Influence of citric acid on thermoplastic wheat flour/poly (lactic acid) blends. II. Barrier properties and water vapor sorption isotherms

The effects of citric acid on wheat flour/glycerol/poly(lactic) acid (PLA) blends prepared by one-step twin-screw extrusion have been studied to improve barrier properties of starch based materials. A series of injected samples were produced from prepared compounds with varying ratio (0-20 part) of citric acid. The effects of citric acid on the water vapor permeability, oxygen permeability and water solubility in the film were then investigated. The barrier properties results proved that citric acid behaves as compatibilizing agent between starch and PLA phases for ratios between 0 and 10 parts. When the added amount exceeds 10 parts, CA acted as a plasticizer and/or promoted the hydrolysis of the starch glycosidic bonds

Réponse biogéochimique des coccolithes du Pléistocène aux variations de pCO2

Results from both in vivo cultures and cell modelling biogeochemical studies have demonstrated a link between the biological fractionation of coccoliths and the CO2 concentration of the living environment of their producers, the coccolithophores. These results have encouraged the use of coccolith vital effects as proxies for the levels of CO2 in the medium. However, a number of biases hinder the application of the empirical calibrations from culture experiments to natural coccolith populations. This work aims at formalizing the transfer function linking the vital effects to the [CO2aq] in natural environments, to be used for the reconstruction of past pCO2. To this end, we use the records from Antarctic ice cores to quantify the forcing of pCO2 on the magnitude of the coccoliths’ vital effects. We evidence, and discuss, a control of CO2 concentrations on the isotopic difference (Δδ18O, Δδ13C) between coccoliths of different sizes produced during the penultimate glacial termination (130-140 ka). The second part of this thesis is dedicated to applying the transfer function to coccoliths from the Mid-Pleistocene Transition (800-1250 ka), a key period of climate change for which pCO2 variations are not documented. The pCO2 record we obtain, which covers the entire transition, exhibits self-consistent amplitudes and variations, thus giving credit to the calibration we present. Our record supports the hypothesis of an increased sensitivity of ice sheets to the radiative forcing of CO2 since the MPT.Des résultats croisés d’études biogéochimiques de cultures in vivo et de modélisations cellulaires ont mis en évidence un lien entre le fractionnement biologique des coccolithes et la concentration en CO2 du milieu de vie de leurs producteurs, les coccolithophoridés. Ces résultats ont ouvert la voie à l’utilisation des effets vitaux des coccolithes comme proxy du CO2 dans le milieu. Toutefois, des biais affectent l’application des calibrations empiriques de culture à des populations naturelles de coccolithes. Ainsi, ce travail cherche à formaliser la fonction de transfert entre les effets vitaux et les [CO2aq] en milieu naturel, qui puisse être appliquée pour reconstruire les pCO2 passées. Nous utilisons pour cela les enregistrements provenant des carottes de glace antarctiques pour quantifier le forçage de la pCO2 sur l’intensité des effets vitaux des coccolithes. Nous mettons notamment en évidence, et discutons, un contrôle des concentrations en CO2 sur la différence isotopique (Δδ18O, Δδ13C) entre coccolithes de différentes tailles produits pendant la pénultième terminaison glaciaire (130-140 ka). Dans un deuxième volet de la thèse, nous appliquons cette fonction de transfert à des coccolithes datant de la transition mi-Pléistocène (800-1250 ka), une période clé de changement climatique, pour laquelle les pCO2 ne sont pas documentées. Nous obtenons un enregistrement de pCO2 avec des amplitudes et des variations cohérentes couvrant l’intégralité de la transition, ce qui accrédite la calibration proposée. Nos travaux permettent d’étayer l’hypothèse d’une sensibilité accrue des calottes glaciaires au forçage radiatif par le CO2 depuis la MPT

