Mars’ atmospheric 40Ar: A tracer for past crustal erosion     

F. Leblanc  E. Chassefière  C. Gillmann  D. Breuer 《Icarus》2012,218(1):561-570

Noble gas ⁴⁰Ar may be used as a tracer of the past evolution of volatiles in Mars’ crust, mantle and atmosphere. ⁴⁰Ar is formed by the radioactive decay of ⁴⁰K in the mantle and in the crust and is released from the mantle to the atmosphere due to volcanism and from the crust by erosion such as eolian and hydrothermal erosion. Furthermore, ⁴⁰Ar can escape from the atmosphere into space via atmospheric escape mechanisms. The evolution of the atmospheric abundance of ⁴⁰Ar thus depends on these three processes whose efficiencies vary with time.In the present study we reconsider atmospheric escape mechanism efficiencies and describe various possible scenarios of the evolution of ⁴⁰Ar with a model describing the three main reservoirs of ⁴⁰Ar, the mantle, crust and atmosphere. First, we show that atmospheric escape, which is stronger in the early evolution, does not significantly influence the present abundance of the atmospheric ⁴⁰Ar. In the early evolution the atmospheric concentration of ⁴⁰Ar is very low as the outgassing of ⁴⁰Ar from the mantle occurs relatively late in the martian evolution. Thus, the atmospheric ⁴⁰Ar concentration is essentially a tracer of Mars’ outgassing history and not of the escape processes. Second, using the results of the most recent published crustal formation models, the calculated present ⁴⁰Ar atmospheric abundance is smaller than its observed value. This discrepancy may be explained by a significant ⁴⁰Ar supply from the crust by erosion (16–30% of the ⁴⁰Ar content of the upper first 10 km of crust). The knowledge of the fraction of crustal ⁴⁰Ar outgassed to the atmosphere is an important constraint for any future global modelling of past Mars’ hydrothermal activity aiming at better characterizing the role of subsurface aqueous alteration processes in Mars climate evolution. One of the main sources of the uncertainty of these results is the present uncertainty in the measured atmospheric ⁴⁰Ar value (±20%). More precise measurements of ⁴⁰Ar and ³⁶Ar in the martian atmosphere are therefore required to better constrain the model.  相似文献   

Long-term groundwater resource observatory for Southwestern Madagascar     

Simon D. Carrière  Thomas Health  Pascale F. M. Rakotomandrindra  Chloé Ollivier  Riva E. Rajaomahefasoa  Heritiana A. Rakoto  Jean Lapègue  Yves E. Rakotoarison  Marie Mangin  Jean Kempf  Théodore Razakamanana  Konstantinos Chalikakis 《水文研究》2021,35(3):e14108

Madagascar has one of the highest poverty rates in the world and consequently the long-term monitoring of groundwater resources is not a priority for the authorities. However, groundwater is often the only sustainable resource that has a satisfactory quality to supply the population. This is especially true in the south-west of the country, which is a semi-arid region and a global change hot spot (intense land use and climate changes). In response to the lack of data, the Groundwater Resource Observatory for Southwestern Madagascar (GROSoM) was established to monitor piezometry and meteorology over the longer term as part of a humanitarian response. The first site was setup in 2014 in a catchment located over a carbonate plateau; in 2018, a second site was installed in an alluvial setting within a crystalline basement catchment and a third site will be installed in 2020 to monitor groundwater dynamics in a coastal setting. The three sites, located between Toliara and Taolagnaro cities, are complementary and representative of various hydrogeological systems in Southwestern Madagascar. Each site includes a weather station and between 3 and 6 piezometric probes. The monitoring data indicate a strong inter-annual variability in precipitation, which induces a strong variability in aquifers recharge. One of the driest years in 2016 seems to be consistent with strong El Niño – Southern Oscillation (ENSO) effects observed at the global scale, while years with higher recharge appear to be related to cyclones such as Fundi in 2015 and Eketsang in 2019. Preliminary results of cross-disciplinary studies demonstrated a link between groundwater and health issues (i.e., admissions to basic health centres). This observatory aims to produce long-term data and has two objectives: (i) strengthening the early warning system for humanitarian crises in Madagascar; (ii) contributing to a better understanding of the effects of climate change on groundwater resources in this semi-arid region.  相似文献   

Dynamics and transport from the boundary Northern Current toward the Toulon Bay: multi-platform observations and downscaling modelling approaches     

Molcard  Anne  Gramoullé  Anthony  Mazoyer  Camille  Bourg  Natacha  Ourmières  Yann 《Ocean Dynamics》2021,71(10):993-1009

Ocean Dynamics - Coastal regions are vulnerable areas with often high population density, as well as tourism and maritime activities that may have negative impact on the environment. From a...  相似文献   

