Impact of prescribed Arctic sea ice thickness in simulations of the present and future climate

This paper describes atmospheric general circulation model climate change experiments in which the Arctic sea-ice thickness is either fixed to 3 m or somewhat more realistically parameterized in order to take into account essentially the spatial variability of Arctic sea-ice thickness, which is, to a first approximation, a function of ice type (perennial or seasonal). It is shown that, both at present and at the end of the twenty-first century (under the SRES-A1B greenhouse gas scenario), the impact of a variable sea-ice thickness compared to a uniform value is essentially limited to the cold seasons and the lower troposphere. However, because first-year ice is scarce in the Central Arctic today, but not under SRES-A1B conditions at the end of the twenty-first century, and because the impact of a sea-ice thickness reduction can be masked by changes of the open water fraction, the spatial and temporal patterns of the effect of sea-ice thinning on the atmosphere differ between the two periods considered. As a consequence, not only the climate simulated at a given period, but also the simulated Arctic climate change over the twenty-first century is affected by the way sea-ice thickness is prescribed.     

Verification of the Weather Research and Forecasting Model when Forecasting Daily Surface Conditions in Southern Alberta

The Weather Research and Forecasting (WRF) model was compared with daily surface observations to verify the accuracy of the WRF model in forecasting surface temperature, pressure, precipitation, wind speed, and direction. Daily forecasts for the following two days were produced at nine locations across southern Alberta, Canada. Model output was verified using station observations to determine the differences in forecast accuracy for each season.

Although there were seasonal differences in the WRF model, the summer season forecasts generally had the greatest accuracy, determined by the lowest root mean square errors, whereas the winter season forecasts were the least accurate. The WRF model generally produced skillful forecasts throughout the year although with a smaller diurnal temperature range than observed. The WRF model forecast the prevailing wind direction more accurately than other directions, but it tended to slightly overestimate precipitation amounts. A sensitivity analysis consisting of three microphysics schemes showed relatively minor differences between simulated precipitation as well as 2?m surface temperatures.     

The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection

The LMDZ4 general circulation model is the atmospheric component of the IPSL–CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley–Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke’s convection scheme, used in previous versions, the Emanuel’s scheme improves the representation of the Hadley–Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke’s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model.     

In situ LA-ICPMS Isotopic and Geochronological Studies on Carbonatites and Phoscorites from the Guli Massif,Maymecha-Kotuy,Polar Siberia

In this study we present a fresh isotopic data, as well as U–Pb ages from different REE-minerals in carbonatites and phoscorites of Guli massif using in situ LA-ICPMS technique. The analyses were conducted on apatites and perovskites from calcio-carbonatite and phoscorite units, as well as on pyrochlores and baddeleyites from the carbonatites. The ⁸⁷Sr/⁸⁶Sr ratios obtained from apatites and perovskites from the phoscorites are 0.70308–0.70314 and 0.70306–0.70313, respectively; and 0.70310–0.70325 and 0.70314–0.70327, for the pyrochlores and apatites from the carbonatites, respectively.Furthermore, the in situ laser ablation analyses of apatites and perovskites from the phoscorite yield εNd from 3.6 (±1) to 5.1 (±0.5) and from 3.8 (±0.5) to 4.9 (±0.5), respectively; εNd of apatites, perovskites and pyrochlores from carbonatite ranges from 3.2 (±0.7) to 4.9 (±0.9), 3.9 (±0.6) to 4.5 (±0.8) and 3.2 (±0.4) to 4.4 (±0.8), respectively. Laser ablation analyses of baddeleyites yielded an eHf(t)d of +8.5 (± 0.18); prior to this study Hf isotopic characteristic of Guli massif was not known. Our new in situ εNd, ⁸⁷Sr/⁸⁶Sr and eHf data on minerals in the Guli carbonatites imply a depleted source with a long time integrated high Lu/Hf, Sm/Nd, Sr/Rb ratios.In situ U–Pb age determination was performed on perovskites from the carbonatites and phoscorites and also on pyrochlores and baddeleyites from carbonatites. The co-existing pyrochlores, perovskites and baddeleyites in carbonatites yielded ages of 252.3 ± 1.9, 252.5 ± 1.5 and 250.8 ± 1.4 Ma, respectively. The perovskites from the phoscorites yielded an age of 253.8 ± 1.9 Ma. The obtained age for Guli carbonatites and phoscorites lies within the range of ages previously reported for the Siberian Flood Basalts and suggest essentially synchronous emplacement with the Permian-Triassic boundary.     

