Biomarker and stable carbon isotope analyses of sedimentary organic matter from Lake Tswaing: evidence for deglacial wetness and early Holocene drought from South Africa

Comparing the organic matter (OM) composition of modern and past lake sediments contributes to the understanding of changes in lacustrine environments over time. We investigate modern plant and lake-water samples as well as modern and ancient sediment samples from the Tswaing Crater in South Africa using biomarker and stable carbon isotope analyses on bulk OM and specific biomarker compounds. The characteristic molecular markers for higher land plants (predominantly C3-type deciduous angiosperms) in Lake Tswaing are long-chain n-alkanes (n-C₂₇₋₃₃), n-alkanols (n-C₂₈₊₃₀), stigmasterol, β-sitosterol, β-amyrin, α-amyrin and lupeol. The C₁₇ n-alkane, tetrahymanol, gammaceran-3-one and C₂₉ sterols dominate the lipid fraction of autochthonously produced OM. By comparing stable carbon isotope analyses on bulk OM and the characteristic biomarkers, we follow the modern carbon cycle in the crater environment and find indications for methanotrophic activity in the lake from isotopically depleted moretene. A comparative study of core sediments reveals changes in the terrestrial (C3 versus C4) and aquatic bioproductivity and allows insights into the variability of the carbon cycle under the influence of changing climatic conditions for the time from the end of the last glacial (Termination I) to the late Holocene, ca. 14,000–2,000 calibrated years before present (years BP). The most pronounced changes occur in the aquatic realm after ca. 10,000 years BP when our results imply climate swings from more humid to more arid and after 7,500 years BP to gradually more humid conditions again, which can be related to a shift in the position of the Inter-Tropical Convergence Zone or to changes in the tropical atmosphere–ocean interaction. Long-chain alkenones (LCAs) have been identified in ancient lake sediments from Africa for the first time. They occur in samples older than 7,500 years BP and their distribution (dominance of C₃₈ and of tri- over tetra-unsaturated LCAs) is distinctly different from other published records suggesting a to date unknown source organism.     

Trace metal and geochemical variability during 5,500 years in the sediment of Lake Lehmilampi,Finland

A high-resolution geochemical profile from a 5,500-year-old sediment core of Lake Lehmilampi in eastern Finland was analyzed to study long-term trends and variability in element concentrations and accumulation rates. The accumulation rates of all studied elements followed the same trend, responding to changes in the total sedimentation rate. Concentration profiles differed among elements and showed considerable variation over time. Principal components analysis (PCA) was used on the concentration data to identify groups of elements that have similar geochemical controls. The first principal component was influenced by changes in mineral matter accumulation, and it incorporated elements that are associated with stable allochthonous minerals (such as Mg, K, Cs, Rb, Li, Ti and Ga), as well as elements in forms that become diluted when mineral matter increases (e.g., S, Fe and Mn). The second and third principal components showed that a large proportion of the variance was accounted for by elements with continuously increasing or decreasing concentrations related to pedogenetical development of the catchment soil. In the case of Hg, Pb and Cd, however, accumulation rates increased faster at the surface than is simply accounted for by changes in total sedimentation rates. For Cu, Cr, Ni and Zn, concentrations increased over the past 150 years, but there were no indications of a significant addition due to atmospheric deposition. These elements had more variable concentrations before the mid nineteenth century than after, as did elements that are often used for normalization. These findings suggest that lake sediments may not properly reflect the history of atmospheric metal deposition in remote areas.     

What governs macrophyte species richness in kettle hole types? A case study from Northeast Germany

Kettle holes are small, pond-like, depressional wetlands in young moraine landscapes. They mostly undergo a wet-dry cycle and have a high potential for biological species diversity. However, their biodiversity and habitat function is often greatly impacted by surrounding intensive agricultural land use practices.In this study, we used statistical analysis of a large data set from the federal state of Brandenburg (Northeast Germany) to characterise the macrophyte species richness of kettle holes in an interregional context and to determine the factors that influence macrophyte occurrence. We proposed that (1) specific environmental factors, (2) hydrogeomorphic kettle hole types and (3) the regional topography have a major impact on macrophyte species richness. The evaluation of the data was performed using the General Linear Model (GLM) and Canonical Correspondence Analysis (CCA). Each of the analysed factors addresses different parts of the macrophyte species richness, including the target variables overall species richness, plant life and growth forms as well as Red List species.None of the analysis showed effects of the tested environmental factors on overall macrophytes species richness, but on the richness of plant life and growth forms as well as on Red List species. We identified hydroperiod, depth, shore width, kettle hole area, pH, electric conductivity, carbonate hardness and oxygen as key factors for the prediction of species richness of plant life and growth forms. Furthermore, we demonstrate that hydrogeomorphic kettle hole types account for relevant parts of variation in species richness and are useful interregional and integrative indicators to identify kettle holes with protection priority for macrophytes.     

Why the <Emphasis Type="Italic">Euler</Emphasis> scheme in particle tracking is not enough: the shallow-sea pycnocline test case

During the last decades, the Euler scheme was the common “workhorse” in particle tracking, although it is the lowest-order approximation of the underlying stochastic differential equation. To convince the modelling community of the need for better methods, we have constructed a new test case that will show the shortcomings of the Euler scheme. We use an idealised shallow-water diffusivity profile that mimics the presence of a sharp pycnocline and thus a quasi-impermeable barrier to vertical diffusion. In this context, we study the transport of passive particles with or without negative buoyancy. A semi-analytic solutions is used to assess the performance of various numerical particle-tracking schemes (first- and second-order accuracy), to treat the variations in the diffusivity profile properly. We show that the commonly used Euler scheme exhibits a poor performance and that widely used particle-tracking codes shall be updated to either the Milstein scheme or second-order schemes. It is further seen that the order of convergence is not the only relevant factor, the absolute value of the error also is.     

