Academic literature on the topic 'Proxies de pCO2'
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Journal articles on the topic "Proxies de pCO2"
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Badger, Marcus P. S., Thomas B. Chalk, Gavin L. Foster, Paul R. Bown, Samantha J. Gibbs, Philip F. Sexton, Daniela N. Schmidt, Heiko Pälike, Andreas Mackensen, and Richard D. Pancost. "Insensitivity of alkenone carbon isotopes to atmospheric CO<sub>2</sub> at low to moderate CO<sub>2</sub> levels." Climate of the Past 15, no. 2 (March 27, 2019): 539–54. http://dx.doi.org/10.5194/cp-15-539-2019.
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Abstract. 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.
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Dupont, Lydie M., Thibaut Caley, and Isla S. Castañeda. "Effects of atmospheric CO<sub>2</sub> variability of the past 800 kyr on the biomes of southeast Africa." Climate of the Past 15, no. 3 (June 19, 2019): 1083–97. http://dx.doi.org/10.5194/cp-15-1083-2019.
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Abstract. Very little is known about the impact of atmospheric carbon dioxide pressure (pCO2) on the shaping of biomes. The development of pCO2 throughout the Brunhes Chron may be considered a natural experiment to elucidate relationships between vegetation and pCO2. While the glacial periods show low to very low values (∼220 to ∼190 ppmv, respectively), the pCO2 levels of the interglacial periods vary from intermediate to relatively high (∼250 to more than 270 ppmv, respectively). To study the influence of pCO2 on the Pleistocene development of SE African vegetation, we used the pollen record of a marine core (MD96-2048) retrieved from Delagoa Bight south of the Limpopo River mouth in combination with stable isotopes and geochemical proxies. Applying endmember analysis, four pollen assemblages could be distinguished representing different biomes: heathland, mountain forest, shrubland and woodland. We find that the vegetation of the Limpopo River catchment and the coastal region of southern Mozambique is influenced not only by hydroclimate but also by temperature and atmospheric pCO2. Our results suggest that the extension of mountain forest occurred during those parts of the glacials when pCO2 and temperatures were moderate and that only during the colder periods when atmospheric pCO2 was low (less than 220 ppmv) open ericaceous vegetation including C4 sedges extended. The main development of woodlands in the area took place after the Mid-Brunhes Event (∼430 ka) when interglacial pCO2 levels regularly rose over 270 ppmv.
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Schwemmer, T. G., H. Baumann, C. S. Murray, A. I. Molina, and J. A. Nye. "Acidification and hypoxia interactively affect metabolism in embryos, but not larvae, of the coastal forage fish Menidia menidia." Journal of Experimental Biology 223, no. 22 (October 12, 2020): jeb228015. http://dx.doi.org/10.1242/jeb.228015.
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ABSTRACTOcean acidification is occurring in conjunction with warming and deoxygenation as a result of anthropogenic greenhouse gas emissions. Multistressor experiments are critically needed to better understand the sensitivity of marine organisms to these concurrent changes. Growth and survival responses to acidification have been documented for many marine species, but studies that explore underlying physiological mechanisms of carbon dioxide (CO2) sensitivity are less common. We investigated oxygen consumption rates as proxies for metabolic responses in embryos and newly hatched larvae of an estuarine forage fish (Atlantic silverside, Menidia menidia) to factorial combinations of CO2×temperature or CO2×oxygen. Metabolic rates of embryos and larvae significantly increased with temperature, but partial pressure of CO2 (PCO2) alone did not affect metabolic rates in any experiment. However, there was a significant interaction between PCO2 and partial pressure of oxygen (PO2) in embryos, because metabolic rates were unaffected by PO2 level at ambient PCO2, but decreased with declining PO2 under elevated PCO2. For larvae, however, PCO2 and PO2 had no significant effect on metabolic rates. Our findings suggest high individual variability in metabolic responses to high PCO2, perhaps owing to parental effects and time of spawning. We conclude that early life metabolism is largely resilient to elevated PCO2 in this species, but that acidification likely influences energetic responses and thus vulnerability to hypoxia.
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Witkowski, Caitlyn R., Sylvain Agostini, Ben P. Harvey, Marcel T. J. van der Meer, Jaap S. Sinninghe Damsté, and Stefan Schouten. "Validation of carbon isotope fractionation in algal lipids as a <i>p</i>CO<sub>2</sub> proxy using a natural CO<sub>2</sub> seep (Shikine Island, Japan)." Biogeosciences 16, no. 22 (November 25, 2019): 4451–61. http://dx.doi.org/10.5194/bg-16-4451-2019.
