Newly identified “Tunnunik” impact structure,Prince Albert Peninsula,northwestern Victoria Island,Arctic Canada

Regional geological mapping of the glaciated surface of northwestern Victoria Island in the western Canadian Arctic revealed an anomalous structure in otherwise flat‐lying Neoproterozoic and lower Paleozoic carbonate rocks, located south of Richard Collinson Inlet. The feature is roughly circular in plan view, approximately 25 km in diameter, and characterized by quaquaversal dips of approximately 45°, decreasing laterally. The core of the feature also exhibits local vertical dips, low‐angle reverse faults, and drag folds. Although brecciation was not observed, shatter cones are pervasive in all lithologies in the central area, including 723 Ma old dikes that penetrate Neoproterozoic limestones. Their abundance decreases distally, and none was observed in surrounding, horizontally bedded strata. This circular structure is interpreted as a deeply eroded meteorite impact crater of the complex type, and the dipping strata as the remnants of the central uplift. The variation in orientation and shape of shatter cones point to variably oriented stresses with the passage of the shock wave, possibly related to the presence of pore water in the target strata as well as rock type and lithological heterogeneities, especially bed thickness. Timing of impact is poorly constrained. The youngest rocks affected are Late Ordovician (approximately 450 Ma) and the impact structure is mantled by undisturbed postglacial sediments. Regional, hydrothermal dolomitization of the Ordovician limestones, possibly in the Late Devonian (approximately 360 Ma), took place before the impact, and widespread WSW–ENE‐trending normal faults of probable Early Cretaceous age (approximately 130 Ma) apparently cross‐cut the impact structure.     

Magnetic fabrics in garnet peridotites–pyroxenites and host felsic granulites in the South Bohemian Granulites (Czech Republic): Implications for distinguishing between primary and metamorphism induced fabrics

In the high-grade Moldanubian Zone of the European Variscides, numerous bodies of ultramafic rocks occur embedded in granulite. The anisotropy of magnetic susceptibility and its low-field variation as well as the anisotropy of magnetic remanence were used to investigate magnetic fabrics of some ultramafic bodies and host granulite. In granulite, the magnetic foliation is roughly parallel to the metamorphic foliation and the magnetic lineation is near the mineral alignment lineation. In ultramafite, the magnetic foliation is relatively scattered spatially, but mostly oriented in a different way than that in granulite. The magnetic lineation is also scattered, but still relatively well defined spatially. Again, its orientation is mostly different than that of granulite. The magnetic fabric in ultramafic rocks is therefore different from that in the host granulite even though both rock types underwent at least partially common structural history. The componental movements forming the granulite fabric, mostly during amphibolite facies retrograde metamorphism, were evidently not intensive enough to strongly overprint the magnetic fabric of ultramafite. The ultramafite is therefore strong enough to maintain its pre-metamorphism fabric even at such high temperatures and pressures that are characteristic of high amphibolite facies retrograde metamorphism.     

A new index for variations in the position of the South Pacific convergence zone 1910/11–2011/2012

Quality controlled and recently homogenised mean sea level pressure records for the South Pacific are used to specify the location and variability of the South Pacific convergence zone (SPCZ) during the austral warm season (November–April). The SPCZ is the world’s largest rainfall band during the austral summer, when it dominates the climate of the South Pacific. A new index called the South Pacific convergence zone index (SPCZI) is derived, and is shown to be coherent with changes in low level wind convergence associated with the SPCZ. This index replaces the earlier SPCZ position index because it uses higher quality mean sea level pressure data than the superseded index and extends the time series further forward in time. The SPCZI allows interannual to decadal variability in the climate of the South Pacific to be tracked for more than a century from 1910/1911 to 2011/2012. During El Niño episodes the SPCZ is displaced by about 1°–3° east, and La Niña events 1°–3° west of the mean position on average. The index indicates a striking movement eastward for the period 1977/78–1998/99, compared with 1944/45–1976/77 in association with the Interdecadal Pacific oscillation (IPO). The eastward movement of the SPCZ in the late twentieth century is related to significant precipitation trends in the South Pacific region. Since 1998/99 the SPCZ has regressed westward with the negative phase change of the IPO. The long-term trend in the SPCZI is very small relative to the interannual to decadal variability and is not statistically significant, suggesting that there has been little overall change in the mean position of the SPCZ over the past century.     

