196,138 research outputs found
Concentration and grain-size of dust particles from ice sections of the Talos Dome ice core (East Antarctica)
No full textCoulter counter data about concentration and grain-size of dust particles from ice sections of the Talos Dome ice core. They have been partially (from the surface to the depth of 900 m) already been published (Baccolo et al. 2018, Albani et al. 2012). For each sample 2 or 3 measurements were carried out and the average value is reported. Data were linearly interpolated and re-sampled with a spatial resolution of 1 m. Concentrations are expressed as ppb, i.e. ngdust g-1ice. The AICC2012 chronolgy has been used (Veres et al. 2013, Bazin et al. 2013)
Neutron activation analysis on sediments from Victoria Land, Antarctica: Multi-elemental characterization of potential atmospheric dust sources
No full textThe elemental composition of 40 samples of mineral sediments collected in Victoria Land, Antarctica, in correspondence of ice-free sites, is presented. Concentration of 36 elements was determined by instrumental neutron activation analysis, INAA. The selection of 6 standard reference materials and the development of a specific analytical procedure allowed to reduce measurements uncertainties and to verify the reproducibility of the results. The decision to analyze sediment samples from Victoria Land ice-free areas is related to recent investigations regarding mineral dust content in the TALos Dome ICE core (159 11′E; 72 49′S, East Antarctica, Victoria Land), in which a coarse local fraction of dust was recognized. The characterization of Antarctic potential source areas of atmospheric mineral dust is the first step to identify the active sources of dust for the Talos Dome area and to reconstruct the atmospheric pathways followed by air masses in this region during different climatic periods. Principal components analysis was used to identify elements and samples correlations; attention was paid specially to rare earth elements (REE) and incompatible/compatible elements (ICE) in respect to iron, which proved to be the most discriminating elemental groups. The analysis of REE and ICE concentration profiles supported evidences of chemical weathering in ice-free areas of Victoria Land, whereas cold and dry climate conditions of the Talos Dome area and in general of East Antarctica. © 2013 Akadémiai Kiadó, Budapest, Hungary
210Pbxs. is a viable alternative to 137Cs for tracing soil redistribution in mountain pastures affected by heterogeneous Chernobyl fallout
No full textSoil mobilization has been investigated by means of fallout radionuclides (FRN) in a first-order catchment of the Eastern Alps. Caesium-137, Pb-210(xs.) (Pb-210 excess or unsupported fraction), and Am-241 have been measured in soil samples collected from a pasture at about 2150 m above sea level. Combining pedological and radioactivity data, including mineral-related radionuclides (primordial K-40 and nuclides belonging to the Th-232 and U-238 decay chains), the distribution of FRNs, their spatial variability, vertical distribution, and relationships with pedological and topographical variables were assessed. Because of low activity concentration, it was not possible to use artificial long-lived Am-241 as a soil tracer, but preliminary results are encouraging. Inventories of Pb-210(xs.) and Cs-137 have been converted into soil mobilization rates applying the MODERN model. Despite the gentle steepness and the absence of evident signs of erosion, the slopes of the considered catchment are affected by erosion at a rate up to 6 t ha(-1) yr(-1), likely related to grazing. A comparison between Pb-210(xs.) and Cs-137 has revealed that at this site Cs-137, the most used FRN for estimating soil redistribution, is not suitable for this purpose, probably due to its irregular spatial distribution on snow-covered ground after the Chernobyl accident. Conversely, Pb-210(xs.), owing to its continuous input, has provided reliable estimates of soil redistribution rates, in accordance with local morphology. The latter has in fact been related to morphometric variables in a regression model to provide an overview of soil erosion/sedimentation across the entire catchment, confirming that Pb-210(xs.) is a viable alternative to trace soil erosion and deposition where the Chernobyl fallout occurred on snow-covered ground
Dust Transport to the Taylor Glacier, Antarctica, During the Last Interglacial
No full textChanges in the composition of dust trapped in ice provide evidence of past atmospheric circulation and earth surface conditions. Investigations of dust provenance in Antarctic ice during glacial and interglacial periods indicate that South America is the primary dust source during both climate regimes. Here, we present results from a new ice core dust archive extracted from the Taylor Glacier in coastal East Antarctica during the deglacial transition from Marine Isotope Stage 6 to 5e. Radiogenic strontium and neodymium isotopes indicate that last interglacial dust is young and volcanic, in contrast to the observed preindustrial and Holocene (Marine Isotope Stage 1) dust composition. The dust composition differences from the last interglacial and current interglacial period at the site require a profound difference in atmospheric transport and environmental conditions. We consider several potential causes for enhanced transport of volcanic material to the site, including increased availability of volcanic material and large‐scale atmospheric circulation changes.Plain Language SummaryFluctuations in the isotopic composition of dust particles transported atmospherically and trapped in East Antarctic ice during glacial and interglacial periods provide glimpses into past earth surface conditions and atmospheric dynamics through time. Here we present new ice core records of dust from the Taylor Glacier (Antarctica), extending back to the transition into the last interglacial period (~130,000 years ago). Dust deposited at this site during the last interglacial period has a significantly more volcanic dust composition compared to the current interglacial dust, caused by a pronounced wind direction change and/or increased subaerial exposure of volcanic material. The distinct dust compositions during two separate interglacial periods suggest significant differences in conditions at the dust source areas and atmospheric dynamics to this peripheral Antarctic site.Key PointsLast interglacial dust composition in Taylor Glacier ice is distinct from MIS 1 recordSr and Nd isotope signatures indicate a young volcanic sourceGeochemical data suggest a change in provenance and atmospheric circulation between MIS 5e and MIS 1Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148354/1/grl58638_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148354/2/grl58638.pd
Mineralogical study of rodingitized microgabbros and associated chromitite seams from the Nain ophiolite, Central Iran
No full textThe Nain-Dehshir-Baft Ophiolitic Belt (NDBOB), which crops out along the Nain-Baft fault, around the Central Iranian Microcontinent (CIM), comprises a set of dismembered ultramafic, mafic and sedimentary complexes.
