Alice Gadea, Pierre Le Pogam, Grichka Biver, Joël Boustie, Anne-Cécile Le Lamer, Françoise Le Dévéhat, Maryvonne Charrier. (2017). Which Specialized Metabolites Does the Native Subantarctic Gastropod Notodiscus hookeri Extract from the Consumption of the Lichens Usnea taylorii and Pseudocyphellaria crocata? (Vol. 22).
Abstract: Notodiscus hookeri is the only representative of terrestrial gastropods on Possession Island and exclusively feeds on lichens. The known toxicity of various lichen metabolites to plant-eating invertebrates led us to propose that N. hookeri evolved means to protect itself from their adverse effects. To validate this assumption, the current study focused on the consumption of two lichen species: Usnea taylorii and Pseudocyphellaria crocata. A controlled feeding experiment was designed to understand how the snail copes with the unpalatable and/or toxic compounds produced by these lichen species. The occurrence of two snail ecophenotypes, represented by a mineral shell and an organic shell, led to address the question of a metabolic response specific to the phenotype. Snails were fed for two months with one of these lichens and the chemical profiles of biological samples of N. hookeri (i.e., crop, digestive gland, intestine, and feces) were established by HPLC-DAD-MS and compared to that of the lichens. N. hookeri appears as a generalist lichen feeder able to consume toxic metabolite-containing lichens, independently of the ecophenotype. The digestive gland did not sequester lichen metabolites. The snail metabolism might be based on four non-exclusive processes according to the concerned metabolites (avoidance, passive transport, hydrolysis, and excretion).
Keywords: Notodiscus hookeri Pseudocyphellaria crocata Usnea taylorii chemical ecology Crozet Archipelago lichens snails
Programme: 136
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Aline Peltier, Arnaud Chulliat. (2010). On the feasibility of promptly producing quasi-definitive magnetic observatory data (Vol. 62).
Abstract: Magnetic observatories currently distribute two types of data: preliminary data, available in less than 72 hrs in the case of INTERMAGNET observatories, and definitive baseline-corrected data, produced only once a year. Several users and groups of users have expressed the need for baseline-corrected observatory data produced in a continuous manner. The main applications for such quasi-definitive data include geomagnetic field modeling and the calculation of geomagnetic activity indices. We present an original method for producing quasi-definitive data at the end of each calendar month using temporary baselines. Preliminary and definitive data at nine INTERMAGNET observatories are used to test this method, simulating the production of quasi-definitive data throughout the year 2008. The temporary baselines obtained are very close to the definitive ones, except during the last few days of each time interval. The means and standard deviations of the differences between quasi-definitive and definitive data do not exceed 0.3 nT, well below the current INTERMAGNET standard of accuracy. This result demonstrates the feasibility of promptly producing quasi-definitive data at most magnetic observatories of INTERMAGNET type.
Keywords: baseline data processing geomagnetic modeling Magnetic observatory quasi-definitive data
Programme: 139
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Alison F. Banwell, Nander Wever, Devon Dunmire, Ghislain Picard. (2023). Quantifying Antarctic-Wide Ice-Shelf Surface Melt Volume Using Microwave and Firn Model Data: 1980 to 2021 (Vol. 50).
Abstract: Antarctic ice-shelf stability is threatened by surface melt, which has been implicated in several ice-shelf collapse events over recent decades. Here, we first analyze cumulative days of wet snow/ice status (“melt days”) for melt seasons from 1980 to 2021 over Antarctica's ice shelves using passive and active microwave satellite observations. As these observations do not directly reveal meltwater volumes, we calculate these using the physics-based multi-layer snow model SNOWPACK, driven by the global climate-reanalysis model Modern-Era Retrospective analysis for Research and Applications Version 2. We find a strong non-linear relationship between melt days and meltwater production volume. SNOWPACK's calculation of melt days shows agreement with observations of both cumulative days, and spatial and interannual variability. Highest melt rates are found on the Peninsula ice shelves, particularly in the 1992/1993 and 1994/1995 austral summers. Over all ice shelves, SNOWPACK calculates a small, but significant, decreasing trend in both annual melt days and meltwater production volume over the 41 years.
