139,361 research outputs found
Understanding the interactions between tectonic processes, erosion, weathering and climate. New insights from the DynSoil-GEOCLIM modelling approach
No full textInternational audienceEarth's long-term climate stability is postulated to be maintained by the silicate weathering feedback. Long-term changes on Earth's surface can significantly affect the strength of this feedback and are proposed as drivers for climatic variations over the course of Earth History. Among these modulating processes, we focus on the role of erosion (eg, Milot et al. 2002, EPSL 196 83-98), regolith development and its shielding effect (eg, Godderis et al. 2014, Earth Sci Rev 128 122-138), and the exhumation of specific geological units, for instance mafic complexes during arc-continent collision (eg, Macdonald et al., 2019, Science 364 181-184). Understanding the interlinked effects of these processes throughout Earth History is a challenge for which numerical modeling can be helpful. The GEOCLIM model (Donnadieu et al., 2006, G3 7(11)) simulates geochemical cycles, specifically the carbon cycle, and climate dynamics on geological timescales. A newly implemented model for weathering fluxes (DynSoil) now explicitly simulates the interaction between physical erosion, climatology, and the development of chemical weathering profiles. We have integrated this model with global spatially resolved lithology to account for the varying carbon sequestration potential of different rock types. This model framework can be used to investigate the equilibrium state of carbon-climate system, as well as transient perturbations, accounting for the potential inertia of weathering profiles. Preliminary results have shown the ambiguous effect of mountain building that affects both climate circulation and continental erosion (Maffre et al. 2018, EPSL 493 174-185). Using this model, we show that the uplift of high weathering potential silicate rocks in the tropics can significantly drawdown atmospheric carbon dioxide and play a role in initiating glacial climate
Modelling the snowball Earth: from its inception to its aftermath
No full textInternational audienceThe relationship between CO2 variation and Neoproterozoic glaciation has deeply evolved these last years. Through the use of an innovative climate-carbon coupled model, the causes of the CO2 decrease that led to the onset of the global glaciation (Sturtian) has been shown to be strongly related to the dislocation of the Rodinia super continent, promoting CO2 consumption through silicate weathering1. Another important issue is the evolution of atmospheric CO2 during the Snowball episode itself. It appears not to be just a linear accumulation with time through the ongoing solid Earth degassing. Indeed, efficient CO2 diffusion in seawater might have promoted the oceanic crust dissolution, resulting in an asymptotic CO2 rise in the atmosphere2,3, stressing the question of the snowball melting threshold. Indeed, it has been shown that greenhouse climate induced by the storage of the CO2 in the atmosphere invoked to escape a snowball Earth was possibly not sufficient to melt the snowball Earth due to thermal inversion in vertical column4. Therefore, CO2 is may be not the only trigger for the deglaciation. Finally, the super greenhouse climate thought to have followed the snowball episode was explored. We demonstrate that, despite very high temperatures under 0.2 bars of CO2, the amount of rainfall might have been limited by the availability of latent heat which cannot be higher that the total energy provided by the sun. As a consequence of limited increase in the water cycling, CO2 consumption by continental weathering might not exceed 10 times its present day value. The return to normal climatic conditions after the snowball melting should thus have lasted several million of years, further increasing the biological perturbations linked to a snowball event5. The aim of this contribution is to revisit the issue of the role of atmospheric CO2 before, during and after a Snowball Earth and to deliver a new picture of its feedbacks with climate. 1. Donnadieu, Y., Y. Godderis, et al. (2004). "A 'snowball Earth' climate triggered by continental break-up through changes in runoff." Nature 428(6980): 303- 306. 2. Ramstein G., Donnadieu Y., Goddéris Y. Proterozoic glaciations. Comptes Rendus Geoscience 336 (7-8): 639-646 Jun 2004 3. Le Hir G., Goddéris Y., Donnadieu Y., Ramstein G. (2008). A geochemical modelling study of the evolution of the chemical composition of seawater linked to a "snowball" glaciation. Biogeosci. 5, 253-267. 4. Le Hir Guillaume , Goddéris Yves, Donnadieu Yannick , Ramstein Gilles (2008) A scenario for the evolution of the atmopsheric pCO2 during a Snowball Earth, Geology, 36 (1): 47-50 5. Pierrehumbert, R.T. (2004). High levels of atmospheric carbon dioxide necessary for the termination of global glaciation: Nature, v. 429, p. 646-649, doi: 10.1038/nature02640. 6. Le Hir Guillaume, Donnadieu Yannick, Goddéris Y, Pierrehumbert Raymond T., Halverson Galen P., Macouin Mélina, Nédélec Anne b, Ramstein Gilles. (2008).The snowball Earth aftermath: Exploring the limits of continental weathering processes, Earth and Planetary Science Letters, EPSL-09573; No of Pages 11
