Tracking past mining activity using trace metals,lead isotopes and compositional data analysis of a sediment core from Longemer Lake,Vosges Mountains,France

A 157-cm-long sediment core from Longemer Lake in the Vosges Mountains of France spans the past two millennia and was analyzed for trace metal content and lead isotope composition. Trace metal accumulation rates highlight three main input phases: Roman Times (cal. 100 BC–AD 400), the Middle Ages (cal. AD 1000–1500), and the twentieth century. Atmospheric contamination displays a pattern that is similar to that seen in peat bogs from the region, at least until the eighteenth century. Thereafter, the lake sediment record is more precise than peat records. Some regional mining activity, such as that in archaeologically identified eighteenth-century mining districts, was detected from the lead isotope composition of sediment samples. Compositional data analysis, using six trace metals (silver, arsenic, cadmium, copper, lead and zinc), enabled us to distinguish between background conditions, periods of mining, and of other anthropogenic trace metal emissions, such as the recent use of leaded gasoline.     

Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project

Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the V_S,30 at a site. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results. The present guidelines provide practical information on the acquisition and analysis of surface wave data by giving some basic principles and specific suggestions related to the most common situations. They are primarily targeted to non-expert users approaching surface wave testing, but can be useful to specialists in the field as a general reference. The guidelines are based on the experience gained within the InterPACIFIC project and on the expertise of the participants in acquisition and analysis of surface wave data.     

Measurements of iron concentration in kaolinites considering disorder broadening of EPR lines

Only one part of the EPR lines of a kaolinite spectrum of structural Fe³⁺ is clearly observable because of the overlapping of other lines with other spectra. For this reason, to determine the structural Fe³⁺ concentration we used the line near g=9, although it is not intense. A standard is needed: powders of ZnS containing given concentrations of Mn²⁺ (isoelectronic to Fe³⁺) were used for this purpose. Using the simulations of the EPR spectra, the concentration (number of Fe³⁺ per Al³⁺) is determined; it is in the range 10^?5 to 10^?4 for our samples. Considering that the crystal-field disorder around Fe³⁺ is responsible for line broadening, we looked for a possible effect of the broadening on the intensity of the EPR spectra. This effect is taken as a distribution of the parameter λ=B₂²/B₂⁰. The influence of the parameter λ and its statistical distribution on the position, shape, width and intensity of the EPR line has been calculated using simulation procedures. The correction due to the disorder on the calculated concentration is of the same order of magnitude as the precision measurement. This method can be applied for other kaolinites by comparing the area of their g=9 lines with known ones.     

Simulation des changements climatiques au cours du XXIe siècle incluant l'ozone stratosphériqueSimulation of climate changes during the 21st century including stratospheric ozone

Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154.     

Redistribution of riverine and rainfall freshwater by the Bay of Bengal circulation

Ocean Dynamics - We use satellite-derived currents and a Lagrangian approach to investigate the redistribution of the precipitation minus evaporation (P-E) and river freshwater inputs into Bay of...     

Impact of the configuration of stretching and ocean–atmosphere coupling on tropical cyclone activity in the variable-resolution GCM ARPEGE

This study starts by investigating the impact of the configuration of the variable-resolution atmospheric grid on tropical cyclone (TC) activity. The French atmospheric general circulation model ARPEGE, the grid of which is rotated and stretched over the North Atlantic basin, was used with prescribed sea surface temperatures. The study clearly shows that changing the position of the stretching pole strongly modifies the representation of TC activity over the North Atlantic basin. A pole in the centre of the North Atlantic basin provides the best representation of the TC activity for this region. In a second part, the variable-resolution climate model ARPEGE is coupled with the European oceanic global climate model NEMO in order to study the impact of ocean–atmosphere coupling on TC activity over the North Atlantic basin. Two pre-industrial runs, a coupled simulation and a simulation forced by the sea surface temperatures from the coupled one, are compared. The results show that the coupled simulation is more active in the Caribbean Sea and the Gulf of Mexico while the forced simulation is more active over eastern Florida and the eastern Atlantic. The difference in the distribution of TC activity is certainly linked with the location of TC genesis. In the forced simulation, tropical cyclogenesis is closer to the west African coast than in the coupled simulation. Moreover, the difference in TC activity over the eastern Atlantic seems to be related to two different mechanisms: the difference in African easterly wave activity over the west of Africa and the cooling produced, in the coupled simulation, by African easterly waves over the eastern Atlantic. Finally, the last part studies the impact of changing the frequency of ocean–atmosphere coupling on Atlantic TC activity. Increasing the frequency of coupling decreases the density of TC activity over the North Atlantic basin. However, it does not modify the spatial distribution of the TC activity. TC rainfalls are decreased by 8?% in the high frequency coupled run.     

