Middle to Late Pleistocene environments based on stable organic carbon and nitrogen isotopes of loess-palaeosol sequences from the Carpathian Basin

Stable organic carbon and nitrogen isotopes can be used to interpret past vegetation patterns and ecosystem qualities. Here we present these proxies for two loess-palaeosol sequences from the southern Carpathian Basin to reconstruct the palaeoenvironment during the past 350 ka and establish regional commonalities and differences. Before now, isotopic studies on loess sequences from this region were only conducted on deposits from the last glacial cycle. We conducted methodological tests involving the complete decalcification of the samples prior to stable isotope analyses. Two decalcification methods (fumigation method and wet chemical acidification), different treatment times, and the reproducibility of carbon isotope analyses were tested. Obtained results indicate that the choice of the decalcification method is important for organic carbon stable isotope analyses of loess-palaeosol sequences because ratios vary by more than 10‰ between the wet chemical and fumigation methods, due to incomplete carbonate removal by the latter. Therefore, we suggest avoiding the fumigation method for studies on loess-palaeosol sequences. In addition, our data show that samples with TOC content <0.2% bear increased potential for misinterpretation of their carbon isotope ratios. For our sites, C₃-vegetation is predominant and no palaeoenvironmental shifts leading to a change of the dominant photosynthesis pathway can be detected during the Middle to Late Pleistocene. Furthermore, the importance of further stable nitrogen isotope studies is highlighted, since this proxy seems to reflect past precipitation patterns and reveals favourable conditions in the southern Carpathian Basin, especially during interstadials.     

PAI-OFF: A new proposal for online flood forecasting in flash flood prone catchments

The Process Modelling and Artificial Intelligence for Online Flood Forecasting (PAI-OFF) methodology combines the reliability of physically based, hydrologic/hydraulic modelling with the operational advantages of artificial intelligence. These operational advantages are extremely low computation times and straightforward operation. The basic principle of the methodology is to portray process models by means of ANN. We propose to train ANN flood forecasting models with synthetic data that reflects the possible range of storm events. To this end, establishing PAI-OFF requires first setting up a physically based hydrologic model of the considered catchment and – optionally, if backwater effects have a significant impact on the flow regime – a hydrodynamic flood routing model of the river reach in question. Both models are subsequently used for simulating all meaningful and flood relevant storm scenarios which are obtained from a catchment specific meteorological data analysis. This provides a database of corresponding input/output vectors which is then completed by generally available hydrological and meteorological data for characterizing the catchment state prior to each storm event. This database subsequently serves for training both a polynomial neural network (PoNN) – portraying the rainfall–runoff process – and a multilayer neural network (MLFN), which mirrors the hydrodynamic flood wave propagation in the river. These two ANN models replace the hydrological and hydrodynamic model in the operational mode. After presenting the theory, we apply PAI-OFF – essentially consisting of the coupled “hydrologic” PoNN and “hydrodynamic” MLFN – to the Freiberger Mulde catchment in the Erzgebirge (Ore-mountains) in East Germany (3000 km²). Both the demonstrated computational efficiency and the prediction reliability underline the potential of the new PAI-OFF methodology for online flood forecasting.     

Extraterrestrial chromite in Middle Ordovician marine limestone at Kinnekulle,southern Sweden—Traces of a major asteroid breakup event

