Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater,Egypt

Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz‐rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high‐pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s^?1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.     

The general circulation model precipitation bias over the southwestern equatorial Indian Ocean and its implications for simulating the South Asian monsoon

Most of current general circulation models (GCMs) show a remarkable positive precipitation bias over the southwestern equatorial Indian Ocean (SWEIO), which can be thought of as a westward expansion of the simulated IO convergence zone toward the coast of Africa. The bias is common to both coupled and uncoupled models, suggesting that its origin does not stem from the way boundary conditions are specified. The spatio-temporal evolution of the precipitation and associated three-dimensional atmospheric circulation biases is comprehensively characterized by comparing the GFDL AM3 atmospheric model to observations. It is shown that the oceanic bias, which develops in spring and reduces during the monsoon season, is associated to a consistent precipitation and circulation anomalous pattern over the whole Indian region. In the vertical, the areas are linked by an anomalous Hadley-type meridional circulation, whose northern branch subsides over northeastern India significantly affecting the monsoon evolution (e.g., delaying its onset). This study makes the case that the precipitation bias over the SWEIO is forced by the model excess response to the local meridional sea surface temperature (SST) gradient through enhanced near-surface meridional wind convergence. This is suggested by observational evidence and supported by AM3 sensitivity experiments. The latter show that relaxing the magnitude of the meridional SST gradient in the SWEIO can lead to a significant reduction of both local and large-scale precipitation and circulation biases. The ability of local anomalies over the SWEIO to force a large-scale remote response to the north is further supported by numerical experiments with the GFDL spectral dry dynamical core model. By imposing a realistic anomalous heating source over the SWEIO the model is able to reproduce the main dynamical features of the AM3 bias. These results indicate that improved GCM simulations of the South Asian summer monsoon could be achieved by reducing the springtime model bias over the SWEIO. Deficiencies in the atmospheric model, and in particular in the convective parameterization, are suggested to play a key role. Finally, the important mechanism controlling the simulated precipitation distribution over South Asia found here should be considered in the interpretation and attribution of regional precipitation variation under climate change.     

Modeling meets science and technology: an introduction to a special issue on negative emissions

This article introduces this special journal issue on climate change impacts on Sierra Nevada water resources and provides a critical summary of major findings and questions that remain open, representing future research opportunities. Some of these questions are long standing, while others emerge from the new research reported in the eight research papers in this special issue. Six of the papers study Eastern Sierra watersheds, which have been under-represented in the recent literature. One of those papers presents hydrologic projections for Owens Valley, benefiting from multi-decadal streamflow records made available by the Los Angeles Department of Water and Power for hydrologic model calibration. Taken together, the eight research papers present an image of localized climatic and hydrologic specificity that allows few region-wide conclusions. A source of uncertainty across these studies concerns the inability of the (statistically downscaled) global climate model results that were used to adequately project future changes in key processes including (among others) the precipitation distribution with altitude. Greater availability of regional climate model results in the future will provide research opportunities to project altitudinal shifts in snowfall and rainfall, with important implications to snowmelt timing, streamflow temperatures, and the Eastern Sierra’s precipitation-shadow effect.     

Direct air capture of CO2 and climate stabilization: A model based assessment

This paper provides a novel assessment of the role of direct air capture of CO₂ from ambient air (DAC) on the feasibility of achieving stringent climate stabilization. We use the WITCH energy-economy-climate model to investigate the long term prospects of DAC, implementing a technological specification based on recent estimates by the American Physical Society (APS 2011). Assuming global cooperation on a stringent climate policy we find that: (1) DAC is deployed only late in century, after other low carbon options, though at a very significant scale; (2) DAC has an impact on the marginal and total abatement costs (reducing them) and on the timing of mitigation (postponing it); (3) DAC also allows for a prolonged use of oil, with a positive welfare impact for energy exporting countries. Finally, we assess the role of DAC in a less than ideal climate policy by exploring its potential for engaging energy exporting countries in climate mitigation activities by means of a “clean oil” market in which oil exporters can sell oil decarbonized via DAC.     

Mapping soil erodibility from composed data set in Sele River Basin, Italy

Evaluation of soil erodibility is an important task for Mediterranean lands, in which fertility and crop yield are significantly affected by soil erosion. The soil physicochemical parameters affecting soil erodibility are highly variable in space and, as for many other environmental variables, sample measurements are generally not enough for assessing its spatial variability with an acceptable level of uncertainty at the scales of practical interest. This study illustrates the procedure applied for estimating the pattern of soil erodibility across the Sele Basin (Southern Italy), where soil properties have been measured on a limited number of sparse samples. Sampled data were integrated with other sparse data estimated by local regression functions, which relate soil erodibility to auxiliary variables, such as terrain attributes and land system class memberships. Sampled and estimated data were merged in a composed data set to assess the spatial pattern of soil erodibility by ordinary kriging. The proposed approach offers effective spatial predictions, and it is exportable to regions where financial costs for soil sampling are not feasible.     