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Abstract. Carbon dioxide concentrations in the atmosphere play an integral role in many Earth system dynamics, including its influence on global temperature. The past can provide insights into these dynamics, but unfortunately reconstructing long-term trends of atmospheric carbon dioxide (expressed in partial pressure; pCO2) remains a challenge in paleoclimatology. One promising approach for reconstructing past pCO2 utilizes the isotopic fractionation associated with CO2 fixation during photosynthesis into organic matter (εp). Previous studies have focused primarily on testing estimates of εp derived from the δ13C of species-specific alkenone compounds in laboratory cultures and mesocosm experiments. Here, we analyze εp derived from the δ13C of more general algal biomarkers, i.e., compounds derived from a multitude of species from sites near a CO2 seep off the coast of Shikine Island (Japan), a natural environment with CO2 concentrations ranging from ambient (ca. 310 µatm) to elevated (ca. 770 µatm) pCO2. We observed strong, consistent δ13C shifts in several algal biomarkers from a variety of sample matrices over the steep CO2 gradient. Of the three general algal biomarkers explored here, namely loliolide, phytol, and cholesterol, εp positively correlates with pCO2, in agreement with εp theory and previous culture studies. pCO2 reconstructed from the εp of general algal biomarkers show the same trends throughout, as well as the correct control values, but with lower absolute reconstructed values than the measured values at the elevated pCO2 sites. Our results show that naturally occurring CO2 seeps may provide useful testing grounds for pCO2 proxies and that general algal biomarkers show promise for reconstructing past pCO2.
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Li, Xianghui, Jingyu Wang, Troy Rasbury, Min Zhou, Zhen Wei, and Chaokai Zhang. "Early Jurassic climate and atmospheric CO<sub>2</sub> concentration in the Sichuan paleobasin, southwestern China." Climate of the Past 16, no. 6 (November 4, 2020): 2055–74. http://dx.doi.org/10.5194/cp-16-2055-2020.
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Abstract. Climatic oscillations have been developed through the (Early) Jurassic from marine sedimentary archives but remain unclear from terrestrial records. This work presents investigation of climate-sensitive sediments and carbon and oxygen isotope analyses of lacustrine and pedogenic carbonates for the Early Jurassic Ziliujing Formation taken from the Basin in southwestern China. Sedimentary and stable isotope proxies manifest that an overall secular (semi)arid climate dominated the Sichuan Basin during the Early Jurassic, except for the Hettangian. This climate pattern is similar to the arid climate in the Colorado Plateau region in western North America but is distinct from the relatively warm and humid climate in northern China and at high latitudes in the Southern Hemisphere. The estimated atmospheric CO2 concentration (pCO2) from carbon isotopes of pedogenic carbonates shows a range of 980–2610 ppmv (∼3.5–10 times the pre-industrial value) with a mean of 1660 ppmv. Three phases of pCO2 (the Sinemurian 1500–2000 ppmv, the Pliensbachian 1000–1500 ppmv, and the early Toarcian 1094–2610 ppmv) and two events of pCO2 rapidly falling by ∼1000–1300 ppmv are observed, illustrating the pCO2 perturbation in the Early Jurassic. The perturbation of pCO2 is compatible with seawater temperature and carbon cycle from the coeval marine sediments, suggesting a positive feedback of climate to pCO2 through the Early Jurassic.
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Thomsen, J., M. A. Gutowska, J. Saphörster, A. Heinemann, K. Trübenbach, J. Fietzke, C. Hiebenthal, et al. "Calcifying invertebrates succeed in a naturally CO<sub>2</sub> enriched coastal habitat but are threatened by high levels of future acidification." Biogeosciences Discussions 7, no. 4 (July 2, 2010): 5119–56. http://dx.doi.org/10.5194/bgd-7-5119-2010.
