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  • 1
    Online Resource
    Online Resource
    Boron Isotopes : The Fifth Element. (2017)
    Cham :Springer International Publishing AG,
    Details
    Keywords: Boron-Isotopes. ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (288 pages)
    Edition: 1st ed.
    ISBN: 9783319646664
    Series Statement: Advances in Isotope Geochemistry Series
    URL: https://ebookcentral.proquest.com/lib/geomar/detail.action?docID=5150695
    DDC: 551.9
    Language: English
    Note: Intro -- Contents -- 1 Boron Isotopes in the Earth and Planetary Sciences-A Short History and Introduction -- Abstract -- 1.1 Introduction -- 1.2 A Short History of Boron Isotope Analyses -- 1.2.1 The Discovery of Boron Stable Isotopes -- 1.2.2 Natural Abundances and Variations -- 1.2.3 TIMS and the Establishment of Standards -- 1.2.4 Plasma Mass Spectrometry and Interlaboratory Comparison -- 1.2.5 The Development of in Situ Techniques -- 1.2.6 Theoretical and Experimental Boron Isotope Fractionation -- 1.3 The Fifth Element -- Acknowledgements -- References -- 2 Boron Isotope Analysis of Geological Materials -- Abstract -- 2.1 Introduction -- 2.2 Digestion and Purification Methods for Boron Isotope Analysis of Geologic Materials -- 2.2.1 Sample Digestion -- 2.2.2 Ion Exchange -- 2.2.3 Purification by Non Exchange Resin Methodologies -- 2.3 Analytical Methods for Boron Isotope Analysis of Geological Materials -- 2.3.1 The Isotopic Analysis of Boron in Solution Mode -- 2.3.1.1 Positive Ion Thermal Ionization Mass Spectrometry -- 2.3.1.2 Negative Ion Thermal Ionization Mass Spectrometry -- 2.3.1.3 Inductively Coupled Plasma Mass Spectrometry -- 2.3.2 The Isotopic Analysis of Boron in Situ -- 2.3.2.1 Secondary Ion Mass Spectrometry (SIMS) -- 2.3.2.2 Laser Ablation Inductively Coupled Mass Spectrometry -- 2.4 Summary and Outlook -- Acknowledgements -- References -- 3 Boron Isotope Fractionation Among Vapor-Liquids-Solids-Melts: Experiments and Atomistic Modeling -- Abstract -- 3.1 Introduction -- 3.2 Notations -- 3.3 Controls of B-Isotopic Fractionation -- 3.4 B-Speciation in Liquids, Vapor, and Melts -- 3.4.1 B-Speciation in Aqueous Fluids -- 3.4.2 Boron Speciation in Vapor -- 3.4.3 Boron Speciation in Melt -- 3.5 Experimental Determination of B-Isotope Fractionation -- 3.5.1 Vapor-Liquid-Melt Boron Isotope Fractionation. , 3.5.1.1 Vapor-Liquid Boron Isotope Fractionation -- 3.5.1.2 Aqueous Fluid-Melt B-Isotope Fractionation -- 3.5.2 Solid-Fluid B-Isotope Fractionation -- 3.5.2.1 Low-Temperature Solid-Aqueous Fluid B-Isotope Fractionation -- Carbonate-Fluid B-Isotope Fractionation -- Clay Mineral-Fluid B-Isotope Fractionation -- Boron-Isotope Fractionation in Other Low-Temperature Solid-Fluid Systems -- 3.5.2.2 High-Temperature Solid-Aqueous Fluid B-Isotope Fractionation -- Mica-Fluid B-Isotope Fractionation -- Tourmaline-Fluid B-Isotope Fractionation -- 3.6 Ab Intio Prediction of B-Isotope Fractionation -- 3.6.1 Computational Approach -- 3.6.1.1 The "Single Atom Approximation" Following Bigeleisen and Mayer (1947) -- 3.6.1.2 Computational Technique -- 3.6.1.3 Error Estimation Technique -- 3.6.2 Computation of Fractionation Factors -- 3.6.2.1 Vapor -- 3.6.2.2 Aqueous Fluid -- 3.6.2.3 Pressure Dependence of the