Réponse biogéochimique des coccolithes du Pléistocène aux variations de pCO2

Results from both in vivo cultures and cell modelling biogeochemical studies have demonstrated a link between the biological fractionation of coccoliths and the CO2 concentration of the living environment of their producers, the coccolithophores. These results have encouraged the use of coccolith vital effects as proxies for the levels of CO2 in the medium. However, a number of biases hinder the application of the empirical calibrations from culture experiments to natural coccolith populations. This work aims at formalizing the transfer function linking the vital effects to the [CO2aq] in natural environments, to be used for the reconstruction of past pCO2. To this end, we use the records from Antarctic ice cores to quantify the forcing of pCO2 on the magnitude of the coccoliths’ vital effects. We evidence, and discuss, a control of CO2 concentrations on the isotopic difference (Δδ18O, Δδ13C) between coccoliths of different sizes produced during the penultimate glacial termination (130-140 ka). The second part of this thesis is dedicated to applying the transfer function to coccoliths from the Mid-Pleistocene Transition (800-1250 ka), a key period of climate change for which pCO2 variations are not documented. The pCO2 record we obtain, which covers the entire transition, exhibits self-consistent amplitudes and variations, thus giving credit to the calibration we present. Our record supports the hypothesis of an increased sensitivity of ice sheets to the radiative forcing of CO2 since the MPT.Des résultats croisés d’études biogéochimiques de cultures in vivo et de modélisations cellulaires ont mis en évidence un lien entre le fractionnement biologique des coccolithes et la concentration en CO2 du milieu de vie de leurs producteurs, les coccolithophoridés. Ces résultats ont ouvert la voie à l’utilisation des effets vitaux des coccolithes comme proxy du CO2 dans le milieu. Toutefois, des biais affectent l’application des calibrations empiriques de culture à des populations naturelles de coccolithes. Ainsi, ce travail cherche à formaliser la fonction de transfert entre les effets vitaux et les [CO2aq] en milieu naturel, qui puisse être appliquée pour reconstruire les pCO2 passées. Nous utilisons pour cela les enregistrements provenant des carottes de glace antarctiques pour quantifier le forçage de la pCO2 sur l’intensité des effets vitaux des coccolithes. Nous mettons notamment en évidence, et discutons, un contrôle des concentrations en CO2 sur la différence isotopique (Δδ18O, Δδ13C) entre coccolithes de différentes tailles produits pendant la pénultième terminaison glaciaire (130-140 ka). Dans un deuxième volet de la thèse, nous appliquons cette fonction de transfert à des coccolithes datant de la transition mi-Pléistocène (800-1250 ka), une période clé de changement climatique, pour laquelle les pCO2 ne sont pas documentées. Nous obtenons un enregistrement de pCO2 avec des amplitudes et des variations cohérentes couvrant l’intégralité de la transition, ce qui accrédite la calibration proposée. Nos travaux permettent d’étayer l’hypothèse d’une sensibilité accrue des calottes glaciaires au forçage radiatif par le CO2 depuis la MPT

Biogeochemical response of coccoliths from the Pleistocene to the variations of pCO2

