40 research outputs found
Phase transition boundary between fcc and hcp structures in Fe-Si alloy and its implications for terrestrial planetary cores
International audienc
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ââGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Emending the Teacher : From Marcus the "Magician" to Valentinus and Back
akzeptierte Manuskriptversio
Altimetry for the future: building on 25 years of progress
In 2018 we celebrated 25âŻyears of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Principaux facteurs impliquĂ©s dans le dĂ©pĂ©rissement des forĂȘts en Europe et en AmĂ©rique du Nord
Le dĂ©pĂ©rissement, aprĂšs avoir dĂ©vastĂ© de nombreuses forĂȘts europĂ©ennes, a fait son apparition en AmĂ©rique du Nord et rĂ©cemment, au QuĂ©bec. Tel qu'il nous apparaĂźt aujourd'hui, il s'agit d'une maladie complexe qui conduit, par un affaiblissement progressif des arbres Ă une dĂ©tĂ©rioration et une perte de feuillage, une rĂ©duction de croissance et une augmentation de susceptibilitĂ© Ă des stress secondaires. On distingue trois classes de facteurs responsables du dĂ©pĂ©rissement: prĂ©disposant, incitant et accessoire. Nous les avons classifiĂ© ici sous forme de facteurs physiques (climatiques, Ă©daphiques et anthropiques), chimiques (polluants atmosphĂ©riques) et biologiques (insectes dĂ©foliateurs, champignons). Les facteurs physiques n'expliquent pas le phĂ©nomĂšne actuel oĂč les dĂ©gĂąts ne cessent de s'aggraver. Les facteurs chimiques reprĂ©sentĂ©s par les polluants atmosphĂ©riques tels le dioxyde de soufre, les oxydes d'azote et l'ozone se manifestent toujours sous forme de mĂ©langes qui, par effet de synergie, obtiennent une toxicitĂ© supĂ©rieure Ă la somme des diffĂ©rents facteurs pris isolĂ©ment. Les facteurs biologiques ne jouent qu'un rĂŽle secondaire; les dĂ©foliations peuvent ĂȘtre considĂ©rĂ©es comme des Ă©pisodes naturels dans la vie d'un arbre; les infestations par certains champignons sont en fait la consĂ©quence mĂȘme d'une dĂ©tĂ©rioration physiologique dĂ©jĂ avancĂ©e des arbres touchĂ©s. Les Ă©rabliĂšres du QuĂ©bec sont situĂ©es parfois sur des stations inadĂ©quates, mais aussi dans les rĂ©gions les plus polluĂ©es du QuĂ©bec. AprĂšs avoir considĂ©rĂ© les causes les plus probables, tout porte Ă croire que le dĂ©pĂ©rissement des forĂȘts est le rĂ©sultat d'un ensemble de facteurs agissant concurremment pour dĂ©balancer le fonctionnement de tout l'Ă©cosystĂšme forestier. Ce dernier rĂ©agira diffĂ©remment selon ses degrĂ©s de rĂ©sistances gĂ©nĂ©tique, physiologique et Ă©daphique mais, si le stress environnemental persiste, la forĂȘt succombera. Une fois amorçé, le processus de dĂ©pĂ©rissement se gĂ©nĂ©ralise et s'intensifie rapidement. En ce qui concerne les forĂȘts de conifĂšres du QuĂ©bec, leur productivitĂ© ne semble pas encore amoindrie mais les symptĂŽmes de dĂ©pĂ©rissement pourraient se manifester bientĂŽt si l'on se rĂ©fĂšre Ă la situation en Europe et aux Etats-Unis qui a Ă©voluĂ© de façon fulgurante depuis les 25 derniĂšres annĂ©es. Il est donc essentiel de poursuivre les Ă©tudes et les expĂ©riences de simulation pour dĂ©celer rapidement la moindre diminution de la productivitĂ© forestiĂšre ou de la qualitĂ© des arbres de nos forĂȘts et, surtout, pour tenter d'y remĂ©dier
Principaux facteurs impliquĂ©s dans le dĂ©pĂ©rissement des forĂȘts en Europe et en AmĂ©rique du Nord
Le dĂ©pĂ©rissement, aprĂšs avoir dĂ©vastĂ© de nombreuses forĂȘts europĂ©ennes, a fait son apparition en AmĂ©rique du Nord et rĂ©cemment, au QuĂ©bec. Tel qu'il nous apparaĂźt aujourd'hui, il s'agit d'une maladie complexe qui conduit, par un affaiblissement progressif des arbres Ă une dĂ©tĂ©rioration et une perte de feuillage, une rĂ©duction de croissance et une augmentation de susceptibilitĂ© Ă des stress secondaires. On distingue trois classes de facteurs responsables du dĂ©pĂ©rissement: prĂ©disposant, incitant et accessoire. Nous les avons classifiĂ© ici sous forme de facteurs physiques (climatiques, Ă©daphiques et anthropiques), chimiques (polluants atmosphĂ©riques) et biologiques (insectes dĂ©foliateurs, champignons). Les facteurs physiques n'expliquent pas le phĂ©nomĂšne actuel oĂč les dĂ©gĂąts ne cessent de s'aggraver. Les facteurs chimiques reprĂ©sentĂ©s par les polluants atmosphĂ©riques tels le dioxyde de soufre, les oxydes d'azote et l'ozone se manifestent toujours sous forme de mĂ©langes qui, par effet de synergie, obtiennent une toxicitĂ© supĂ©rieure Ă la somme des diffĂ©rents facteurs pris isolĂ©ment. Les facteurs biologiques ne jouent qu'un rĂŽle secondaire; les dĂ©foliations peuvent ĂȘtre considĂ©rĂ©es comme des Ă©pisodes naturels dans la vie d'un