Modelling the snowball Earth: from its inception to its aftermath
No full textInternational audienceThe relationship between CO2 variation and Neoproterozoic glaciation has deeply evolved these last years. Through the use of an innovative climate-carbon coupled model, the causes of the CO2 decrease that led to the onset of the global glaciation (Sturtian) has been shown to be strongly related to the dislocation of the Rodinia super continent, promoting CO2 consumption through silicate weathering1. Another important issue is the evolution of atmospheric CO2 during the Snowball episode itself. It appears not to be just a linear accumulation with time through the ongoing solid Earth degassing. Indeed, efficient CO2 diffusion in seawater might have promoted the oceanic crust dissolution, resulting in an asymptotic CO2 rise in the atmosphere2,3, stressing the question of the snowball melting threshold. Indeed, it has been shown that greenhouse climate induced by the storage of the CO2 in the atmosphere invoked to escape a snowball Earth was possibly not sufficient to melt the snowball Earth due to thermal inversion in vertical column4. Therefore, CO2 is may be not the only trigger for the deglaciation. Finally, the super greenhouse climate thought to have followed the snowball episode was explored. We demonstrate that, despite very high temperatures under 0.2 bars of CO2, the amount of rainfall might have been limited by the availability of latent heat which cannot be higher that the total energy provided by the sun. As a consequence of limited increase in the water cycling, CO2 consumption by continental weathering might not exceed 10 times its present day value. The return to normal climatic conditions after the snowball melting should thus have lasted several million of years, further increasing the biological perturbations linked to a snowball event5. The aim of this contribution is to revisit the issue of the role of atmospheric CO2 before, during and after a Snowball Earth and to deliver a new picture of its feedbacks with climate. 1. Donnadieu, Y., Y. Godderis, et al. (2004). "A 'snowball Earth' climate triggered by continental break-up through changes in runoff." Nature 428(6980): 303- 306. 2. Ramstein G., Donnadieu Y., Goddéris Y. Proterozoic glaciations. Comptes Rendus Geoscience 336 (7-8): 639-646 Jun 2004 3. Le Hir G., Goddéris Y., Donnadieu Y., Ramstein G. (2008). A geochemical modelling study of the evolution of the chemical composition of seawater linked to a "snowball" glaciation. Biogeosci. 5, 253-267. 4. Le Hir Guillaume , Goddéris Yves, Donnadieu Yannick , Ramstein Gilles (2008) A scenario for the evolution of the atmopsheric pCO2 during a Snowball Earth, Geology, 36 (1): 47-50 5. Pierrehumbert, R.T. (2004). High levels of atmospheric carbon dioxide necessary for the termination of global glaciation: Nature, v. 429, p. 646-649, doi: 10.1038/nature02640. 6. Le Hir Guillaume, Donnadieu Yannick, Goddéris Y, Pierrehumbert Raymond T., Halverson Galen P., Macouin Mélina, Nédélec Anne b, Ramstein Gilles. (2008).The snowball Earth aftermath: Exploring the limits of continental weathering processes, Earth and Planetary Science Letters, EPSL-09573; No of Pages 11
Understanding the interactions between tectonic processes, erosion, weathering and climate. New insights from the DynSoil-GEOCLIM modelling approach
No full textInternational audienceEarth's long-term climate stability is postulated to be maintained by the silicate weathering feedback. Long-term changes on Earth's surface can significantly affect the strength of this feedback and are proposed as drivers for climatic variations over the course of Earth History. Among these modulating processes, we focus on the role of erosion (eg, Milot et al. 2002, EPSL 196 83-98), regolith development and its shielding effect (eg, Godderis et al. 2014, Earth Sci Rev 128 122-138), and the exhumation of specific geological units, for instance mafic complexes during arc-continent collision (eg, Macdonald et al., 2019, Science 364 181-184). Understanding the interlinked effects of these processes throughout Earth History is a challenge for which numerical modeling can be helpful. The GEOCLIM model (Donnadieu et al., 2006, G3 7(11)) simulates geochemical cycles, specifically the carbon cycle, and climate dynamics on geological timescales. A newly implemented model for weathering fluxes (DynSoil) now explicitly simulates the interaction between physical erosion, climatology, and the development of chemical weathering profiles. We have integrated this model with global spatially resolved lithology to account for the varying carbon sequestration potential of different rock types. This model framework can be used to investigate the equilibrium state of carbon-climate system, as well as transient perturbations, accounting for the potential inertia of weathering profiles. Preliminary results have shown the ambiguous effect of mountain building that affects both climate circulation and continental erosion (Maffre et al. 2018, EPSL 493 174-185). Using this model, we show that the uplift of high weathering potential silicate rocks in the tropics can significantly drawdown atmospheric carbon dioxide and play a role in initiating glacial climate
