Estimating carbon release caused by land use changes over Canada's north during 1985–1990 and 1990–2000 using satellite Earth observation

This study estimates the greenhouse gas removal/emission due to land use changes (LUC) over Canada's arctic and subarctic landmass to meet Canada's reporting obligation to the United Nations Framework Convention on Climate Change (UNFCCC). Using Landsat scenes circa 1985, 1990, and 2000, as well as GIS information, we estimated the rate of LUC over Canada's north being 548 ha a −1 during 1985–1990 and 725 ha a −1 during 1990–2000. We then developed circa 2000 baseline aboveground biomass maps for the areas affected by these LUC by applying the relationships between measured aboveground biomass and a combination of Landsat and JERS‐1 data. From these aboveground biomass maps and LUC estimates, we calculated that the LUC activities over Canada's north released 29,000 ± 4400 t CO 2 a −1 during 1985–1990 and 41,000 ± 6200 t CO 2 a −1 during 1990–2000. Only aboveground biomass was considered. Monte Carlo simulation method was used to quantify the overall error caused by uncertainties in estimates of LUC area and CO 2 emission. Because soil carbon stock over Canada's arctic and subarctic ecosystems can be 10–100 time larger than that of aboveground biomass, accurately quantifying soil carbon stock change caused by LUC should be a priority in future studies.

A pressure solution creep law for quartz from indentation experiments

Indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions. This deformation mechanism contributes to Earth's crust geodynamics, controlling processes as different as fault permeability, strength, and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism. Indenter experiments have been performed at 350°C and 20–120 MPa during months with differential stress varying from 25 to 350 MPa. Several experimental parameters were varied: nature of quartz (synthetic or natural), nature of fluid, manner in which the solid/solution/solid interface was filled, and orientation of the indented surfaces versus quartz crystallographic c axis. Significant strain rates could only be obtained when using high‐solubility solutions (NaOH 1 mol L −1 ). Displacement rates of the indenter were found activated by differential stress, with exponential dependence, as theoretically predicted. The mean thickness of the trapped fluid phase below the indenter was estimated in the range 2–10 nm. Moreover, the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution. The indenter displacement rate was driven by differential stress, and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface. Conversely, marginal strain energy driven dissolution was observed around the indenter, and its kinetics was controlled by free‐surface reaction. These experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones, providing characteristic time scales for postseismic transitory creep and sealing processes in quartz‐rich rocks.

Upper mantle anisotropy beneath Australia and Tahiti from P wave polarization: Implications for real‐time earthquake location

We report measurements of long‐period P wave polarization ( P pol ) in Australia and Tahiti made by combining modeling of the polarization deviation and harmonic analysis. The analysis of the deviation of the horizontal polarization of the P wave as a function of event back azimuth may be used to obtain information about (1) sensor misorientation, (2) dipping discontinuities, (3) seismic anisotropy, and (4) velocity heterogeneities beneath a seismic station. The results from harmonic analysis and a grid search using Snell's law suggest the presence of a dipping seismic discontinuity beneath stations CTAO and CAN in Australia. These results are consistent with published receiver function studies for these stations. The P pol fast axis orientation is close to the N–S absolute plate motion direction at station TAU (Tasmania), which may be due to plate‐motion‐driven alignment of olivine crystals in the asthenosphere. Interestingly, measurements of SKS splitting at Tahiti (French Polynesia) show an apparent isotropy, whereas an inversion of P pol observations at PPTL seismic station located in Tahiti suggests the presence of two anisotropic layers. The fast axis azimuth is oriented E–W in the upper layer, and it is close to the NW–SE orientation in the lower layer. Since P pol orientations are used for real‐time earthquake locations, especially in poorly instrumented areas such as the South Pacific, we show that the bias from anisotropy and sensor misorientation determined here can be corrected to improve the location accuracy, which yields fundamental data for rapid location necessary for effective tsunami warning.

Forward and adjoint quasi‐geostrophic models of the geomagnetic secular variation

We introduce a quasi‐geostrophic model of core dynamics, which aims at describing core processes on geomagnetic secular variation timescales. It extends the formalism of Alfvén torsional oscillations by incorporating nonzonal motions. Within this framework, the magnetohydrodynamics takes place in the equatorial plane; it involves quadratic magnetic quantities, which are averaged along the direction of rotation of the Earth. In addition, the equatorial flow is projected on the core‐mantle boundary. It interacts with the magnetic field at the core surface, through the radial component of the magnetic induction equation. That part of the model connects the dynamics and the observed secular variation, with the radial component of the magnetic field acting as a passive tracer. We resort to variational data assimilation to formally construct the relationship between model predictions and observations. Variational data assimilation seeks to minimize an objective function by computing its sensitivity to its control variables. The sensitivity is efficiently calculated after integration of the adjoint model. We illustrate that framework with twin experiments, performed first in the case of the kinematic core flow inverse problem and then in the case of Alfvén torsional oscillations. In both cases, using the adjoint model allows us to retrieve core state variables which, while taking part in the dynamics, are not directly sampled at the core surface. We study the effect of several factors on the solution (width of the assimilation time window, amount and quality of data), and we discuss the potential of the model to deal with real geomagnetic observations.

