Internal kinematics and dynamical models of dwarf spheroidal galaxies around the Milky Way

We review our current understanding of the internal dynamical properties of the dwarf spheroidal galaxies surrounding the Milky Way. These are the most dark matter dominated galaxies, and as such may be considered ideal laboratories to test the current concordance cosmological model, and in particular provide constraints on the nature of the dominant form of dark matter. We discuss the latest observations of the kinematics of stars in these systems, and how these may be used to derive their mass distribution. We tour through the various dynamical techniques used, with emphasis on the complementarity and limitations, and discuss what the results imply also in the context of cosmological models. Finally we provide an outlook on exciting developments in this field.     

Channel belt architecture formed by a meandering river

Stratification in channel belts is the key to reconstructing formative channel dimensions and palaeoflow conditions; this requires an understanding of the relation between river morphodynamics and set thickness. So far, theories for reconstruction of the original morphology from preserved stratification have not been tested for meandering river channels due to the lack of detailed bathymetry. This paper reports the results of an experiment that reproduced a dynamic meandering gravel‐bed river with the objectives to: (i) test the prediction of set thickness as a function of the morphology formed by a meandering river channel; and (ii) explore and explain spatial and temporal set thickness variations in the resulting channel belt. High‐resolution measurements of time‐dependent surface elevation were used to quantitatively relate the preserved stratification to the meandering river morphology. Mean set thickness agrees well with the theoretical prediction from channel morphology. The mean preserved set thickness was 30% of the mean channel depth. Due to the absence of aggradation during the experiment, this provides a lower limit for the preserved mean set thickness which is also to be expected for aggrading systems, because reworking is some orders of magnitude faster than aggradation. Furthermore, the time required to mature a channel belt and its set thickness distribution was about the same as the time required to develop and propagate bends that fill the channel belt surface. Finally, there was much systematic spatial variation in set thickness related to repetitive point bar growth and chute cut‐off. Undisturbed and thick sets occurred close to channel belt margins and more irregular stratification with stacked thinner sets was observed in the centre of the channel belt.     

Radiative transfer in disc galaxies – II. The influence of scattering and geometry on the attenuation curve

We investigate the influence of scattering and geometry on the attenuation curve in disc galaxies. We investigate both qualitatively and quantitatively which errors are made by either neglecting or approximating scattering, and which uncertainties are introduced as a result of a simplification of the star–dust geometry. We find that the magnitude of these errors depends on the inclination of the galaxy and, in particular, that, for face-on galaxies, the errors due to improper treatment of scattering dominate those due to imprecise star–dust geometry. Therefore we argue that, in all methods aimed at determining the opacity of disc galaxies, scattering should be taken into account in a proper way.     

Bottom-simulating reflections and geothermal gradients across the western Svalbard margin

Seismic reflection data reveal prominent bottom-simulating reflections (BSRs) within the relatively young (<0.78 Ma) sediments along the West Svalbard continental margin. The potential hydrate occurrence zone covers an area of c. 1600 km². The hydrate accumulation zone is bound by structural/tectonic features (Knipovich Ridge, Molloy Transform Fault, Vestnesa Ridge) and the presence of glacigenic debris lobes inhibiting hydrate formation upslope. The thickness of the gas-zone underneath the BSR varies laterally, and reaches a maximum of c. 150 ms. Using the BSR as an in-situ temperature proxy, geothermal gradients increase gradually from 70 to 115 °C km⁻¹ towards the Molloy Transform Fault. Anomalies only occur in the immediate vicinity of normal faults, where the BSR shoals, indicating near-vertical heat/fluid flow within the fault zones. Amplitude analyses suggest that sub-horizontal fluid migration also takes place along the stratigraphy. As the faults are related to the northwards propagation of the Knipovich Ridge, long-term disturbance of hydrate stability appears related to incipient rifting processes.     

Radiocarbon wiggle-match dating of proglacial lake sediments – Implications for the 8.2 ka event

The problem of insufficient age-control limits the utilisation of the 8.2 ka BP event for modelling freshwater forcing in climate change studies. High-resolution radiocarbon dates, magnetic susceptibility and lithostratigraphic evidence from a lake sediment core from Nedre Hervavatnet located at Sygnefjell in western Norway provide a record of the early Holocene. We use the method of radiocarbon wiggle-match dating of the lake sediments using the non-linear relationship between the ¹⁴C calibration curve and the consecutive accumulation order of the sample series in order to build a high-resolution age-model. The timing and duration of Holocene environmental changes is estimated using 38 AMS radiocarbon dates on terrestrial macrofossils, insects and chironomids covering the time period from 9750 to 1180 cal BP. Chironomids, Salix and Betula leaves produce the most consistent results. Sedimentological and physical properties of the core suggest that three meltwater events with high sedimentation rates are superimposed on a long-term trend with glacier retreat between 9750 and 8000 cal BP. The lake sediment sequence of Nedre Hervavatnet demonstrates the following: only a reliable high-resolution geochronology based on carefully selected terrestrial macrofossils allows the reconstruction of a more refined and complex environmental change history before and during the 8.2 ka event.