Molecular fossils from chemical degradation of macromolecular organic matter

Hydrogenolysis with rhodium-on-charcoal was found to be an effective method for degrading different types of macromolecular material of geological origin. Between 6 and 70% of coals, kerogens and humic substances were transferred into low-molecular-weight soluble materials. The reaction products contained a series of monomeric and dimeric lignin-derived compounds which strongly suggest intact fossil lignin as their source. The substitutional patterns of the released phenols reflect the type and amount of terrestrial organic matter input and diagenetic alterations.In addition to the lignin constituents, a complete suite of hydrocarbons differing from those of the low-molecular-weight fraction was obtained after hydrogenolysis of the sample material. Hydrocarbons released by the hydrogenolytic degradation technique were attached to the polymeric matrix as monoor polyethers. Deuterium was used in the degradation experiment to evaluate the sites of chemical bonds by which 4-methylsteranes and hopanes are attached to the kerogen matrix. These experiments suggested a linkage of the released molecules with ring A and the side-chain, respectively.     

Pre-Hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the Schwarzwald crystalline,SW-Germany

Lead isotopes of K-feldspars from five granites of the SE-Schwarzwald and from metamorphites are positively correlated in 207/204 as well- as 208/204- vs. 206/204-diagrams. The linear alignments may be due to correlated laststage lead isotope evolution (lead-lead isochron) and result in a secondary isochron model age of nearly 3 Ga for the Southern Schwarzwald basement. This calculation implies a long-lasting undisturbed lead isotope evolution in the Schwarzwald basement since the Archaean. This is not supported however by geochronological studies. On the other hand the data together with U/Pb-analyses of whole rock samples from metamorphites are consistent with pre-Hercynian mantle lead addition to the basement. This presumably happened during early Paleozoic polymetamorphism. The interpretation of the lead isotope correlations as mantle-crust mixing lines needs a rather homogeneous pre-Hercynian mantle lead of the MORB-type, delivered to the crust probably in part by ascending volatile phases. Thus geodynamical models are supported which involve subduction of oceanic crust or mantle pluming during the early Paleozoic. In Part I of this report, the trends in Schwarzwald lead isotopes are discussed as secondary isochrons and as mixing lines. Constraints are derived for a pre-Hercynian mantlecrust interaction and for lead redistribution by the Hercynian basement activation.     

Use of biological traits for interpreting functional relationships in large rivers

Altogether 64 predominantly biological traits were coded for more than 600 macroinvertebrate species from European rivers. The main question was: Are biological traits able to reflect “biological functionality” in large rivers and if so, is it possible to deduce an assessment system based on functionality? Analysis of the raw trait structure of all species indicates that these traits are not completely independent from their higher systematic units. To avoid mis-interpretations when judging from mixtures of habitats (β-biocoenosis) we used for our investigations only sample series from -biocoenosis, pre-tested by a mathematical criterion of homogeneity. Within -biocoenosis, traits are shown to be able to compensate for drastic changes with respect to species number and species composition along a river continuum, demonstrating their functional quality. Long-term changes in the trait and species structures of German waterways were studied using multivariate methods, based on an analysis of 142 sampling series. A shift from traits typical for K-strategists to traits typical for r-strategists was detected to be the main background variable. The rK-strategy is regarded as a true functional character of species. We calculated the relative positions of all trait-coded species on this rK-scale, and plotted the functional diversity of our samples against the structural diversity of the species from several river systems. Rivers extremely dominated by r-strategists show a deficit in functional diversity. Rivers dominated by K-strategists also show deficits, possibly in concordance with modern ecological theories such as the intermediate disturbance theory. The quantitative proportions of extreme r- to K-Strategists in -biocoenosis can be used as a general disturbance measure.     

