Halogen contamination in Antarctic H5 and H6 chondrites and relation to sites of recovery     

Marcel Langenauer  Urs Kr  henbü  hl 《Earth and Planetary Science Letters》1993,120(3-4):431-442

The distribution of the elements F, Cl, Br and I was analysed in layers removed stepwise from Antarctic H5 and H6 chondrites. All meteorites show higher concentrations of these elements on their surfaces than in their interiors. The degree of halogen enrichment cannot be correlated with the degree of visual weathering and is proportional to the time the meteorites were residing on the surface of the Antarctic ice. During this period, aerosols, salts and gaseous components are deposited on the surfaces of the meteorites and diffuse into their interior. The observed contamination level of the meteorites is influenced by leaching properties and diffusion behaviour of the individual halogens. The major contamination source for F, Cl and probably Br is air-borne seaspray; for I it is the gaseous compound methyl iodide (CH₃I) produced by biological processes in the sea. Methyl iodide and its oxidation products formed in the Antarctic atmosphere (e.g., I₂) can be transported over longer distances to the interior of Antarctica than air-borne seaspray. Therefore, the ratio of the halogen contamination is related to the collection site of the meteorites. All meteorites that were found in the Antarctic interior are contaminated to a lesser degree by F, Cl and Br relative to I than those found near the coast. The measured enrichment ratio of I/F is a function of the distance between the collection site and the open sea, and increases from the Allan Hills to the Thiel Mountains. By revealing the degree of contamination of a meteorite it is possible to determine its maximum surface residence time on the Antarctic ice.  相似文献   

Residence time distribution functions of chemical elements in the ocean     

Marcel Ovidiu Vlad 《Mathematical Geology》1988,20(7):815-819

The mean residence times of chemical elements in the ocean are usually evaluated assuming that supply and removal rates are equal. In this note, a general approach is developed which removes the above restriction. Considering a time scale larger than the homogenization time of the ocean (>10³ yr), the method allows evaluation of residence time distribution functions and of the corresponding moments.  相似文献   

The International Geophysical Year (1957–1958): Great achievements and minor obstacles     

Marcel Nicolet Dr. 《GeoJournal》1984,8(4):303-320

A short survey is given of the circumstances in which the First and the Second Polar Years were held: (1882–83 and 1932–33). This is followed by an a ccount of the main events relating to the original conception of the International Geophysical Year and to the develooment and execution of the scientific programme. Attention is drawn to the willing cooperation, in many different disciplines, of scientists throughout the world.  相似文献   

On the production of nitric oxide by cosmic rays in the mesosphere and stratosphere     

Marcel Nicolet 《Planetary and Space Science》1975,23(4):637-649

Nitric oxide is formed in the atmosphere through the ionization and dissociation of molecular nitrogen by galactic cosmic rays. One NO molecule is formed for each ion pair produced by cosmic ray ionization.The height-integrated input (day and night) to the lower stratosphere is of the order of 6 × 10⁷ NO molecules cm^?2/sec in the auroral zone (geomagnetic latitude Φ ? 60°) during the minimum of the sunspot cycle and 4 × 10⁷ NO molecules cm^?2/sec in the subauroral belt and auroral region (Φ? 45°) at the maximum of solar activity. The tropical production is less than 10^?7 NO molecules cm^?2/sec above 17 km and at the equator the production is only 3 × 10⁶NO molecules cm^?2/sec.  相似文献   

On the molecular scattering in the terrestrial atmosphere : An empirical formula for its calculation in the homosphere     

Marcel Nicolet 《Planetary and Space Science》1984,32(11):1467-1468

A recent determination by D. R. Bates of the Rayleigh scattering cross section (σ_RS) for air from 0.2 to 1 μm leads to a simple empirical formula (λ in μm) $\text{σ}{}_{\mathrm{RS}}\text{=}\text{4.02 × 10}{}^{\mathrm{?28}}\text{λ}{}^{\mathrm{4+x}}\text{cm}{}^2$ where $\text{x =}\text{0.389λ + 0.09426}\text{λ ? 0.3228}$ for the spectral region 0.2 μm < λ < 0.55 μm ; the accuracy is within ±0.5%. From the visible at 0.55 μm to the infrared (i.r.) at 1 μm, the same accuracy can be obtained using a constant value, x = 0.04. The formula accounts for the degree of depolarization which varies with the wavelength according to the latest determination by Bates.  相似文献   