Modelling the snowball Earth: from its inception to its aftermath
No full textInternational audienceThe relationship between CO2 variation and Neoproterozoic glaciation has deeply evolved these last years. Through the use of an innovative climate-carbon coupled model, the causes of the CO2 decrease that led to the onset of the global glaciation (Sturtian) has been shown to be strongly related to the dislocation of the Rodinia super continent, promoting CO2 consumption through silicate weathering1. Another important issue is the evolution of atmospheric CO2 during the Snowball episode itself. It appears not to be just a linear accumulation with time through the ongoing solid Earth degassing. Indeed, efficient CO2 diffusion in seawater might have promoted the oceanic crust dissolution, resulting in an asymptotic CO2 rise in the atmosphere2,3, stressing the question of the snowball melting threshold. Indeed, it has been shown that greenhouse climate induced by the storage of the CO2 in the atmosphere invoked to escape a snowball Earth was possibly not sufficient to melt the snowball Earth due to thermal inversion in vertical column4. Therefore, CO2 is may be not the only trigger for the deglaciation. Finally, the super greenhouse climate thought to have followed the snowball episode was explored. We demonstrate that, despite very high temperatures under 0.2 bars of CO2, the amount of rainfall might have been limited by the availability of latent heat which cannot be higher that the total energy provided by the sun. As a consequence of limited increase in the water cycling, CO2 consumption by continental weathering might not exceed 10 times its present day value. The return to normal climatic conditions after the snowball melting should thus have lasted several million of years, further increasing the biological perturbations linked to a snowball event5. The aim of this contribution is to revisit the issue of the role of atmospheric CO2 before, during and after a Snowball Earth and to deliver a new picture of its feedbacks with climate. 1. Donnadieu, Y., Y. Godderis, et al. (2004). "A 'snowball Earth' climate triggered by continental break-up through changes in runoff." Nature 428(6980): 303- 306. 2. Ramstein G., Donnadieu Y., Goddéris Y. Proterozoic glaciations. Comptes Rendus Geoscience 336 (7-8): 639-646 Jun 2004 3. Le Hir G., Goddéris Y., Donnadieu Y., Ramstein G. (2008). A geochemical modelling study of the evolution of the chemical composition of seawater linked to a "snowball" glaciation. Biogeosci. 5, 253-267. 4. Le Hir Guillaume , Goddéris Yves, Donnadieu Yannick , Ramstein Gilles (2008) A scenario for the evolution of the atmopsheric pCO2 during a Snowball Earth, Geology, 36 (1): 47-50 5. Pierrehumbert, R.T. (2004). High levels of atmospheric carbon dioxide necessary for the termination of global glaciation: Nature, v. 429, p. 646-649, doi: 10.1038/nature02640. 6. Le Hir Guillaume, Donnadieu Yannick, Goddéris Y, Pierrehumbert Raymond T., Halverson Galen P., Macouin Mélina, Nédélec Anne b, Ramstein Gilles. (2008).The snowball Earth aftermath: Exploring the limits of continental weathering processes, Earth and Planetary Science Letters, EPSL-09573; No of Pages 11
Modelling the snowball Earth: from its inception to its aftermath
No full textInternational audienceThe relationship between CO2 variation and Neoproterozoic glaciation has deeply evolved these last years. Through the use of an innovative climate-carbon coupled model, the causes of the CO2 decrease that led to the onset of the global glaciation (Sturtian) has been shown to be strongly related to the dislocation of the Rodinia super continent, promoting CO2 consumption through silicate weathering1. Another important issue is the evolution of atmospheric CO2 during the Snowball episode itself. It appears not to be just a linear accumulation with time through the ongoing solid Earth degassing. Indeed, efficient CO2 diffusion in seawater might have promoted the oceanic crust dissolution, resulting in an asymptotic CO2 rise in the atmosphere2,3, stressing the question of the snowball melting threshold. Indeed, it has been shown that greenhouse climate induced by the