Global implications of joint fossil fuel subsidy reform and nuclear phase-out: an economic analysis

This paper uses the OECD’s global recursive-dynamic general equilibrium model ENVLinkages to examine the mid-term economic consequences and the optimal energy supply mix adjustments of a simultaneous implementation of i) a progressive fossil fuel subsidy reform in emerging and developing economies and ii) a progressive phase out of nuclear energy, mostly affecting OECD countries, China and Russia. The analysis is then transposed in the context of climate change mitigation to depict the corresponding implications for CO2 emissions, to assess the interactions between the two energy policies, and to derive how the associated costs are affected by the different policies. The phase-out scenario projects a nuclear capacity halved by 2035 as compared to the Baseline, corresponding to $120 billion losses in value-added of the nuclear industry for that year. The nuclear phase-out leaves GDP and real household consumption marginally affected in energy importing countries. A multilateral subsidy reform is more likely to affect international fossil fuel prices and alter patterns of global energy use. The fossil fuel subsidy reform, when implemented together with nuclear phase-out, more than offsets negative consequences on household consumption but still leads to a decrease in global CO2 emissions. The combined policies help save the equivalent of current energy consumption in the Middle East. Combining a climate policy, an effective fossil fuel subsidy reform, even with a lower nuclear share in the power mix, brings about multiple benefits to OECD countries which reduce their energy bill and achieve large climate change mitigation at lower cost.     

Reminiscences and acknowledgements from a lover of deserts near the end of her professional life

Following the IPS-2012 Symposium where I received an award medal for « my lifetime achievements », this is a short note where I explained when, how and why I became interested in paleolimnology. I am grateful to the many people with whom I have worked.     

Estuarine sediment deposition during wetland restoration: A GIS and remote sensing modeling approach

Restoration is currently underway in the industrial salt flats of San Francisco Bay, California. Remote sensing of suspended sediment concentration and other GIS predictor variables were used to model sediment deposition within recently restored ponds. Suspended sediment concentrations were calibrated to reflectance values from Landsat TM 5 and ASTER satellite image data using three statistical techniques—linear regression, multivariate regression, and Artificial Neural Network (ANN) regression. Multivariate and ANN regressions using ASTER proved to be the most accurate methods, yielding r² values of 0.88 and 0.87, respectively. Predictor variables such as sediment grain size and tidal frequency were used in the Marsh Sedimentation (MARSED) model for predicting deposition rates. MARSED results show a root mean square deviation (RMSD) of 66.8 mm (<1σ) between modeled and field observations. This model was applied to a pond breached in November 2010 and indicated that the pond will reach sediment equilibrium levels after 60 months of tidal inundation.     

Testing spatial autocorrelation in weighted networks: the modes permutation test

In a weighted spatial network, as specified by an exchange matrix, the variances of the spatial values are inversely proportional to the size of the regions. Spatial values are no more exchangeable under independence, thus weakening the rationale for ordinary permutation and bootstrap tests of spatial autocorrelation. We propose an alternative permutation test for spatial autocorrelation, based upon exchangeable spatial modes, constructed as linear orthogonal combinations of spatial values. The coefficients obtain as eigenvectors of the standardized exchange matrix appearing in spectral clustering and generalize to the weighted case the concept of spatial filtering for connectivity matrices. Also, two proposals aimed at transforming an accessibility matrix into an exchange matrix with a priori fixed margins are presented. Two examples (inter-regional migratory flows and binary adjacency networks) illustrate the formalism, rooted in the theory of spectral decomposition for reversible Markov chains.     

Recalibrating aeolian sand transport models

A quality‐controlled data set comprising measurements of aeolian sand transport rates obtained at three disparate field sites is used to evaluate six commonly employed transport rate models (those of Bagnold, Kawamura, Zingg, Owen, Hsu, and Lettau and Lettau) and to recalibrate the empirical constants in those models. Shear velocity estimates were obtained using the von Kármán constant and an apparent von Kármán parameter. Models were recalibrated using non‐linear regression and non‐linear regression with least‐squares lines forced through axes origins. Recalibration using the apparent von Kármán parameter and forced regression reduced the empirical constants for all models. The disparity between the predictions from the different models is reduced from about an order of magnitude to about a quarter of an order of magnitude. The recalibrated Lettau and Lettau model provided the greatest statistical agreement between observed and predicted transport rates, with a coefficient of determination of 0·77. Evaluation of the results suggests that our estimations of threshold shear velocity may be too slow, causing errors in predicted transport rates. Copyright © 2012 John Wiley & Sons, Ltd.     

Energy fluxes and melt rate of a seasonal snow cover in the Moroccan High Atlas

ABSTRACT

In this study, we used an energy balance model and two simple methods based on readily available data to identify the processes driving the point-scale energy and mass balance of the snowpack. Data were provided from an experimental site located at 3200 m. All models were evaluated by comparing observed and modelled snow water equivalents. Performances are variable from one season to the next and the energy balance model gives better results (mean of root mean square error, RMSE = 25 mm and r² = 0.90) than the two simplified approaches (mean of RMSE = 54 mm and r² = 0.70). There are significant amounts of snow sublimation but they are highly variable from season to season, depending on wind conditions (between 7 and 20% of the total). While the main source of energy for melting is net radiation, the amount of heat brought by sensible heat flux is significant for two of the most windy snow seasons.

Editor Z.W. Kundzewicz Associate editor not assigned