Correlation between the rainfall,sediment recharge,and triggering of torrential flows in the Rebaixader catchment (Pyrenees,Spain)     

Roberta Pastorello  Marcel Hürlimann  Vincenzo D’Agostino 《Landslides》2018,15(10):1921-1934

The debris flow (DF) and debris flood (DFD) activity in the Rebaixader catchment (Spanish Pyrenees) is analyzed in this study. The research is focused on how precipitation leads to the triggering of torrential floods and influences the sediment availability during the recharge period, in a supply-unlimited catchment. Two kinds of correlations are studied: (1) the correlation between the rainfall features (intensity and kinetic energy) and the DF/DFD triggering and (2) the correlation between the hyetograph and the DF/DFD volumes. The tested hypothesis was that a greater amount of rainfall during the recharge period would produce a greater DF/DFD volume. The period between two consecutive DF/DFD events is processed using a variable, the Erosion Index, originally developed for the Universal Soil Loss Equation. This analysis considered the rainfall time series and 22 DF/DFD events registered during the period 2009–2015. The results show that the precipitation of the recharge period does not seem to have a strong influence on the mobilized volumes. In many cases, a second DF/DFD event was triggered soon after the previous event, which highlighted the role of the first event in creating an unstable state of the catchment. Additionally, a threshold relationship between the kinetic energy of the rainfall event and the maximum rainfall intensity for a 30-min period seems to be a good criterion to discriminate between triggering and non-triggering rainfall events. The results show no clear trends with which to forecast the sediment volume from precipitation, weakening the role of rainfall characteristics in determining the return period of mobilized sediment volumes in catchments similar to the Rebaixader torrent.  相似文献   

Advancing the understanding of variations of Arctic sea ice optical and thermal behaviors through an international research and mobility project     

Marcel Nicolaus  Caixin Wang  Sebastian Gerland  LI Na  LI Zhijun  Bin Cheng  Don K Perovich  Mats A Granskog  SHI Liqiong  LEI Ruibo  LI Qun  LU Peng 《极地研究(英文版)》2015,(2)

In recent decades, significant changes of Arctic sea ice have taken place. These changes are expected to influence the surface energy balance of the ice-covered Arctic Ocean. To quantify this energy ba...  相似文献   

Impacts of future climate and land cover changes on landslide susceptibility: regional scale modelling in the Val d’Aran region (Pyrenees,Spain)     

Hürlimann  Marcel  Guo  Zizheng  Puig-Polo  Carol  Medina  Vicente 《Landslides》2022,19(1):99-118

It is widely accepted that future environmental changes will affect rainfall-induced shallow slides in high-mountain areas. In this study, the Val d’Aran region located in the Central Pyrenees was selected to analyze and quantify the impacts of land use and land cover (LULC) and climate changes on regional landslides susceptibility. We analyzed 26 climate models of the EURO-CORDEX database focussing on the future rainfall conditions. The IDRISI TerrSet software suite was used to create the future LULC maps. These two inputs were analyzed individually and in a combined way defining 20 different scenarios. All these scenarios were incorporated in a physically based stability model to compute landslides susceptibility maps. The results showed that both environmental conditions will considerably change in the future. The daily rainfall will increase between 14 and 26% assuming a return period of 100 years. This intensification of precipitation will produce an overall decrease of the stability condition in the study area. Regarding the LULC prediction, the forest area will significantly increase, while in particular grassland, but also shrubs decrease. As a consequence, the overall stability condition improves, because the root strength is higher in forest than in grassland and shrubs. When we analyzed the combined impacts, the results showed that the positive effect of LULC changes is larger than the negative influence of rainfall changes. Hence, when combining the two aspects in the future scenarios, the stability condition in the study area will improve.

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Optical and crystal-chemical changes in aquamarines and yellow beryls from Thanh Hoa province,Vietnam induced by heat treatment   总被引：1，自引：0，他引：1  

Jana Fridrichová  Peter Bačík  Petra Rusinová  Peter Antal  Radek Škoda  Valéria Bizovská  Marcel Miglierini 《Physics and Chemistry of Minerals》2015,42(4):287-302

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New geochronological and archaeological data for the Sheaman Clovis site,eastern Wyoming,U.S.A.     

C. Vance Haynes  Marcel Kornfeld  George C. Frison 《Geoarchaeology》2004,19(4):369-379

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