First results of the micrometeoroid experiment s 215 on the HEOS 2 satellite

The experiment measures the mass, speed and approximate influx direction of the micrometeoroids. They are detected by the plasma produced during their impact on the sensor. In the first year after launch 173 particles were registrated.The temporal distribution of the particles indicates three different categories. Category 1 consists of 3 large groups of particles (“swarms”) each of which encountered the detector within some tens of minutes. Category 2 includes 8 small groups of particles each of which was detected within hours. Category 3 is made up by the remaining particles which are randomly distributed. The swarms are of very recent origin, possibly supplied by (1) meteoroids grazing the Earth's atmosphere, (2) ejecta from the Moon, and (3) collisions of dust particles. The groups may be dissipated swarms or particles from the outer zone of swarms. The randomly distributed particles consist of sporadic interplanetary particles and completely dissipated groups.The comparison of both the “particle rates” (number of detected particles per day) and the cumulative particle flux curves for the Earth's apex, antiapex, ecliptic north and south directions shows that the rates vary only within a factor of 2, whereas the particle flux is extremely anisotropic. The flux for the apex direction at 10^?12 g is 7 × 10^?5 m^?2 s^?1 which is 1 to 2 orders of magnitude higher than the flux values for the other directions.     

IAP/LASG海洋环流模式对风应力的响应

为了检验第三代IAP/LASG全球海洋环流模式在模拟20世纪80年代热带太平洋年际变化方面特别是ElNino和LaNina事件的能力,作者使用了三种风应力资料强迫该模式.然后,将模拟的海温同NCEP海洋同化资料相比较.分析表明,在赤道附近,模式对风应力的响应在SST分布、温跃层的描绘以及突出E1Nino和LaNina事件方面同NCEP海洋同化资料有许多共同点.然而,在描绘l0°N以北和l0°S以南的SST异常以及描写季节循环方面,响应是不够精确的.另外,模拟的温度异常滞后于NCEP海洋同化数据两个月左右.     

Stability of lysosomal and cell membranes in haemocytes of the common mussel (Mytilus edulis): effect of low temperatures.

Expanding industrial activities in the Arctic require an urgent assessment of the toxicity of chemicals at low temperatures. Organisms acclimatized to low temperature exhibit specific adaptations. For example, the amount of unsaturated lipids is increased to maintain the fluidity of the cell membranes. It has been hypothesized that such temperature-induced alterations in membrane lipid composition may affect the stability of lysosomal and cell membranes in the common mussel, Mytilus edulis, an organism exposed to seasonal temperature extremes. As mussels may be exposed to petroleum compounds along industrialized coastlines, we tested the combined effects of exposure to low temperature and the petroleum compound, phenanthrene, on haemocyte membrane stability. Test animals, acclimated to either 0 or 10 degrees C, were exposed to phenanthrene (0 = control or 500 micrograms l-1) and haemocytes were examined using the neutral red retention assay (lysosomal stability) and a fluorescence assay (cell membrane stability). At 0 degree C, lysosomal and cell membranes from uncontaminated mussels were destabilized compared with 10 degrees C (P = 0.0005). No significant effects (P > 0.05) of phenanthrene were detected at either temperature. Possible mechanisms underlying membrane destabilization include a weaker physical resistance of the membrane due to a higher amount of unsaturated lipids, a potentially higher level of reactive oxygen radicals at low temperature and the higher susceptibility of unsaturated lipids to oxidative stress. More work is required to better understand the consequences of this membrane destabilization at low temperature on the susceptibility of the organism to pollutants.     

