Extremes of near-surface wind speed over Europe and their future changes as estimated from an ensemble of RCM simulations

In this study, we analyse the uncertainty of the effect of enhanced greenhouse gas conditions on windiness projected by an ensemble of regional model simulations driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100, were prepared by the Hadley Centre based on the IPCC SRES/A2 scenario. The basic data sets consist of simulated daily maximum and daily mean wind speed fields (over land) from the PRUDENCE data archive at the Danish Meteorological Institute. The main focus is on the results from the standard 50 km-resolution runs of eight regional models. The best parameter for determining possible future changes in extreme wind speeds and possible change in the number of storm events is maximum daily wind speed. It turned out during this study that the method for calculating maximum daily wind speed differs among the regional models. A comparison of simulated winds with observations for the control period shows that models without gust parameterisation are not able to realistically capture high wind speeds. The two models with gust parametrization estimate an increase of up to 20% of the number of storm peak (defined as gusts?≥?8 Bft in this paper) events over Central Europe in the future. In order to use a larger ensemble of models than just the two with gust parameterisation, we also look at the 99th percentile of daily mean wind speed. We divide Europe into eight sub-regions (e.g., British Isles, Iberian Peninsula, NE Europe) and investigate the inter-monthly variation of wind over these regions as well as differences between today’s climate and a possible future climate. Results show differences and similarities between the sub-regions in magnitude, spread, and seasonal tendencies. The model ensemble indicates a possible increase in future mean daily wind speed during winter months, and a decrease during autumn in areas influenced by North Atlantic extra-tropical cyclones.     

Raman study of radiation-damaged zircon under hydrostatic compression

Pressure-induced changes of Raman band parameters of four natural, gem-quality zircon samples with different degrees of self-irradiation damage, and synthetic ZrSiO₄ without radiation damage, have been studied under hydrostatic compression in a diamond anvil cell up to ~10 GPa. Radiation-damaged zircon shows similar up-shifts of internal SiO₄ stretching modes at elevated pressures as non-damaged ZrSiO₄. Only minor changes of band-widths were observed in all cases. This makes it possible to estimate the degree of radiation damage from the width of the ν₃(SiO₄) band of zircon inclusions in situ, almost independent from potential “fossilized pressures” or compressive strain acting on the inclusions. An application is the non-destructive analysis of gemstones such as corundum or spinel: broadened Raman bands are a reliable indicator of self-irradiation damage in zircon inclusions, whose presence allows one to exclude artificial color enhancement by high-temperature treatment of the specimen.     

Future productivity and phenology changes in European grasslands for different warming levels: implications for grassland management and carbon balance

Background

Europe has warmed more than the global average (land and ocean) since pre-industrial times, and is also projected to continue to warm faster than the global average in the twenty-first century. According to the climate models ensemble projections for various climate scenarios, annual mean temperature of Europe for 2071–2100 is predicted to be 1–5.5 °C higher than that for 1971–2000. Climate change and elevated CO₂ concentration are anticipated to affect grassland management and livestock production in Europe. However, there has been little work done to quantify the European-wide response of grassland to future climate change. Here we applied ORCHIDEE-GM v2.2, a grid-based model for managed grassland, over European grassland to estimate the impacts of future global change.

Results

Increases in grassland productivity are simulated in response to future global change, which are mainly attributed to the simulated fertilization effect of rising CO₂. The results show significant phenology shifts, in particular an earlier winter-spring onset of grass growth over Europe. A longer growing season is projected over southern and southeastern Europe. In other regions, summer drought causes an earlier end to the growing season, overall reducing growing season length. Future global change allows an increase of management intensity with higher than current potential annual grass forage yield, grazing capacity and livestock density, and a shift in seasonal grazing capacity. We found a continual grassland soil carbon sink in Mediterranean, Alpine, North eastern, South eastern and Eastern regions under specific warming level (SWL) of 1.5 and 2 °C relative to pre-industrial climate. However, this carbon sink is found to saturate, and gradually turn to a carbon source at warming level reaching 3.5 °C.