Zoning and exsolution in alkali feldspars from Laacher See volcano (Western Germany): constraints on temperature history prior to eruption

Compositional zoning and exsolution patterns of alkali feldspars in carbonatite-bearing cognate syenites from the 6.3 km³ (D.R.E) phonolitic Laacher See Tephra (LST) deposit in western Germany (12.9 ka) are reported. These rocks represent the cooler outer portion and crystal-rich products of a cooling magma reservoir at upper crustal levels. Major and trace-element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt. Trace-element differences measured by LA–ICP–MS are in accordance with silicate–carbonate unmixing. Across the core–rim boundary, we extracted gray-scale profiles from multiple accumulations of back-scattered electron images. Gray scales directly represent K/Na ratios owing to low concentrations of Ba and Sr (<?30 ppm). Diffusion gradients are modeled to solve for temperature using known pre-eruptive U–Th zircon ages (0–20 ky) of each sample (Schmitt et al., J Petrol 51:1053–1085, 2010). Estimated temperatures range from 630 °C to 670 °C. For the exsolution boundaries, a diffusive homogenization model is constrained by the solvus temperature of ~ 712^_725 °C and gives short time scales of only 15–50 days. Based on our results, we present a model for the temperature–time history of these rocks. The model also constrains the thermal variation across the cooling crystal-rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates, the cooling carapace, and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir.     

Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps)

Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone (IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite (300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic (anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at 210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower Jurassic. Received: 7 July 1998 / Accepted: 4 November 1998     

Die tektonische Evolution der Erde von Pangäa zur Gegenwart ein plattentektonisches Modell

Zusammenfassung Das hier vorgestellte Modell basiert auf der Annahme, daß sich unter großen Landmassen, wie Pangäa zum Beispiel, in tektonischen Ruheperioden Wärme aus dem Erdinneren anstaut. Infolgedessen entwickelte sich vom Perm bis zur Kreide ein weites Konvektionstumorsystem; Pangäa zersplitterte und die kontinentalen Platten bewegten sich vom afrikanischen Zentrum weg. Die ozeanischen Rücken des Atlantiks und Indiks folgten den abwandernden Platten wie sich »öffnende Ringe«. Panthalassa, der Eo-Pazifik, wurde von allen Seiten überdriftet. Es muß einen Gegenstrom vom Pazifik im Mantel geben, welcher für die Auffüllung der zwischen den Pangäabruchstücken entstehenden ozeanischen Räume mit Mantelmaterial sorgt. Auch die ozeanischen Platten des Pazifiks bewegen sich vom zentralen »Darwin-Rise« weg. Der ostpazifische Rükken folgte der Bewegung und bildet heute einen ausgedehnten ostwärts gekrümmten Bogen. In den ozeanischen »Außenbögen« bildeten sich infolge der Dehnung Querrifts. Die Transformstörungen sind in beiden Systemen radial angeordnet. Die Terrains an Nordamerikas Westküste können nur östlich eines ostpazifischen Rückens aus ihrer ursprünglichen Position im zentralen Pazifik herausgewandert sein, also synchron mit dem sich öffnenden Pazifik. Die Kontinente bewegen sich möglicherweise solange von ihrer ursprünglichen Position weg, bis erneut eine große Landmasse zusammengedriftet ist. Unterhalb einer solchen »Neogäa« könnte sich wieder ein Konvektionstumor infolge von Wärmestau entfalten. Das findet vielleicht in Intervallen von einigen hundert Millionen Jahren statt und könnte die WILSON-Zyklen der Erdgeschichte erklären.