Complete metamorphic cycle and long-lived anatexis in the c. 2.1 Ga Mistinibi Complex,Canada

Secular changes in the architecture, thermal state, and metamorphic style of global orogens are thought to have occurred since the Archean; however, despite widespread research, the driving mechanisms for such changes remain unclear. The Paleoproterozoic may prove to be a key era for investigating secular changes in global orogens, as it marks the earliest stage of an eon that saw the onset of modern-style global tectonics. The 2.1 Ga granulite-facies Mistinibi-Raude Domain (MRD), located in the Southeastern Churchill Province, Canada, offers a rare exposure of Paleoproterozoic high metamorphic grade supracrustal sequences (Mistinibi Complex, MC). Rocks from this domain were subjected to petrochronological investigations to establish P–T–t–X evolutions and to provide first order thermal state, burial and exhumation rates, and metamorphic gradients for the transient Paleoproterozoic times. To obtain comprehensive insight into the P–T–t–X evolution of the MRD, we used multi-method geochronology—Lu–Hf on garnet and U–Pb on zircon and monazite—integrated with detailed petrography, trace element chemistry, and phase equilibria modelling. Despite the extensive use of zircon and monazite as geochronometers, their behaviour in anatectic conditions is complex, leading to substantial ambiguity in interpreting the timing of prograde metamorphism. Our results indicate a clockwise metamorphic path involving significant melt extraction from the metasedimentary rocks, followed by cooling from >815°C to ~770°C at ~0.8 GPa. The timing of prograde burial and cooling from supra- to subsolidus conditions is constrained through garnet, monazite, and zircon petrochronology at 2,150–2,120 Ma and at 2,070–2,080 Ma, respectively. These results highlight long-lived residence of the rocks at mid-crustal supra-solidus conditions (55–70 Ma), with preserved prograde and retrograde supra-solidus monazite and zircon. The rocks record extremely slow burial rates (0.25–0.30 km/Ma) along a high metamorphic gradient (900–1,000°C/GPa), which appears symptomatic of Paleoproterozoic orogens. The MC did not record any significant metamorphism after 2,067 Ma, despite having collided with terranes that record high-grade metamorphism during the major 1.9–1.8 Ga Trans-Hudson orogeny. The MC would therefore represent a remnant of a local early Paleoproterozoic metamorphic infrastructure, later preserved as superstructure in the large hot Trans-Hudson orogen.     

Reassessment of the ‘Abbevillien’ in the perspective of new discoveries from the Lower Palaeolithic and Quaternary sites of Abbeville (Somme,northern France)

North-West Europe yields few traces of early human occupation, in particular for the Acheulean. In this context, the Somme Valley in northern France offers a route to Britain during various Pleistocene low sea levels, and has provided numerous evidence of Lower Palaeolithic human occupation through fieldwork initiated during the 19th century. These localities are associated with the original definition in the 1930s by the French prehistorian Abbé Henri Breuil of the ‘Abbevillien’ (Abbevillian facies), based on lithic pieces including crudely made bifaces recovered in particular in some famous key localities of Abbeville, Carpentier, Léon and Moulin Quignon quarries. The history of the term and its definition subsequently gave rise to debates concerning the chronocultural framework of Palaeolithic assemblages among the scientific community of prehistorians over time, from Jacques Boucher de Perthes, Gabriel de Mortillet, Geoffroy d'Ault du Mesnil, Victor Commont, Henri Breuil and François Bordes. New investigations at these three localities, all associated with the High Terrace of the Somme system, pushed back the age of the expansion of the Acheulean both in northern France and in Western Europe to c. 670–650 000 years. They imply that early hominins were able to settle in North-West Europe during both climatic temperate and cold phases. Our work, including new excavations and associated field observations of the three Abbeville localities involved at the onset of the controversy, allows a re-examination of the Abbevillian and contributes to the discussion of the history of Prehistoric Science and the Earliest ‘Acheuleans’ in North-West Europe.     

Volcanic sands of Iceland ‐ Diverse origins of aeolian sand deposits revealed at Dyngjusandur and Lambahraun