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Abstract. CO2 emissions are leading to an acidification of the oceans. Predicting marine community vulnerability towards acidification is difficult, as adaptation processes cannot be accounted for in most experimental studies. Naturally CO2 enriched sites thus can serve as valuable proxies for future changes in community structure. Here we describe a natural analogue site in the Western Baltic Sea. Seawater pCO2 in Kiel Fjord is elevated for large parts of the year due to upwelling of CO2 rich waters. Peak pCO2 values of >230 Pa (>2300 μatm) and pH values of <7.5 are encountered during summer and autumn, average pCO2 values are ~70 Pa (~700 μatm). In contrast to previously described naturally CO2 enriched sites that have suggested a progressive displacement of calcifying auto- and heterotrophic species, the macrobenthic community in Kiel Fjord is dominated by calcifying invertebrates. We show that blue mussels from Kiel Fjord can maintain control rates of somatic and shell growth at a pCO2 of 142 Pa (1400 μatm, pH=7.7). Juvenile mussel recruitment peaks during the summer months, when high water pCO2 values of ~100 Pa (~1000 μatm) prevail. Our findings indicate that calcifying keystone species may be able to cope with surface ocean pH values projected for the end of this century. However, owing to non-linear synergistic effects of future acidification and upwelling of corrosive water, peak seawater pCO2 in Kiel Fjord and many other productive estuarine habitats could increase to values >400 Pa (>4000 μatm). These changes will most likely affect calcification and recruitment, and increase external shell dissolution.
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Thomsen, J., M. A. Gutowska, J. Saphörster, A. Heinemann, K. Trübenbach, J. Fietzke, C. Hiebenthal, et al. "Calcifying invertebrates succeed in a naturally CO<sub>2</sub>-rich coastal habitat but are threatened by high levels of future acidification." Biogeosciences 7, no. 11 (November 26, 2010): 3879–91. http://dx.doi.org/10.5194/bg-7-3879-2010.
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Abstract. CO2 emissions are leading to an acidification of the oceans. Predicting marine community vulnerability towards acidification is difficult, as adaptation processes cannot be accounted for in most experimental studies. Naturally CO2 enriched sites thus can serve as valuable proxies for future changes in community structure. Here we describe a natural analogue site in the Western Baltic Sea. Seawater pCO2 in Kiel Fjord is elevated for large parts of the year due to upwelling of CO2 rich waters. Peak pCO2 values of >230 Pa (>2300 μatm) and pHNBS values of <7.5 are encountered during summer and autumn, average pCO2 values are ~70 Pa (~700 μatm). In contrast to previously described naturally CO2 enriched sites that have suggested a progressive displacement of calcifying auto- and heterotrophic species, the macrobenthic community in Kiel Fjord is dominated by calcifying invertebrates. We show that blue mussels from Kiel Fjord can maintain control rates of somatic and shell growth at a pCO2 of 142 Pa (1400 μatm, pHNBS = 7.7). Juvenile mussel recruitment peaks during the summer months, when high water pCO2 values of ~100 Pa (~1000 μatm) prevail. Our findings indicate that calcifying keystone species may be able to cope with surface ocean pHNBS values projected for the end of this century when food supply is sufficient. However, owing to non-linear synergistic effects of future acidification and upwelling of corrosive water, peak seawater pCO2 in Kiel Fjord and many other productive estuarine habitats could increase to values >400 Pa (>4000 μatm). These changes will most likely affect calcification and recruitment, and increase external shell dissolution.
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Noonan, Sam H. C., and Katharina E. Fabricius. "Ocean acidification affects productivity but not the severity of thermal bleaching in some tropical corals." ICES Journal of Marine Science 73, no. 3 (July 22, 2015): 715–26. http://dx.doi.org/10.1093/icesjms/fsv127.
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Abstract Increasing carbon dioxide (CO2) emissions are raising sea surface temperature (SST) and causing ocean acidification (OA). While higher SST increases the frequency of mass coral bleaching events, it is unclear how OA will interact to affect this process. In this study, we combine in situ bleaching surveys around three tropical CO2 seeps with a 2-month two-factor (CO2 and temperature) tank experiment to investigate how OA and SST in combination will affect the bleaching susceptibility of tropical reef corals. Surveys at CO2 seep and control sites during a minor regional bleaching event gave little indication that elevated pCO2 influenced the bleaching susceptibility of the wider coral community, the four most common coral families (Acroporidae, Faviidae, Pocilloporidae, or Poritidae), or the thermally sensitive coral species Seriatopora hystrix. In the tank experiment, sublethal bleaching was observed at 31°C after 5 d in S. hystrix and 12 d in Acropora millepora, whereas controls (28°C) did not bleach. None of the measured proxies for coral bleaching was negatively affected by elevated pCO2 at pHT 7.79 (vs. 7.95 pHT in controls), equivalent to ∼780 µatm pCO2 and an aragonite saturation state of 2.5. On the contrary, high pCO2 benefitted some photophysiological measures (although temperature effects were much stronger than CO2 effects): maximum photosystem II quantum yields and light-limited electron transport rates increased in both species at high pCO2, whereas gross photosynthesis and pigment concentrations increased in S. hystrix at high pCO2. The field and laboratory data in combination suggest that OA levels up to a pHT of 7.8 will have little effect on the sensitivity of tropical corals to thermal bleaching. Indeed, some species appear to be able to utilize the more abundant dissolved inorganic carbon to increase productivity; however, these gains offset only a small proportion of the massive bleaching-related energy losses during thermal stress.