Des résultats croisés d’études biogéochimiques de cultures in vivo et de modélisations cellulaires ont mis en évidence un lien entre le fractionnement biologique des coccolithes et la concentration en CO2 du milieu de vie de leurs producteurs, les coccolithophoridés. Ces résultats ont ouvert la voie à l’utilisation des effets vitaux des coccolithes comme proxy du CO2 dans le milieu. Toutefois, des biais affectent l’application des calibrations empiriques de culture à des populations naturelles de coccolithes. Ainsi, ce travail cherche à formaliser la fonction de transfert entre les effets vitaux et les [CO2aq] en milieu naturel, qui puisse être appliquée pour reconstruire les pCO2 passées. Nous utilisons pour cela les enregistrements provenant des carottes de glace antarctiques pour quantifier le forçage de la pCO2 sur l’intensité des effets vitaux des coccolithes. Nous mettons notamment en évidence, et discutons, un contrôle des concentrations en CO2 sur la différence isotopique (Δδ18O, Δδ13C) entre coccolithes de différentes tailles produits pendant la pénultième terminaison glaciaire (130-140 ka). Dans un deuxième volet de la thèse, nous appliquons cette fonction de transfert à des coccolithes datant de la transition mi-Pléistocène (800-1250 ka), une période clé de changement climatique, pour laquelle les pCO2 ne sont pas documentées. Nous obtenons un enregistrement de pCO2 avec des amplitudes et des variations cohérentes couvrant l’intégralité de la transition, ce qui accrédite la calibration proposée. Nos travaux permettent d’étayer l’hypothèse d’une sensibilité accrue des calottes glaciaires au forçage radiatif par le CO2 depuis la MPT.Results from both in vivo cultures and cell modelling biogeochemical studies have demonstrated a link between the biological fractionation of coccoliths and the CO2 concentration of the living environment of their producers, the coccolithophores. These results have encouraged the use of coccolith vital effects as proxies for the levels of CO2 in the medium. However, a number of biases hinder the application of the empirical calibrations from culture experiments to natural coccolith populations. This work aims at formalizing the transfer function linking the vital effects to the [CO2aq] in natural environments, to be used for the reconstruction of past pCO2. To this end, we use the records from Antarctic ice cores to quantify the forcing of pCO2 on the magnitude of the coccoliths’ vital effects. We evidence, and discuss, a control of CO2 concentrations on the isotopic difference (Δδ18O, Δδ13C) between coccoliths of different sizes produced during the penultimate glacial termination (130-140 ka). The second part of this thesis is dedicated to applying the transfer function to coccoliths from the Mid-Pleistocene Transition (800-1250 ka), a key period of climate change for which pCO2 variations are not documented. The pCO2 record we obtain, which covers the entire transition, exhibits self-consistent amplitudes and variations, thus giving credit to the calibration we present. Our record supports the hypothesis of an increased sensitivity of ice sheets to the radiative forcing of CO2 since the MPT

Reconstruction des pCO2 atmosphériques quaternaires par la géochimie des coccolithes

International audienc

Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: Developing a new paleo-CO₂ probe

Beyond the pCO 2 records provided by ice core measurements, the quantification of atmospheric CO 2 concentrations and changes thereof relies on proxy data, the development of which represents a foremost challenge in paleoceanography. In the paleoceanographic toolbox, the coccolithophores occupy a notable place, as the magnitude of the carbon isotopic 15 fractionation between ambient CO 2 and a type of organic compounds that these photosynthetic microalgae synthesize (the alkenones) represents a relatively robust proxy to reconstruct past atmospheric CO 2 concentrations during the Cenozoic. The isotopic composition of coeval calcite biominerals found in the sediments and also produced by the coccolithophores (the coccoliths) have been found to record an ambient CO 2 signal through culture and sediment analyses. These studies have, however, not yet formalized a transfer function that quantitatively ties the isotopic composition of coccolith calcite to the 20 concentrations of aqueous CO 2 , and, ultimately, to atmospheric CO 2 levels. Here, we make use of a micro-separation protocol to compare the isotopic response of two size-restricted coccolith assemblages from the North Atlantic to changes in surface ocean CO 2 during Termination II (ca. 130-140 ka). Performing paired measurements of the isotopic composition (δ 13 C and δ 18 O) of relatively large and small coccoliths provides an isotopic offset that can be designated as a "differential vital effect". We find that the evolution of this offset follows that of aqueous CO 2 concentrations computed from the ice core CO 2 curve 25 and an independent temperature signal. We interpret this biogeochemical feature to be the result of converging carbon fixation strategies between large and small cells as the degree of carbon limitation for cellular growth decreases across the deglaciation. We are therefore able to determine a transfer function between the coccolith differential vital effects and aqueous CO 2 in the range of Quaternary CO 2 concentrations. We here consolidate a new coccolith ∆δ 13 C proxy that overtakes the strong assumptions that have to be made pertaining to the chemistry of the carbonate system in seawater, as required in CO 2 proxy 30 methods such as the boron isotope and alkenone proxies

Enhancing our palaeoceanographic toolbox using paired foraminiferal and coccolith calcite measurements from pelagic sequences

International audienc

Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: developing a new paleo-CO2_2 probe

