bsw is likely to have been different to modern. Palaeo δ11Bsw can be estimated by simultaneously constraining the vertical gradients in foraminiferal δ11B (∆δ11B) and pH (∆pH). A number of subtly different techniques have been used to estimate ∆pH in the past, all broadly based on assumptions about vertical gradients in oxygen, and/or carbon, or other carbonate system constraints. In this work we pull together existing data estimates alongside limitations on the rate of change of δ11Bsw from modelling, and combine these into an overarching statistical framework called a Gaussian Process. The Gaussian Process technique allows us to bring together data and constraints on the rate of change in δ11Bsw to generate random plausible evolutions of δ11Bsw. We reconstruct δ11Bsw, and by extension palaeo pH, across the last 65Myr using this novel methodology. Reconstructed δ11Bsw is compared to other seawater isotope ratios, namely 87/86Sr, 187/188Os, and δ7Li, which we also reconstruct with Gaussian Processes. Our method provides a template for incorporation of future δ11Bsw constraints, and a mechanism for propagation of uncertainty in δ11Bsw into future studies.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    Revisiting the Middle Eocene Climatic Optimum ‘Carbon Cycle Conundrum’ with new estimates of atmospheric pCO2 from boron isotopes (2020)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-02-08
    Description: The Middle Eocene Climatic Optimum (MECO) was a gradual warming event and carbon cycle perturbation that occurred between 40.5 and 40.1 Ma. A number of characteristics, including greater-than-expected deep-sea carbonate dissolution, a lack of globally-coherent negative δ 13 40 C excursion in marine carbonates, a duration longer than the characteristic timescale of carbon-cycle recovery, and the absence of a clear trigger mechanism, challenge our current understanding of the Earth system and its regulatory feedbacks. This makes the MECO one of the most enigmatic events in the Cenozoic, dubbed a middle Eocene ‘carbon cycle conundrum’. Here we use boron isotopes in planktic foraminifera to better constrain pCO2 changes over the event. Over the MECO itself, we find that pCO2 rose by only 0.55-0.75 doublings, thus requiring a much more modest carbon injection than previously indicated by the alkenone δ 13 C-pCO2 proxy. In addition, this rise in pCO2 was focused around the peak of the 400 kyr warming trend. Before this, considerable global carbonate δ 18 O change was asynchronous with any coherent ocean pH (and hence pCO2) excursion. This finding suggests that middle Eocene climate (and perhaps a nascent cryosphere) was highly sensitive to small changes in radiative forcing.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The PhanSST global database of Phanerozoic sea surface temperature proxy data (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Paleotemperature proxy data form the cornerstone of paleoclimate research and are integral to understanding the evolution of the Earth system across the Phanerozoic Eon. Here, we present PhanSST, a database containing over 150,000 data points from five proxy systems that can be used to estimate past sea surface temperature. The geochemical data have a near-global spatial distribution and temporally span most of the Phanerozoic. Each proxy value is associated with consistent and queryable metadata fields, including information about the location, age, and taxonomy of the organism from which the data derive. To promote transparency and reproducibility, we include all available published data, regardless of interpreted preservation state or vital effects. However, we also provide expert-assigned diagenetic assessments, ecological and environmental flags, and other proxy-specific fields, which facilitate informed and responsible reuse of the database. The data are quality control checked and the foraminiferal taxonomy has been updated. PhanSST will serve as a valuable resource to the paleoclimate community and has myriad applications, including evolutionary, geochemical, diagenetic, and proxy calibration studies.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions): Inter‐laboratory δ 11 B and Trace Element Ratio Value Assignment (2021)
    Wiley
    Details
    Publication Date: 2024-02-07
    Description: The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca 〈 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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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
  • 8
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    Boron-CO2 workshop: Testing and extending the limits of the foraminiferal boron proxy for seawater pH and atmospheric CO2 reconstructions (2023)
    PAGES
    Details
    Publication Date: 2023-05-26
    Description: Workshop report - Bergen, Norway, 4 September 2022 Atmospheric carbon dioxide (CO2) is the key driver of global temperatures over geological time, but calculating the exact sensitivity of Earth’s climate to CO2, and hence the trajectory of anthropogenic climate change, requires accurate quantification of past CO2. Determining past CO2 and fluxes among Earth's carbon reservoirs is difficult, particularly prior to ice-core records of the last 800 kyrs. Attempts have been made to compile multi-proxy atmospheric CO2 proxy data through time (Foster et al. 2017; Hönisch 2021; Rae et al. 2021) which have gained considerable traction, including in the Intergovernmental Panel on Climate Change reports (IPCC 2021). However, many of these compilations can include inaccuracies and apparent contradictions arising from differing assumptions and auxiliary inputs used when translating proxy data to CO2. To move forward as a community, ensuring the robustness of future CO2 data contributions and reducing noise in a crucial dataset, such inconsistencies must be minimized, and uncertainties systematically accounted for (Fig. 1).