A nitrogen fixation estimate for the Baltic Sea based on continuous pCO2 measurements on a cargo ship and total nitrogen data

Organic matter production and nitrogen fixation in the central Baltic Sea were studied on the basis of high-resolution CO₂ partial pressure data that were obtained from an automated measurement system deployed on a cargo ship. The net organic carbon (OC) production was calculated from a surface water CO₂ mass balance and used to estimate the nitrogen uptake by organic matter during the period March to August 2005. It was shown that the net OC production continued despite the exhaustion of dissolved inorganic nitrogen (DIN) after the spring bloom in April. The nitrogen demand for this production was calculated on the basis of the C/N ratio of organic matter. It was of the same order of magnitude than the winter DIN concentration that fuelled the spring bloom. Since the atmospheric DIN deposition was negligible and no indications of alternative DIN sources were found, it was assumed that N₂ fixation had taken place despite the low temperatures (4–8 °C) in April/May. This “cold fixation” amounted to 74 mmol m^?2 whereas a value of 99 mmol m^?2 was obtained for the summer N₂ fixation during June/July. Due to the contribution of the April/May N₂ fixation, a total annual rate (173±35 mmol m^?2) was obtained for 2005 which is considerably higher than presently accepted estimates. These findings were confirmed by a nitrogen budget based on long-term data (1993–2006) for total nitrogen and total phosphorus concentrations. Furthermore, these data revealed a 30% increase in N₂ fixation during the years 1994–2006.     

Comparison of USGS and DLR topographic models of Comet Borrelly and photometric applications

Stereo analysis of images obtained during the 2001 flyby of Comet Borrelly by NASA's Deep Space 1 (DS1) probe allows us to quantify the shape and photometric behavior of the nucleus. The shape is complex, with planar facets corresponding to the dark, mottled regions of the surface whereas the bright, smooth regions are convexly curved. The photometric as well as textural differences between these regions can be explained in terms of topography (roughness) at and below the image resolution, without invoking significant variations in single-particle properties; the material on Borrelly's surface could be quite uniform. A statistical comparison of the digital elevation models (DEMs) produced from the three highest-resolution images independently at the USGS and DLR shows that their difference standard deviation is 120 m, consistent with a matching error of 0.20 pixel (similar to reported matching accuracies for many other stereo datasets). The DEMs also show some systematic differences attributable to manual versus automatic matching. Disk-resolved photometric modeling of the nucleus using the DEM shows that bright, smooth terrains on Borrelly are similar in roughness (Hapke roughness θ=20°) to C-type asteroid Mathilde but slightly brighter and more backscattering (single-scattering albedo w=0.056, Henyey-Greenstein phase parameter g=−0.32). The dark, mottled terrain is photometrically consistent with the same particles but with roughnesses as large as 60°. Intrinsically darker material is inconsistent with the phase behavior of these regions. Many local radiance variations are clearly related to topography, and others are consistent with a topographic explanation; one need not invoke albedo variations greater than a few tens of percent to explain the appearance of Borrelly.     

Organic compound tracers of fine soil and sand particles during summer in the metropolitan area of Riyadh,Saudi Arabia

Soil and sand fine particles, which may be resuspended as fine dust in the atmosphere, contain a variety of anthropogenic and natural organic components. Samples of fine soil and sand particles (sieved to <125 μM) were collected from the Riyadh area in the summer of 2003 and extracted with a mixture of dichloromethane and methanol (3:1, v:v). The derivatized total extracts were analyzed by gas chromatography–mass spectrometry in order to characterize the composition and sources of the organic components. Both anthropogenic and natural biogenic inputs were the major sources of the organic compounds in these extracts. Discarded plastics and vehicular emission products were the major anthropogenic sources in the fine particles from populated areas of the city. Their tracers were plasticizers, UCM, n-alkanes, hopanes and traces of steranes. Vegetation was the major natural source of organic compounds in samples from outside Riyadh and included n-alkanols, n-alkanoic acids, n-alkanes, methyl alkanoates, sterols and triterpenoids. Carbohydrates had high concentrations (42–54%) in all samples and indicate sources from decomposition of cellulose and/or the presence of viable microbiota such as bacteria and fungi. The results were also compared with the data obtained in winter 2002 and showed that anthropogenic inputs were higher in summer than in winter, whereas the opposite trend was observed for natural inputs.     