Segregated ice structures in various heaved permafrost landforms through CT Scan

The growth of segregated ice lenses in frost susceptible sediments in the discontinuous permafrost zone is the dominant mechanism for the formation of permafrost mounds, such as palsas, lithalsas and permafrost plateaus. Thawing of these mounds creates thermokarst lakes, which are particularly abundant in Nunavik, east of the Hudson Bay area. The inception of the permafrost in mounds and their growth are regulated by climate conditions, by local Quaternary geology and by environmental factors such as topography, vegetation, snow cover and surface humidity. Variable sizes and morphology of the permafrost mounds can be attributed to local factors that affect the ice segregation process, particularly the supply of water needed for ice‐lens growth and grain‐size composition of the soil into which aggradation takes place. Computer image analysis of CT scans on high quality cores obtained from permafrost mounds and plateaus of various shapes reveal that the ice layer sequences and permafrost internal structure vary with landform types. A relationship therefore exists between different morphological type within a family of landforms and their microscale internal structure. Copyright © 2007 John Wiley & Sons, Ltd.     

Dating the Tethyan Ocean in the Western Alps with radiolarite pebbles from synorogenic Oligocene molasse basins (southeast France)

For the first time in the Western Alps, radiolarite pebbles collected from Tertiary foreland molasse conglomerates are treated for microfossil extraction and dated. Among forty pebbles collected in the field, seven of them released diagnostic radiolarian assemblages ranging in age from Late Bajocian?CEarly Callovian to Middle Oxfordian?CEarly Tithonian. These ages overlap previous biochronological data obtained from in situ localities of the Schistes Lustrés Piemont zone of the French-Italian Alps and triple the number of diagnostic radiolarite samples known so far in this segment of the chain. The diagnostic pebbles are characterized by low grade metamorphism, showing that some eroded thrust-sheets from the oldest parts of the ocean escaped any tectonic burial during the Alpine convergence. Mixing of low and high-grade radiolarites, mafics and ultramafics pebbles implies that various ocean-derived units were exposed. This tectonic scenario involves tight refolding and severe uplift of the Eocene subduction wedge in the Early Oligocene.     

Seismicity in the block mountains between Halle and Leipzig,Central Germany: centroid moment tensors,ground motion simulation,and felt intensities of two <Emphasis Type="Italic">M</Emphasis> ≈ 3 earthquakes in 2015 and 2017

On April 29, 2017 at 0:56 UTC (2:56 local time), an M_W =?2.8 earthquake struck the metropolitan area between Leipzig and Halle, Germany, near the small town of Markranstädt. The earthquake was felt within 50 km from the epicenter and reached a local intensity of I₀ = IV. Already in 2015 and only 15 km northwest of the epicenter, a M_W =?3.2 earthquake struck the area with a similar large felt radius and I₀ = IV. More than 1.1 million people live in the region, and the unusual occurrence of the two earthquakes led to public attention, because the tectonic activity is unclear and induced earthquakes have occurred in neighboring regions. Historical earthquakes south of Leipzig had estimated magnitudes up to M_W ≈?5 and coincide with NW-SE striking crustal basement faults. We use different seismological methods to analyze the two recent earthquakes and discuss them in the context of the known tectonic structures and historical seismicity. Novel stochastic full waveform simulation and inversion approaches are adapted for the application to weak, local earthquakes, to analyze mechanisms and ground motions and their relation to observed intensities. We find NW-SE striking normal faulting mechanisms for both earthquakes and centroid depths of 26 and 29 km. The earthquakes are located where faults with large vertical offsets of several hundred meters and Hercynian strike have developed since the Mesozoic. We use a stochastic full waveform simulation to explain the local peak ground velocities and calibrate the method to simulate intensities. Since the area is densely populated and has sensitive infrastructure, we simulate scenarios assuming that a 12-km long fault segment between the two recent earthquakes is ruptured and study the impact of rupture parameters on ground motions and expected damage.     

Development and decay of a lithalsa in Northern Québec: A geomorphological history

The complete life cycle of a permafrost mound is reconstructed from its growth until its degradation. The study site is a lithalsa, which is the subject of a long-term monitoring that includes geocryological observations, measurements of permafrost properties on cores, ground temperature measurements, and observations of landform changes. The landform likely grew as a palsa under cold climatic conditions in the past. The peat cover was subsequently eroded. Early stages of degradation are witnessed since 2003 as a new thermokarst pond is starting to form though mound collapse. Settlement of the structure has been observed, and a rim ridge has begun to form. Ultimately, the lithalsa shall disappear and be replaced by a circular thermokarst pond surrounded by a rampart, similar to many other ones in the study area. The monitoring of the thermal regime of the lithalsa illustrates the pattern of internal warming and points to the causes of its degradation.