GPS network monitors the Western Alps' deformation over a five-year period: 1993–1998

  The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at each site. GPS data processing has been done by three independent teams using different software. The different solutions have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and 2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation. Received: 27 November 2000 / Accepted: 17 September 2001     

Respiration of Recently-Fixed Plant Carbon Dominates Mid-Winter Ecosystem CO2 Production in Sub-Arctic Heath Tundra

Arctic ecosystems could provide a substantial positive feedback to global climate change if warming stimulates below-ground CO₂ release by enhancing decomposition of bulk soil organic matter reserves.Ecosystem respiration during winter is important in this context because CO₂ release from snow-covered tundra soils is a substantial component of annual net carbon (C) balance, and because global climate models predict that the most rapid rises in regional air temperature will occur in the Arctic during winter. In this manipulative field study, the relative contributions of plant and bulk soil organic matter C pools to ecosystem CO₂ production in mid-winter were investigated. We measured CO₂ efflux rates in Swedish sub-arctic heath tundra from control plots and from plots that had been clipped in the previous growing season to disrupt plant activity. Respiration derived from recently-fixed plant C (i.e., plant respiration, and respiration associated with rhizosphere exudates and decomposition of fresh litter) was the principal source of CO₂ efflux, while respiration associated with decomposition of bulk soil organic matter was low, and appeared relatively insensitive to temperature. These results suggest that warmer mid-winter temperatures in the Arctic may have a much greater impact on the cycling of recently-fixed, plant-associated C pools than on the depletion of tundra bulk soil C reserves, and consequently that there is a low potential for significant initial feedbacks from arctic ecosystems to climate change during mid-winter.     

LONG TERM EFFECTS OF REHABILITATION MEASURES ON BED LOAD TRANSPORT AT THE SALZACH RIVER

1 BASIC PROBLEMFlood protecton, sPreaing of settlements and occuPatin Of river valleys were maor reasons to damand lindt rivers throughout Europe in the ndd 19th century. Engineers of those days often knew very wellabout the effects of their plannings: shortening the river length would accelerat the now and thusencourage the erosion into the river's sedAnents. Two vital advanages could be obtalned from that kindof constrUction, landuse of the fOrmer flood plains on the one and increasin…     

RESUSPENSION OF FINE SEDIMENT IN RESERVOIRS - A CASE STUDY OF THE LOWER INN RIVER

1 THE LOWhR unR INNThe Inn river has its source in the alPine region of the GraubUnden canton of Switzerand. ThecatChment area of about 260(X} kIn2 includes mountains of the central Alpes up to 40(X) m. The river runs5l7 km thrOugh the countries of SwitZerand, Austria and Germany on itS way into the Danube mver. Thedischarge of the river at its mouth in the city of Passau is mainly infiuenced by the snow melt in themountainous catchment area and vches between apProx. 200 m3ls durin…     

Climate change in Yellowstone National Park: Is the drought-related risk of wildfires increasing?

The increased frequency of wildfires in the United States has become a common prediction associated with the build-up of greenhouse gases. In this investigation, variations in annual wildfire data in Yellowstone National Park are compared to variations in historical climate conditions for the area. Univariate and multivariate analytical techniques reveal that (a) summer temperatures in the Park are increasing, (b) January-June precipitation levels are decreasing, and (c) variations in burn area within the Park are significantly related to the observed variations in climate. Outputs from four different general circulation model simulations for 2 × CO₂ are included in the analyses; model predictions for increasing aridity in the Yellowstone Park area are generally in agreement with observed trends in the historical climate records.     

