The Experts below are selected from a list of 2376 Experts worldwide ranked by ideXlab platform
Christine Bounama - One of the best experts on this subject based on the ideXlab platform.
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On the habitability of Earth and Mars
2000Co-Authors: Siegfried Franck, Christine Bounama, W. Von BlohAbstract:Our Earth system model is a stylized geosphere-biosphere model to analyze the evolution from the geological past to the planetary future in 1.5 billion years. It consists of the components solid Earth, Hydrosphere, atmosphere, and biosphere and couples the increasing solar luminosity, the silicate-rock weathering rate, and the global energy balance to estimate the partial pressure of atmospheric and soil carbon dioxide, mean global surface temperature, and the biological productivity as a function of time. The crucial point is the long-term balance between the CO2 sink in the atmosphere-ocean system and the metamorphic (plate-tectonic) source. In our approach, the HZ for an Earth-like planet is the region around the Sun within which the surface temperature of the planet stays between 0°C and 100°C and the atmospheric CO 2 content is higher than 10 ppm suitable for photosynthesis-based life.
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Modelling the global carbon cycle for the past and future evolution of the Earth system
Chemical Geology, 1999Co-Authors: Siegfried Franck, Konrad J. Kossacki, Christine BounamaAbstract:The Earth may be described as a global system consisting of the components solid Earth, Hydrosphere, atmosphere, and biosphere. This system evolves under the external influence of increasing solar luminosity. In spite of this changing external forcing, the Earth's climate has been stabilized by negative feedbacks against global freezing in the past (faint young Sun paradox). The future long-term trend of further increasing solar luminosity will cause a further atmospheric CO2 decrease. Atmospheric CO2 will fall below the critical level for photosynthesis and the plant based biosphere will die out. In the present paper we propose a modelling study of the evolution of the carbon cycle from the Archaean to the planetary future. Our model is based on a paper published previously by Caldeira and Kasting [Caldeira, K., Kasting, J.F., 1992. The life span of the biosphere revisited. Nature 360, 721–723]. The difference of the current study with respect to this work resides in the forcing function used for the silicate weathering rate. While Caldeira and Kasting used a constant weathering rate over time, we calculate the time evolution of this rate by assuming a balance between the weathering flux and the CO2 release flux by volcanism and metamorphism. We use the geodynamics theory to couple the two internal forcing functions continental area (for weathering) and spreading (for CO2 release flux) which were generally considered as independent in previous models. This coupling introduces an additional feedback in the system. We find a warmer climate in the past and a shortening of the life span of the biosphere up to some hundred million years.
Siegfried Franck - One of the best experts on this subject based on the ideXlab platform.
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On the habitability of Earth and Mars
2000Co-Authors: Siegfried Franck, Christine Bounama, W. Von BlohAbstract:Our Earth system model is a stylized geosphere-biosphere model to analyze the evolution from the geological past to the planetary future in 1.5 billion years. It consists of the components solid Earth, Hydrosphere, atmosphere, and biosphere and couples the increasing solar luminosity, the silicate-rock weathering rate, and the global energy balance to estimate the partial pressure of atmospheric and soil carbon dioxide, mean global surface temperature, and the biological productivity as a function of time. The crucial point is the long-term balance between the CO2 sink in the atmosphere-ocean system and the metamorphic (plate-tectonic) source. In our approach, the HZ for an Earth-like planet is the region around the Sun within which the surface temperature of the planet stays between 0°C and 100°C and the atmospheric CO 2 content is higher than 10 ppm suitable for photosynthesis-based life.