The origin, formation and evolution of volcanic sands are less well known than the formation of the much more common quartz‐rich sand sheets. Combining active volcanism and a cold climate, Iceland is covered for about 21% of its surface by sandy areas. The sands were analyzed in detail at two sites and results reveal their diverse origins. The first site is Dyngjusandur, located north of Vatnajökull, and the second site is the Lambahraun area, located south of Langjökull. At both sites, the sand origin is determined from field observations (wind directions from ventifacts), chemical and mineralogical analyses of rocks and sands. At Dyngjusandur, the sand is dominated by glass grains, a situation typical of sand plains in Iceland. Hyaloclastite ridges presently buried beneath Vatnajökull are the dominant source of the sand, and only large size plagioclase crystals (0.5 cm) in sands seem to be derived from the lava flows. Hyaloclastite ridges were crushed by glaciers and mechanically eroded sediments were washed out by melt‐water onto flood plains. The sand chemical composition is spatially homogeneous and similar to the average composition of neighboring sub‐aerial lava flows, reflecting efficient mixing of distinct sources below the glacier. The presence of sand north of Dyngjujökull can be taken as a way to explore the average chemical composition of non‐exposed volcanic material beneath the glacier. In the case of Lambahraun, prevailing winds indicate several potential sources of sand at the north of the sand sheet. Comparison of chemical and mineralogical analyses of sands and rock samples helped to refine the exact origin. In contrast with the first site, the sand is dominated by crystals and is chemically consistent with a mixture of material derived from the lava flows of Eldborgir and Skersli shield volcanoes. Analysis of the contact between the lava flows and the glacier reveals that basaltic sand grains formed as the result of recent advances of the glacier abrading the rocks. The direct interaction of glacial and fluvio‐glacial activity with basaltic plains appears to be necessary to produce a large amount of sands in a relatively short period of time (<4000 years). This site appears to be an excellent natural laboratory for further studies concerning the sand evolution and physical sorting processes in basaltic material, which have important implications for understanding aeolian processes on Mars. Copyright © 2011 John Wiley & Sons, Ltd.     

Meteorological effects on seasonal displacements of the ?knes rockslide, western Norway

In the alpine topography along one of the long fjords with steep and high mountain sides in western Norway the large ?knes rockslide area is defined by a distinct back scarp rising from 800 to 1,000 m a.s.l. In 2004, an extensive monitoring program started, including establishment of a meteorological station above the upper tension crack, 900 m a.s.l. This paper evaluates the significance of meteorological conditions affecting the displacements recorded by five extensometers and two laser sensors in the tension crack from November 2004 to August 2008. Meteorological factors of importance for the recorded activity in the tension crack are found to be melt water in spring and large temperature fluctuations around the freezing point in spring, autumn, and early winter. The records show less acceleration phases in the measured distance across the tension crack in the second half of the analyzed period even though annual displacements are increasing, indicating that other processes, like disintegration of irregularities along unfilled joints and disintegration of intact rock bridges in the sliding plane have become more important.     

Une methode d'etude experimentale “in situ” de la zone d'echange entre les nuages convectifs et leur environnement

Le développement d'un projet de recherche consacré à l'étude des nuages convectifs a amené les auteurs à concevoir et à élaborer un système complet de mesures adapté à cette étude. Les grandeurs thermodynamiques classiques (Température, Pression, Humidité) ainsi que les vitesses d'ascendance autour et à l'intérieur des nuages sont mesurées grâce à l'utilisation d'un avion Cessna 206 équipé de ce système. Une première étape consiste à mettre en évidence les phénomènes relatifs aux échanges entre le nuage et le milieu environnant.     

MODELING THE SPORADIC METEOROID BACKGROUND CLOUD

The orbital distributions of dust particles in interplanetary space are revised in the ESA meteoroid model to incorporate more observational data and to comply with the constraints due to the long-term particle dynamics under the planetary gravity and Poynting–Robertson effect. Infrared observations of the zodiacal cloud by the COBE Earth-bound observatory, flux measurements by the dust detectors on board Galileo and Ulysses spacecraft, and the crater size distributions on lunar rock samples retrieved by the Apollo missions are fused into a single model. Within the model, the orbital distributions are expanded into a sum of contributions due to a number of known sources, including the asteroid belt with the emphasis on the prominent families Themis, Koronis, Eos and Veritas, as well as comets on Jupiter-encountering orbits. An attempt to incorporate the meteor orbit database acquired by the Advanced Meteor Orbit Radar at Christchurch is also discussed. Work was done during D. Galligan’s stay at the University of Canterbury.