Comparing fire-history interpretations based on area, number and estimated volume of macroscopic charcoal in lake sediments

Sedimentary charcoal particles from lakes are commonly used to investigate fire history. Fire-history reconstructions are based on measuring the surface area or counting the number of charcoal fragments in adjacent samples. Recently, the volume of charcoal particles was advised as a more accurate method for quantifying past charcoal production. Large charcoal datasets, used to synthesize global fire history, include these different types of charcoal measurements and implicitly assume that they provide comparable fire-history information. However, no study has demonstrated that this assumption is valid. Here we compare fire-frequency reconstructions based on measurements of charcoal area and number, and estimates of charcoal volume from two lake sediment records from the eastern Canadian boreal forest. Results indicate that the three proxies provide comparable fire-history interpretations when using a locally defined threshold to identify fire events.     

Pb isotope variations in hydrogenetic Fe–Mn crusts from the Izu–Bonin fore-arc

Fe–Mn crusts were recovered from the western escarpment of the Bonin Ridge in the Izu–Bonin fore-arc region (dive site #824: 28.612°N, 141.803°E) at water depths of c. 2900 m using the Shinkai 6500 submersible during cruise YK 04–05. Major and trace element data and XRD mineralogy indicate that the crusts are hydrogenetic in origin. We present profiles of variations in Pb isotope composition measured in-situ by laser ablation MC-ICP-MS across two of the crusts. The isotopic variations are systematic and can be matched up between the two crusts, indicating similar growth rates. The crust Pb isotope composition rules out any local source for Pb from within the Izu–Bonin–Mariana arc system, either from hydrothermal activity or through leaching of volcanic detritus. Input of a globally well-mixed volcanic Pb component, either from aerosols or as an absorbed component on aeolian dust, has been proposed as a mechanism to explain the Pb isotope composition of Central Pacific deep water. However, the Izu–Bonin crusts are displaced to lower ²⁰⁶Pb/²⁰⁴Pb and higher ²⁰⁸Pb/²⁰⁴Pb, which requires an additional Pb source. One possibility is that as water is advected from the south, outboard of the Luzon–Ryukyu–Honshu arc system, it is progressively polluted by Pb derived by weathering and erosion of these young island arc volcanic systems. Using a constant Co-flux model, growth rates are estimated at ～ 7–13 mm/Ma, which would suggest that these crusts provide a record of changes in the composition of deep water in the Izu–Bonin fore-arc region of the western Pacific Ocean over the last 4–8 Ma. Over this interval, the main feature has been a progressive decrease in ²⁰⁷Pb/²⁰⁶Pb (0.843 to 0.839) and ²⁰⁸Pb/²⁰⁶Pb (2.088 to 2.080) with time. The interior parts have compositions similar to those of crusts from the Izu–Bonin fore-arc, while the rims have compositions similar to crusts from the central Western Pacific.     

The thermal decomposition studies of three Polish bituminous coking coals and their blends

The objective of this work was to investigate the thermal decomposition of various bituminous coal blends. Three Polish coals of varying rank (82.7, 86.2 and 88.7 wt.% carbon content) and caking ability (weak, moderate and strong) were collected from the Krupiński, Szczygłowice and Zofiówka mines, respectively. These coals were used to prepare binary and ternary blends. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used. The weight loss and heat flow during pyrolysis, and storage/loss elastic modulus measured as a function of increasing temperature were related to the caking ability of coals. Parameters determined with the TGA and the DSC methods in the binary and ternary blends were correlated with the proportion of strongly-caking-coal concentration in the blend. The weight loss of coal blends was found to be additive parameter. The DSC thermograms of binary blends were found to be different from those of the ternary blends, which suggests a different course for this blend pyrolysis.     

Identification of a sulfide derivative with a bicyclic hydrocarbon skeleton related to squalene. Part I: synthesis of a dithiane triterpenoid

In order to confirm the tentative structure of a dithiane sulfide with a bicyclic squalene hydrocarbon skeleton representing the predominant alkyl sulfide in Shell Beach samples from the Monterey Formation (Miocene, CA) and also occurring in various immature sulphur-rich sediments [Schouten, S., Sinninghe Damsté, J.S., de Leeuw, J.W., 1995. A novel triterpenoid carbon skeleton in immature sulphur-rich sediments. Geochimica et Cosmochimica Acta 59, 953–958], synthesis of a reference compound bearing two thiochromane moieties has been carried out. The product was obtained as a diastereomeric mixture appearing in the form of five peaks (partly) resolved in gas chromatography (GC). This is in sharp contrast with the geochemical compound, which appears as a single broad peak in GC. Co-elution experiments showed that none of the peaks from the synthetic mixture coelute in GC with that of the geochemical sulfide. Furthermore, the different synthetic isomers have identical mass spectra, which are clearly distinct from that of the naturally-occurring compound. The results unambiguously indicate that the natural compound is not the dithiane triterpenoid originally envisaged. Instead, we propose that the compound has a structure of a bicyclic squalene derivative bearing two “S-spiro”-type moieties as is the case for other sulfides related to regular polycyclic polyprenoids and hopanoids in Monterey sediments.     

V440 Per: the longest-period overtone Cepheid

V440 Per is a Population I Cepheid with a period of 7.57 d and low-amplitude, almost sinusoidal light and radial velocity curves. With no reliable data on the first harmonic, its pulsation mode identification remained controversial. We obtained a radial velocity curve of V440 Per with our new high-precision and high-throughput Poznań Spectroscopic Telescope. Our data reach an accuracy of 130 m s⁻¹ per individual measurement and yield a secure detection of the first harmonic with an amplitude of   A ₂= 140 ± 15 m s⁻¹  . The velocity Fourier phase φ₂₁ of V440 Per is inconsistent at the 7.25σ level with those of fundamental-mode Cepheids, implying that the star must be an overtone Cepheid, as originally proposed by Kienzle et al. Thus, V440 Per becomes the longest-period Cepheid with securely established overtone pulsations. We show that a convective non-linear pulsation hydrocode can reproduce the Fourier parameters of V440 Per very well. The requirement to match the observed properties of V440 Per constrains the free parameters of the dynamical convection model used in the pulsation calculations, in particular the radiative loss parameter.     

