An investigation of sulphur in carbonaceous and enstatite chondrites by stepped combustion

A stepped combustion technique has been developed to resolve the different sulphur-bearing components of meteorites. The technique has been applied to studies of carbonaceous and enstatite chondrites. Stepped combustion of C1 and C2 carbonaceous chondrites provides evidence for the presence of secondary sulphur minerals. Evidence for six different sulphur components has been found (elemental and organic sulphur, sulphides, FESON and sulphates). Most of the sulphur in C1 and C2 chondrites both contain the same sulphur components suggesting that hydrothermal alteration may have evolved along a common pathway. Changes in sulphur isotopic composition associated with alteration have led to an enrichment of 34S in elemental sulphur and sulphates compared to the starting sulphide material. Most of the sulphur in C3, C4 and C5/6 chondrites is present as sulphide, but stepped combustion has demonstrated that there is also a component of preterrestrial oxidised sulphur in these materials. Chemical evidence suggests that oxidised sulphur may occur as FESON or anhydrite. This finding indicates that C3 and C4 chondrites have undergone a small amount of hydrous alteration on the meteorite parent body and this provides an important evolutionary link with C1 and C2 meteorites. The stepped combustion method has been used as a means of assessing the relative abundances of the two main sulphides (troilite and oldhamite) in enstatite chondrites and aubrites. It was found that troilite and oldhamite abundances both decrease systematically with petrologic grade. The variability of these two minerals provides constraints on models envisaged for the evolution of the enstatite chrondrite parent body. Enstatite chondrites have whole-rock delta34S values of close to 0%, whereas aubrites are depleted in 32S by up to 2%

Rhyolite volcanism at Öræfajökull volcano, S.E. Iceland : a window on Quaternary climate change

Öræfajökull is an ice-capped stratovolcano situated in the south east of Iceland which has developed throughout the mid to late Quaternary. It has erupted basaltic and rhyolitic lavas during interglacial and glacial periods, many of which display strong physical evidence of volcano-ice interaction. This makes Öræfajökull an ideal location to reconstruct terrestrial palaeo-environments. The area of Goðafjall and Hrútsfjall is one of a small number of rhyolitic depositional centres situated on the south west flanks of the volcano and is the first rhyolitic area of Öræfajökull to be mapped in detail.The relatively high K content of the rhyolitic units make them good candidates for 40Ar/39Ar dating, yielding eruption ages that provide a temporal constraint on the development of the stratovolcano. 40Ar/39Ar dating of young rocks (<1 My) is challenging and many of the samples were found to contain both excess and atmospheric argon. A small number exhibited a fractionated argon source with a sub-atmospheric 40Ar/36Ar ratio that could not be explained by a single episode of mass fractionation. Soret thermal diffusion has been suggested as a possible mechanism for fractionation, although further investigation is required.Two dominant rhyolite eruptions have been identified by detailed field mapping supported by the geochemical application of chemostratigraphy. The stratigraphically lower group of lavas outcrop between 100 to 380 m.a.s.l. and were erupted subaerially into a relatively ice-free environment at the base of the edifice. A 40Ar/39Ar age of 202 ± 9 ka implies that eruption occurred during the interglacial MIS 7. Conversely the upper group of lavas show strong evidence of volcano-ice interaction, suggesting that they were erupted subglacially and confined by ice with a minimum ice surface elevation of at least 800 m.a.s.l. These lavas yield a 40Ar/39Ar age of 116 ± 14 ka, which implies that eruption occurred during the transitional period between the MIS5e interglacial and colder sub-stages prior to MIS 4.At least two further glacial advances have occurred since the emplacement of the subglacial rhyolite unit. In addition, an ice confined trachydacite flow from the Vatnafjall ridge situated 20 km north east of Goðafjall has also been dated yielding a 40Ar/39Ar age of 95 ± 7 k. This lava was emplaced at an elevation of over 700 m in the presence of an adjacent valley fill glacier was at least 700 m thick.Ice thickness has varied dramatically throughout the evolution of Öræfajökull and glacial erosion has played an important role in its topographic development.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Non-target by-catch in the Maltese bluefin tuna (Thunnus thynnus) longline fishery (Central Mediterranean)

The Bluefin Tuna longline fishery is one of the most important pelagic fisheries in the Mediterranean but recently there has been increasing concern about the catches of non-target species. This study presents an assessment of the non-target by-catch from the Maltese Bluefin Tuna longline fleet and examines the effect of various environmental and spatiotemporal factors on non-target species catch rates. Field observations were made during 85 fishing days. In terms of number, Bluefin Tuna comprised a relatively small portion of the total catch while the Loggerhead Turtle (Caretta caretta) was the predominant by-catch species. Catch Per Unit Effort (CPUE) was calculated in terms of weight (kg/1000hooks/hr) and number (no/1000hooks/hr) for all the species caught. General Linear Mixed Models (GLMMs) were applied to examine the effect of environmental and spatiotemporal variables on non-target bycatch CPUE. The model for CPUE (number) was not found to be significant. Date, lunar cycle, species and longitude were found to be significantly correlated with CPUE (weight). The results of this study suggests the need for the continual implementation of mitigation measures to minimise the impacts of fishing activities on threatened non-target species in the Mediterranean.peer-reviewe

When Autumn Comes Around

Silhouette of man and woman with orange leaves in backgroundhttps://scholarsjunction.msstate.edu/cht-sheet-music/6704/thumbnail.jp