Low‐frequency electromagnetic modeling of conductive obstacles buried in subsoil as coupled ellipsoids

The electromagnetic characterization of one or more conductive obstacles buried in a conductive subsoil from low‐frequency data (induction regime) is expected to benefit from a fast yet fairly accurate solution of the direct problem associated to it. Here, an approximate model is proposed to that effect. It is based on the localized nonlinear approximation, coupling between obstacles (whenever two or more) being approached via the Lax‐Foldy theory of multiple diffraction. The obstacles are modeled as generic ellipsoids, with spheres as the limit case. The exact primary field due to an electrical loop (or a magnetic dipole) is calculated, and its low‐frequency expansion is introduced. A semianalytical solution of the direct problem is developed from the exact field formulation, analytical solutions being proposed in the most simple cases of either sources or configurations. The model is validated by comparison with numerical experimentations carried out by tools available from the CIVA platform and by the FEKO code. Limits of the model are explored also, notably about the retrieval of the pertinent geometric and electric parameters of an ellipsoid buried in a half‐space from sparse data collected above it.

The eastern termination of the Zagros Fold‐and‐Thrust Belt, Iran: Structures, evolution, and relationships between salt plugs, folding, and faulting

The Zagros Mountains result from the ongoing collision between the Arabian and central Iran plates. The main features of the eastern Zagros are (1) numerous emerged or buried salt diapirs, made up of Late Precambrian Hormuz salt and (2) the irregular along‐strike shape of the collision‐related detachment folds with frequent bending. To understand this layout, four geological cross sections have been constructed from the Persian Gulf foreland basin to the inner part of the Zagros Fold‐and‐Thrust Belt. Shortening in the deformed parts of the sections is less than 10% and is mainly accommodated by detachment folding. We show that late Cenozoic folding occurred in a region that was already punctuated by salt domes and diapirs. In fact, almost continuous halokinesis developed since the earlier Paleozoic, i.e., just short time after the deposition of the Hormuz salt, and continued up to the Present. These preexisting salt structures and their relevant local thickening strongly influenced both the localization and the direction of folds.

Leaching systematics and matrix elimination for the determination of high‐precision Pb isotope compositions of ocean island basalts

Ocean island basalts from Hawaii and Kerguelen were analyzed for their Pb isotopic compositions to assess the effect of acid leaching and matrix elimination by Pb anion exchange columns on reproducibility and accuracy. Unleached samples consistently yield Pb isotopic ratios that reflect the incorporation of foreign material. Leaching removes up to 70–80% of the total Pb content of the samples with corresponding weight losses between 35 and 60%. The older and more altered Kerguelen basalts show better external reproducibility than the Hawaiian basalts, which appears to be due to the presence in the Hawaiian samples of more radiogenic contaminants (e.g., seawater Pb, drilling mud, and related alteration phases). All leached samples purified twice on anion exchange columns show more radiogenic Pb isotopic ratios than those processed once. The difference is larger for tholeiitic basalts (Hawaiian and Kerguelen Plateau) than for transitional to alkalic basalts (Kerguelen Archipelago). The small differences in measured ratios of total procedural triplicates reflect differential elimination of residual alteration via leaching and matrix effects. The effectiveness of matrix elimination depends on the specific basalt composition, and tholeiitic basalts (i.e., low Pb concentrations) require two passes on anion exchange columns. This study shows that all steps in sample processing are critical for achieving accurate high‐precision Pb isotopic compositions of ocean island basalts.

Jean Dausset (1916–2009)

Association of Ornithine Transcarbamylase Gene Polymorphisms With Hypertension and Coronary Artery Vasomotion

Previous studies have suggested that the activity of enzymes involved in the urea cycle may modulate nitric oxide (NO) production, arterial vasomotion, and hypertension. Our aim was to determine whether hypertension and coronary vasomotion could be associated with polymorphisms within the ornithine transcarbamylase (OTC) gene, located on chromosome X and coding for a key-enzyme of the urea cycle.

Allogeneic hematopoietic SCT for patients with autoimmune diseases

Allogeneic hematopoietic SCT (HSCT) has been used as treatment for single patients with autoimmune diseases (AD). To summarise currently available information, we analyzed all patients who underwent allogeneic HSCT for AD and who reported to the European Group for Blood and Marrow Transplantation (EBMT) database. Thirty-five patients receiving 38 allogeneic transplantations for various hematological and non-hematological AD were identified. Four patients had had an allogeneic HSCT for a conventional hematological indication in the past. Fifty-five per cent of the transplantation procedures led to a complete clinical response of the refractory AD and 23% to at least a partial response. The median duration of response at the last follow-up was 70.7 (15.2-130) months. Three patients relapsed at a median of 12.3 months after HSCT. Treatment-related mortality at 2 years was 22.1% (95% CI: 7.3-36.9%). Two deaths were caused by progression of AD. The probability of survival at 2 years was 70%. No single factor predicting the outcome could be identified. The retrospective nature of this study and the heterogeneous, partly incomplete data are its limitations. However, allogeneic HSCT can induce remission in patients suffering from refractory AD. These data provide the basis for carefully conducted prospective trials.