Simulation of the interaction of galactic cosmic ray protons with meteoroids: On the production of 3H and light noble gas isotopes in isotropically irradiated thick gabbro and iron targets

Abstract— Thick spherical targets, one made of gabbro (R = 25 cm) and one made of iron (R = 10 cm), were irradiated isotropically with 1.6 GeV protons at Laboratoire National Saturne (LNS)/Saclay to simulate the interactions of galactic cosmic ray protons with meteoroids in space. At various depths, both artificial meteoroids contained a large number of high‐purity, single‐element target foils and chemical compounds of up to 28 target elements. In these individual target foils, the elemental production rates of radionuclides and noble gas isotopes were measured. Here, we report the results for the light noble gas isotopes ^3,4He, ^20,21,22Ne, and ^36,38,39Ar for the most cosmochemically relevant target elements as well as for some meteoritic material from Jilin, Farmington, and Cape York. From ³He analyses done several years apart, ³H diffusive losses during sample storage have been obtained, and direct as well as cumulative ³He production rates for O, Mg, Al, Si, Fe, Ni, and the meteoritic material are given. Losses by diffusion of tritium from metallic Mg and Fe are found to occur on time scales of months, while metallic Al, Si, and stone meteorites are much more retentive. The production rate ratios P(³H)/P(³He)_d obtained in the simulation experiments are 0.73, 1.28, and 1.16 for O, Al, and Si, respectively. These rates are based on our best knowledge about the ³H and ³He production rates and should, therefore, replace data published earlier (Leya et al. 2000a). The earlier calculations for ⁴He, ^20,21,22Ne, and ^36,38,39Ar remain valid. The new modeled correlation ³He_cum/²¹Ne versus ²²Ne/²¹Ne for chondrites exposed to cosmic rays with an energy spectrum characterized by a modulation parameter of φ = 650 MeV is in fair agreement with the empirical relationship (“Berne plot”). However, for small meteorites and little shielding in larger ones, there are systematic differences that most likely are due to an underestimation of the spallogenic ²²Ne/²¹Ne ratio by ?2%.     

Production rates and proton‐induced production cross sections of 129I from Te and Ba: An attempt to model the 129I production in stony meteoroids and 129I in a Knyahinya sample

Abstract— Proton‐induced production cross sections of ¹²⁹I from Te and Ba are presented. Earlier assumptions that Te is the most important target element in meteoroids are confirmed. Based on this data set and the experimental production rates of ¹²⁹I from thick‐target experiments, the production of ¹²⁹I in stony meteoroids is modeled using a GCR flux density of 4.06 cm^?2 s^?1. The results of this modeling must be considered preliminary because the contribution from neutron capture on ¹²⁸Te needs further investigation. We obtained modeled production rates that agree with experimental results for samples from two medium‐sized meteorites (Abee and Knyahinya). However, we find that this model does not describe ⁴¹Ca in lunar rocks well and seems to overestimate ¹²⁹I production in larger bodies, such as Allende. We present elemental production rates from Te and Ba based on our modeling as well as for a model that describes neutron capture products. For ¹²⁹I analysis of Knyahinya, a novel method to separate Te and analysis using ICP‐MS was used, enabling the use of experimental elemental concentrations obtained from the same meteorite to calculate ¹²⁹I production.     

不同气候变化情景下亚洲北山羊（Capra sibirica）的响应（英文）

目前很少见到关于气候变化影响亚洲北山羊物种栖息地的研究。通过调查气候变化对塔吉克斯坦东部亚洲北山羊(Capra sibirica)分布的影响,并采用生态位建模比较了亚洲北山羊的适宜栖息地的当前与未来分布情况。预计到2070年,现有适宜栖息地的18%(2689 km^2)将变得不适宜亚洲北山羊的生存,损失的区域主要位于研究区域的东南部和西北部地区。新的适宜栖息地可能会扩展到当前亚洲北山羊范围之外:到2070年将扩展30%(4595 km^2)的范围,这些区域与亚洲北山羊现有的分布有很强的相关性。东南部的损失与该地区当前大多数的亚洲北山羊栖息地重叠,主要出现在比研究区域海拔低得多的区域(3500–4000 m)。当同时考虑损失和收益时,亚洲北山羊可能会净扩展到新的适宜栖息地。到2070年,亚洲北山羊的平均栖息地增加量约为30%(1379 km^2),表明适宜栖息地已向北部低温栖息地转移。研究结果有助于规划气候变化情景下塔吉克斯坦东部山区对生物多样性保护的潜在影响。应该特别注意东南地区的高地山羊种群,那里的栖息地可能由于气候对山区生态系统的影响而变得不适合该物种继续生存。     