Mary Anning,Alfred Nicholson Leeds and Steve Etches. Comparing the three most important UK ‘amateur’ fossil collectors and their collections     

Leslie F. Noè  Marcela Gómez-Pérez  Robert Nicholls 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(3-4):366-389

Mary Anning, Alfred Nicholson Leeds and Steve Etches form part of a long line of individuals who furnished a substantial addition to our understanding of marine and terrestrial ecosystems through collecting significant numbers of superb fossils. For all three collectors, fossils became a factor that dominated their lives, and their fossil collecting led to the discovery of numerous taxa new to science. Extensive collecting was made possible by the fortunate circumstances of living ‘in the right place at the right time’, close to fine-grained UK Jurassic deposits (Lagerstätten) with well-preserved large Jurassic marine reptiles. All three were highly-motivated and developed a considerable skill sets for discovering, collecting, preparing, conserving and displaying fossils. They developed personal and professional interactions with family and friends, and university and museum professionals, although their collecting resulted in variable recognition of their work. Each collector can be considered a complex mix of amateur and professional: Mary Anning, a professional fossil collector and amateur palaeontologist; Alfred Leeds transitioned from amateur to professional fossil collector, but remained an amateur palaeontologist; and Steve Etches has remained an amateur fossil collector and palaeontologist. However, all three exhibited an entirely professional outlook to collecting, and should be considered professionals of the highest degree. The impact of Mary Anning, Alfred Nicholson Leeds and Steve Etches has been critical for the development of Palaeontology as a science, and without whom palaeontology, with all its associated benefits to a wide scientific and non-scientific audience, would not be as rich as we currently know it.  相似文献   

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring     

Sébastien Gogo  Jean-Baptiste Paroissien  Fatima Laggoun-Défarge  Jean-Marc Antoine  Léonard Bernard-Jannin  Guillaume Bertrand  Philippe Binet  Stéphane Binet  Guillaume Bouger  Yohann Brossard  Thierry Camboulive  Jean-Pierre Caudal  Stéphane Chevrier  Geneviève Chiapiuso  Benoît D'Angelo  Pilar Durantez  Chris Flechard  André-Jean Francez  Didier Galop  Laure Gandois  Daniel Gilbert  Christophe Guimbaud  Louis Hinault  Adrien Jacotot  Franck Le Moing  Emilie Lerigoleur  Gaël Le Roux  Fabien Leroy  Alexandre Lhosmot  Qian Li  Elodie Machado Da Silva  Jean-Sébastien Moquet  Juanita Mora-Gomez  Laurent Perdereau  Thomas Rosset  Marie-Laure Toussaint 《水文研究》2021,35(6):e14244

Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long-term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 ( https://www.sno-tourbieres.cnrs.fr/ ). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available ( https://data-snot.cnrs.fr/data-access/ ). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution ( https://zenodo.org/communities/sno_tourbieres_data/ ).  相似文献   

The 1‐million‐year‐old quartz assemblage from Pont‐de‐Lavaud (Centre,France) in the European context          下载免费PDF全文

Jackie Despriée  Marie‐Hélène Moncel  Marta Arzarello  Gilles Courcimault  Pierre Voinchet  Jean‐Jacques Bahain  Christophe Falguères 《第四纪科学杂志》2018,33(6):639-661

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Neogene upper‐crustal cooling of the Olympus range (northern Aegean): major role of Hellenic back‐arc extension over propagation of the North Anatolia Fault Zone     

Isabelle Coutand  Michael Walsh  Bertha Louis  Frank Chanier  Jacky Ferrière  Jean‐Yves Reynaud 《地学学报》2014,26(4):287-297

The North Anatolian Fault Zone (NAFZ) is one of the most hazardous active faults on Earth, yet its Pliocene space‐time propagation across the north Aegean domain remains poorly constrained. We use low‐temperature multi‐thermochronology and inverse thermal modelling to quantify the cooling history of the upper crust across the Olympus range. This range is located in the footwall of a system of normal faults traditionally interpreted as resulting from superposed Middle–Late Miocene N–S stretching, related to the back‐arc extension of the Hellenic subduction zone, and a Pliocene‐Quaternary transtensional field, attributed to the south‐westward propagation of the NAFZ. We find that accelerated exhumational cooling occurred between 12 and 6 Ma at rates of 15–35 °C Ma^?1 and decreased to <3 °C Ma^?1 by 8–6 Ma. The absence of significant Plio‐Pleistocene cooling across Olympus suggests that crustal exhumation there is driven by late Miocene back‐arc extension, while the impact of the NAFZ remains limited.  相似文献   

Radionuclides produits par le rayonnement cosmique dans la météorite Saint-Séverin     