Conclusions

This study provides a European-wide assessment of the future changes in productivity and phenology of grassland, and their consequences for the management intensity and the carbon balance. The simulated productivity increase in response to future global change enables an intensification of grassland management over Europe. However, the simulated increase in the interannual variability of grassland productivity over some regions may reduce the farmers’ ability to take advantage of the increased long-term mean productivity in the face of more frequent, and more severe drops of productivity in the future.

     

Nondestructive imaging of hypervelocity impact-induced damage zones beneath laboratory-created craters by means of ultrasound travel-time tomography

Since the 1960s, hypervelocity impact experiments have been conducted to study the complex deformation mechanisms which occur in the subsurface of meteorite craters. Here, we present ultrasound tomography measurements of the damage zone underneath seven experimentally produced impact craters in sandstone cubes. Within the framework of the Multidisciplinary Experimental and Modeling Impact Research Network and the NEOShield Project, decimeter-sized sandstone targets were impacted by aluminum and steel projectiles with radii of 2.5, 4, and 5 mm at velocities between ~3.0 and ~7.4 km s⁻¹. The 2-D ultrasound tomography clearly shows a correlation between impact energy and the damaged volume within the target blocks. When increasing impact energies from 805 to 2402 J, a corresponding increase in the damage radius from ~13.1 cm to ~17.6 cm was calculated. p-Wave velocity reductions up to 18.3% (for the highest impact energy) were observed in the vicinity of the craters. The reduction in seismic velocity decreased uniformly and linearly with increasing distance from the impact point. The damage intensities correspond to peak damage parameters of 0.4–0.51 compared to undamaged target blocks. In addition to the damage zone below the crater, we could identify weakened zones at the sandstone walls which represent precursors of spalling. The volume of the damaged subsurface beneath experimentally produced craters determined through ultrasound tomography is larger than that obtained from previously reported p-wave velocity reductions or to microscopic and microcomputed tomography observations of crack densities in experimentally produced craters.     

Effects of nanoparticles in Mytilus edulis gills and hepatopancreas - a new threat to marine life?

Every day new extraordinary properties of nanoparticles (a billionth of a meter) are discovered and worldwide millions are invested into nanotechnology and nanomaterials. Risks to marine organisms are still not fully understood and biomarkers to detect health effects are not implemented, yet. We used the filter feeding blue mussel as a model to analyse uptake and effects of nanoparticles from glass wool, a new absorbent material suggested for use in floating oil spill barriers. In both, gills and hepatopancreas we analysed uptake of nanomaterials by transmission electronmicroscopy (TEM) in unstained ultrathin sections over a period of up to 16 days. Lysosomal stability and lipofuscin content as general indicators of cellular pathology and oxidative stress were also measured. As portals of uptake, diffusion and endocytosis were identified resulting in nanoparticle accumulation in endocytotic vesicles, lysosomes, mitochondria and nuclei. Dramatic decrease of lysosomal membrane stability occurred after 12h of exposure. Lysosomal damage was followed by excessive lipofuscin accumulation indicative of severe oxidative stress. Increased phagocytosis by granulocytes, autophagy and finally apoptosis of epithelial cells of gills and primary and secondary digestive tubules epithelial cells indicated progressive cell death. These pathological responses are regarded as general indices of toxic cell injury and oxidative stress. By the combinational use of biomakers with the ultrastructural localisation of nanoparticle deposition, final evidence of cause-effect relationships is delivered.     

The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton,Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana

This paper presents combined U/Pb, Th/U and Hf isotope analyses on detrital and magmatic zircon grains together with whole-rock geochemical analyses of two basement and eight sedimentary rock samples from the Namuskluft and the Dreigratberg in southern Namibia (Gariep Belt). The sedimentary sections evolved during the Cryogenian on the SW part of the Kalahari Craton and where therefore deposited in an active rift setting during the break-up of Rodinia. Due to insufficient palaeomagnetic data, the position of the Kalahari Craton within Rodinia is still under discussion. There are possibilities to locate Kalahari along the western side of Australia/Mawsonland (Pisarevski et al. in Proterozoic East Gondwana: supercontinent assembly and break-up, Geological Society, London, 2003; Evans in Ancient Orogens and modern analogues. Geological Society, London, 2009; and others) or together with the Congo-Sao Francisco and Rio de la Plata Cratons (Li et al. in Prec Res 45: 203–2014, 2008; Frimmel et al. in Int J Earth Sci (Geol Rundsch) 100: 323–354, 2011; and others). It is sill unclear which craton rifted away from the Kalahari Craton during the Cryogenian. Although Middle to Upper Cryogenian magmatic activity is known for the SE Kalahari Craton (our working area) (Richtersveld Suite, Rosh Pinah Fm), all the presented samples show no U/Pb zircon ages younger than ca. 1.0 Ga and non-older than 2.06 Ga. The obtained U/Pb ages fit very well to the exposed basement of the Kalahari Craton (1.0–1.4 Ga Namaqua Province, 1.7–2.0 Ga Vioolsdrif Granite Suite and Orange River Group) and allow no correlation with a foreign craton such as the Rio de la Plata or Australia/Mawsonland. Lu–Hf isotopic signatures of detrital zircon point to the recycling of mainly Palaeoproterozoic and to a smaller amount of Archean crust in the source areas. εHf(t) signatures range between ?24 and +14.8, which relate to T_DM model ages between 1.05 and 3.1 Ga. Only few detrital zircon grains derived from magmas generated from Mesoproterozoic crustal material show more juvenile εHf(t) signatures of +14, +8 to +4 with T_DM model ages of 1.05–1.6 Ga. During Neoproterozoic deposition, only old cratonic crust with an inherited continental arc signature was available in the source area clearly demonstrated by Hf isotope composition of detrital zircon and geochemical bulk analysis of sedimentary rocks. The granodiorites of the Palaeoproterozoic basement underlying Namuskluft section are ca. 1.9 Ga old and show εHf(t) signatures of ?3 to ?5.5 with T_DM model ages of 2.4–2.7 Ga. These basement rocks demonstrate the extreme uplift and deep erosion of the underlying Kalahari Craton at its western margin before general subsidence during Cryogenian and Ediacaran time. The sedimentary sequence of the two examined sections (Namuskluft and Dreigratberg) proposes the presence of a basin and an increasing subsidence at the SW part of the Kalahari Craton during the Cryogenian. Therefore, we propose the initial formation of an intra-cratonic sag basin during the Lower Cryogenian that evolved later to a rift basin at the cratonic margin due to increasing crustal tension and rifting together with the opening of the Adamastor Ocean. As the zircons of the sedimentary rocks filling this basin show neither rift-related U/Pb ages nor an exotic craton as a possible source area, the only plausible sedimentary transport direction providing the found U/Pb ages would be from the E or the SE, directly from the heart of the Kalahari Craton. Due to subsidence and ongoing sedimentation from E/SE directions, the rift-related magmatic rocks were simply covered by the input of old intra-cratonic material that explains the absence of Neoproterozoic zircon grains in our samples. The geochemical analyses show the erosion of a continental arc and related sedimentary rocks with an overall felsic provenance. The source area was a deeply eroded and incised magmatic arc that evolved on continental crust, without any evidence for a passive margin. All of this can be explained by the erosion of rocks related to the Namaqua Belt, which represents one of the two major peaks of zircon U–Pb ages in all analysed samples. Therefore, the Namaqua Belt was well exposed during the Cryogenian, available to erosion and apart from the also well-exposed Palaeoproterozoic basement of the Kalahari Craton one potential source area for the sedimentary rocks in the investigated areas.     

