Extended dust emission in NGC 7465

We present SCUBA 850-μm, JCMT  CO( J =2→1)  , B -band imaging and VLA H  i observations of the NGC 7465/4/3 group of galaxies. The 850-μm emission associated with NGC 7465 extends to at least ∼2 R ₂₅ and is well correlated with the H  i . We investigate a range of possible mechanisms by which dust beyond R ₂₅ may be heated to give the observed extended submillimetre emission. By modelling the dust heating by stars in two extreme geometries, we fail to find any reasonable star formation scenario that is consistent with both the 850-μm and optical data. Furthermore, we do not detect any  CO( J =2→1)  emission coincident with the extended dust and atomic gas as would be expected if significant star formation were occurring. We show that shock-heating of dust via cloud–cloud collisions in the stripped interstellar medium of NGC 7465 could be sufficient to explain the extended 850-μm emission and lack of optical emission in the stripped gas, and suggest that cloud–cloud collisions may be an important dust heating mechanism in gas-rich systems.     

Observation of snowfall with a low-power FM-CW K-band radar (Micro Rain Radar)

Quantifying snowfall intensity especially under arctic conditions is a challenge because wind and snow drift deteriorate estimates obtained from both ground-based gauges and disdrometers. Ground-based remote sensing with active instruments might be a solution because they can measure well above drifting snow and do not suffer from flow distortions by the instrument. Clear disadvantages are, however, the dependency of e.g. radar returns on snow habit which might lead to similar large uncertainties. Moreover, high sensitivity radars are still far too costly to operate in a network and under harsh conditions. In this paper we compare returns from a low-cost, low-power vertically pointing FM-CW radar (Micro Rain Radar, MRR) operating at 24.1?GHz with returns from a 35.5?GHz cloud radar (MIRA36) for dry snowfall during a 6-month observation period at an Alpine station (Environmental Research Station Schneefernerhaus, UFS) at 2,650?m height above sea level. The goal was to quantify the potential and limitations of the MRR in relation to what is achievable by a cloud radar. The operational MRR procedures to derive standard radar variables like effective reflectivity factor (Z _e) or the mean Doppler velocity (W) had to be modified for snowfall since the MRR was originally designed for rain observations. Since the radar returns from snowfall are weaker than from comparable rainfall, the behavior of the MRR close to its detection threshold has been analyzed and a method is proposed to quantify the noise level of the MRR based on clear sky observations. By converting the resulting MRR-Z _e into 35.5?GHz equivalent Z _e values, a remaining difference below 1?dBz with slightly higher values close to the noise threshold could be obtained. Due to the much higher sensitivity of MIRA36, the transition of the MRR from the true signal to noise can be observed, which agrees well with the independent clear sky noise estimate. The mean Doppler velocity differences between both radars are below 0.3?ms^?1. The distribution of Z _e values from MIRA36 are finally used to estimate the uncertainty of retrieved snowfall and snow accumulation with the MRR. At UFS low snowfall rates missed by the MRR are negligible when comparing snow accumulation, which were mainly caused by intensities between 0.1 and 0.8 mm?h^?1. The MRR overestimates the total snow accumulation by about 7%. This error is much smaller than the error caused by uncertain Z _e?Csnowfall rate relations, which would affect the MIRA36 estimated to a similar degree.     

S-type ignimbrites with polybaric crystallisation histories: the Tolmie Igneous Complex,Central Victoria,Australia

The Late Devonian Tolmie Igneous Complex (in north-eastern Victoria, Australia) contains S-type, intracaldera, rhyolitic ignimbrites with multiple generations of phenocrysts of biotite, garnet, cordierite and orthopyroxene; one unit also contains fayalitic olivine. Geothermometry and calculated phase relations indicate high-T deep- to mid-crustal origins for the magmas, with crystallisation at several levels. At least four separate magma groups make up the complex. Compositional variations within and between ignimbrites are adequately modelled by selective entrainment of peritectic garnet, ilmenite, orthopyroxene and plagioclase into the magmas. Neither crystal fractionation nor mafic-felsic magma mixing played a role. Chemical and isotope data suggest that the magma sources were once variably Ba-enriched arc greywackes with different proportions of clay. The deep origin of some of the Tolmie Complex magmas means that supracrustal rocks underlie parts of north-eastern Victoria at depths of around 35 km. This has important implications for understanding the region’s tectonic development.     

Investigating the impact of initial soil moisture conditions on total infiltration by using an adapted double-ring infiltrometer

ABSTRACT

This study presents an adaptation of the double-ring infiltrometer (DRI) device, which allows several infiltration experiments to be conducted at the same location. Hence, it becomes possible to use the DRI method to investigate infiltration behaviour under different initial soil moisture conditions. The main feature is the splitting of the inner ring into two parts. While the lower part remains in the soil throughout the investigation period, the upper part is attached to the lower one just before the infiltration experiment. This method was applied to eight test sites in an Alpine catchment, covering different land-use/cover types. The results demonstrated the applicability of the adapted system and showed correlations between total water infiltration and initial soil moisture conditions on pastures, independent of the underlying soil type. In contrast, no correlation was found at forest sites or wetlands. Thus, the study emphasizes the importance of paying special attention to the impact of initial soil moisture conditions on the infiltration—and consequently the runoff behaviour—at managed areas. Given the differences in the total infiltrated water of between 30 and 1306 mm, consideration of the interplay between initial soil moisture conditions, land-use/cover type, and soil properties in rainfall–runoff models is a prerequisite to predict runoff production accurately.