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Sigwart, Julia D., Gillian Lyons, Artur Fink, Magdalena A. Gutowska, Darren Murray, Frank Melzner, Jonathan D. R. Houghton, and Marian Yong-an Hu. "Elevated pCO2 drives lower growth and yet increased calcification in the early life history of the cuttlefish Sepia officinalis (Mollusca: Cephalopoda)." ICES Journal of Marine Science 73, no. 3 (October 29, 2015): 970–80. http://dx.doi.org/10.1093/icesjms/fsv188.
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Abstract Ocean acidification is an escalating environmental issue and associated changes in the ocean carbonate system have implications for many calcifying organisms. The present study followed the growth of Sepia officinalis from early-stage embryos, through hatching, to 7-week-old juveniles. Responses of cuttlefish to elevated pCO2 (hypercapnia) were investigated to test the impacts of near-future and extreme ocean acidification conditions on growth, developmental time, oxygen consumption, and yolk utilization as proxies for individual fitness. We further examined gross morphological characteristics of the internal calcareous cuttlebone to determine whether embryonically secreted shell lamellae are impacted by environmental hypercapnia. Embryonic growth was reduced and hatching delayed under elevated pCO2, both at environmentally relevant levels (0.14 kPa pCO2 similar to predicted ocean conditions in 2100) and extreme conditions (0.40 kPa pCO2). Comparing various metrics from control and intermediate treatments generally showed no significant difference in experimental measurements. Yet, results from the high pCO2 treatment showed significant changes compared with controls and revealed a consistent general trend across the three treatment levels. The proportion of animal mass contributed by the cuttlebone increased in both elevated pCO2 treatments. Gross cuttlebone morphology was affected under such conditions and cuttlebones of hypercapnic individuals were proportionally shorter. Embryonic shell morphology was maintained consistently in all treatments, despite compounding hypercapnia in the perivitelline fluid; however, post-hatching, hypercapnic animals developed denser cuttlebone laminae in shorter cuttlebones. Juvenile cuttlefish in acidified environments thus experience lower growth and yet increased calcification of their internal shell. The results of this study support recent findings that early cuttlefish life stages are more vulnerable towards hypercapnia than juveniles and adults, which may have negative repercussions on the biological fitness of cuttlefish hatchlings in future oceans.
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Hu, Jin-Jin, Yao-Wu Xing, Tao Su, Yong-Jiang Huang, and Zhe-Kun Zhou. "Stomatal frequency of Quercus glauca from three material sources shows the same inverse response to atmospheric pCO2." Annals of Botany 123, no. 7 (March 12, 2019): 1147–58. http://dx.doi.org/10.1093/aob/mcz020.
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AbstractBackground and AimsThe inverse correlation between atmospheric CO2 partial pressure (pCO2) and stomatal frequency in many plants has been widely used to estimate palaeo-CO2 levels. However, apparent discrepancies exist among the obtained estimates. This study attempts to find a potential proxy for palaeo-CO2 concentrations by analysing the stomatal frequency of Quercus glauca (section Cyclobalanopsis, Fagaceae), a dominant species in East Asian sub-tropical forests with abundant fossil relatives.MethodsStomatal frequencies of Q. glauca from three material sources were analysed: seedlings grown in four climatic chambers with elevated CO2 ranging from 400 to 1300 ppm; extant samples collected from 14 field sites at altitudes ranging from 142 to 1555 m; and 18 herbarium specimens collected between 1930 and 2011. Stomatal frequency–pCO2 correlations were determined using samples from these three sources.Key ResultsAn inverse correlation between stomatal frequency and pCO2 was found for Q. glauca through cross-validation of the three material sources. The combined calibration curves integrating data of extant altitudinal samples and historical herbarium specimens improved the reliability and accuracy of the curves. However, materials in the climatic chambers exhibited a weak response and relatively high stomatal frequency possibly due to insufficient treatment time.ConclusionsA new inverse stomatal frequency–pCO2 correlation for Q. glauca was determined using samples from three sources. These three material types show the same response, indicating that Q. glauca is sensitive to atmospheric pCO2 and is an ideal proxy for palaeo-CO2 levels. Quercus glauca is a nearest living relative (NLR) of section Cyclobalanopsis fossils, which are widely distributed in the strata of East Asia ranging from the Eocene to Pliocene, thereby providing excellent materials to reconstruct the atmospheric CO2 concentration history of the Cenozoic. Quercus glauca will add to the variety of proxies that can be widely used in addition to Ginkgo and Metasequoia.