Winds and infalling gas in Lyman break galaxies

A model for gas outflows is proposed which simultaneously explains the correlations between the (i) equivalent widths of low-ionization and Lyα lines, (ii) outflow velocity, and (iii) star formation rate observed in Lyman break galaxies (LBGs). Our interpretation implies that LBGs host short-lived (30 ± 5 Myr) starburst episodes observed at different evolutionary phases. Initially, the starburst powers a hot wind bound by a denser cold shell, which after ≈5 Myr becomes dynamically unstable and fragments; afterwards the fragment evolution is approximately ballistic while the hot bubble continues to expand. As the fragments are gravitationally decelerated, their screening ability of the starlight decreases as the ultraviolet (UV) starburst luminosity progressively dims. LBG observations sample all these evolutionary phases. Finally, the fragments fall back on to the galaxy after ≈60 Myr. This phase cannot be easily probed as it occurs when the starburst UV luminosity has already largely faded; however, galaxies dimmer in the UV than LBGs should show infalling gas.     

Determination of regional net radiation and soil heat flux over a heterogeneous landscape of the Tibetan Plateau

This paper explores the potential for documenting regional fields of surface energy fluxes over the Tibetan plateau using published algorithms and previously calibrated empirical formulae with data from NOAA‐14 AVHRR and atmospheric data collected during the GAME‐Tibet field experiment. Comparison with observations at three field sites suggests errors in the resulting estimates are less than 10% in the clear sky conditions necessary for application of this approach. Because of the need for clear skies, it was only possible to calculate the desired regional fields for one satellite scene during the 5 month study period. Maps of surface energy fluxes, and frequency analyses of these maps, are presented for this scene. The need for an alternative, more consistently applicable, satellite‐based method to map surface energy fields is highlighted. Copyright © 2002 John Wiley & Sons, Ltd.     

Clinopyroxene chemistry in Tertiary alkaline volcanic rocks from Taleghan,central Alborz,Iran: Implications for two parental melts

In the Taleghan area of Alborz mountain range, two distinct units of alkaline rocks are identified. Whole rock major and trace element data does not provide a clue as to their common or different parental melts. However, major and trace element geochemistry of their included clinopyroxene phenocrysts, combined with the whole rock data, helped to infer that two parental magmas were involved in the evolution of volcanic succession in the Taleghan area.     

U–Pb zircon dating and nature of metavolcanics and metarkoses from the Monte Grighini Unit: new insights on Late Ordovician magmatism in the Variscan belt in Sardinia, Italy

In the external units of the Sardinian Variscides Nappe Zone, volcanic and volcanoclastic successions of Middle Ordovician age follow Lower Paleozoic calc-alkaline magmatism developed at the northern Gondwana margin. We present geochemical and zircon U–Pb isotopic data for the Truzzulla Formation, a low-to-medium-grade metamorphic volcanic–volcanoclastic succession belonging to the Monte Grighini Unit, the deepest unit in the Nappe Zone. Geochemical and radiometric data allow us to define a Late Ordovician (Katian) magmatic (volcanic) event of calc-alkaline affinity. These new data, in conjunction with previously published data, indicate that in the Sardinian Variscides, the age of Lower Paleozoic Andean-type calc-alkaline magmatism spans from Middle to Late Ordovician. Moreover, the age distribution of calc-alkaline volcanics and volcanoclastic rocks in the Nappe Zone is consistent with a diachronous development of Middle–Late Ordovician Andean-type magmatic arc through the portion of the northern Gondwanian margin now represented by the Sardinian Variscides. This reconstruction of the Sardinian Variscides reflects the complex magmatic and tectonic evolution of the northern margin of Gondwana in the Lower Paleozoic.     

A deep, stratigraphically and structurally controlled landslide: the case of Mount La Civita (Molise, Italy)

The present paper illustrates the results of an integrated study of a large landslide located on the southern slope of Mount la Civita (Molise, Southern Apennine), an E–W elongated, SSE dipping and 890-m-high monocline carbonate ridge. The upper part of the slope affected by the landslide is largely controlled by strata attitude while its basal part is marked by a strike–slip fault causing the tectonic juxtaposition of the carbonate successions against predominantly clayey flysch units. An integrated study, including geological, geomorphological and geotechnical investigations, was carried out to determine the features of the landslide and to plan further investigation and monitoring. In particular, from 2002 to 2004, Differential Global Positioning System monitoring and core drillings, coupled with inclinometer measurements, were carried out to determine the landslide’s kinematics, extent, depth to the surface of rupture and rates of movement. Inclinometer data revealed the presence of the rupture surface at a depth of about 20 m. DGPS monitoring allowed rates of movement up to several tens of centimetres per year to be recorded. The nearby village of Civitanova del Sannio can still be considered at risk due to the landslide, as recent remedial works, consisting mainly of very shallow re-shaping of the slope by blasting and partial filling of trenches, did not succeed in stopping its movement.