EDITOR Z.W. Kundzewicz; ASSOCIATE EDITOR not assigned     

Granite suites: a problematic concept?

Abstract

In Australian stratigraphic nomenclature, the concept of granitic rock suites has been in formal use for over a decade. The basis for this suite classification of granitic rocks is inconsistent and, in eastern Australian usage, unsound on several levels. We also note that the approach used in Western Australia is different. Granitic intrusions are probably not truly amenable to any strict, comprehensive, lithostratigraphic classification. If these rocks are integrated into such a scheme, group- and supergroup-level units (i.e. formal suites and supersuites) should not be incorporated. For the present, mappable units should be recognised at the levels of formation and member. The use of granite suites and supersuites in formal stratigraphic hierarchies is not recommended. Instead, granitic bodies could be grouped into individual plutons, which may or may not form parts of larger batholiths.

1. KEY POINTS

2. The suite-based classification of granitic bodies, as currently used in the Australian Stratigraphic Units Database, is based on unsound principles, and is not employed in a consistent manner.

3. Granitic intrusive rocks probably cannot be grouped using lithostratigraphic principles that are consistent with either the local or international codes.

4. Granitic bodies can be grouped into batholiths, plutons and members, but the names of these units should, for the moment, remain informal.

     

Discrimination of Nuclear Explosions against Civilian Sources Based on Atmospheric Xenon Isotopic Activity Ratios

A global monitoring system for atmospheric xenon radioactivity is being established as part of the International Monitoring System that will verify compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) once the treaty has entered into force. This paper studies isotopic activity ratios to support the interpretation of observed atmospheric concentrations of ¹³⁵Xe, ^133mXe, ¹³³Xe and ^131mXe. The goal is to distinguish nuclear explosion sources from civilian releases. Simulations of nuclear explosions and reactors, empirical data for both test and reactor releases as well as observations by measurement stations of the International Noble Gas Experiment (INGE) are used to provide a proof of concept for the isotopic ratio based method for source discrimination.     

Cumulative effects of land use on fish metrics in different types of running waters in Austria

The catchment land-use composition of 249 fish sampling sites in Austrian running waters revealed effects on the biological integrity. Beyond correlative analysis, we investigated (1) which land-use category had the strongest effect on fish, (2) whether metrics of functional fish guilds reacted differently, (3) whether there were cumulative effects of land-use categories, and (4) whether effects varied in strength across river types. We fed 5 land-use categories into regression trees to predict the European Fish Index or fish metric of intolerant species (mainly Salmo trutta fario). Agriculture and urbanisation were the best predictors and indicated significant effects at levels of >23.3 and >2%, respectively. Model performance was R ² = 0.15 with the Fish Index and R ² = 0.46 with intolerant species. The tree structure showed a cumulative effect from agriculture and urbanisation. For the intolerant species metric, a combination of high percentages for agriculture and urbanisation was related to moderate status, whereas <7.3% agriculture were related to good status, although urbanisation was higher than 1.8%. Headwater river types showed stronger responses to land use than river types of lower gradient and turned out to be more sensitive to urbanisation than agriculture.     

Protocol for Quantitative Detection of Elemental Sulfur and Polysulfide Zero-Valent Sulfur Distribution in Natural Aquatic Samples

A HPLC-based protocol has been developed for the determination of zero-valent sulfur (ZVS) speciation, including solid, colloidal elemental sulfur and individual inorganic polysulfides in natural aquatic samples. The protocol includes four experimental procedures: (1) determination of polysulfide speciation by rapid single-phase derivatisation with methyl trifluoromethanesulfonate; (2) determination of the sum of polysulfide and colloidal sulfur by reaction with hydrogen cyanide (cyanolysis); (3) determination of total zero-valent sulfur by treatment with zinc chloride followed by extraction with chloroform; and (4) chromatographic determination of polythionates without sample pre-treatment. With proper sampling and preservation techniques in the field or on board ship, this combination of methods allowed the quantitative determination of: (a) individual polysulfide species; (b) dispersed colloidal sulfur; (c) dispersed solid elemental sulfur; and (d) tetra-, penta- and hexathionates. With minor modification, the method could be expanded to include other polythionates. Sixteen various wet chemical and liquid chromatographic methods were tested on nine synthetic reference samples (including solid elemental sulfur, colloidal elemental sulfur, inorganic polysulfides and polythionates) to establish the optimal protocol. The protocol was further evaluated by analysing the zero-valent sulfur content in microbially-produced sulfur and in sulfur from two natural samples of sulfide-rich seawater from tidal flats pools of the Wadden Sea (Germany).