A recent build-up of atmospheric CO2 over Europe. Part 1: observed signals and possible explanations

We analysed interannual and decadal changes in the atmospheric CO₂ concentration gradient (ΔCO₂) between Europe and the Atlantic Ocean over the period 1995–2007. Fourteen measurement stations are used, with Mace-Head being used to define background conditions. The variability of ΔCO₂ reflects fossil fuel emissions and natural sinks activity over Europe, as well as atmospheric transport variability. The mean ΔCO₂ increased by 1–2 ppm at Eastern European stations (∼30% growth), between 1990–1995 and 2000–2005. This built up of CO₂ over the continent is predominantly a winter signal. If the observed increase of ΔCO₂ is explained by changes in ecosystem fluxes, a loss of about 0.46 Pg C per year would be required during 2000–2005. Even if severe droughts have impacted Western Europe in 2003 and 2005, a sustained CO₂ loss of that magnitude is unlikely to be true. We sought alternative explanations for the observed CO₂ build-up into transport changes and into regional redistribution of fossil fuel CO₂ emissions. Boundary layer heights becoming shallower can only explain 32% of the variance of the signal. Regional changes of emissions may explain up to 27% of the build-up. More insights are given in the Aulagnier et al. companion paper.     

Holocene lake-level fluctuations in Jura and the northern subalpine ranges, France: regional pattern and climatic implications

Holocene lake-level fluctuations in Jurassian and French subalpine lakes are reconstructed using sedimentological analysis, and a regional pattern of palaeohydrological changes is put forward. Major transgressive phases culminated at about 8500 BP, 6500 BP, 4800 BP, 3500–2300 BP and 450 BP. (1) The synchroncity of Holocene lake-level changes demonstrated for a large number of lakes, (2) close correlations attested between certain lakes and (3) the coincidence between rises in lake-levels in Jura and French subalpine ranges, and glacier advances in Swiss and Austrian Alps argue for a climatic control of these Holocene lake-level fluctuations.     

Allan Hills 88019: An Antarctic H-chondrite with a very long terrestrial age

Abstract— We have measured the concentrations of the cosmogenic radionuclides ¹⁰Be, ²⁶Al and ³⁶Cl (half-lives 1.51 Ma, 716 ka, and 300 ka, respectively) in two different laboratories by accelerator mass spectrometry (AMS) techniques, as well as concentrations and isotopic compositions of stable He, Ne and Ar in the Antarctic H-chondrite Allan Hills (ALH) 88019. In addition, nuclear track densities were measured. From these results, it is concluded that the meteoroid ALH 88019 had a preatmospheric radius of (20 ± 5) cm and a shielding depth for the analyzed samples of between 4 and 8 cm. Using calculated and experimentally determined production rates of cosmogenic nuclides, an exposure age of ～40 Ma is obtained from cosmogenic ²¹Ne and ³⁸Ar. The extremely low concentrations of radionuclides are explained by a very long terrestrial age for this meteorite of 2 ± 0.4 Ma. A similarly long terrestrial age was found so far only for the Antarctic L-chondrite Lewis Cliff (LEW) 86360. Such long ages establish one boundary condition for the history of meteorites in Antarctica.     

Intrusion and Crystallization of a Spinifex-Textured Komatiite Sill in Dundonald Township, Ontario

Although komatiite has been defined as an ultramafic volcanicrock characterized by spinifex texture, there is a growing recognitionthat similar textures can also form in high-level dykes andsills. Here, we report the results of a petrological and geochemicalinvestigation of a 5 m thick komatiite sill in Dundonald Township,Ontario, Canada. This unit forms part of a series of komatiitesand komatiitic basalts, some of which clearly intruded unconsolidatedsediments. The komatiite sill is differentiated into a spinifex-texturedupper part and an olivine cumulate lower part. Features characteristicof the upper sections of lava flows, such as volcanic brecciaand a thick glassy chilled margin, are absent and, instead,the upper margin of the sill is marked by a layer of relativelylarge (1–5 mm) solid, polyhedral olivine grains that gradesdownwards over a distance of only 2 cm into unusually large,centimetre-sized, skeletal hopper olivine grains. This is underlainby a 1 m thick zone of platy spinifex-textured olivine and coarse,complex, dendritic, spinifex-textured olivine. The texture ofthe olivine cumulate zone in the overlying unit is uniform rightdown to the contact and a lower chilled margin, present at thebase of all lava flows, is absent. The textures in the silland the overlying unit are interpreted to indicate that thesill intruded the olivine cumulate zone of the overlying unit.Thermal modelling suggests that soon after intrusion, a narrowinterval of the overlying cumulate partially melted and thatthe liquid in the upper part of the sill became undercooled.The range of olivine morphologies in the spinifex-textured partof the sill was controlled by nucleation and crystallizationof olivine in these variably undercooled liquids. KEY WORDS: komatiite; intrusion; spinifex texture; olivine     

