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.     

Eemian crustal deformation in the eastern Baltic area in the light of the new sites at Peski, Russia and Põhja-Uhtju, Estonia

Several Eemian (Mikulino) marine deposits are known from the northwestern part of Russia and from Estonia. The best-known deposits are situated at Mga, Russia and at Prangli, Estonia. Two new sites with clayey and silty deposits covered by till were studied for pollen and diatoms at Peski, Russia and Põhja-Uhtju, Estonia. At Peski, the deposit representing the Eemian Interglacial is 3.8 m thick at the depth of 13.4–9.6 m above present sea-level. At Põhja-Uhtju, the deposit representing the Eemian is 3.5 m thick at the depth of 47.9–51.4 m below present sea-level. Although Peski is situated at a higher altitude than Põhja-Uhtju at present, the diatom stratigraphy at these sites indicates deeper and more saline conditions in the Peski area than at Põhja-Uhtju during the Eemian. This result is similar to some previous studies, which indicate, that although the Russian deposits (e.g. Peski, Mga) are now at a higher altitude than those in Estonia (Põhja-Uhtju and Prangli), the diatoms in the Russian deposits are indicative of a considerable depth of water during the time of deposition. These deposits suggest that the Eemian shore levels ascend from Estonia eastwards, while the Late Weichselian and Holocene shorelines tilt downwards in the same general direction. The present material from Estonia and northwestern part of Russia shows marked differences between the Eemian and Late Weichselian/Holocene crustal deformations, which probably resulted from different ice loads during the final glaciation phases and probably also from different deglaciation patterns during the Saalian and Late Weichselian.     

Geochemistry and Sr, Nd, Pb isotopic composition of the Central Atlantic Magmatic Province (CAMP) in Guyana and Guinea

The Central Atlantic Magmatic Province (CAMP) is one of the largest igneous provinces on Earth, extending more than 5000 km north to south, on both sides of the Atlantic Ocean. Its emplacement occurred about 200 Ma ago, at the Triassic–Jurassic boundary, and is linked to the initial breakup of Pangaea. Two areas of the province are studied here: French Guyana/Surinam (South America) and Guinea (West Africa), in order to document the petrogenesis and geodynamical significance of high-Ti and low-Ti basaltic magmas from the CAMP.

In Guyana, doleritic and gabbroic dykes are located on the edge of the Guiana Shield, and represent limited volumes of magma. They display low SiO₂ (47–50%), high TiO₂ (2.5–3.5%) and high FeO tholeiitic trends and show variably enriched trace element patterns ((La/Yb)_n=1.5–5.1). Their isotopic signature and ratios of very incompatible elements (εNd_i=+5.8 to +4.2, (⁸⁷Sr/⁸⁶Sr)_i=0.703–0.705, (²⁰⁷Pb/²⁰⁴Pb)_i=15.46–15.64) match a depleted PREMA (prevalent mantle)-like source. Their genesis can be modeled by ca. 15% partial melting of a lherzolite source, and a subsequent limited fractional crystallization (5–10%) or a slight upper crustal assimilation–fractional crystallization (AFC, r=0.1, Proterozoic contaminant). In Guinea, in contrast, huge volumes of CAMP magmas were intruded along the Rockelides suture and the West African craton, forming the Fouta Djalon sills and the Kakoulima laccolith. The laccolith is more than 1000 m thick. These features consist of gabbros, dolerites, diorites and mafic (gabbro) and ultramafic (dunite, wherlite) cumulates. Guinean tholeiites show high SiO₂ (51–58%), low TiO₂ (0.7–1.2%) and FeO trends, with high LILE/HFSE ratios and slight negative Nb–Ta anomalies. Isotopic signatures (εNd_i=+0.4 to −5.3, (⁸⁷Sr/⁸⁶Sr)_i=0.705–0.710, (²⁰⁷Pb/²⁰⁴Pb)_i=15.57–15.66) indicate a more enriched source than for Guyana as well as a higher rate of magma–upper crust interaction through an AFC process (r=0.3, Birimian crust contaminant) and, probably, an additional upper crustal contamination for the most differentiated sample.

This geochemical study supports the prevalence in Guinea, as for other low-Ti CAMP tholeiites, of a lithospheric mantle source, previously enriched during ancient subduction events, and preferentially reactivated in late Triassic times by edge-driven convection between cratonic and mobile belt domains. A larger contribution from a depleted asthenospheric source is required to generate high-Ti tholeiites in Guyana, which may reflect the development of CAMP rifting towards the initiation of the Central Atlantic oceanic crust.     

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.