Holocene climate change in the Central Tibetan Plateau inferred by lacustrine sediment geochemical records

Multi-proxies of lacustrine sediments, such as total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), total sulfur (TS), hydrogen index (HI), oxygen index (OI) and stable carbon isotopic composition of organic matter (δ 13Corg), were analyzed using a 7.3 m core from Zigê Tangco. The source of the organic matter in the sediment was mainly from autochthonous phytoplankton, therefore the significances of proxies can be interpreted as that high TOC, TOC/TS, HI and δ13Corg values, low TC, TIC values corresponded to warm and wet climatic condition, and vice versa. The process of climatic development in the Zigê Tangco region was hence recovered. During the early and Mid-Holocene, the climate was warm and wet and intensive cold events occurred during the periods of 8600 to 8400 cal a BP and 7400 to 7000 cal a BP. In the second half of Holocene, the climate became cold and dry gradually. The palaeoclimatic process during Holocene in Zigê Tangco region matched well with that in Co Ngoin region which is ca 40 km to the south-east. Therefore this palaeoclimatic process represents the Holocene climatic feature in the Central Tibetan Plateau which has the same pattern in the Northern Tibetan Plateau, but the time and duration of some climatic events might be different. We can conclude that in Holocene solar insolation controlled the climatic pattern on the central Tibetan Plateau.     

Organic tracers from biomass burning in atmospheric particulate matter over the ocean

Particulate matter from the atmosphere over the Atlantic Ocean along the South American and African Continents has been analyzed for organic tracers from natural and biomass burning emissions. The major biomarker compounds characterized are natural products from continental vegetation consisting primarily of epicuticular wax components. For example, n-alkanes ranged from C₂₅ to C₃₅, with an odd carbon number predominance and carbon maxima (C_max) at 29 or 31. Concentrations of n-alkanes varied from 0.3 to 680 ng/m³. Nevertheless, n-alkanols are the dominant terrestrial tracers in almost all samples (concentrations from 0.1 to 780 ng/m³) and ranged from C₂₂ to C₃₄ with an even carbon number predominance. Despite the major presence of the natural tracers, organic components from biomass burning emissions are also present in the particulate matter. The major tracers from this source are thermal degradation products from the biopolymer cellulose, namely the dianhydromonosaccharide derivatives levoglucosan, galactosan, and mannosan. In general, the concentrations of levoglucosan, the major derivative from this source in all samples, varied from 0.0008 to 0.15 ng/m³ in atmospheric samples collected over the ocean and from 0.04 to 4860 ng/m³ in terrestrial particulate matter, used as reference in this study. Dehydroabietic acid, another marker compound emitted from burning of Gymnosperm fuel, is also detectable in most oceanic samples at concentrations ranging from 0.0001 to 0.4 ng/m³, whereas in terrestrial aerosol particulate matter, this component is present at much higher concentrations (0.23–440 ng/m³). The presence of these tracers in atmospheric particulate matter over the ocean confirms the long-range transport of smoke from biomass burning off the continents.     

Discrete simulations of a triaxial compression test for sand by DEM

A quasi‐static homogeneous drained triaxial compression test on cohesionless sand under constant lateral pressure was simulated using a three‐dimensional discrete element method. Grains were modelled by means of particle clusters composed of rigid spheres or spheres with contact moments imitating irregular particle shapes. Attention was paid to the effect of initial void ratio and grain shape mixture on the shear strength, volume changes, force chains, kinetic, elastic and dissipated energies. In addition, the effect of the mean grain size, grain size distribution, grain size range, specimen size and roughness and stiffness of boundaries was numerically analysed in initially dense sand. Some numerical results were compared with available experimental results. Copyright © 2014 John Wiley & Sons, Ltd.