Fractionation Factor in Aqueous Fluids -- 3.6.3 Computationally Determined Mineral-Fluid B-Isotope Fractionation -- 3.6.3.1 Tourmaline-Neutral Fluid B-Isotope Fractionation -- 3.6.3.2 Boromuscovite-Strongly Basic Fluid B-Isotope Fractionation -- 3.6.3.3 Boromuscovite-Neutral Fluid B-Isotope Fractionation -- 3.6.4 B-Isotope Fractionation Among Minerals -- 3.7 Conclusions -- References -- 4 Boron Incorporation into Marine CaCO3 -- Abstract -- 4.1 Introduction -- 4.2 Marine Calcium Carbonate Minerals -- 4.2.1 Carbonate Mineral Formation -- 4.2.1.1 Terrace-Ledge-Kink (TLK) Growth -- 4.2.1.2 Non-classical Crystal Growth -- 4.2.2 Impurity Incorporation in Carbonates -- 4.2.2.1 Reaction-Limited Impurity Incorporation -- 4.2.2.2 Diffusion-Limited Surface Environments -- 4.2.2.3 Impurity Incorporation in Non-classical Growth -- 4.3 Boron Incorporation in Calcium Carbonates -- 4.3.1 Aqueous Boron Chemistry -- 4.3.2 Boron in Synthetic Carbonates. , 4.3.2.1 Synthetic Aragonite -- 4.3.2.2 Synthetic Calcite -- 4.3.2.3 Differences Between Calcite and Aragonite -- 4.3.2.4 The Variability of B in Calcite: Possible Causes -- 4.3.2.5 The Variability of B in Calcite: A Surface Kinetic Explanation? -- 4.4 Boron in Carbonate Biominerals -- Acknowledgements -- References -- 5 Boron Isotopes in Foraminifera: Systematics, Biomineralisation, and CO2 Reconstruction -- Abstract -- 5.1 Introduction -- 5.1.1 Aqueous Boron Isotope Systematics -- 5.1.2 The Carbonate δ11B-pH Proxy -- 5.2 Methods of Boron Isotope Analysis in Foraminifera -- 5.2.1 Samples -- 5.2.1.1 Sample Size and Preparation -- 5.2.1.2 Preservation and Diagenesis -- 5.2.2 Cleaning of Foraminiferal Samples -- 5.2.3 Chemical Purification -- 5.2.3.1 Column Chromatography -- 5.2.3.2 Microsubliation -- 5.2.4 Mass Spectrometry -- 5.2.4.1 NTIMS -- 5.2.4.2 MC-ICPMS -- 5.2.4.3 In Situ Analysis -- 5.3 Boron Isotope Systematics in Modern Foraminifera -- 5.3.1 Results of Boron Isotope Calibration Studies on Modern Foraminifera -- 5.3.1.1 Deep Sea Benthic Foraminifera-A Model System? -- 5.3.1.2 Planktic Foraminifera-Key Proxy Carriers -- 5.3.1.3 Other Benthic Foraminifera-Enigmatic Signals in High-Mg Calcite and Aragonite -- 5.3.2 Discussion of Boron Isotope Calibration on Modern Foraminifera -- 5.3.2.1 Boron Incorporation in Foraminifera -- 5.3.2.2 Boron Isotope Fractionation in Foraminifera -- 5.3.2.3 Boron Isotope Constraints on Biomineralisation -- 5.4 δ11B-Derived pH and CO2 -- 5.4.1 pH from δ11B -- 5.4.1.1 δ11B of Borate and pH -- 5.4.1.2 KB -- 5.4.1.3 δ11B of Seawater -- 5.4.2 CO2 from pH -- 5.5 Proxy Application: Examples -- 5.5.1 Glacial-Interglacial CO2 -- 5.5.2 pH and CO2 Beyond the Ice Cores -- 5.6 Summary and Outlook -- Acknowledgements -- References -- 6 Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation -- Abstract. , 6.1 Introduction -- 6.2 Calcification in Scleractinian Corals -- 6.3 Boron Isotopic Systematics -- 6.4 Boron Isotopic Compositions of Scleractinian Corals -- 6.5 Experimental Constraints on the Relationship Between Calcifying Fluid pH and Seawater pH -- 6.6 Cold-Water Corals -- 6.7 pH Up-Regulation in the Natural Environment -- 6.7.1 Corals Under Free Ocean Carbon Enrichment (FOCE) Conditions -- 6.7.2 Corals Under Natural Conditions of Seasonal Forcing -- 6.8 Summary and Conclusions -- Acknowledgements -- References -- 7 Boron in the Weathering Environment -- Abstract -- 7.1 The Main Fractionating Mechanisms of Boron on Terrestrial Surfaces -- 7.1.1 The Crystallochemistry of Boron -- 7.1.2 Interaction of Dissolved Boron with Mineral Surfaces -- 7.1.3 Coprecipitation of Boron into Solids -- 7.1.4 Behavior of Boron During Evaporation and Condensation Processes -- 7.1.5 Behavior of Boron in Biological Processes -- 7.2 Biogeochemistry of Boron in the Critical Zone -- 7.2.1 Boron Isotopes in Precipitation -- 7.2.2 Boron Isotopes in Soil Profiles -- 7.2.3 Boron Isotopes at the Catchment Scale -- 7.2.4 Boron Isotopes in Groundwaters -- 7.2.5 Boron Isotopes in River Systems -- 7.2.6 Partitioning of Boron Isotopes Between Water and Modern Day River Sediments -- 7.2.7 Boron Isotopes in Lakes -- 7.3 The Riverine Input of Boron to the Ocean and Secular Evolution of the Ocean -- 7.3.1 The Riverine Input of Boron to the Ocean -- 7.3.2 Boron as an Integrated Tracer of Global Weathering and Erosion -- 7.3.3 The Secular Evolution of Boron Isotopes in the Ocean -- 7.4 Conclusion -- Acknowledgements -- References -- 8 Boron Isotopes in the Ocean Floor Realm and the Mantle -- Abstract -- 8.1 Introduction -- 8.2 The Oceanic Crust -- 8.3 Mid-Ocean Ridge Basalts -- 8.4 Ocean Island Basalts -- 8.5 The Mantle -- 8.6 Hydrothermal Alteration and Weathering. , 8.6.1 Alteration of the Igneous Crust -- 8.6.2 Serpentinization -- 8.6.3 Hydrothermal Vent Fluids -- 8.6.4 Subaerial Hydrothermal Alteration -- 8.7 Oceanic Sediments -- 8.8 Paleo-Ocean Chemistry of Boron -- 8.9 Summary and Outlook -- Acknowledgements -- References -- 9 Boron Isotopes as a Tracer of Subduction Zone Processes -- Abstract -- 9.1 Introduction -- 9.2 Metamorphic Processes in the Subducting Slab -- 9.2.1 Physical and Thermal Geometry of Subduction Zones -- 9.2.2 Subduction Metamorphism: Sediments Including Their Pore Waters -- 9.2.3 Subduction Metamorphism: Altered Oceanic Crust -- 9.2.4 Serpentinized Oceanic Floor and Mantle -- 9.3 Mantle Wedge Processes and the Subduction Interface -- 9.3.1 Boron Isotope Composition of Mantle Wedge Serpentinites -- 9.3.2 Role of the Subduction Interface in B Recycling -- 9.4 Modelling of B Isotope Fractionation During Subduction -- 9.5 Boron Isotope Signature of Volcanic Arcs -- 9.5.1 Global Boron Isotopic Database from Volcanic Arcs -- 9.5.2 Variations of Boron Isotope Signatures with Subducting Slab Parameters -- 9.5.3 Variations of Boron Isotope Signatures with Geochemical Proxies -- 9.6 Deep B Recycling -- 9.7 Outstanding Issues and Future Work Needed -- Acknowledgements -- References -- 10 Boron Isotopes in the Continental Crust: Granites, Pegmatites, Felsic Volcanic Rocks, and Related Ore Deposits -- Abstract -- 10.1 Introduction -- 10.2 Boron in the Continental Crust -- 10.3 B-Isotope Systematics in Crustal Processes -- 10.3.1 Metamorphism and Partial Melting -- 10.3.2 Boron in Granitic Magmas -- 10.3.2.1 Boron in I-Type Magmas -- 10.3.2.2 Processes Affecting B-Isotope Composition in I-Type Magmas: Differentiation, Assimilation, Degassing -- 10.3.2.3 Boron in S-Type Magmas -- 10.3.2.4 Implications for B-Isotope Composition of the Continental Crust. , 10.3.3 Late-Stage Granites and Pegmatites: The Magmatic-Hydrothermal Transition.