arbre; les infestations par certains champignons sont en fait la consĂ©quence mĂȘme d'une dĂ©tĂ©rioration physiologique dĂ©jĂ avancĂ©e des arbres touchĂ©s. Les Ă©rabliĂšres du QuĂ©bec sont situĂ©es parfois sur des stations inadĂ©quates, mais aussi dans les rĂ©gions les plus polluĂ©es du QuĂ©bec. AprĂšs avoir considĂ©rĂ© les causes les plus probables, tout porte Ă croire que le dĂ©pĂ©rissement des forĂȘts est le rĂ©sultat d'un ensemble de facteurs agissant concurremment pour dĂ©balancer le fonctionnement de tout l'Ă©cosystĂšme forestier. Ce dernier rĂ©agira diffĂ©remment selon ses degrĂ©s de rĂ©sistances gĂ©nĂ©tique, physiologique et Ă©daphique mais, si le stress environnemental persiste, la forĂȘt succombera. Une fois amorçé, le processus de dĂ©pĂ©rissement se gĂ©nĂ©ralise et s'intensifie rapidement. En ce qui concerne les forĂȘts de conifĂšres du QuĂ©bec, leur productivitĂ© ne semble pas encore amoindrie mais les symptĂŽmes de dĂ©pĂ©rissement pourraient se manifester bientĂŽt si l'on se rĂ©fĂšre Ă la situation en Europe et aux Etats-Unis qui a Ă©voluĂ© de façon fulgurante depuis les 25 derniĂšres annĂ©es. Il est donc essentiel de poursuivre les Ă©tudes et les expĂ©riences de simulation pour dĂ©celer rapidement la moindre diminution de la productivitĂ© forestiĂšre ou de la qualitĂ© des arbres de nos forĂȘts et, surtout, pour tenter d'y remĂ©dier
Mantle helium in Southern Quebec groundwater: A possible fossil record of the New England hotspot
International audienceThe Monteregian Hills are an alignment of magmatic intrusions of Cretaceous age located in the St. Lawrence Lowlands, Quebec, Canada. Their origin is controversial and numerous studies have failed to decipher between a hotspot trail or sub-continental magmatism related to the opening of the North Atlantic Ocean. Here, we show that 17.7 ± 9.6% of the helium of the modern to Holocene-aged groundwater from the regional aquifer is of mantle origin, with a 3He/4He (R) of up to 1.42 times the atmospheric ratio (Ra). It suggests that a fossil Monteregian Hills magmatic signal, diluted by local radiogenic helium and preserved in the Monteregian Hills intrusions, is leached locally by flowing modern or sub-modern groundwater. Helium isotopic measurements by pyrolysis in Monteregian Hills bulk rocks and clinopyroxene separates show R/Ra values of up to 4.96, suggesting that fossil mantle helium has been partially preserved in these rocks and their mineral phases. Monte Carlo simulations of a magma aging model shows that the initial 3He/4He ratio in these Cretaceous intrusions could have been between 21 ± 10Ra and 33 ± 28Ra (2Ï), favoring the hypothesis that the Monteregian Hills are the product of the passage of the North American plate over the New England hotspot. This study raises the prospect of using modern groundwater as an archive of mantle He over a hundreds of millions of years timescale
Ecotoxicological assessment of Rare Earth Elements for aquatic ecosystems by normalized assays
International audienc
<sup>87</sup>Sr/<sup>86</sup>Sr Ratios and Atmospheric Noble Gases in Theistareykir Geothermal Fluids: A Record of Glacial Water
The determination of the current and past recharge sources, as well as the reconstruction of the timing of the recharge in geothermal reservoirs, is required in order to correctly assess the resource potential of these systems. Theistareykir is a newly developed geothermal field close to the well-known exploited fields of Krafla and NĂĄmafjall in NE Iceland. In this study, the 87Sr/86Sr ratios measured in deep geothermal fluids are presented and, together with the Cl and noble gas signatures, are used to place constraints on the fluid sources. The Cl/Sr and 87Sr/86Sr ratios show a peculiar and unique composition among Icelandic geothermal fluids. The 87Sr/86Sr ratios range from 0.70355 to 0.70671, suggesting the presence of a significant seawater componentâpossibly marine aerosols added to rain or snowfallâas well as an additional source of Sr leached from local basalts. Moreover, a correlation between the atmospheric noble gas (ANGs) elemental ratios Ne/Ar, Kr/Ar and Xe/Ar, and the 87Sr/86Sr ratios is observed. The latter results from the mixing of meteoric water with Sr leached from local basalts, meteoric water containing unrelated Sr from seawater, and recharge water with ANGs derived from trapped air bubbles in snow. We suggest that the combined ANGs and Sr seawater signatures are representative of a glacial water source derived from the melting of compacting snow
Fate, accumulation and biological effects of Rare Earth Element (REE) mixtures in a model freshwater food web
International audienc