Abstract— The distribution of sediment‐dispersed extraterrestrial chromite grains and other Cr‐rich spinels (>63 μm) has been studied in Middle Ordovician Orthoceratite Limestone from two quarries at Kinnekulle, southern Sweden. In the Thorsberg quarry, an ?3.2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment‐dispersed extraterrestrial chromite grains. Typically, 1–3 grains are found per kilogram of limestone. In the nearby Hällekis quarry, the same beds show similarly high concentrations of extraterrestrial chromite grains, but in samples representing the 9 m downward continuation of the section exposed at this site, only 5 such grains were found in a total of 379 kg of limestone. The extraterrestrial (equilibrated ordinary chondritic) chromite grains can be readily distinguished by a homogeneous and characteristic major element chemistry, including 2.0–3.5 wt% TiO₂ and stable V₂O₃ concentrations close to 0.7 wt%. Terrestrial Cr‐rich spinels have a wide compositional range and co‐exist with extraterrestrial chromite in some beds. These grains may be derived, for example, from mafic dykes exposed and weathered at the sea floor. Considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied. Instead, the difference may be primarily related to an increase in the ancient flux of extraterrestrial matter to Earth in connection with the disruption of the L chondrite parent body in the asteroid belt at about this time. The coexistence in some beds of high concentrations of chondritic chromite and terrestrial Cr‐rich spinels, however, indicates that redistribution of heavy minerals on the sea floor, related to changes in sea level and sea‐floor erosion and currents, must also be considered.     

Trading more food: Implications for land use,greenhouse gas emissions,and the food system

The volume of agricultural trade increased by more than ten times throughout the past six decades and is likely to continue with high rates in the future. Thereby, it largely affects environment and climate. We analyse future trade scenarios covering the period of 2005–2045 by evaluating economic and environmental effects using the global land-use model MAgPIE (“Model of Agricultural Production and its Impact on the Environment”). This is the first trade study using spatially explicit mapping of land use patterns and greenhouse gas emissions. We focus on three scenarios: the reference scenario fixes current trade patterns, the policy scenario follows a historically derived liberalisation pathway, and the liberalisation scenario assumes a path, which ends with full trade liberalisation in 2045.Further trade liberalisation leads to lower global costs of food. Regions with comparative advantages like Latin America for cereals and oil crops and China for livestock products will export more. In contrast, regions like the Middle East, North Africa, and South Asia face the highest increases of imports. Deforestation, mainly in Latin America, leads to significant amounts of additional carbon emissions due to trade liberalisation. Non-CO₂ emissions will mostly shift to China due to comparative advantages in livestock production and rising livestock demand in the region. Overall, further trade liberalisation leads to higher economic benefits at the expense of environment and climate, if no other regulations are put in place.     

Shock history of the fossil ungrouped achondrite Österplana 065: Raman spectroscopy and TEM of relict chrome-spinel grains

Chrome-spinel grains from the fossil ungrouped achondrite Österplana 065 (Öst 065) recovered from Middle Ordovician limestone in Sweden were studied using Raman spectroscopy and TEM. All the studied chrome-spinel grains have a high density of planar fractures and planar features, not seen in chromites from the other L chondritic Ordovician fossil meteorites. Raman spectra of the host chrome-spinel grain and its planar features are similar and no signatures of high-pressure phases of chromite were found. The planar features occur along planar fractures, are enriched in ZnO, and are most probably produced due to enhanced leaching during terrestrial weathering in the marine sediment. Dislocation densities within two FIB sections prepared from two chrome-spinel grains from Öst 065 are similar to the dislocation densities found within chromite grains from the matrix of Tenham L6 chondrite. Using this observation and taking into account the presence of significant fracturing in all the grains, we conclude that the Öst 065 chrome-spinel grains were subjected to moderate to very strong shock corresponding to shock stages of S4–S6. This makes Öst 065 fossil achondrite the highest shocked fossil meteorite studied so far. This is consistent with the hypothesis that Öst 065 is a piece of the impactor that led to the L chondrite parent body breakup.     