Roland Bibron  Concèle Leger  Jacques Tobailem  Yfji Yokoyama  Hisao Mabuchi  Noëlle Baillard 《Geochimica et cosmochimica acta》1974,38(2):197-205

]The activities of 18 radionuclides in 4 samples from the Saint-Séverin meteorite have been measured after chemical separation. The results show that the DI sample from the D piece has been less irradiated than the samples B₂, B₃ and B₄ from the B piece. This is based on activities of isotopes produced both by spallation as ²⁶Al, ⁵³Mn, ⁵⁴Mn, ⁵⁵Fe, ⁵⁷Co and by thermal neutron capture as ⁵⁹Ni and ⁶⁰Co.Comparison of experimental values to calculated production rates suggests that the D piece was connected to the main body of the meteorite by a small surface, and that the DI sample in this piece was opposite to the main body of the meteorite.  相似文献   

Combining low-carbon economic development and oil exploration in Brazil? An energy–economy assessment     

Julien Lefèvre  William Wills  Jean-Charles Hourcade 《Climate Policy》2018,18(10):1286-1295

Brazil's nationally determined contribution (NDC) pledged under the Paris Agreement has marked a new stage in its climate policy towards strengthening low-carbon economic development beyond the recent drastic cuts in emissions from deforestation. Brazil especially means to limit oil consumption driven by future economic growth and to increase energy efficiency and biofuel use in the transport sector. On the other hand, Brazil still aspires to become a major petroleum province given its huge reserves of ‘pre-salt’ oil. This article aims to clarify under what conditions low-carbon economic development and oil exploration can possibly be combined in Brazil and what would be the energy system, environmental and macroeconomic implications of enabling policies for doing so. To address these questions, an energy–economy computable general equilibrium (CGE) model of the Brazilian economy is used to simulate alternative scenarios up to 2030. The results first show that implementing the most recent energy plans, which take into account the new economic reality in Brazil, should lead to over 20% lower domestic CO₂ emissions in 2030 than the indicative NDC target, and to the export of the bulk of newfound crude oil. Second, with the same level of oil production, deeper domestic decarbonization, triggered by additional carbon pricing and sustainable efficiency measures, appears achievable with very small gross domestic product (GDP) loss and maximum oil exports, while being aligned with a 2°C emission pathway. However, (i) extra oil exports may induce net additional emissions outside Brazil and be seen as a perverse incentive and (ii) the economic growth strategy based on high oil exports may hinder the necessary diversification of the Brazilian economy.

Key policy insights

• Low-carbon development goals will strongly interact with oil policy in Brazil.

• The 2030 NDC target should be easy to achieve considering the new economic reality in Brazil.

• Deeper domestic decarbonization is achievable with very limited GDP loss and significant oil exports, while being aligned with a 2°C emission pathway.

• A broad strategic vision is needed to reconcile climate policy, energy policy and other economic development objectives.

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Momentum- and Heat-Flux Parametrization at Dome C,Antarctica: A Sensitivity Study     

Etienne Vignon  Christophe Genthon  Hélène Barral  Charles Amory  Ghislain Picard  Hubert Gallée  Giampietro Casasanta  Stefania Argentini 《Boundary-Layer Meteorology》2017,162(2):341-367

An extensive meteorological observational dataset at Dome C, East Antarctic Plateau, enabled estimation of the sensitivity of surface momentum and sensible heat fluxes to aerodynamic roughness length and atmospheric stability in this region. Our study reveals that (1) because of the preferential orientation of snow micro-reliefs (sastrugi), the aerodynamic roughness length \(z_{0}\) varies by more than two orders of magnitude depending on the wind direction; consequently, estimating the turbulent fluxes with a realistic but constant \(z_{0}\) of 1 mm leads to a mean friction velocity bias of \(24\,\%\) in near-neutral conditions; (2) the dependence of the ratio of the roughness length for heat \(z_{0t}\) to \(z_{0}\) on the roughness Reynolds number is shown to be in reasonable agreement with previous models; (3) the wide range of atmospheric stability at Dome C makes the flux very sensitive to the choice of the stability functions; stability function models presumed to be suitable for stable conditions were evaluated and shown to generally underestimate the dimensionless vertical temperature gradient; as these models differ increasingly with increases in the stability parameter z / L, heat flux and friction velocity relative differences reached \(100\,\%\) when \(z/L > 1\); (4) the shallowness of the stable boundary layer is responsible for significant sensitivity to the height of the observed temperature and wind data used to estimate the fluxes. Consistent flux results were obtained with atmospheric measurements at heights up to 2 m. Our sensitivity study revealed the need to include a dynamical parametrization of roughness length over Antarctica in climate models and to develop new parametrizations of the surface fluxes in very stable conditions, accounting, for instance, for the divergence in both radiative and turbulent fluxes in the first few metres of the boundary layer.  相似文献