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  • 2
    Online Resource
    Online Resource
    Boron Isotopes : The Fifth Element (2018)
    Cham : Springer
    Details Availability
    Keywords: Earth sciences ; Earth Sciences ; Geochemistry ; Mineralogy ; Oceanography ; Bor ; Isotopengeochemie ; Biogeochemie ; Biomineralisation ; Mineralchemie ; Borisotop ; Geochemie ; Kosmochemie ; Erdkruste ; Subduktion ; Borisotop ; Ozeanische Erdkruste ; Kontinentale Erdkruste ; Erdmantel ; Erzlagerstätte ; Saures Gestein ; Bor ; Isotopengeochemie ; Biogeochemie ; Biomineralisation ; Mineralchemie ; Borisotop ; Geochemie ; Kosmochemie ; Erdkruste ; Subduktion ; Borisotop ; Ozeanische Erdkruste ; Kontinentale Erdkruste ; Erdmantel ; Erzlagerstätte ; Saures Gestein
    Description / Table of Contents: This new volume on boron isotope geochemistry offers review chapters summarizing the cosmochemistry, high-temperature and low-temperature geochemistry, and marine chemistry of boron. It also covers theoretical aspects of B isotope fractionation, experiments and atomic modeling, as well as all aspects of boron isotope analyses in geologic materials using the full range of solutions and in-situ methods. The book provides guidance for researchers on the analytical and theoretical aspects, as well as introducing the various scientific applications and research fields in which boron isotopes currently play a major role. The last compendium to summarize the geochemistry of boron and address its isotope geochemistry was published over 20 years ago (Grew &Anovitz, 1996, MSA Review, Vol.33), and there have since been significant advances in analytical techniques, applications and scientific insights into the isotope geochemistry of boron. This volume in the “Advances in Isotope Geochemistry” series provides a valuable source for students and professionals alike, both as an introduction to a new field and as a reference in ongoing research. Chapters 5 and 8 of this book are available open access under a CC BY 4.0 license at link.springer.com
    Type of Medium: Online Resource
    Pages: Online-Ressource (V, 289 p. 89 illus., 83 illus. in color, online resource)
    ISBN: 9783319646664
    Series Statement: Advances in Isotope Geochemistry
    URL: https://doi.org/10.1007/978-3-319-64666-4
    DOI: 10.1007/978-3-319-64666-4
    Language: English
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  • 3
    Electronic Resource
    Electronic Resource
    Negligible glacial–interglacial variation in continental chemical weathering rates (2006)
    [s.l.] : Nature Publishing Group
    Nature 444 (2006), S. 918-921 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide, and on millennial timescales chemical weathering affects the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05365
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  • 4
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    DeepMIP: Model intercomparison of early Eocene climatic optimum (EECO) large-scale climate features and comparison with proxy data (2021)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Climate of the Past, COPERNICUS GESELLSCHAFT MBH, 17(1), pp. 203-227, ISSN: 1814-9324
    Details
    Publication Date: 2021-07-26
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Lessons on Climate Sensitivity From Past Climate Changes (2016)
    Springer
    In:  EPIC3Current Climate Change Reports, Springer, 2(4), pp. 148-158, ISSN: 2198-6061
    Details
    Publication Date: 2019-10-01
    Description: Over the last decade, our understanding of cli- mate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equi- librium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geolog- ical records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitiv- ity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 6
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    Comparing Climate Sensitivity, Past and Present (2018)
    ANNUAL REVIEWS
    In:  EPIC3Annual Review of Marine Science, ANNUAL REVIEWS, 10, pp. 261-288, ISSN: 1941-1405
    Details
    Publication Date: 2018-05-09
    Description: Climate sensitivity represents the global mean temperature change caused by changes in the radiative balance of climate; it is studied for both present/future (actuo) and past (paleo) climate variations, with the former based on instrumental records and/or various types of model simulations. Paleo-estimates are often considered informative for assessments of actuo-climate change caused by anthropogenic greenhouse forcing, but this utility remains debated because of concerns about the impacts of uncertainties, assumptions, and incomplete knowledge about controlling mechanisms in the dynamic climate system, with its multiple interacting feedbacks and their potential dependence on the climate background state. This is exacerbated by the need to assess actuo- and paleoclimate sensitivity over different timescales, with different drivers, and with different (data and/or model) limitations. Here, we visualize these impacts with idealized representations that graphically illustrate the nature of time-dependent actuo- and paleoclimate sensitivity estimates, evaluating the strengths, weaknesses, agreements, and differences of the two approaches. We also highlight priorities for future research to improve the use of paleo-estimates in evaluations of current climate change.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics (2013)
    Elsevier
    In:  EPIC3Chemical Geology, Elsevier, 355(0), pp. 69 - 87, ISSN: 0009-2541
    Details
    Publication Date: 2018-08-10
