Sediment transport patterns determined from grain size parameters: Overview and state of the art

Grain size trends have been applied in many diverse sedimentary environments to determine sediment transport paths, generally coinciding with information from tracer studies, current measurements and the orientation of sedimentary structures. The different methods proposed to date are critically analysed and compared with reference to recent field studies. It is concluded that the two-dimensional methods produce comparable results and may in fact complement each other.In spite of the advances, several problems still exist, which include the sampling method and density, the choice of trend types, the relative weight of grain size parameters and the interpretation of results. These are discussed together with possible solutions.     

Reconstructing basin evolution from sedimentary thickness; the importance of palaeobathymetric control, with reference to the North Sea

Abstract The structural evolution of a basin cannot be reconstructed from sedimentary thicknesses alone without data on palaeobathymetry. Two classes of geological horizons, are defined, profiles and traces. Profiles are time-lines and bound depositional units. Traces were formed at a known water depth and contain implicit palaeobathymetric data.
Rock units bounded by traces are diachronous lithostratigraphic units, and the thicknesses of such units are controlled directly by subsidence, while the thicknesses of profile-bounded units may be unaffected by the subsidence or even the palaeotopography of the basin.
Dating fault movement from thickness variations in profile-bounded units is difficult without prior knowledge of the palaeobathymetry, and it is impossible to distinguish between synsedimentary fault movement and onlap to a pre-existing fault scarp from thickness alone.
Reconstruction of the basin history of the North Sea is difficult due to the lack of trace-bounded units in the post-Jurassic. The validity of previously published studies depends largely on the quality and quantity of palaeobathymetric data included. An alternative basin history is proposed based on the few trace-bounded units in the North Viking Graben. This includes rifting episodes in the Triassic and Late Jurassic, and a period of uplift in the Palaeocene.     

Fused rock from Köfels,Tyrol

The vesicular glass from Köfels, Tyrol, contains grains of quartz that have been partially melted but not dissolved in the matrix glass. This phenomenon has been observed in similar glasses formed by friction along a thrust fault and by meteorite impact, but not in volcanic glasses. The explosion of a small nuclear device buried behind a steep slope produced a geologic structure that is a good small-scale model of that at Köfels. Impact of a large meteorite would have an effect analogous to that of a subsurface nuclear explosion and is the probable cause of the Köfels feature.

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Zusammenfassung Der Bimsstein von Köfels, Tirol, enthält Körner von Quarz, welche teilweise geschmolzen, aber nicht im Mutterglas gelöst sind. Diese Erscheinung wurde in ähnlichen Gläsern beobachtet, welche durch Reibung entlang von Rutschverwerfungen und durch Meteoriteneinschläge entstanden, aber nicht in vulkanischen Gläsern. Die Explosion eines kleinen nuklearen Gerätes, eingegraben in einem steilen Abhang, brachte eine geologische Struktur hervor, welche ein gutes Modell im kleinen Maßstab des Vorganges bei Köfels darstellt. Der Einschlag eines großen Meteoriten würde einen Effekt hervorrufen, der analog ist einer unterirdischen nuklearen Explosion, und ist wahrscheinlich der Grund für die Bildungen von Köfels.

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Wit 4 Figures

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Publication authorized by the Director, U. S. Geological Survey.     

Climate change and river floods in the European Union: Socio-economic consequences and the costs and benefits of adaptation

This study presents the first appraisal of the socio-economic impacts of river floods in the European Union in view of climate and socio-economic changes. The assessment is based on two trajectories: (a) no adaptation, where the current levels of protection are kept constant, and (b) adaptation, where the level of protection is increased to defend against future flooding events. As a basis for our analysis we use an ensemble-based pan-European flood hazard assessment for present and future conditions. Socio-economic impacts are estimated by combining flood inundation maps with information on assets exposure and vulnerability. Ensemble-based results indicate that current expected annual population affected of ca. 200,000 is projected to increase up to 360,000 due to the effects of socio-economic development and climate change. Under the no adaptation trajectory current expected annual damages of €5.5 billion/year are projected to reach €98 billion/year by the 2080s due to the combined effects of socio-economic and climate change. Under the adaptation trajectory the avoided damages (benefits) amount to €53 billion/year by the 2080s. An analysis of the potential costs of adaptation associated with the increase in protection suggests that adaptation could be highly cost-effective. There is, however, a wide range around these central numbers reflecting the variability in projected climate. Analysis at the country level shows high damages, and by association high costs of adaptation, in the United Kingdom, France, Italy, Romania, Hungary and Czech Republic. At the country level, there is an even wider range around these central values, thus, pointing to a need to consider climate uncertainty in formulating practical adaptation strategies.     