storage of the CO2 in the atmosphere invoked to escape a snowball Earth was possibly not sufficient to melt the snowball Earth due to thermal inversion in vertical column4. Therefore, CO2 is may be not the only trigger for the deglaciation. Finally, the super greenhouse climate thought to have followed the snowball episode was explored. We demonstrate that, despite very high temperatures under 0.2 bars of CO2, the amount of rainfall might have been limited by the availability of latent heat which cannot be higher that the total energy provided by the sun. As a consequence of limited increase in the water cycling, CO2 consumption by continental weathering might not exceed 10 times its present day value. The return to normal climatic conditions after the snowball melting should thus have lasted several million of years, further increasing the biological perturbations linked to a snowball event5. The aim of this contribution is to revisit the issue of the role of atmospheric CO2 before, during and after a Snowball Earth and to deliver a new picture of its feedbacks with climate. 1. Donnadieu, Y., Y. Godderis, et al. (2004). "A 'snowball Earth' climate triggered by continental break-up through changes in runoff." Nature 428(6980): 303- 306. 2. Ramstein G., Donnadieu Y., Goddéris Y. Proterozoic glaciations. Comptes Rendus Geoscience 336 (7-8): 639-646 Jun 2004 3. Le Hir G., Goddéris Y., Donnadieu Y., Ramstein G. (2008). A geochemical modelling study of the evolution of the chemical composition of seawater linked to a "snowball" glaciation. Biogeosci. 5, 253-267. 4. Le Hir Guillaume , Goddéris Yves, Donnadieu Yannick , Ramstein Gilles (2008) A scenario for the evolution of the atmopsheric pCO2 during a Snowball Earth, Geology, 36 (1): 47-50 5. Pierrehumbert, R.T. (2004). High levels of atmospheric carbon dioxide necessary for the termination of global glaciation: Nature, v. 429, p. 646-649, doi: 10.1038/nature02640. 6. Le Hir Guillaume, Donnadieu Yannick, Goddéris Y, Pierrehumbert Raymond T., Halverson Galen P., Macouin Mélina, Nédélec Anne b, Ramstein Gilles. (2008).The snowball Earth aftermath: Exploring the limits of continental weathering processes, Earth and Planetary Science Letters, EPSL-09573; No of Pages 11
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
La 'circunstancia' de 'Herederos y Pretendientes
No full textIn June 2010, the Ortega y Gasset Foundation hosted a Conference about the “Spanish Philosophical Transition” in order to debate the book of Francisco Vázquez, La filosofía española. Herederos y Pretendientes. Una lectura sociológica (1963-1990), recently published. This paper is the author’s response to criticism raised in the Conference and to published reviews received by this book. First, the author summarized the argument of Herederos y pretendientes. Secondly he responds and takes into account the most important objections against the book’s hypothesis and methodology. Finally the author evaluates the favorable judgments received by the book and suggests the limits of the historian’s task.Fundación Ortega y Gasset-Marañó
Author self-citation in orthodontics is associated with author origin and gender.
No full textBACKGROUND
The aims of this bibliometric study were to determine author self-citation trends in high-impact orthodontic literature and to investigate possible association between self-citation and publication characteristics.
METHODS
Six orthodontic journals with the highest impact factor as ranked by 2017 Journal Citation Reports were screened for a full publication year (2018) for original research articles, reviews, and case reports. Eligible articles were scrutinized for article and author characteristics and citation metrics. Univariable and multivariable negative binomial regression was used to examine associations between self-citation incidence and publication characteristics.
RESULTS
Medians for author self-citation rate of the most self-citing authors and self-citations were 3.03% (range 0-50) and 1 (range 0-19), respectively. In the univariable analysis, there was no association between self-citation counts and study type (P = 0.41), article topic (P = 0.61), number of authors (P = 0.62), and rank of authors (P = 0.56). Author origin (P = 0.001), gender (P = 0.001) and journal (P = 0.05) were associated with self-citation counts and in the multivariable analysis only origin and gender remained strong self-citation predictors. Asian authors and females self-cited significantly less often than all other regions and male authors.
CONCLUSIONS
Authors in orthodontics do not self-cite at a frequency that suggests potential citation manipulation. Author origin and gender were the only variables associated with citations counts. More bibliometric research is necessary to draw solid conclusions about author self-citation trends in orthodontic literature
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