Programme: 1110
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Alison F. Banwell, Rajashree Tri Datta, Rebecca L. Dell, Mahsa Moussavi, Ludovic Brucker, Ghislain Picard, Christopher A. Shuman, Laura A. Stevens. (2021). The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula (Vol. 15).
Abstract: In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of distinctly lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer and scatterometer data, which are sensitive to meltwater on the ice shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (2013 to 2020) and Sentinel-2 (2017 to 2020), record volumes of surface meltwater ponding were also observed on the northern GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of ponded meltwater on 19 January. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ≥0 ∘C for anomalously long periods (55 to 90 h) from late November onwards, which limited meltwater refreezing. The sustained warm periods were likely driven by warm, low-speed (≤7.5 m s−1) northwesterly and northeasterly winds and not by foehn wind conditions, which were only present for 9 h total in the 2019/2020 melt season. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting.
Programme: 1110
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Alison Ming, V. Holly L. Winton, James Keeble, Nathan L. Abraham, Mohit C. Dalvi, Paul Griffiths, Nicolas Caillon, Anna E. Jones, Robert Mulvaney, Joël Savarino, Markus M. Frey, Xin Yang. (2020). Stratospheric Ozone Changes From Explosive Tropical Volcanoes: Modeling and Ice Core Constraints (Vol. 125).
Abstract: Major tropical volcanic eruptions have emitted large quantities of stratospheric sulfate and are potential sources of stratospheric chlorine although this is less well constrained by observations. This study combines model and ice core analysis to investigate past changes in total column ozone. Historic eruptions are good analogs for future eruptions as stratospheric chlorine levels have been decreasing since the year 2000. We perturb the preindustrial atmosphere of a chemistry-climate model with high and low emissions of sulfate and chlorine. The sign of the resulting Antarctic ozone change is highly sensitive to the background stratospheric chlorine loading. In the first year, the response is dynamical, with ozone increases over Antarctica. In the high HCl (2 Tg emission) experiment, the injected chlorine is slowly transported to the polar regions with subsequent chemical ozone depletion. These model results are then compared to measurements of the stable nitrogen isotopic ratio, , from a low snow accumulation Antarctic ice core from Dronning Maud Land (recovered in 2016–2017). We expect ozone depletion to lead to increased surface ultraviolet (UV) radiation, enhanced air-snow nitrate photochemistry and enrichment in in the ice core. We focus on the possible ozone depletion event that followed the largest volcanic eruption in the past 1,000 years, Samalas in 1257. The characteristic sulfate signal from this volcano is present in the ice core but the variability in dominates any signal arising from changes in ultraviolet from ozone depletion. Prolonged complete ozone removal following this eruption is unlikely to have occurred over Antarctica.
Keywords: Antarctica chemistry-climate modeling isotopes in ice cores ozone Samalas volcanic eruption
Programme: 1177
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Alix C. (2003). Sélection du bois d’arc par les thuléens de l’Arctique nord-américain : un choix dicté par la façonnage. In Au fil du bois : Définition des critères de sélection des bois d’oeuvre. Cahier des thèmes transversaux ArScAn III, 2001/2002, 204–213.
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Alix C. (2002). Acquisition, transformation et circulation des ressources ligneuses dans l’Arctique nord-américain (culture de Thulé). Contribution des données ethnographiques et archéologiques. Cahier des thèmes transversaux ArScAn II, 2001/2002, 114–116.
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Alix C. (2003). Wood Artifacts and Technology at Qitchauvik. In O. K. Mason, M. L. Ganley, M. Sweeney, C. Alix and V. Barber: Ipiutak Outlier – 1500 years old Qarigi on the Golovnin Lagoon. (Vol. 6).
Abstract: Golovin Heritage Field School 1992-2000. Final Report to the Shared Beringian He
Programme: 402
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Alix C. (2003). Wood Remains from the 2002 Excavation at Uivvaq, Cape Lisburne..
Abstract: In Mason O. K. (Ed. ) Uivvaq Heritage Project Field Season 2002 Final Report. Draft Report to Aglaq/CONAM GeoArch Alaska
Programme: 402
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Alix C. (2003). Preliminary Report. Ongoing study of the Deering wood collection..
Abstract: Northern Land Use Research Inc
Programme: 402
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