Sensitivity analysis of prior model probabilities and the value of prior knowledge in the assessment of conceptual model uncertainty in groundwater modelling

A key point in the application of multi‐model Bayesian averaging techniques to assess the predictive uncertainty in groundwater modelling applications is the definition of prior model probabilities, which reflect the prior perception about the plausibility of alternative models. In this work the influence of prior knowledge and prior model probabilities on posterior model probabilities, multi‐model predictions, and conceptual model uncertainty estimations is analysed. The sensitivity to prior model probabilities is assessed using an extensive numerical analysis in which the prior probability space of a set of plausible conceptualizations is discretized to obtain a large ensemble of possible combinations of prior model probabilities. Additionally, the value of prior knowledge about alternative models in reducing conceptual model uncertainty is assessed by considering three example knowledge states, expressed as quantitative relations among the alternative models. A constrained maximum entropy approach is used to find the set of prior model probabilities that correspond to the different prior knowledge states. For illustrative purposes, a three‐dimensional hypothetical setup approximated by seven alternative conceptual models is employed. Results show that posterior model probabilities, leading moments of the predictive distributions and estimations of conceptual model uncertainty are very sensitive to prior model probabilities, indicating the relevance of selecting proper prior probabilities. Additionally, including proper prior knowledge improves the predictive performance of the multi‐model approach, expressed by reductions of the multi‐model prediction variances by up to 60% compared with a non‐informative case. However, the ratio between‐model to total variance does not substantially decrease. This suggests that the contribution of conceptual model uncertainty to the total variance cannot be further reduced based only on prior knowledge about the plausibility of alternative models. These results advocate including proper prior knowledge about alternative conceptualizations in combination with extra conditioning data to further reduce conceptual model uncertainty in groundwater modelling predictions. Copyright © 2009 John Wiley & Sons, Ltd.     

Space-time variability of the Amazon River plume based on satellite ocean color

Satellite ocean color images were used to determine the space-time variability of the Amazon River plume from 2000–2004. The relationship between sea-surface salinity (SSS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) absorption coefficient for dissolved and detrital material (a_dg) (r²=0.76, n=30, rmse=0.4) was used to identify the Amazon River plume low-salinity waters (<34 psu). The plume's spatial information was extracted from satellite bi-weekly time series using two metrics: plume area and plume shape. These metrics identified the seasonal variability of plume dimensions and dispersion patterns. During the study period, the plume showed the largest areas from July to August and the smallest from December to January. The mean annual amplitude and the mean, maximum and minimum plume areas were 1020×10³ km², 680×10³ km², 1506×10³ km² and 268×10³ km², respectively. Three main shapes and dispersion pattern periods were identified: (1) flow to the northeastern South American coast, in a narrow band adjacent to the continental shelf, from January to April; (2) flow to the Caribbean region, from April to July; and (3) flow to the Central Equatorial Atlantic Ocean, from August to December. Cross-correlation techniques were used to quantify the relationship between the plume's spatial variability and environmental forcing factors, including Amazon River discharge, wind field and ocean currents. The results showed that (1) river discharge is the main factor influencing plume area variability, (2) the wind field regulates the plume's northwestward flow velocity and residence time near the river mouth, and (3) surface currents have a strong influence over river plume dispersion patterns.     