The northernmost branch of this ophiolitic belt is known as “Nain ophiolitic mélange” and hosts small chromitite bodies, as pods and lenses, within completely serpentinized peridotites.
The focus of the present study is the interaction between a 50 cm thick chromitite lens and a crosscutting rodingite dyke. For this purpose, a full transect across chromitite, rodingite and serpentinite was continuously sampled and studied in reflected and transmitted light microscopy. Mineral chemistry of sulfides, silicates, carbonates and oxydes was determined through EMP analyses.
Rodingite shows a calc-silicate assemblage with an association of clinopyroxene, xonotlite, chlorite, garnet, vesuvianite, titanite, hornblende and chromite. Chromitite has 60-80% modal chromite, that sporadically shows a slight Fe-chromitization. Silicate assemblage is dominated by serpentine with relics of olivine and, occasionally, diopside, enstatite, hornblende and phlogopite. Later calcite veins crosscut both rodingite and chromitite, extending within serpentinite too.
Rodingite shows a widespread range of copper sulfides, the most common ones being chalcocite, followed by native copper, digenite, geerite, and few spotted grains of possible yarrowite and sponkiopite. As secondary Cu oxydes and hydroxydes tenorite and spertiinite were found.
In chromitite, close to the upper contact with rodingite, usual secondary sulfides like heazlewoodite and millerite were found together with shandite. Close to the lower rodingite contact, the presence of pyrrhotite, native iron and pentlandite was detected. Very close to the lower contact, again an unusual sulfide assemblage was found, with bornite and galena.
Within rodingite clinopyroxenes show both diopside and augite compositions, with XMg ((Mg/(Mg+Fe2+)) of 0.93-0.96 for the former and 0.82-0.86 for the latter. Garnets are grossular and hydrogrossular in the upper rodingite, to which andradite is added in the lower rodingite. Chlorite shows a wide range of compositions with XMg increasing towards the contact with chomitite from 0.47 to 0.60. Very close to the contact XMg of chlorite ranges between 0.67 and 0.94. Chromite accessory grains have XMg ranging between 0.52 and 0.68 and XCr (Cr/(Cr+Al)) ranging between 0.75 and 0.80.
Chromite in chromitite has XMg ranging between 0.65 and 0.71 and XCr ranging between 0.68 and 0.71. Olivine is forsteritic with XMg ranging between 0.95 and 0.97 and orthopyroxene is enstatitic with XMg around 0.94-0.95.
Chlorite is very rare and has around 3.5 wt% Cr2O3.
Rodingite intrusion postdates serpentinization of mantle assemblage and did not affect the chomite+silicate chromitite assemblage. The effect on sulfide variety and distribution was instead remarkable. At least lead and copper were introduced in the contact zone within chromitite to form shandite and bornite. Reducing conditions during rodingite emplacement are witnessed by the abundance of native copper and the presence of native iron.
The effect of interaction in rodingite is mainly recorded by the wide range of chlorite compostions that increases its Mg content towards chromitite
Development of a low background alpha–beta/gamma coincidence detector
No full textDeveloping detectors operating in time coincidence is a possible way to increase the sensitivity in gamma spectroscopy. Such design allows both the selection of specific events and the rejection of background. In this work we present a new low background detector mainly developed for the determination of radioactive contamination of liquid samples. The system was constructed by combining a liquid organic scintillator, for the detection of alpha and beta particles, and a High Purity Germanium for the detection of correlated gamma rays. Despite being located in a non-underground laboratory, the instrument can reach sensitivities in the range of tens mBq/kg for U-238, U-235 and Th-232, exploiting alpha-gamma and beta-gamma coincidence events
ALLERGIA A LATICE NEI LAVORATORI DELLA SANITA': FREQUENZA, QUANTIFICAZIONE DELL'ESPOSIZIONE, EFFICACIA DI CRITERI PER LA FORMULAZIONE DEL GIUDIZIO DI IDONEITA'
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