Evidence for a mid‐Pleistocene shift of ice‐drift pattern in the Nordic seas

Sediment proxy records from a continuous, 1.5 million year long deep‐sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid‐Pleistocene Revolution (MPR). Red‐green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid‐Pleistocene climate shift was accompanied by a general change in ice‐drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses. Copyright © 2003 John Wiley & Sons, Ltd.     

2D/3D Dust Continuum Radiative Transfer Codes to Analyze and Predict VLTI Observations

Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric device MIDI. This revised version was published online in July 2006 with corrections to the Cover Date.     

“Comet‐tail” ejecta streaks: A predicted cratering landform unique to Titan

Abstract— A model for an impact ejecta landform peculiar to Saturn's moon Titan is presented. Expansion of the ejecta plume from moderate‐sized craters is constrained by Titan's thick atmosphere. Much of the plume is collimated along the incoming bolide's trajectory, as was observed for plumes from impacts on Jupiter of P/Shoemaker‐Levy‐9, but is retained as a linear, diagonal ejecta cloud, unlike on Venus where the plume “blows out.” On Titan, the blowout is suppressed because the vertically‐extended atmosphere requires a long wake to reach the vacuum of space, and the modest impact velocities mean plume expansion along the wake is slow enough to allow the wake to close off. Beyond the immediate ejecta blanket around the crater, distal ejecta is released into the atmosphere from an oblique line source: this material is winnowed by the zonal wind field to form streaks, with coarse radar‐bright particles transported less far than fine radar‐dark material. Thus, the ejecta form two distinct streaks faintly reminiscent of dual comet tails, a sharply W‐E radar‐dark one, and a less swept and sometimes comma‐shaped radar‐bright one.     

Radiocarbon on Titan

Abstract— We explore the likely production and fate of ¹⁴C in the thick nitrogen atmosphere of Saturn's moon Titan and investigate the constraints that measurements of ¹⁴C might place on Titan's photochemical, atmospheric transport and surface‐atmosphere interaction processes. Titan's atmosphere is thick enough that cosmic‐ray flux limits the production of ¹⁴C: absence of a strong magnetic field and the increased distance from the Sun suggest production rates of ?9 atom/cm²/s, ?4x higher than Earth. The fate and detectability of ¹⁴C depends on the chemical species into which it is incorporated: as methane it would be hopelessly diluted even in only the atmosphere. However, in the more likely case that the ¹⁴C attaches to the haze that rains out onto the surface (as tholin, HCN or acetylene and their polymers), haze in the atmosphere or recently deposited on the surface would be quite radioactive. Such radioactivity may lead to a significant enhancement in the electrical conductivity of the atmosphere which will be measured by the Huygens probe. Measurements with simple detectors on future missions could place useful constraints on the mass deposition rates of photochemical material on the surface and identify locations where surface deposits of such material are “freshest”.     

Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia

Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e., the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land subsidence plays an important role in long-term coastal zone management in Semarang.     

Die Intensitätsverteilung der Himmelsstrahlung während der totalen Sonnenfinsternis Am 15. 2. 1961 auf Grund photographischer Messungen

Zusammenfassung Es wird über eine photographische Methode berichtet, die gestattet, die Verteilung der Himmelsstrahlung zu bestimmen. Der Himmel wird mit einer Weitwinkelkamera photographiert und die Aufnahmen werden mit einem Photometer ausgewertet. Über einen Graukeil, der auf das gleiche filmmaterial aufbelichtet und mit den Aufnahmen zusammen entwickelt wird, lassen sich die mit dem Photometer ermittelten Schwärzungswerte in (relative) Intensitätswerte der Himmelsstrahlung umrechnen. Der durch das Photoobjektiv bedingte Helligkeitsabfall von der Bildmitte aus nach den Bildrändern zu wird experimentell ermittelt und als Korrektur an den Meßwerten angebracht. Die Intensitätsverteilung der Himmelsstrahlung während der totalen Sonnenfinsternis am 15. Februar 1961 in Viareggio (Norditalien), am Abend zuvor und am Folgetag wird wiedergegeben und diskutiert. Während der totalen Verfinsterung spiegelt sich insbesondere die Wanderung des Mondschattens relativ zum Beobachtungsort in den Darstellungen wieder. Während der partiellen Verfinsterung ist dagegen die relative Helligkeitsverteilung praktisch die gleiche wie bei unverfinsterter Sonne.