Unusual sources of fossil micrometeorites deduced from relict chromite in the small size fraction in ~467 Ma old limestone

Extraterrestrial chrome spinel and chromite extracted from the sedimentary rock record are relicts from coarse micrometeorites and rarely meteorites. They are studied to reconstruct the paleoflux of meteorites to the Earth and the collisional history of the asteroid belt. Minor element concentrations of Ti and V, and oxygen isotopic compositions of these relict minerals were used to classify the meteorite type they stem from, and thus to determine the relative meteorite group abundances through time. While coarse sediment-dispersed extraterrestrial chrome-spinel (SEC) grains from ordinary chondrites dominate through the studied time windows in the Phanerozoic, there are exceptions: We have shown that ~467 Ma ago, 1 Ma before the breakup of the L chondrite parent body (LCPB), more than half of the largest (>63 μm diameter) grains were achondritic and originated from differentiated asteroids in contrast to ordinary chondrites which dominated the meteorite flux throughout most of the past 500 Ma. Here, we present a new data set of oxygen isotopic compositions and elemental compositions of 136 grains of a smaller size fraction (32–63 μm) in ~467 Ma old pre-LCPB limestone from the Lynna River section in western Russia, that was previously studied by elemental analysis. Our study constitutes the most comprehensive oxygen isotopic data set of sediment-dispersed extraterrestrial chrome spinel to date. We also introduce a Raman spectroscopy-based method to identify SEC grains and distinguish them from terrestrial chrome spinel with ~97% reliability. We calibrated the Raman method with the established approach using titanium and vanadium concentrations and oxygen isotopic compositions. We find that ordinary chondrites are approximately three times more abundant in the 32–63 μm fraction than achondrites. While abundances of achondrites compared to ordinary chondrites are lower in the 32–63 μm size fraction than in the >63 μm one, achondrites are approximately three times more abundant in the 32–62 μm fraction than they are in the present flux. We find that the sources of SEC grains vary for different grain sizes, mainly as a result of parent body thermal metamorphism. We conclude that the meteorite flux composition ~467 Ma ago ~1 Ma before the breakup of the LCPB was fundamentally different from today and from other time windows studied in the Phanerozoic, but that in contrast to the large size fraction ordinary chondrites dominated the flux in the small size fraction. The high abundance of ordinary chondrites in the studied samples is consistent with the findings based on coarse extraterrestrial chrome-spinel from other time windows.     

The crustal structure of the Guayana Shield, Venezuela, from seismic refraction and gravity data

We present results from a seismic refraction experiment on the northern margin of the Guayana Shield performed during June 1998, along nine profiles of up to 320 km length, using the daily blasts of the Cerro Bolívar mines as energy source, as well as from gravimetric measurements. Clear Moho arrivals can be observed on the main E–W profile on the shield, whereas the profiles entering the Oriental Basin to the north are more noisy. The crustal thickness of the shield is unusually high with up to 46 km on the Archean segment in the west and 43 km on the Proterozoic segment in the east. A 20 km thick upper crust with P-wave velocities between 6.0 and 6.3 km/s can be separated from a lower crust with velocities ranging from 6.5 to 7.2 km/s. A lower crustal low velocity zone with a velocity reduction to 6.3 km/s is observed between 25 and 25 km depth. The average crustal velocity is 6.5 km/s. The changes in the Bouguer Anomaly, positive (30 mGal) in the west and negative (−20 mGal) in the east, cannot be explained by the observed seismic crustal features alone. Lateral variations in the crust or in the upper mantle must be responsible for these observations.     

Amplitude versus offset analyses of the deep sedimentary structures at the northern flank of the Porcupine Basin,SW of Ireland

This paper represents an attempt of analysing the amplitude versus offset (AVO) behaviour and specific seismic attributes of sedimentary structures from the Porcupine Basin, SW of Ireland. During the last decade, a huge number of carbonate mounds were investigated in this region in water depths of 600–1,000 m, but the genesis and growth of these mounds are still not clearly identified. The aim of this paper is to give a better understanding of the connection between fluid migration pathways in the deeper underground and surface expressions of their fluid expulsions like gas chimneys and pockmarks through which the mounds may generate themselves. The data used in this study to determine boundary conditions for the physical properties of the underlaying strata were gathered from the northern flank of the Porcupine Basin, where a huge amount of fluid and/or gas chimneys covers the seabed. Marine seismic reflection data contain information about the elastic properties of the underlying earth, mainly based on the observed variations in the seismic reflection amplitude at different shot–receiver offsets. To extract elastic parameters from the data, inversion techniques were used, which presume that input amplitudes are proportional to reflection coefficients for plane wave reflection. To calibrate the AVO analyses with the existing stratigraphy in the working area we have used the well logs from several bore holes in the region. The results of this study show clearly that the investigated and identified pockmarks on the seafloor are the surface expression of hydrocarbon seepage in the deeper sedimentary underground.     