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The tectonic evolution of the earth from Pangea to the present a plate tectonic model

The model proposed here is based on the assumption that beneath giant landmasses (e.g. Pangea) heat from the inner earth is stored up and accumulated during periods of tectonic inactivity. Consequently below Pangea a huge convection bulge system developed from the Permian to the Cretaceous; Pangea split up and the continental plates moved away from the African centre. The oceanic ridges of the Atlantic and the Indic also followed the movement of the withdrawing continents like »opening rings«. The oceanic ridges always maintained their position in the middle of the spreading oceans above unidirectional flows in the upper mantle. Panthalassa which surrounded Pangea, was over-drifted from all sides. Since the »expansion« of Pangea is continuing even today, there must be a counter current of mantle material from the Pacific area, compensating the gaps between the fragments of Pangea. Consequently at the subduction zones a suction should exist, which pulls the Pacific plates under the advancing plates of the former Pangean continent. In the centre of Panthalassa another bulge from the upper mantle developed simultaneously with the bulge under Pangea. The Pacific oceanic plates moved away outwards from this central »Darwin rise«. The Eastpacific ridge also followed this movement eastwards and forms today a wide, ringlike arc. In the outer arcs of the Pangean and Pacific spreading ocean systems transverse ridges developed as a result of the extension of the older oceanic crust. The transform faults are radial structures in both »expanding« systems. The hotspot spurs of the Hawaii and Polynesian islands can be explained as the result of material derived from an independent slowly ESE moving deeper part of the mantle. The terrains on North Americas West cost moved away from their original position in the central Pacific ocean synchronously with the opening ocean on the east side of the advancing East Pacific ridge.The energy which drives the whole system is residual plus radioactive heat. Kinetic movements compensate the heat surplus of the earth. The continental plates of the Pangean system are moving away from their original position until a new giant landmass is formed by collision. Below such a stationary »Neogea« a heat bulge can develop again. This may take place perhaps in intervals of hundred of million years, explaining the WILSON-cycles in earth history.

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Résumé Le modèle présenté ici est basé sur l'hypothèse qu'endessous des grandes masses continentales — comme la Pangée p.ex. - il s'accumule, pendant les périodes de calme tectonique, de la chaleur d'origine interne. En conséquence, depuis le Permien jusqu'au Crétacé, un vaste système de convection s'est développé; la Pangée s'est morcelée et les plaques continentales se sont éloignées du centre africain. Les dorsales océaniques circum-africaines ont suivi le mouvement de ces plaques à la manière d'»anneaux concentriques«. La Panthalassa, précurseur du Pacifique, a été chevauchée de tous les côtés. Il doit s'être établi, dans le manteau, à partir du Pacifique, un contre-courant qui compense l'ouverture des océans en formation entre les fragments de la Pangée. Le Pacifique a donné lieu, lui aussi, à une expansion centrifuge; la dorsale est-pacifique a suivi le mouvement et forme aujourd'hui un arc bombé vers l'est. Dans les arcs océaniques extérieurs, l'expansion a provoqué la formation de dorsales transverses. Les failles transformantes montrent, dans les deux systèmes, des dispositions radiales. Les terrains de la côte W de l'Amérique du N ne peuvent provenir que d'une région située à l'Est de la dorsale est-pacifique dans sa position d'origine. Les continents s'éloigment et forme aujourd'hui un arc bombé vers l'est. Dans les arcs océaniques extérieurs, l'expansion a provoqué la forSous une telle »Néogée«, une nouvelle cellule de convection pourrait ensuite se développer. Ces phénomènes pourraient se dérouler dans un intervalle de quelques centaines de millions d'années, expliquant ainsi les cycles de Wilson dans l'histoire de la Terre.

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Mass fluxes of xenobiotics below cities: challenges in urban hydrogeology

Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany.     

Pure elastic stiffness of sand represented by response envelopes derived from cyclic triaxial tests with local strain measurements

Acta Geotechnica - The elastic stiffness of a fine sand at small to moderate strains ( $$\varepsilon \le 2 \times 10^{-4}$$ ) has been studied based on cyclic triaxial tests on cube-shaped samples...     

Modelling of the vertical fluxes of nitric acid,ammonia, and ammonium nitrate

Results from numerical investigations regarding the exchange of HNO₃, NH₃, and NH₄NO₃ between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc ₁=[HNO₃]+[NH₄NO₃] (total nitrate),c ₂=[NH₃]+[NH₄NO₃] (total ammonia), andc ₃=[HNO₃]-[NH₃] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO₃, NH₃, and NH₄NO₃) measured at a reference height by stations of a monitoring network.