Dissertations / Theses on the topic "Proxies de pCO2"
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Barker, S. "Planktonic foraminiferal proxies for temperature and pCO2." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596364.
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The thesis aims to describe developments in the uses of planktonic foraminiferal calcite for oceanographic applications, specifically Mg/Ca ratios and foraminiferal shell weights as proxies for calcification temperature and paleo-pCO2 respectively. Sample preparation for the analysis of Mg/Ca and Sr/Ca ratios in foraminiferal calcite is investigated with the aim of defining a method that will give reproducible results and minimise signal contaminations. Each step of the cleaning procedure is scrutinised in order to gauge which are most important and which may be omitted as unnecessary and potentially detrimental to the elemental measurements being made. Success in the application of Mg/Ca-thermometry depends on the ability to quantify and compensate for any alteration of the primary signal after deposition. Compositional variations in foraminiferal calcite may be associated with partial dissolution at the seaflow. Investigation is made into the excessive scatter observed within a latitudinal transect of core-top Mg/Ca and Sr/Ca ratios and attributed to partial dissolution. Possible means of correcting or minimising the effects of such alteration are investigated and assessed. Recent interest in planktonic foraminiferal shell weight loss as a proxy for dissolution, and as such a potential means of quantifying compositional variability, demands investigation into the possibility that initial shell weight may not be constant. It is demonstrated that considerable variability does occur in the shell weights of several species of planktonic foraminifera in the modern surface ocean. It is proposed that initial shell weight is a function of calcification rate and controlled ultimately by the carbonate ion concentration, [CO3=], of ambient seawater during calcification. A first attempt is made to calibrate the effects of [CO3=] on shell weight in the modern ocean. The potential effects of anthropogenic atmospheric CO2 increases on marine calcification are then synthesised using the mineral relations between [CO3=] and calcification rate.
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Godbillot, Camille. "Réponse biogéochimique des coccolithes du Pléistocène aux variations de pCO2." Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS140.
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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 MPTResults 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
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Plancq, Julien. "Identification des producteurs d’alcénones dans le registre sédimentaire du Cénozoïque : implications pour l’utilisation des proxys de paléo-température (UK’ 37) et de paléo-pCO2 (ɛp37 : 2)." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10037/document.