Climatological Ertel’s potential-vorticity flux and mean meridional circulation in the extratropical troposphere – lower stratosphere

We investigated to what extent the isentropic, non-geostrophic formulation of zonally averaged circulation derived for stratospheric conditions is applicable to climatological transport in the extratropical troposphere and lower stratosphere. The study is based on 10 years of daily data of ECMWF analysis and on the ECHAM3 climate model of the German Climate Computing Centre. The main result is a scalar isentropic mixing coefficient, K_yy, and a mean meridional transport circulation consistently derived from the same data base. For both data sources, isentropic mean meridional circulation is derived from horizontal mass flow rate for 4 representative months. Alternatively, a mean meridional circulation is calculated from total diabatic heating rates of the ECHAM3 model. It is shown that only the latter is in good agreement with the ECMWF mean meridional circulation. Isentropic analysis also comprises the seasonal cycle of the climatological meridional gradient and flux of Ertels potential vorticity (PV). Application of Tungs flux-gradient relation yields that for all seasons K_yy is positive in height-latitude regions where statistical significance is reached. Large K_yy values, marking regions of more efficient mixing, have been found in the subtropical vertical band of weak westerly wind and in mid-latitudes in regions of upward-propagating baroclinic wave activity in the middle and upper troposphere. Based on the ECMWF data and results of baroclinic-wave behaviour, strong indications are presented that positive zonally averaged PV flux polewards of the jet core in the NH is strengthened by stationary waves and nonlinear effects. Reduced eddy transport is apparent in winter and spring slightly below the subtropical tropopause jet. The seasonal cycle of K_yy from ECHAM3 data is to a great extent in agreement with the result based on ECMWF analysis. In the model, reduced interannual variability enlarges the height-latitude range where sign of K_yy is significant.     

Quality Assurance of Hydrocarbon Measurements for the German Tropospheric Research Focus (TFS)

In the German Focus on Tropospheric Research (TFS) independent quality assurance procedures were implemented in order to obtain information on data quality and comparability of the different measurements made in the different field campaigns. This paper describes the results for measurements of hydrocarbons using in-situ gas chromatographictechniques and off line analysis of samples collected in canisters (analysed by two central laboratories CL-1 and CL-2) and samples collected on adsorption tubes. The QA-procedures included comparisons with synthetic standards (prepared by EN 45001 certified laboratories), absolute calibration with a diffusion source, and an instrument/methodology comparison in ambient air. Harmonisation of the ambient measurements was achieved with a complex mixture (NCAR/BERLIOZ) containing 70 commonly observed hydrocarbons at mixing ratios of 0.2 to 10 ppb (mole fraction) in nitrogen, which was calibrated by referencing to hydrocarbon standards of the National Institute for Standards and Technology (NIST).For the certified synthetic standards, the experienced groups agreed to within ± 20% for most compounds. Much larger discrepancies were observed for the new Airmotec HC2010 instruments due to problems with identification, co-elution and blanks/memory effects. The results in ambient air were similar: Reasonable agreement was found for the results from the experienced groups with well characterised in situ instruments andfor the charcoal tubes, whereas larger discrepancies were observed for the results from new groups and instruments. For the latter, only selected compounds met the data quality objectives (DQO). The canister samples analysed by CL-2 were in good agreement with the reference instrument, whereas large deviations were found for a number of compounds in the analysis of the same canisters by CL-1. The results of the comparison provided the final basis for flagging and harmonising the data from all participants prior to their submission to the TFS central data bank.