2-Gyr Simulation of the Oort-cloud Formation II. A Close View of the Inner Oort cloud after the First Two Giga-years

We simulate the formation of the Oort cloud (OC) till the age of 2 Gyr starting from an initial disc of planetesimals made by 10 038 test particles. The results on the outer part of the distant comet reservoir are reported by Neslu?an et al. (this issue). Here we deal with the evolution of the population and structure at 2 Gyr of the complementary inner part of the Oort cloud. The dynamical evolution of the massless test particles was followed via the numerical integration of their orbits. We considered the perturbations produced by four giant planets assuming they have their current orbits and masses, as well as the perturbations caused by the Galactic tide and passing stars. The efficiency of the formation of inner OC is found to be very low: only about 1.1% of all considered particles ended in this part of the OC. At 2 Gyr, the dynamics of the inner cloud is mainly governed by the dominant z-term of the Galactic tide. The number density of the bodies is proportional to the heliocentric distance, r, as r ^?3.53. The directional distribution of orbits is still strongly inhomogeneous. There are large empty regions in the space angles around the Galactic Equator points with the galactic longitude 90 and 270° (non-rotating frame), or there are only few bodies having the ecliptical latitude higher than +60° or lower than 60°. A strong concentration of objects at the Ecliptic is apparent up to ≈1,000 AU, with a possible—but still not proved—extension to ≈1,500 AU. Beyond r ≈ 6,000 AU, bodies directly above and below the Sun, with respect to the Ecliptic, are absent.     

Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817−330

We build a simple model of the optical/ultraviolet (UV) emission from irradiation of the outer disc by the inner disc and coronal emission in black hole binaries. We apply this to the broad-band Swift data from the outburst of the black hole binary XTE J1817−330 to confirm previous results that the optical/UV emission in the soft state is consistent with a reprocessing a constant fraction of the bolometric X-ray luminosity. However, this is very surprising as the disc temperature drops by more than a factor of 3 in the soft state, which should produce a marked change in the reprocessing efficiency. The easiest way to match the observed constant reprocessed fraction is for the disc skin to be highly ionized (as suggested 30 yr ago by van Paradijs), so that the bulk of the disc flux is reflected and only the hardest X-rays heat the disc. The constant reprocessed fraction also favours direct illumination of the disc over a scattering origin as the optical depth/solid angle of any scattering material (wind/corona) over the disc should decrease as the source luminosity declines. By contrast, the reprocessed fraction increases very significantly (by a factor of ∼6) as the source enters the hard state. This dramatic change is not evident from X-ray/UV flux correlations as it is masked by bandpass effects. However, it does not necessarily signal a change in emission, for example, the emergence of the jet dominating the optical/UV flux as the reflection albedo must change with the dramatic change in spectral shape.     

Resurfacing of Titan by ammonia-water cryomagma

The Cassini Titan Radar Mapper observed on Titan several large features interpreted as cryovolcanic during the October 26, 2004 pass at high northern latitudes [Lopes, R.M.C., and 43 colleagues, 2007. Icarus 186, 395-412]. To date, models of ammonia-water resurfacing have not been tied to specific events or evolutionary stages of Titan. We propose a model of cryovolcanism that involves cracking at the base of the ice shell and formation of ammonia-water pockets in the ice. As these ammonia-water pockets undergo partial freezing in the cold ice shell, the ammonia concentration in the pockets increases, decreasing the negative buoyancy of the ammonia-water mixture. If the ice shell is contaminated by silicates delivered in impacts, the liquid-solid density difference would be even less. While the liquid cannot easily become buoyant relative to the surrounding ice, these concentrated ammonia-water pockets are sufficiently close to the neutral buoyancy point that large-scale tectonic stress patterns (tides, non-synchronous rotation, satellite volume changes, solid state convection, or subsurface pressure gradients associated with topography) would enable the ammonia to erupt effusively onto the surface. Rather than suggesting steady-state volcanism over the history of the Solar System, we favor a scenario where the cryovolcanic features could have been associated with episodic (potentially late) geological activity.     

How well do we understand cosmological recombination?

The major theoretical limitation for extracting cosmological parameters from the cosmic microwave background (CMB) sky lies in the precision with which we can calculate the cosmological recombination process. Uncertainty in the details of hydrogen and helium recombination could effectively increase the errors or bias the values of the cosmological parameters derived from the Planck satellite, for example. Here, we modify the cosmological recombination code recfast by introducing one more parameter to reproduce the recent numerical results for the speed-up of the helium recombination. Together with the existing hydrogen fudge factor, we vary these two parameters to account for the remaining dominant uncertainties in cosmological recombination. By using the C osmo MC code with Planck forecast data, we find that we need to determine the parameters to better than 10 per cent for He  i and 1 per cent for H, in order to obtain negligible effects on the cosmological parameters. For helium recombination, if the existing studies have calculated the ionization fraction to the 0.1 per cent level by properly including the relevant physical processes, then we already have numerical calculations which are accurate enough for Planck . For hydrogen, setting the fudge factor to speed up low-redshift recombination by 14 per cent appears to be sufficient for Planck . However, more work still needs to be done to carry out comprehensive numerical calculations of all the relevant effects for hydrogen, as well as to check for effects which couple hydrogen and helium recombination through the radiation field.