     

Sedimentationsabläufe im Atlas-Golf (Kreide Küstenbecken Marokko)

The Geological Institute of Bonn University since 1975 investigates in connection with DSDP/IPOD the Cretaceous of the Atlantic coastal basin in south-western Morocco. 30 main stratigraphic sections and numerous auxiliary ones were taken along several traverses, running along distances of 150 to 200 km in west-east direction. The recognized epicontinental facies-pattern along the traverse of the southern High Atlas mountain range depicts clearly, that we cut here the critical region of intertonguing marine, fine-clastic-carbonaceous sediments and continental detritic deposits. The littoral zone successively progrades with three major transgressions (Neocomian, Upper Aptian, Turonian) towards the African Continent. Sedimentation processes, stratigraphy, paleomagnetics, geochemistry, sedimentology and paleogeography are investigated, taking selected horizons on one hand and complete stratigraphic columns on the other. A new sedimentation model reflecting transgression and regression events in the Cretaceous “Atlas Gulf” show some probabilities of eustatic sea-level changes. There are similarities between the Atlas Gulf and other coastal basins on both sides of the Atlantic Ocean. There are certain relations between the sedimentary record of the proand regrading littoral zone on the continent and in the nearby deep sea deposits. There is an exciting coincidence between the stratigraphie succession of the downwarping Atlas Gulf and the sedimentary cover of the interior of Africa, especially the Mesozoic Sahara Basin.     

A simple gibbsite analyzer for rapid field determination of the available alumina content in bauxites

A portable gibbsite analyzer suited for field operation and intended for rapid determination of available alumina is described. The available alumina content is calculated from the relative weight loss caused by the dehydration of gibbsite. More than 100 samples of gibbsite-containing bauxites of different origin, were analyzed with this apparatus. The results always appeared to be correct within 10% of the actual content. In the laboratory, an accuracy of ±2.60% gibbsite, and a reproducibility of ±1.87% gibbsite, both at the 95% confidence interval, could be achieved. The apparatus can be used under tropical conditions. Its weight is 13 kg. It can be fed from a motor-driven generator weighing 18 kg. The duration of a single analysis in the field is 30–40 minutes. In the laboratory about 25 analyses can be performed within 8 hours. The apparatus can be handled by an untrained operator. One operator can run at least two analyzers at a time. The complete set-up, including the generator, costs less than US $ 1500.

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Zusammenfassung Ein tragbarer Apparat für die Gibbsit Bestimmung im Freien wird beschrieben. Der Gibbsitgehalt wird berechnet aus dem Gewichtsverlust während der Entwässerung. Für Gibbsit-haltige Bauxite, die mit diesem Apparat analysiert sind, wurden Resultate gefunden, die immer weniger als 10% vom richtigen Gehalt abwichen. Im Labor konnte eine Genauigkeit von ±2.60% Gibbsit und eine Reproduzierbarkeit von ±1.87% Gibbsit, beide mit einer Wahrscheinlichkeit von 95%, erreicht werden. Der Apparat ist ausgerüstet für den Gebrauch in den Tropen. Er wiegt 13 kg und kann von einem durch einen Benzinmotor angetriebenen Generator gespeist werden. Der Generator hat ein Gewicht von 18 kg. Eine einzige Bestimmung im Freien dauert 30–40 Minuten. Im Labor können etwa 25 Bestimmungen innerhalb von 8 Stunden gemacht werden. Ein Mann kann mindestens zwei Apparate zugleich beobachten. Apparat und Generator kosteten weniger als US $ 1500.

     

Ekman portion of surface currents,as measured by radar in different areas

Summary Surface currents, as measured by the HF-radar CODAR (COstal raDAR), are investigated with respect to their dependence on wind. Time series of wind are available from single weather stations, while CODAR yields current velocities on a grid with a resolution of some 3 km. As part of various research programs experiments have been carried out by the University of Hamburg (Germany) in different areas. Two of the areas under consideration are located in the Baltic Sea, two in the North Sea, and one covering the northern part of the Dead Sea. Time series of about two weeks with 2-hourly sampling are available for some 50 grid points of each area.Vector-correlation techniques are used to determine the linear relation of surface currents on wind velocity and also windstress. In both cases, significant correlation of about the same order has been found. 35% to 60% of the variance in surface currents may be explained by linear forcing from the vectors of wind velocity or windstress. Current-to-wind ratios range from 0.015 to 0.025, and a veering to the right of currents against wind has been observed. The decomposition of horizontal two-dimensional current fields into empirical orthogonal eigenfunctions (EOF) yields higher amounts of variance in the 1. EOF as may be explained by linear windforcing.Two possible mechanisms for wind-driven currents are discussed, Ekman circulation and Stokes drift. Assuming the vertical eddy viscosity to be independent on wind velocity and water depth, it may be estimated. Values of about 5×10^–4 m²s^–1 are found in the Baltic and 20×10^–4 m²s^–1 in the North Sea, which are in reasonable agreement with those used in numerical models.