Correcting for crystal tilt in HRTEM images of minerals: the case of orthopyroxene

High-resolution transmission electron microscopy (HRTEM) is a powerful technique for crystal structure imaging and real structure analysis. It is theoretically possible to resolve inter-atomic distances with modern high resolution microscopes. In practice, however, the effects of sample and lens parameters such as crystal tilt and phase contrast transfer function (CTF) distort the images, reduce the resolution offered, and make image interpretation difficult. We have analyzed to what extent it is possible to reconstruct interpretable images of a tilted mineral by image processing.HRTEM images of orthopyroxene were simulated for a series of crystal tilts and thicknesses under Scherzer defocus condition using the parameters of a 400 kV microscope. The tilted images were reconstructed by crystallographic image processing. After correcting for crystal tilt, the images were as good as electron density maps calculated from X-ray diffraction structure factors.     

Die entwicklungsprobleme im “nordkalottgebiet” Schwedens Development problems in the northernmost parts of Sweden Les problèmes de développement dans la région suédoise de la “calotte du nord”

Sweden's high economic and social standard has been gained through a hard past and present structural rationalization process in the economy. This process has had the regional consequence that Norrland and especially its northernmost parts have met with considerable difficulties in maintaining services and full employment. A large number of farmers and forest workers migrated southward. Swedish location policy after 1965 aims at creating one or two growth poles in northern Norrland; Luleå and its neighbouring towns of Piteå and Boden appear to have good prerequisites. However, Umeå has the strongest population increase, a result of the newly established university which has developed very rapidly. It appears that the growth potentials in northern Norrland are greatest on the coast. Long distances, a widely spread population, and a bad urban structure with too many small communities and no big expansive ones make the inland of northern Norrland the greatest regional-political problem in Sweden.     

Glass crust on intratelluric phenocrysts in volcanic ash as a measure of eruptive violence

A comparison of each of the volumes of nine deposits of airborne volcanic ash from the Coatepeque Volcano in El Salvador, Central America to the amount of glass crust adhering to intratelluric phenocrysts shows an inverse relationship. As violence, volume, and eruptive abrasion increase, glass crusts decrease. The eruptive violence of a prehistoric eruption and the original volume of ash can thus be calculated from glass-to-crystal ratios observed in erosional remnants.     

Luna 20: mineralogy and petrology of fragments less than 125 μm size

Two milligrams of less than 125 μm size particles from the Luna 20 soil sample (22001,17) have been examined. The results of the mineral identification and analysis verify earlier assumptions that the nature of the lunar highlands is predominantly anorthositic in composition. The presence of highly magnesian clinopyroxene, orthopyroxene and olivine suggests crystallization of Highland rocks in an ultrabasic environment. No fragments were observed that could be unequivocally assigned to mare basalt types.     

Energy flow and elemental concentrations in the Steina River ecosystem (Black Forest, Germany)

Considering food web energetics and elemental cycling together allows the testing of hypotheses about the coevolution of biological systems and their physical environment. We investigated the energy flow and the distribution of 25 elements in the Steina River.¶We constructed an annual energy flow network and estimated the emergy ("embodied energy" that includes all the energy involved in a process) contributions of resources sustaining the system. Furthermore, we measured the concentration of various macronutrients, essential elements, and heavy metals in the physical environment and trophic compartments. Finally, we examined the hypothesis of a positive relationship between the "rarity" of an element and its tendency to bioaccumulate. To do so, we used transformity, the relative energy input required to sustain a compartment's net production or the concentration differential of an element between the living community and the physical environment.¶The resulting energy flow network is one of the most complete available for streams. In the Steina, over 99% of the energy input is transported through the system without being processed. Dissolved inorganic matter and sunlight are the largest inputs, but uptake efficiency is much higher for dissolved and particulate organic matter. Transformities of trophic compartments and elements span 6 to 7 orders of magnitude.¶The tendency to bioaccumulate was as predicted for most elements, with macronutrients showing no accumulation and heavy elements accumulating in high-transformity compartments. However, Na and K were found at highest concentrations in consumers, and Pb, Ga, and Cd in algae. Improved estimates may become possible as more knowledge is available on ecosystem flows. We suggest further ways of testing hypotheses about strategies of element processing.