A multi-model comparison of Atlantic multidecadal variability

A multi-model analysis of Atlantic multidecadal variability is performed with the following aims: to investigate the similarities to observations; to assess the strength and relative importance of the different elements of the mechanism proposed by Delworth et al. (J Clim 6:1993–2011, 1993) (hereafter D93) among coupled general circulation models (CGCMs); and to relate model differences to mean systematic error. The analysis is performed with long control simulations from ten CGCMs, with lengths ranging between 500 and 3600 years. In most models the variations of sea surface temperature (SST) averaged over North Atlantic show considerable power on multidecadal time scales, but with different periodicity. The SST variations are largest in the mid-latitude region, consistent with the short instrumental record. Despite large differences in model configurations, we find quite some consistency among the models in terms of processes. In eight of the ten models the mid-latitude SST variations are significantly correlated with fluctuations in the Atlantic meridional overturning circulation (AMOC), suggesting a link to northward heat transport changes. Consistent with this link, the three models with the weakest AMOC have the largest cold SST bias in the North Atlantic. There is no linear relationship on decadal timescales between AMOC and North Atlantic Oscillation in the models. Analysis of the key elements of the D93 mechanisms revealed the following: Most models present strong evidence that high-latitude winter mixing precede AMOC changes. However, the regions of wintertime convection differ among models. In most models salinity-induced density anomalies in the convective region tend to lead AMOC, while temperature-induced density anomalies lead AMOC only in one model. However, analysis shows that salinity may play an overly important role in most models, because of cold temperature biases in their relevant convective regions. In most models subpolar gyre variations tend to lead AMOC changes, and this relation is strong in more than half of the models.     

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.     

An evaluation of the surface radiation budget over North America for a suite of regional climate models against surface station observations

Components of the surface radiation budget (SRB) [incoming shortwave radiation (ISR) and downwelling longwave radiation (DLR)] and cloud cover are assessed for three regional climate models (RCM) forced by analysed boundary conditions, over North America. We present a comparison of the mean seasonal and diurnal cycles of surface radiation between the three RCMs, and surface observations. This aids in identifying in what type of sky situation simulated surface radiation budget errors arise. We present results for total-sky conditions as well as overcast and clear-sky conditions separately. Through the analysis of normalised frequency distributions we show the impact of varying cloud cover on the simulated and observed surface radiation budget, from which we derive observed and model estimates of surface cloud radiative forcing. Surface observations are from the NOAA SURFRAD network. For all models DLR all-sky biases are significantly influenced by cloud-free radiation, cloud emissivity and cloud cover errors. Simulated cloud-free DLR exhibits a systematic negative bias during cold, dry conditions, probably due to a combination of omission of trace gas contributions to the DLR and a poor treatment of the water vapor continuum at low water vapor concentrations. Overall, models overestimate ISR all-sky in summer, which is primarily linked to an underestimate of cloud cover. Cloud-free ISR is relatively well simulated by all RCMs. We show that cloud cover and cloud-free ISR biases can often compensate to result in an accurate total-sky ISR, emphasizing the need to evaluate the individual components making up the total simulated SRB.     

Climate simulation over CORDEX Africa domain using the fifth-generation Canadian Regional Climate Model (CRCM5)

The new fifth-generation Regional Climate Model (CRCM5) was driven by ERA reanalyses for the period 1984–2008 over the African continent following the CORDEX experimental protocol. Overall the model succeeds in reproducing the main features of the geographical distribution and seasonal cycle of temperature and precipitation, the diurnal cycle of precipitation, and the West African Monsoon (WAM). Biases in surface temperature and precipitation are discussed in relation with some circulation defects noted in the simulation. In the African regions near the equator, the model successfully reproduces the double peak of rainfall due to the double passage of the tropical rainbelt, although it better simulates the magnitude and timing of the second peak of precipitation. CRCM5 captures the timing of the monsoon onset for the Sahel region but underestimates the magnitude of precipitation. The simulated diurnal cycle is quite well simulated for all of the regions, but is always somewhat in advance for the timing of rainfall peak. In boreal summer the CRCM5 simulation exhibits a weak cold bias over the Sahara and the maximum temperature is located too far south, resulting in a southward bias in the position of the Saharan Heat Low. The region of maximum ascent in the deep meridional circulation of the Hadley cell is well located in the CRCM5 simulation, but it is somewhat too narrow. The core of the African Easterly Jet is of the right strength and almost at the right height, but it is displayed slightly southward, as a consequence of the southward bias in the position of the Saharan Heat Low and the thermal wind relationship. These biases appear to be germane to the WAM rainfall band being narrower and not moving far enough northward, resulting in a dry bias in the Sahel.