The 2009–2010 fade of Jupiter’s South Equatorial Belt: Vertical cloud structure models and zonal winds from visible imaging

The South Equatorial Belt (SEB) of Jupiter is known to alternate its appearance at visible wavelengths from a classical belt-like band most of the time to a short-lived zone-like aspect which is called a “fade” of the belt, hereafter SEBF. The albedo change of the SEB is due to a change in the structure and properties of the clouds and upper hazes. Recent works based on infrared observations of the last SEBF have shown that the aerosol density below 1 bar increased in parallel with the reflectivity change. However, the nature of the change in the upper clouds and hazes that produces the visible reflectivity change and whether or not this reflectivity change is accompanied by a change in the winds at the upper cloud level remained unknown. In this paper we focus in the near ultraviolet to near infrared reflected sunlight (255–953 nm) to address these two issues. We characterize the vertical cloud structure above the ammonia condensation level from Hubble Space Telescope images, and the zonal wind velocities from long-term high-quality images coming from the International Outer Planet Watch database, both during the SEB and SEBF phases. We show that reflectivity changes do not happen simultaneously in this wavelength range, but they start earlier in the most deep-sensing filters and end in 2010 with just minor changes in those sensing the highest particle layers. Our models require a substantial increase of the optical thickness of the cloud deck at 1.0 ± 0.4 bar from τ_cloud = 6 ± 2 in July 2009 (SEB phase) to semiinfinite at visual wavelengths in 2010 (SEBF). Upper tropospheric particles (～240–1400 mbar) are also required to become substantially reflectant and their single scattering albedo in the blue changes from ?₀ = 0.905 ± 0.005 in November 2009 to ?₀ = 0.95 ± 0.01 in June 2010. No significant changes were found in the cloud top heights or in the particle density of the tropospheric haze. The disturbance travels from the levels below ～3 bar to a level about 400 ± 100 mbar. We derive an upward velocity of 0.15 ± 0.05 cm/s, in agreement with a diffusive process in Jupiter’s upper troposphere requiring a mean eddy coefficient K ～ 8 × 10⁵ cm² s^?1. On the other hand, cloud tracking on the IOPW imaging showed no significant changes in the zonal wind profile between the SEB and SEBF stages. As in other visually huge changes in Jupiter’s cloud morphology and structure, the wind profile remains robust, possibly indicating a deeply rooted dynamical regime.     

Towards the main sequence: detailed analysis of weak line and post-T Tauri stars

A detailed study was performed for a sample of low-mass pre-main-sequence (PMS) stars, previously identified as weak-line T Tauri stars, which are compared to members of the Tucanae and Horologium Associations. Aiming to verify if there is any pattern of abundances when comparing the young stars at different phases, we selected objects in the range from 1 to 100 Myr, which covers most of PMS evolution. High-resolution optical spectra were acquired at European Southern Observatory and Observatório do Pico dos Dias . The stellar fundamental parameters effective temperature and gravity were calculated by excitation and ionization equilibria of iron absorption lines. Chemical abundances were obtained via equivalent width calculations and spectral synthesis for 44 per cent of the sample, which shows metallicities within 0.5 dex solar. A classification was developed based on equivalent width of Li  i 6708 Å and Hα lines and spectral types of the studied stars. This classification allowed a separation of the sample into categories that correspond to different evolutive stages in the PMS. The position of these stars in the Hertzsprung–Russell diagram was also inspected in order to estimate their ages and masses. Among the studied objects, it was verified that our sample actually contains seven weak-line T Tauri stars, three are Classical T Tauri, 12 are Fe/Ge PMS stars and 21 are post-T Tauri or young main-sequence stars. An estimation of circumstellar luminosity was obtained using a disc model to reproduce the observed spectral energy distribution. Most of the stars show low levels of circumstellar emission, corresponding to less than 30 per cent of the total emission.     

Downscaling extreme month-long anomalies in southern South America

We investigate the performance of one stretched-grid atmospheric global model, five different regional climate models and a statistical downscaling technique in simulating 3 months (January 1971, November 1986, July 1996) characterized by anomalous climate conditions in the southern La Plata Basin. Models were driven by reanalysis (ERA-40). The analysis has emphasized on the simulation of the precipitation over land and has provided a quantification of the biases of and scatter between the different regional simulations. Most but not all dynamical models underpredict precipitation amounts in south eastern South America during the three periods. Results suggest that models have regime dependence, performing better for some conditions than others. The models’ ensemble and the statistical technique succeed in reproducing the overall observed frequency of daily precipitation for all periods. But most models tend to underestimate the frequency of dry days and overestimate the amount of light rainfall days. The number of events with strong or heavy precipitation tends to be under simulated by the models.