X-ray enabled MOCASSIN: a 3D code for photoionized media

We present a new version of the fully 3D photoionization and dust radiative transfer code, MOCASSIN, that uses a Monte Carlo approach for the transfer of radiation. The X-ray enabled MOCASSIN allows a fully geometry independent description of low-density gaseous environments strongly photoionized by a radiation field extending from radio to gamma rays. The code has been thoroughly benchmarked against other established codes routinely used in the literature, using simple plane parallel models designed to test performance under standard conditions. We show the results of our benchmarking exercise and discuss applicability and limitations of the new code, which should be of guidance for future astrophysical studies with MOCASSIN.Comment: Accepted for publication in ApJS 9 pages, 5 figure

Glacier velocities and dynamic ice discharge from the Queen Elizabeth Islands, Nunavut, Canada

Recent studies indicate an increase in glacier mass loss from the Canadian Arctic Archipelago as a result of warmer summer air temperatures. However, no complete assessment of dynamic ice discharge from this region exists. We present the first complete surface velocity mapping of all ice masses in the Queen Elizabeth Islands and show that these ice masses discharged ~2.6 ± 0.8 Gt a−1 of ice to the oceans in winter 2012. Approximately 50% of the dynamic discharge was channeled through non surge-type Trinity and Wykeham Glaciers alone. Dynamic discharge of the surge-type Mittie Glacier varied from 0.90 ± 0.09 Gt a−1 during its 2003 surge to 0.02 ± 0.02 Gt a−1 during quiescence in 2012, highlighting the importance of surge-type glaciers for interannual variability in regional mass loss. Queen Elizabeth Islands glaciers currently account for ~7.5% of reported dynamic discharge from Arctic ice masses outside Greenland.We thank NSERC, Canada Foundation for Innovation, Ontario Research Fund, ArcticNet, Ontario Graduate Scholarship, University of Ottawa and the NSERC Canada Graduate Scholarship for funding. RADARSAT-2 data were provided by MacDonald, Dettwiler and Associates under the RADARSAT-2 Government Data Allocation administrated by the Canadian Space Agency. Support to DB is provided through the Climate Change Geosciences Program, Earth Sciences Sector, Natural Resources Canada (ESS Contribution #20130293). We also acknowledge support from U.K NERC for grants R3/12469 and NE/K004999 to JAD.This is the accepted version of an article published in Geophysical Research Letters. An edited version of this paper was published by AGU. Copyright (2014) American Geophysical Union. The final version is available at http://onlinelibrary.wiley.com/doi/10.1002/2013GL058558/abstract;jsessionid=6A3AD907C4383DA5D4E20C4924D6EC18.f02t02

Development of Crop.LCA, an adaptable screening life cycle assessment tool for agricultural systems: a Canadian scenario assessment

There is an increasing demand for sustainable agricultural production as part of the transition towards a globally sustainable economy. To quantify impacts of agricultural systems on the environment, life cycle assessment (LCA) is ideal because of its holistic approach. Many tools have been developed to conduct LCAs in agriculture, but they are not publicly available, not open-source, and have a limited scope. Here, a new adaptable open-source tool (Crop.LCA) for carrying out LCA of cropping systems is presented and tested in an evaluation study with a scenario assessment of 4 cropping systems using an agroecosystem model (DNDC) to predict soil GHG emissions. The functional units used are hectares (ha) of land and gigajoules (GJ) of harvested energy output, and 4 impact categories were evaluated: cumulative energy demand (CED), 100-year global warming potential (GWP), eutrophication and acidification potential. DNDC was used to simulate 28 years of cropping system dynamics, and the results were used as input in Crop.LCA. Data were aggregated for each 4-year rotation and statistically analyzed. Introduction of legumes into the cropping system reduced CED by 6%, GWP by 23%, and acidification by 19% per ha. These results highlight the ability of Crop.LCA to capture cropping system characteristics in LCA, and the tool constitutes a step forward in increasing the accuracy of LCA of cropping systems as required for bio-economy system assessments. Furthermore, the tool is open-source, highly transparent and has the necessary flexibility to assess agricultural systems

Development of Crop.LCA, an adaptable screening life cycle assessment tool for agricultural systems: a Canadian scenario assessment

There is an increasing demand for sustainable agricultural production as part of the transition towards a globally sustainable economy. To quantify impacts of agricultural systems on the environment, life cycle assessment (LCA) is ideal because of its holistic approach. Many tools have been developed to conduct LCAs in agriculture, but they are not publicly available, not open-source, and have a limited scope. Here, a new adaptable open-source tool (Crop.LCA) for carrying out LCA of cropping systems is presented and tested in an evaluation study with a scenario assessment of 4 cropping systems using an agroecosystem model (DNDC) to predict soil GHG emissions. The functional units used are hectares (ha) of land and gigajoules (GJ) of harvested energy output, and 4 impact categories were evaluated: cumulative energy demand (CED), 100-year global warming potential (GWP), eutrophication and acidification potential. DNDC was used to simulate 28 years of cropping system dynamics, and the results were used as input in Crop.LCA. Data were aggregated for each 4-year rotation and statistically analyzed. Introduction of legumes into the cropping system reduced CED by 6%, GWP by 23%, and acidification by 19% per ha. These results highlight the ability of Crop.LCA to capture cropping system characteristics in LCA, and the tool constitutes a step forward in increasing the accuracy of LCA of cropping systems as required for bio-economy system assessments. Furthermore, the tool is open-source, highly transparent and has the necessary flexibility to assess agricultural systems