International audienceBeyond the pCO$_2$ records provided by ice core measurements, the quantification of atmospheric CO$_2$ concentrations and changes thereof relies on proxy data, the development of which represents a foremost challenge in paleoceanography. In the paleoceanographic toolbox, the coccolithophores occupy a notable place, as the magnitude of the carbon isotopic fractionation between ambient CO$_2$ and a type of organic compounds that these photosynthetic microalgae synthesize (the alkenones) represents a relatively robust proxy to reconstruct past atmospheric CO$_2$ concentrations during the Cenozoic. The isotopic composition of coeval calcite biominerals found in the sediments and also produced by the coccolithophores (the coccoliths) have been found to record an ambient CO$_2$ signal through culture and sediment analyses. These studies have, however, not yet formalized a transfer function that quantitatively ties the isotopic composition of coccolith calcite to the concentrations of aqueous CO$_2$ and, ultimately, to atmospheric CO$_2$ levels. Here, we make use of a microseparation protocol to compare the isotopic response of two size-restricted coccolith assemblages from the North Atlantic to changes in surface ocean CO$_2$ during Termination II (ca. 130–140 ka). Performing paired measurements of the isotopic composition (δ$^{13}$C and δ$^{18}$O) of relatively large and small coccoliths provides an isotopic offset that can be designated as a “differential vital effect”. We find that the evolution of this offset follows that of aqueous CO$_2$ concentrations computed from the ice core CO$_2$ curve and an independent temperature signal. We interpret this biogeochemical feature to be the result of converging carbon fixation strategies between large and small cells as the degree of carbon limitation for cellular growth decreases across the deglaciation. We are therefore able to outline a first-order trend between the coccolith differential vital effects and aqueous CO$_2$ in the range of Quaternary CO$_2$ concentrations. Although this study would benefit from further constraints on the other controls at play on coccolith geochemistry (growth rate, air–sea gas exchange, etc.), this test of the drivers of coccolith Δδ$^{13}$C and Δδ$^{18}$O in natural conditions is a new step in the development of a coccolith paleo-CO$_2$ probe

Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: Developing a new paleo-CO₂ probe

Beyond the pCO 2 records provided by ice core measurements, the quantification of atmospheric CO 2 concentrations and changes thereof relies on proxy data, the development of which represents a foremost challenge in paleoceanography. In the paleoceanographic toolbox, the coccolithophores occupy a notable place, as the magnitude of the carbon isotopic 15 fractionation between ambient CO 2 and a type of organic compounds that these photosynthetic microalgae synthesize (the alkenones) represents a relatively robust proxy to reconstruct past atmospheric CO 2 concentrations during the Cenozoic. The isotopic composition of coeval calcite biominerals found in the sediments and also produced by the coccolithophores (the coccoliths) have been found to record an ambient CO 2 signal through culture and sediment analyses. These studies have, however, not yet formalized a transfer function that quantitatively ties the isotopic composition of coccolith calcite to the 20 concentrations of aqueous CO 2 , and, ultimately, to atmospheric CO 2 levels. Here, we make use of a micro-separation protocol to compare the isotopic response of two size-restricted coccolith assemblages from the North Atlantic to changes in surface ocean CO 2 during Termination II (ca. 130-140 ka). Performing paired measurements of the isotopic composition (δ 13 C and δ 18 O) of relatively large and small coccoliths provides an isotopic offset that can be designated as a "differential vital effect". We find that the evolution of this offset follows that of aqueous CO 2 concentrations computed from the ice core CO 2 curve 25 and an independent temperature signal. We interpret this biogeochemical feature to be the result of converging carbon fixation strategies between large and small cells as the degree of carbon limitation for cellular growth decreases across the deglaciation. We are therefore able to determine a transfer function between the coccolith differential vital effects and aqueous CO 2 in the range of Quaternary CO 2 concentrations. We here consolidate a new coccolith ∆δ 13 C proxy that overtakes the strong assumptions that have to be made pertaining to the chemistry of the carbonate system in seawater, as required in CO 2 proxy 30 methods such as the boron isotope and alkenone proxies

Analysis of water binding in starch plasticized films

International audiencehe water-binding properties of wheat starch films were studied through the determination of water vapour adsorption isotherms at 20°C. Starch films were obtained by casting after mixing native starch at 95°C for 15 min with different ratios of plasticizer (glycerol)