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Summary A photographic method is described which permits to determinate the distribution of the sky radiation. The sky is photographed by a wide angle camera and the resulting pictures are evaluated by a photometer. A photometric step wedge copied on a film of the same type and number is developed together with the pictures. Then the density values measured by the photometer can be transformed into (relative) intensity values of the sky radiation. The decrease in brightness from the centre of the picture to the rim caused by the photographic lens is determined experimentally and is taken into account as a correction to the density values. The distribution of intensity of the sky radiation in Viareggio (North Italy) during the total eclipse of the sun on the 15th of february 1961, on the previous evening and on the following day are shown and discussed. During the total eclipse especially the migration of the moon's shadow in relation to the observation point is clearly defined. During the partial eclipse, however, practically the same relative distribution of sky radiation is found as without eclipse.

     

Glacial-interglacial relationship between carbonate components and sediment reflectance in the North Atlantic

A high-resolution composite sediment record from intermediate water depths in the North Atlantic, dating back to marine isotope stage (MIS) 13, was investigated in order to determine the relationship between sediment reflectance (gray level%) and carbonate content (weight%). For this purpose, a detailed analysis of the coarse (>20 µm) and fine (<20 µm) carbonate components was carried out to assess which of the two carbonate components drives glacial-interglacial changes in sediment gray level. The results indicate that the bulk carbonate component is clearly dominated by the fine carbonate fraction, regardless of glacial or interglacial climatic mode, suggesting that the sediment gray level is usually controlled by fluctuations of the fine carbonate content. However, a comparison of MIS 1 and 5.5 indicates that, besides this difference in the contents of the two carbonate size fractions, changing modes in carbonate preservation, i.e., the preservational state of planktonic Foraminifera, may also have a profound influence on total sediment reflectance.     

Seasonal dynamics of elemental sulfur in two coastal sediments

A spectrophotometric method for elemental sulfur (S⁰) analysis without interference from other reduced sulfur compounds was adapted for the use in reducing sediments. The S⁰ distribution in two coastal sediments was studied regularly from summer to winter and compared to factors regulating the S⁰ accumulation, such as redox potentials, the rate of bacterial sulfide production and the general sulfur chemistry. Dense coatings of sulfur bacteria developed on the sediment surface of a sulfuretum which had an S⁰ concentration of up to 41 μmol S cm^?3. The 2·5-mm thick bacterial coating contained 40% of all S⁰ in the sediment. A more typical marine sediment with a few cm thick oxidized surface layer had an S⁰ maximum of 1–3 μmol S cm^?3 at 2–4 cm depth. The S⁰ maximum in both sediments increased from summer to winter as the sediments gradually became more oxidized. The deeper layers maintained a low S⁰ concentration. Most of the S⁰ in the upper few mm of a laboratory sulfuretum was present inside sulfur bacteria and actively migrated up and down with the bacteria depending upon the changing light and oxygen conditions.     

Dust metamorphosis in the galaxy

Summary Cosmic dust grains play an important role for the thermal, dynamical, and chemical structure of the interstellar medium. This is especially true for the star formation process and the late stages of stellar evolution. Dust grains determine the spectral appearance of protostars, very young stellar objects with disk-like structures as well as of evolved stars with circumstellar envelopes.In this review, we will demonstrate that solid particles in interstellar space are both agent and subject of galactic evolution. We will especially discuss the different dust populations in circumstellar envelopes, the diffuse interstellar medium, and the molecular clouds with strong emphasis on the evolutionary aspects and the metamorphosis of these populations.     

Tilted electromagnetic Bianchi type III cosmological solution

An exact cosmological solution to the Einstein-Maxwell equations for the case of Bianchi type III symmetry with stiff matter and an electromagnetic field is constructed. The behaviour of the solution near the singularity and at late stages of the expansion is investigated.