Younger Dryas and early Holocene lake-level fluctuations in the Jura mountains, France

Lake-level fluctuations in the Jura mountains (France) during the Younger Dryas and the early Holocene are reconstructed using sedimentological analyses. Major transgressive phases culminated just before the Laacher See tephra deposition, at the beginning of the Younger Dryas, between 9000 and 8000 BP and between 7000 and 6000 BP. The Younger Dryas appears to be characterized by increasing dryness. Other major lowering phases occurred during the middle Allerød and during the Preboreal. A transgressive event developed between c . 9700 and 9500 BP. These palaeohydrological changes can be related to climatic oscillations reconstructed from pollen and isotopic records in Swiss lakes, from glacier movements and timberline variations in the Alps, and from isotopic records in the Greenland ice sheet.     

Rheological Transitions During Partial Melting and Crystallization with Application to Felsic Magma Segregation and Transfer

We consider the rheological behaviour of felsic magma in thezone of partial melting and during subsequent crystallization.We also introduce and combine concepts (mushy zone, percolationtheory, granular flow, shear localization) derived from thenon-geological literature and apply them to field observationson migmatites and granites. Segregation and transportation offelsic magmas is commonly observed in association with non-coaxialdeformation, suggesting that gravity forces have limited influenceduring magma segregation. Solid to liquid and liquid to solidtransitions are shown to be rheologically different, which infirmsthe concept of a unique rheological critical melt percentagefor both transitions. Four stages are examined, which dependon the melt fraction present. (1) A minimum of 8% melt by volume must first be produced toovercome the liquid percolation threshold (LPT) above whichmelt pockets can connect, thus allowing local magma displacement.Transport of the liquid phase is amplified by deformation towarddilatant sinks and is restricted to a very local scale. Thiscorresponds to partially molten domains illustrated by incipientmigmatites. (2) When more melt (20–25%) is present, a melt escapethreshold (MET) allows segregation and transport of the meltand part of the residual solid phase, over large distances.This corresponds to segregation and transfer of magma towardsthe upper crust. (3) Segregation of magma also occurs during granite emplacementand crystallization. In a flowing magma containing few particles(20%), particles rotate independently within the flow, defininga fabric. As soon as sufficient crystals are formed, they interactto construct a rigid skeleton. Such a random loose packed frameworkinvolves 55% solids and corresponds to the rigid percolationthreshold (RPT). Above the RPT, clusters of particles can sustainstress, and the liquid fraction can still flow. The only remainingpossibilities for rearranging particles are local shear zones,often within the intrusion rim, which, as a consequence, developsdilatancy. This stage of segregation during crystallizationis totally different from that of magma segregation during incipientmelting. (4) Finally, the system becomes totally locked when random closepacking is reached, at 72–75% solidification; this isthe particle locking threshold (PLT). The introduction of four thresholds must be viewed in the contextof a two-fold division of the cycle that generates igneous rocks,first involving a transition from solid to liquid (i.e. partialmelting) and then a transition from liquid to solid (i.e. crystallization).Neither transition is simply the reverse of the other. In thecase of melting, pockets of melt have to be connected to afforda path to escaping magma. This is a bond-percolation, in thesense of physical percoloation theory. In the case of crystallization,randomly distributed solid particles mechanically interact,and contacts between them can propagate forces. Building a crystalframework is a site-percolation, for which the threshold ishigher than that of bond-percolation. For each transition twothresholds are applicable. The present approach, which basicallydiffers from that based on a unique critical melt fraction,expands and clarifies the idea of a first and a second percolationthreshold. One threshold in each transition (LPT and RPT, respectively)corresponds to a percolation threshold in the sense of physicalpercolation theory. Its value is independent of external forces,but relies on the type and abundance of minerals forming thematrix within which melt connectivity is developing. The exactvalue of the second threshold (MET or PLT) will vary accordingto external forces, such as deformation and the particle shape. KEY WORDS: migmatites; partial melting; granites; magma segregation; magma solidification ^*Corresponding author. Telephone: 33 03 83 44 19 00. Fax: 33 03 83 44 00 29. e-mail: jlv{at}cregu.cnrs-nancy.fr