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 9
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    Revisiting the Middle Eocene Climatic Optimum “Carbon Cycle Conundrum” With New Estimates of Atmospheric pCO2 From Boron Isotopes (2021)
    Details
    Publication Date: 2021-10-15
    Description: The Middle Eocene Climatic Optimum (MECO) was a gradual warming event and carbon cycle perturbation that occurred between 40.5 and 40.1 Ma. A number of characteristics, including greater-than-expected deep-sea carbonate dissolution, a lack of globally coherent negative δ13C excursion in marine carbonates, a duration longer than the characteristic timescale of carbon cycle recovery, and the absence of a clear trigger mechanism, challenge our current understanding of the Earth system and its regulatory feedbacks. This makes the MECO one of the most enigmatic events in the Cenozoic, dubbed a middle Eocene “carbon cycle conundrum.” Here we use boron isotopes in planktic foraminifera to better constrain pCO2 changes over the event. Over the MECO itself, we find that pCO2 rose by only 0.55–0.75 doublings, thus requiring a much more modest carbon injection than previously indicated by the alkenone δ13C-pCO2 proxy. In addition, this rise in pCO2 was focused around the peak of the 400 kyr warming trend. Before this, considerable global carbonate δ18O change was asynchronous with any coherent ocean pH (and hence pCO2) excursion. This finding suggests that middle Eocene climate (and perhaps a nascent cryosphere) was highly sensitive to small changes in radiative forcing.
    Keywords: 551 ; boron isotopes ; pCO2 reconstruction ; Middle Eocene Climatic Optimum ; carbon cycle ; paleoclimate ; cryosphere
    Language: English
    Type: map
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    CITATION GEO-LEO
  • 10
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    Planktonic foraminifera of sediment trap samples (2013)
    PANGAEA
    In:  Supplement to: Marshall, Brittney J; Thunell, Robert C; Henehan, Michael J; Astor, Yrene; Wejnert, Katherine (2013): Planktonic foraminiferal area density as a proxy for carbonate ion concentration: A calibration study using the Cariaco Basin ocean time series. Paleoceanography, 28(2), 363-376, https://doi.org/10.1002/palo.20034
    Details
    Publication Date: 2023-01-13
    Description: Biweekly sediment trap samples and concurrent hydrographic measurements collected between March 2005 and October 2008 from the Cariaco Basin, Venezuela, are used to assess the relationship between [CO3]2- and the area densities (ho A) of two species of planktonic foraminifera (Globigerinoides ruber (pink) and Globigerinoides sacculifer). Calcification temperatures were calculated for each sample using species-appropriate oxygen isotope (d18O) temperature equations that were then compared to monthly temperature profiles taken at the study site in order to determine calcification depth. Ambient [CO3]2- was determined for these calcification depths using alkalinity, pH, temperature, salinity, and nutrient concentration measurements taken during monthly hydrographic cruises. The rho A, which is representative of calcification efficiency, is determined by dividing individual foraminiferal shell weights (±0.43 µg) by their associated silhouette areas and taking the sample average. The results of this study show a strong correlation between rho A and ambient [CO3]2- for both G. ruber and G. sacculifer (R**2 = 0.89 and 0.86, respectively), confirming that [CO3]2- has a pronounced effect on the calcification of these species. Though the rho A for both species reveal a highly significant (p 〈 0.001) relationship with ambient [CO3]2-, linear regression reveals that the extent to which [CO3]2- influences foraminiferal calcification is species specific. Hierarchical regression analyses indicate that other environmental parameters (temperature and [PO4]3-) do not confound the use of G. ruber and G. sacculifer rho A as a predictor for [CO3]2-. This study suggests that G. ruber and G. sacculifer rho A can be used as reliable proxies for past surface ocean [CO3]2--
    Keywords: CARIACO_Trap; Cariaco Basin; Trap, sediment; TRAPS
    Type: Dataset
    Format: application/zip, 2 datasets
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    DATA PANGAEA
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