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Ekman-Anteil an den durch Radar gemessenen Oberflächenströmungen in verschiedenen Seegebieten

Zusammenfassung Oberflächenströmungen, gemessen mit dem Hochfrequenzradar CODAR (COastal RaDAR), werden hinsichtlich ihrer Windabhängigkeit untersucht. CODAR mißt Strömungsgeschwindigkeiten in einem Gitter mit 3 km Auflösung. Zeitserien des Windes stammen von naheliegenden Wetterstationen. Messungen wurden von der Universität Hamburg im Rahmen von Forschungsprojekten in verschiedenen Meeresgebieten durchgeführt. Zwei dieser Gebiete liegen in der Ostsee, zwei in der Nordsee und eines umfaßt den nördlichen Teil des Toten Meeres. Von allen Gebieten existieren Meßserien an etwa 50 Gitterpunkten mit zweistündiger Abtastung und etwa 2 Wochen Dauer.Zur Bestimmung der linearen Abhängigkeit der Strömung sowohl vom Wind als auch vom Windschub werden Vektorkorrelationen berechnet. In beiden Fällen ergibt sich eine signifikante Korrelation von etwa gleichem Betrag. 35% bis 60% der Varianz der Oberflächenströmungen kann durch linearen Antrieb des Windes oder Windschubes erklärt werden. Der Quotient von Strömungs- zu Windgeschwindigkeit liegt im Bereich 0,015 bis 0,025, und es ist eine Drehung der Strömung nach rechts gegenüber dem Wind zu beobachten. Die Zerlegung des zweidimensionalen Strömungsfeldes in EOFs (empirical orthogonal eigenfunctions) ergibt für die 1. EOF einen höheren Varianzanteil als durch linearen Windantrieb erklärt werden kann.Zwei unterschiedliche Antriebsmechanismen für winderzeugte Strömungen werden diskutiert, Ekman Zirkulation und Stokes Drift. Der vertikale Austauschkoeffizient kann aus Daten bestimmt werden, vorausgesetzt daß er nicht vom Wind und der Wassertiefe abhängt. Werte von etwa 5×10^–4 m²s^–1 werden für die Ostsee und 20×10^–4 m²s^–1 für die Nordsee gefunden. Diese Werte liegen in dem Bereich, der für numerische Modelle benutzt wird.

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Ekman-Part des courants de surface, mesurés par Radar dans différents endroits

Résumé Les courants de surface mesurés par le radar CODAR (COastal raDAR), sont analysés par rapport à leur dépendence vis-à-vis du vent. Les séries temporelles du vent sont disponibles á chaque station météorologique alors que CODAR donne les vitesses des courants sur une grille de 3 km de résolution. Dans le cadre de plusieurs programmes de recherche, des études ont été faites par l'Université de Hamburg (Allemagne) dans différents endroits. Deux des zones considérées sont situées dans la Mer Baltique, deux dans la Mer du Nord et une couvre la partie Nord de la Mer Morte. Des séries temporelles d'environ 2 semaines avec un échantillonnage de 2-heures sont disponibles sur 50 points pour chaque zone.Des techniques de correlation vectorielle sont employées pour déterminer la relation linéaire entre courants de surface et d'une part la vitesse et d'autre part la pousée du vent. Dans les deux cas nous avons trouvé une correlation significative du même ordre. Le modèle linéaire forcé par les vecteurs de vitesse et pousée de vent représente de 35%–60% de la variance des courants de surface. Les rapports courant-vent varient de 0.015–0.025 et la rotation vers la droite des courants par rapport au vent a été observée. La décomposition des champs bi-dimensionnels de courant sur des fonctions propres empiriques orthogonales (EOF) donnent des taux de variance plus importants dans la lère EOF, comme expliqué par le forçage linéaire du vent.Deux mécanismes possibles de courants induits par les vents sont discutés, la circulation d'Ekman et la dérive de Stokes. Supposant une viscosité de tourbillon verticale indépendente de la vitesse du vent et de la profondeur, la viscosité est estimée. Des valeurs d'environ 5×10^–4 m²s^–1 et de 20×10^–4 m²s^–1 sont trouvées respectivement pour la Mer Baltique et la Mer du Nord, ce qui est en accord raisonable avec les valeurs utilisées dans les modèles numériques.

     

Seasonal dynamics of microbial sulfate reduction in temperate intertidal surface sediments: controls by temperature and organic matter

The role of microbial sulfate reduction on organic matter oxidation was studied quantitatively in temperate intertidal surface sediments of the German Wadden Sea (southern North Sea) on a seasonal base in the years 1998–2007. The sampling sites represent the range of sediments found in the back-barrier tidal area of Spiekeroog Island: sands, mixed and muddy flats. The correspondingly different contents in organic matter, metals, and porosities lead to significant differences in the activity of sulfate-reducing bacteria with volumetric sulfate reduction rates (SRR) in the top 15 cm of up to 1.4 μmol cm^?3 day^?1. Depth-integrated areal SRR ranged between 0.9 and 106 mmol m^?2 day^?1, with the highest values found in the mudflat sediments and lower rates measured in sands at the same time, demonstrating the impact of both temperature and organic matter load. According to a modeling approach for a 154-km² large tidal area, about 39, 122, and 285 tons of sulfate are reduced per day, during winter, spring/autumn, and summer, respectively. Hence, the importance of areal benthic organic matter mineralization by microbial sulfate reduction increases during spring/autumn and summer by factors of about 2 and 7, respectively, when compared to winter time. The combined results correspond to an estimated benthic organic carbon mineralization rate via sulfate reduction of 78 g C m^?2 year^?1.     

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.