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Modelling the global carbon cycle for the past and future evolution of the Earth system
Chemical Geology, 1999Co-Authors: Siegfried Franck, Konrad J. Kossacki, Christine BounamaAbstract:The Earth may be described as a global system consisting of the components solid Earth, Hydrosphere, atmosphere, and biosphere. This system evolves under the external influence of increasing solar luminosity. In spite of this changing external forcing, the Earth's climate has been stabilized by negative feedbacks against global freezing in the past (faint young Sun paradox). The future long-term trend of further increasing solar luminosity will cause a further atmospheric CO2 decrease. Atmospheric CO2 will fall below the critical level for photosynthesis and the plant based biosphere will die out. In the present paper we propose a modelling study of the evolution of the carbon cycle from the Archaean to the planetary future. Our model is based on a paper published previously by Caldeira and Kasting [Caldeira, K., Kasting, J.F., 1992. The life span of the biosphere revisited. Nature 360, 721–723]. The difference of the current study with respect to this work resides in the forcing function used for the silicate weathering rate. While Caldeira and Kasting used a constant weathering rate over time, we calculate the time evolution of this rate by assuming a balance between the weathering flux and the CO2 release flux by volcanism and metamorphism. We use the geodynamics theory to couple the two internal forcing functions continental area (for weathering) and spreading (for CO2 release flux) which were generally considered as independent in previous models. This coupling introduces an additional feedback in the system. We find a warmer climate in the past and a shortening of the life span of the biosphere up to some hundred million years.
Nasa - One of the best experts on this subject based on the ideXlab platform.
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Determination of crustal motions using satellite laser ranging
2013Co-Authors: NasaAbstract:Satellite laser ranging has matured over the last decade into one of the essential space geodesy techniques. It has demonstrated centimeter site positioning and millimeter per year velocity determinations in a frame tied dynamically to the mass center of the solid Earth Hydrosphere atmosphere system. Such a coordinate system is a requirement for studying long term eustatic sea level rise and other global change phenomena. Earth orientation parameters determined with the coordinate system have been produced in near real time operationally since 1983, at a relatively modest cost. The SLR ranging to Lageos has also provided a rich spectrum of results based upon the analysis of Lageos orbital dynamics. These include significant improvements in the knowledge of the mean and variable components of the Earth's gravity field and the Earth's gravitational parameter. The ability to measure the time variations of the Earth's gravity field has opened as exciting area of study in relating global processes, including meteorologically derived mass transport through changes in the satellite dynamics. New confirmation of general relativity was obtained using the Lageos SLR data.
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Earth System Dynamics: The Determination and Interpretation of the Global Angular Momentum Budget using the Earth Observing System
2013Co-Authors: NasaAbstract:The objective of this investigation has been to examine the mass and momentum exchange between the atmosphere, oceans, solid Earth, Hydrosphere, and cryosphere. The investigation has focused on changes in the Earth's gravity field, its rotation rate, atmospheric and oceanic circulation, global sea level change, ice sheet change, and global ground water circulation observed by contemporary sensors and models. The primary component of the mass exchange is water. The geodetic observables provided by these satellite sensors are used to study the transport of water mass in the hydrological cycle from one component of the Earth to another, and they are also used to evaluate the accuracy of models. As such, the investigation is concerned with the overall global water cycle. This report provides a description of scientific, educational and programmatic activities conducted during the period July 1, 1999 through June 30,2000. Research has continued into measurements of time-varying gravity and its relationship to Earth rotation. Variability of angular momentum and the related excitation of polar motion and Earth rotation have been examined for the atmosphere and oceans at time-scales of weeks to several years. To assess the performance of hydrologic models, we have compared geodetic signals derived from them with those observed by satellites. One key component is the interannual mass variability of the oceans obtained by direct observations from altimetry after removing steric signals. Further studies have been conducted on the steric model to quantify its accuracy at global and basin-scales. The results suggest a significant loss of water mass from the Oceans to the land on time-scales longer than 1-year. These signals are not reproduced in any of the models, which have poorly determined interannual fresh water fluxes. Output from a coupled atmosphere-ocean model testing long-term climate change hypotheses has been compared to simulated errors from the Gravity Recovery and Climate Experiment (GRACE) mission. Results indicate that GRACE will be able to observe seasonal signals at half-wavelengths ranging from 1000 to 10000 km, and may be able to observe secular trends at half- wavelengths of greater than 2000-3000 km for soil moisture and snow depth if they are as large as some of the climate experiments predict.
Konrad J. Kossacki - One of the best experts on this subject based on the ideXlab platform.