Product Evaluation for the Control of Chemical Emissions to Indoor Air – 10 Years of Experience with the AgBB Scheme in Germany

Emissions from construction products may have a significant impact on the quality of indoor air, particularly in energy‐efficient buildings, where the normal rate of air exchange with fresh ambient air may be limited. In this context, reduction strategies to mitigate the concentration of chemicals in the indoor environment have become even more important. German authorities wanted to foster the development of low‐emission products, and as a result it was necessary to quantify and qualify these emissions in a reliable and objective manner. The core principles for evaluation of the standardized measurements in emission tests were established by the “Committee for Health‐Related Evaluation of Building Products” (AgBB) and published in the so‐called “AgBB scheme”. Relevant for evaluation are: (i) Assessment of the emission levels of substances with known toxicological properties; (ii) limits for non‐assessable or unknown substances; (iii) limits for the total amount of chemical emissions. This review describes the stepwise implementation of the test procedure in Germany and the experience gained in evaluation of product emissions over the years. A comprehensive overview of the philosophy, history, current practices, and future directions of the German AgBB scheme for VOC emissions is also provided. Special emphasis is given to the evaluation of a list of about 170 single substances which have an agreed “lowest concentration of interest” (LCI) value for the indoor environment – values that are updated periodically according to present toxicological knowledge.     

Properties of the ionised gas of circumnuclear star-forming regions in early-type spirals

A study of circumnuclear star-forming regions (CNSFRs) in several early-type spirals has been carried out in order to investigate their main properties: stellar and gas kinematics, dynamical masses, ionising stellar masses, chemical abundances and other properties of the ionised gas. Both high resolution (R～20,000) and moderate resolution (R～5000) have been used. In some cases, these regions (about 100–150 pc in size) are composed of several individual star clusters with sizes between 1.5 and 4.9 pc, estimated from Hubble Space Telescope images. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km?s^?1, with the Hβ emission lines being narrower than both the stellar lines and the [Oiii]λ5007 Å lines. The twice ionised oxygen, on the other hand, shows velocity dispersions comparable to those of stars. We have applied the virial theorem to estimate dynamical masses of the clusters, assuming that the systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10⁷ to 10⁸ M_⊙ for the full CNSFRs. We obtain oxygen abundances which are comparable to those found in high-metallicity disc Hii regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC3504, 12+log(O/H)=8.85, about 1.5 times solar. The derived N/O ratios are, on average, larger than those found in high-metallicity disc Hii regions, and they do not seem to follow the trend of N/O vs. O/H which marks the secondary behaviour of nitrogen. On the other hand, the S/O ratios span a very narrow range—between 0.6 and 0.8 times solar. Compared to high-metallicity disc Hii regions, CNSFRs show values of the O₂₃ and the N2 parameters whose distributions are shifted to lower and higher values, respectively. Hence, even though their derived oxygen and sulphur abundances are similar, higher values would in principle be obtained for the CNSFRs if pure empirical methods were used to estimate abundances. CNSFRs also exhibit lower ionisation parameters than their disc counterparts, as derived from [Sii]/[Siii]. Their ionisation structure also seems to be different, with CNSFRs showing radiation-field properties more similar to Hii galaxies than to disc high-metallicity Hii regions.     

Sub-terahertz,Microwaves and High Energy Emissions During the 6 December 2006 Flare,at 18:40 UT

The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes, both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by the Solar Submilimeter Telescope (SST) and microwaves (1 – 18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments onboard satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer (TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and γ-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal counterparts only in the higher energy X- and γ-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters were difficult to be reconciled with a purely thermal emission component. We discuss possible mechanisms to explain the double spectral components at microwaves and in the THz ranges.     

Cross-Calibration of SMART-1 XSM with GOES and RHESSI

A number of X-ray instruments have been active in observing the solar coronal X-ray radiation this decade. We have compared XSM observations with simultaneous GOES and RHESSI observations. We present flux calibrations for all instruments and compare XSM and GOES total emission measures (TEM) and temperatures (T).     

Einstein Gravity Explorer–a medium-class fundamental physics mission

The Einstein Gravity Explorer mission (EGE) is devoted to a precise measurement of the properties of space-time using atomic clocks. It tests one of the most fundamental predictions of Einstein’s Theory of General Relativity, the gravitational redshift, and thereby searches for hints of quantum effects in gravity, exploring one of the most important and challenging frontiers in fundamental physics. The primary mission goal is the measurement of the gravitational redshift with an accuracy up to a factor 10⁴ higher than the best current result. The mission is based on a satellite carrying cold atom-based clocks. The payload includes a cesium microwave clock (PHARAO), an optical clock, a femtosecond frequency comb, as well as precise microwave time transfer systems between space and ground. The tick rates of the clocks are continuously compared with each other, and nearly continuously with clocks on earth, during the course of the 3-year mission. The highly elliptic orbit of the satellite is optimized for the scientific goals, providing a large variation in the gravitational potential between perigee and apogee. Besides the fundamental physics results, as secondary goals EGE will establish a global reference frame for the Earth’s gravitational potential and will allow a new approach to mapping Earth’s gravity field with very high spatial resolution. The mission was proposed as a class-M mission to ESA’s Cosmic Vision Program 2015–2025.