Examinando por Autor "MacDonell, Shelley"

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    Black carbon and other light-absorbing impurities in snow in the Chilean Andes
    (Nature Publishing Group, 2019-12) Rowe, Penny M.; Cordero, Raul R.; Warren, Stephen G.; Stewart, Emily; Doherty, Sarah J.; Pankow, Alec; Schrempf, Michael; Casassa, Gino; Carrasco, Jorge; Pizarro, Jaime; MacDonell, Shelley; Damiani, Alessandro; Lambert, Fabrice; Rondanelli, Roberto; Huneeus, Nicolas; Fernandoy, Francisco; Neshyba, Steven
    Vertical profiles of black carbon (BC) and other light-absorbing impurities were measured in seasonal snow and permanent snowfields in the Chilean Andes during Austral winters 2015 and 2016, at 22 sites between latitudes 18°S and 41°S. The samples were analyzed for spectrally-resolved visible light absorption. For surface snow, the average mass mixing ratio of BC was 15 ng/g in northern Chile (18–33°S), 28 ng/g near Santiago (a major city near latitude 33°S, where urban pollution plays a significant role), and 13 ng/g in southern Chile (33–41°S). The regional average vertically-integrated loading of BC was 207 µg/m 2 in the north, 780 µg/m 2 near Santiago, and 2500 µg/m 2 in the south, where the snow season was longer and the snow was deeper. For samples collected at locations where there had been no new snowfall for a week or more, the BC concentration in surface snow was high (~10–100 ng/g) and the sub-surface snow was comparatively clean, indicating the dominance of dry deposition of BC. Mean albedo reductions due to light-absorbing impurities were 0.0150, 0.0160, and 0.0077 for snow grain radii of 100 µm for northern Chile, the region near Santiago, and southern Chile; respective mean radiative forcings for the winter months were 2.8, 1.4, and 0.6 W/m 2 . In northern Chile, our measurements indicate that light-absorption by impurities in snow was dominated by dust rather than BC. © 2019, The Author(s).
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    Dinámica glaciar de la Plataforma de Hielo Müller, Antártica
    (Universidad Andrés Bello, 2022) Prado Sepúlveda, Alberto Eduardo; Fernandoy Pedreros, Francisco; Casanova Pino, Edgardo; MacDonell, Shelley; González, Inti; Facultad de Ingeniería; Escuela de Ciencias de la Tierra
    La Plataforma de Hielo Müller es la plataforma de hielo más septentrional de la Peninsula Antartica Occidental. Las plataformas de hielo cumplen un rol fundamental en la estabilización de las capas de hielo de la Antártica al funcionar como un tapón para los flujos de hielo que llegan al océano. En los últimos años las plataformas de hielo han presentado retrocesos significativos como el caso de la Plataforma Larsen C o colapsos como la Plataforma Jones. Trabajos anteriores indican que la plataforma presenta dos flujos de hielo con velocidades de 0.5 a 1.6 metros por día. Utilizando técnicas de teledetección se realizó un análisis de velocidades de hielo durante las temporadas de verano polar antártico con tal de determinar dinámica de la Plataforma de Hielo Müller y de los flujos de hielo que la alimentan. Se determinó que los flujos presentan comportamientos distintos, uno esporádico y el otro continuo. Los resultados sugieren que el comportamiento de los flujos de hielo junto a factores estructurales y meteorológicos controlan el retroceso de la plataforma.
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    Elemental and Mineralogical Composition of the Western Andean Snow (18°S–41°S)
    (Nature Publishing Group, 2019-12) Alfonso, Juan A.; Cordero, Raul R.; Rowe, Penny M.; Neshyba, Steven; Casassa, Gino; Carrasco, Jorge; MacDonell, Shelley; Lambert, Fabrice; Pizarro, Jaime; Fernandoy, Francisco; Feron, Sarah; Damiani, Alessandro; Llanillo, Pedro; Sepulveda, Edgardo; Jorquera, Jose; Garcia, Belkis; Carrera, Juan M.; Oyola, Pedro; Kang, Choong-Min
    The snowpack is an important source of water for many Andean communities. Because of its importance, elemental and mineralogical composition analysis of the Andean snow is a worthwhile effort. In this study, we conducted a chemical composition analysis (major and trace elements, mineralogy, and chemical enrichment) of surface snow sampled at 21 sites across a transect of about 2,500 km in the Chilean Andes (18–41°S). Our results enabled us to identify five depositional environments: (i) sites 1–3 (in the Atacama Desert, 18–26°S) with relatively high concentrations of metals, high abundance of quartz and low presence of arsenates, (ii) sites 4–8 (in northern Chile, 29–32°S) with relatively high abundance of quartz and low presence of metals and arsenates, (iii) sites 9–12 (in central Chile, 33–35°S) with anthropogenic enrichment of metals, relatively high values of quartz and low abundance of arsenates, (iv) sites 13–14 (also in central Chile, 35–37°S) with relatively high values of quartz and low presence of metals and arsenates, and v) sites 15–21 (in southern Chile, 37–41°S) with relatively high abundance of arsenates and low presence of metals and quartz. We found significant anthropogenic enrichment at sites close to Santiago (a major city of 6 million inhabitants) and in the Atacama Desert (that hosts several major copper mines). © 2019, The Author(s).