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Modelling the global carbon cycle for the past and future evolution of the Earth system
Chemical Geology, 1999Co-Authors: Siegfried Franck, Konrad J. Kossacki, Christine BounamaAbstract:The Earth may be described as a global system consisting of the components solid Earth, Hydrosphere, atmosphere, and biosphere. This system evolves under the external influence of increasing solar luminosity. In spite of this changing external forcing, the Earth's climate has been stabilized by negative feedbacks against global freezing in the past (faint young Sun paradox). The future long-term trend of further increasing solar luminosity will cause a further atmospheric CO2 decrease. Atmospheric CO2 will fall below the critical level for photosynthesis and the plant based biosphere will die out. In the present paper we propose a modelling study of the evolution of the carbon cycle from the Archaean to the planetary future. Our model is based on a paper published previously by Caldeira and Kasting [Caldeira, K., Kasting, J.F., 1992. The life span of the biosphere revisited. Nature 360, 721–723]. The difference of the current study with respect to this work resides in the forcing function used for the silicate weathering rate. While Caldeira and Kasting used a constant weathering rate over time, we calculate the time evolution of this rate by assuming a balance between the weathering flux and the CO2 release flux by volcanism and metamorphism. We use the geodynamics theory to couple the two internal forcing functions continental area (for weathering) and spreading (for CO2 release flux) which were generally considered as independent in previous models. This coupling introduces an additional feedback in the system. We find a warmer climate in the past and a shortening of the life span of the biosphere up to some hundred million years.
B J Murton - One of the best experts on this subject based on the ideXlab platform.
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fe xanes analyses of reykjanes ridge basalts implications for oceanic crust s role in the solid Earth oxygen cycle
Earth and Planetary Science Letters, 2015Co-Authors: Oliver Shorttle, Yves Moussallam, Margaret E Hartley, John Maclennan, Marie Edmonds, B J MurtonAbstract:Abstract The cycling of material from Earth's surface environment into its interior can couple mantle oxidation state to the evolution of the oceans and atmosphere. A major uncertainty in this exchange is whether altered oceanic crust entering subduction zones can carry the oxidised signal it inherits during alteration at the ridge into the deep mantle for long-term storage. Recycled oceanic crust may be entrained into mantle upwellings and melt under ocean islands, creating the potential for basalt chemistry to constrain solid Earth–Hydrosphere redox coupling. Numerous independent observations suggest that Iceland contains a significant recycled oceanic crustal component, making it an ideal locality to investigate links between redox proxies and geochemical indices of enrichment. We have interrogated the elemental, isotope and redox geochemistry of basalts from the Reykjanes Ridge, which forms a 700 km transect of the Iceland plume. Over this distance, geophysical and geochemical tracers of plume influence vary dramatically, with the basalts recording both long- and short-wavelength heterogeneity in the Iceland plume. We present new high-precision Fe-XANES measurements of Fe 3 + / ∑ Fe on a suite of 64 basalt glasses from the Reykjanes Ridge. These basalts exhibit positive correlations between Fe 3 + / ∑ Fe and trace element and isotopic signals of enrichment, and become progressively oxidised towards Iceland: fractionation-corrected Fe 3 + / ∑ Fe increases by ∼0.015 and ΔQFM by ∼0.2 log units. We rule out a role for sulfur degassing in creating this trend, and by considering various redox melting processes and metasomatic source enrichment mechanisms, conclude that an intrinsically oxidised component within the Icelandic mantle is required. Given the previous evidence for entrained oceanic crustal material within the Iceland plume, we consider this the most plausible carrier of the oxidised signal. To determine the ferric iron content of the recycled component ( [ Fe 2 O 3 ] source ) we project observed liquid compositions to an estimate of Fe2O3 in the pure enriched endmember melt, and then apply simple fractional melting models, considering lherzolitic and pyroxenitic source mineralogies, to estimate [ Fe 2 O 3 ] ( source ) content. Propagating uncertainty through these steps, we obtain a range of [ Fe 2 O 3 ] ( source ) for the enriched melts (0.9–1.4 wt%) that is significantly greater than the ferric iron content of typical upper mantle lherzolites. This range of ferric iron contents is consistent with a hybridised lherzolite–basalt (pyroxenite) mantle component. The oxidised signal in enriched Icelandic basalts is therefore potential evidence for seafloor–Hydrosphere interaction having oxidised ancient mid-ocean ridge crust, generating a return flux of oxygen into the deep mantle.