    Description: Abstract Radiocarbon and uranium-thorium dating results are presented from a genus of calcitic Antarctic cold-water octocorals (family Coralliidae), which were collected from the Marie Byrd Seamounts in the Amundsen Sea (Pacific sector of the Southern Ocean) and which to date have not been investigated geochemically. The geochronological results are set in context with solution and laser ablation-based element/Ca ratios (Li, B, Mg, Mn, Sr, Ba, U, Th). Octocoral radiocarbon ages on living corals are in excellent agreement with modern ambient deep-water �14C, while multiple samples of individual fossil coral specimens yielded reproducible radiocarbon ages. Provided that local radiocarbon reservoir ages can be derived for a given time, fossil Amundsen Sea octocorals should be reliably dateable by means of radiocarbon. In contrast to the encouraging radiocarbon findings, the uranium-series data are more difficult to interpret. The uranium concentration of these calcitic octocorals is an order of magnitude lower than in the aragonitic hexacorals that are conventionally used for geochronological investigations. While modern and Late Holocene octocorals yield initial δ234U in good agreement with modern seawater, our results reveal preferential inward diffusion of dissolved alpha-recoiled 234U and its impact on fossil coral δ234U. Besides alpha-recoil related 234U diffusion, high-resolution sampling of two fossil octocorals further demonstrates that diagenetic uranium mobility has offset apparent coral U-series ages. Combined with the preferential alpha-recoil 234U diffusion, this process has prevented fossil octocorals from preserving a closed system U-series calendar age for longer than a few thousand years. Moreover, several corals investigated contain significant initial thorium, which cannot be adequately corrected for because of an apparently variable initial 232Th/230Th. Our results demonstrate that calcitic cold-water corals are unsuitable for reliable U-series dating. Mg/Ca ratios within single octocoral specimens are internally strikingly homogeneous, and appear promising in terms of their response to ambient temperature. Magnesium/lithium ratios are significantly higher than usually observed in other deep marine calcifiers and for many of our studied corals are remarkably close to seawater compositions. Although this family of octocorals is unsuitable for glacial deep-water �14C reconstructions, our findings highlight some important differences between hexacoral (aragonitic) and octocoral (calcitic) biomineralisation. Calcitic octocorals could still be useful for trace element and some isotopic studies, such as reconstruction of ambient deep water neodymium isotope composition or pH, via boron isotopic measurements.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels (2019)
    copernicus publications
    In:  EPIC3Climate of the Past, copernicus publications, 15(2), pp. 539-554, ISSN: 1814-9332
    Details
    Publication Date: 2019-03-28
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels (2019)
    European Geosciences Union
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Badger, M. P. S., Chalk, T. B., Foster, G. L., Bown, P. R., Gibbs, S. J., Sexton, P. F., Schmidt, D. N., Paelike, H., Mackensen, A., & Pancost, R. D.. Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels. Climate of the Past, 15(2), (2019):539-554 doi:10.5194/cp-15-539-2019.
    Description: Atmospheric pCO2 is a critical component of the global carbon system and is considered to be the major control of Earth's past, present, and future climate. Accurate and precise reconstructions of its concentration through geological time are therefore crucial to our understanding of the Earth system. Ice core records document pCO2 for the past 800 kyr, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO2: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ11B) of foraminifer shells. Here, we present alkenone and δ11B-based pCO2 reconstructions generated from the same samples from the Pliocene and across a Pleistocene glacial–interglacial cycle at Ocean Drilling Program (ODP) Site 999. We find a muted response to pCO2 in the alkenone record compared to contemporaneous ice core and δ11B records, suggesting caution in the interpretation of alkenone-based records at low pCO2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO2.
    Description: This study used samples provided by the International Ocean Discovery Program (IODP). We thank Alex Hull and Gemma Bowler for laboratory work, Lisa Schönborn and Günter Meyer for technical assistance, Alison Kuhl and Ian Bull for research support, and Andy Milton at the University of Southampton for maintaining some of the mass spectrometers used in this study. This study was funded by NERC grant NE/H006273/1 to Richard D. Pancost, Daniela N. Schmidt and Gavin L. Foster (which supported Marcus P. S. Badger). We also acknowledge the ERC Award T-GRES and a Royal Society Wolfson Research Merit Award to Richard D. Pancost. Gavin L. Foster is also supported by a Royal Society Wolfson Research Merit Award. We thank Kirsty Edgar for comments on an early draft of the manuscript, the two anonymous reviewers of this submission, and reviewers through various rounds of review whose comments greatly improved the manuscript. We are grateful to Thomas Bauska for encouraging us to do better at referencing the ice core data, and John Jasper for discussion of the early days of the alkenone palaeobarometer.
    Repository Name: Woods Hole Open Access Server
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  • 10
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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
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