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Les alcénones sont largement utilisées comme proxys pour estimer des températures d’eaux de surface océanique ou des pressions partielles de CO2 (pCO2) dans des périodes anciennes. Dans les océans actuels, ces cétones à longues chaînes carbonées sont essentiellement produites par les coccolithophoridés Emiliania huxleyi et Gephyrocapsa oceanica. Il existe toutefois un écart temporel important entre le premier enregistrement sédimentaire des alcénones au Crétacé (~120 Ma) et la première apparition des producteurs actuels (< 2 Ma). Il apparaît donc essentiel d’identifier les producteurs anciens d’alcénones afin d’assurer la fiabilité des proxys environnementaux basés sur ces biomarqueurs pour les périodes préquaternaires. Cette thèse présente trois cas d’étude correspondant à des périodes clés de l’évolution de la famille des Noëlaerhabdaceae, qui comprend les ancêtres cénozoïques des producteurs actuels d’alcénones. La comparaison entre le contenu en alcénones (distribution et concentrations) et les abondances relatives et absolues des différentes espèces de Noëlaerhabdaceae dans des sédiments marins datant de l’Eocène-Oligocène (35-31 Ma), del’Oligocène-Miocène (25-16 Ma) et du Pliocène supérieur (3,6-2,6 Ma) montre que,contrairement aux hypothèses précédentes, Reticulofenestra n’était pas le seul genre responsable de la production d’alcénones au Cénozoïque. Les résultats démontrent également qu’il est essentiel d’identifier avec précision les producteurs et la taille de leur cellule pour les estimations de pCO2. Au contraire, l’identification formelle des producteurs ne semble pas indispensable pour obtenir des estimations de températures cohérentesAlkenones have been widely used as proxies for the reconstruction of sea surface temperatures and of partial pressure of CO2 (pCO2) in ancient periods. In modern oceans, these long-chain ketones are mainly produced by the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica. However, there is a huge gap between the first record of alkenonesin the Cretaceous (~120 Ma) and the first occurrence of the modern alkenone producers (< 2Ma). Thus, it seems crucial to identify ancient alkenone producers to ensure the applicability of environmental proxies based on these biomarkers in pre-Quaternary sediments. In this PhD thesis, three case studies are considered corresponding to key periods in the evolution history of the Noelaerhabdaceae family, which includes the Cenozoic ancestors of modern alkenone producers. The comparison between alkenone contents (distribution and concentrations) andNoelaerhabdaceae species-specific relative and absolute abundances in marine sedimentsdating back to the Eocene-Oligocene (35-31 Ma), the Oligocene-Miocene (25-16 Ma) and thelate Pliocene (3.6-2.6 Ma) shows that, contrary to common assumptions, Reticulofenestra was not the only genus responsible for alkenone production during the Cenozoic. Results also underscore the importance of a careful identification of alkenone producers and of their cellsize for pCO2 reconstructions for pre-Quaternary periods. On the contrary, the identificationof producers does not seem essential to obtain consistent paleo-temperature estimates
Book chapters on the topic "Proxies de pCO2"
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Knoll, Andrew H., and Woodward W. Fischer. "Skeletons and Ocean Chemistry: The Long View." In Ocean Acidification. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199591091.003.0009.
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In present-day seas, animals, algae, and protozoa are threatened by ocean acidification, amplified in many regions by seawater warming and hypoxia (Doney et al . 2009 ). Many species may be affected adversely by 21st-century environmental change, but a decade of research suggests that the hypercalcifying animals responsible for reef accretion may be especially vulnerable to an acidity-driven decrease in the saturation state (Ω; see Box 1.1) of surface seawater with respect to calcite and aragonite. The geological record reveals that natural changes in the marine carbonate system have affected the evolution and abundance of calcifying organisms throughout the Phanerozoic Eon (542 million years (Myr) ago to the present). This being the case, we can use our understanding of the dynamic behaviour of the carbon cycle and the stratigraphic comings and goings of reef-building organisms to inform us about what, if any, lessons can be drawn from the long-term past and applied to our nearterm future. If there is one thing that geology makes clear it is that the earth and its biota are in a continual state of change. Because of its relationship to climate, the partial pressure of CO2 (pCO2) in the atmosphere has been of particular interest to geologists and geochemists, but direct measurement of ancient CO2 levels is impossible for intervals older than those recorded in glacial ice preserved today near the poles and at high altitude (Petit et al . 1999). Therefore, deep-time estimates of pCO2 rely on models, broadly constrained by geochemical proxy data. For example, the widely applied models of Berner and colleagues (e.g. GEOCARB III; Berner and Kothavala 2001; Berner 2006; Fig. 4.1C) estimate fluxes of carbon from one reservoir to another, based on geochemical proxies (mainly isotope ratios and abundances of sedimentary carbonate and organic carbon), and then calculate successive steady states of the system through time. Additional parameters are considered, including estimates of carbon fluxes due to erosion, river run-off, plant evolution, volcanic weathering, global CO2 degassing, and land area; these also influence the model results.
Conference papers on the topic "Proxies de pCO2"
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Zhu, Lu, Neil J. Tabor, and Neil J. Tabor. "EARLY PERMIAN ATMOSPHERIC pCO2 ESTIMATES AND REPRODUCIBILITY OF PALEOSOLS AS ISOTOPIC PROXIES FOR PALEOCLIMATE, EASTERN SHELF OF THE MIDLAND BASIN, NORTH-CENTRAL TEXAS." In 54th Annual GSA South-Central Section Meeting 2020. Geological Society of America, 2020. http://dx.doi.org/10.1130/abs/2020sc-343559.
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