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Obrebski M J, Ardhuin F, Stutzmann E, Schimmel M, . (2012). How moderate sea states can generate loud seismic noise in the deep ocean
. Geophysical Research Letters, 39(11), L11601–.
Abstract: The location of oceanic sources of the micrometric ground displacement recorded at land stations in the 0.10.3 Hz frequency band (double frequency microseisms) is still poorly known. Here we use one particularly strong noise event in the Pacific to show that small swells from two distant storms can be a strong deep-water source of seismic noise, dominating temporarily the signals recorded at coastal seismic stations. Our interpretation is based on the analysis of noise polarization recorded all around the source, and the good fit achieved for this event and year-round between observed and modeled seismic data. The model further suggests that this is a typical source of these infrequent loud noise bursts, which supports previous inconclusive evidences of the importance of such sources. This new knowledge based on both modeling and observations will expand today's limits on the use of noise for climate studies and seismic imaging.
Keywords: microseisms, polarization analysis, wave model, 4215 Climate and interannual variability, 4255 Numerical modeling, 4560 Surface waves and tides, 7220 Oceanic crust, 7255 Surface waves and free oscillations,
Programme: 133
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Schimmel M, Stutzmann E, Ardhuin F, Gallart J, . (2011). Polarized Earth's ambient microseismic noise
. 1525-2027, 12(7), Q07014–.
Abstract: We quantify, analyze, and characterize the frequency-dependent microseismic noise recorded by worldwide distributed seismic stations. Microseismic noise is generated through the interaction of ocean waves. It is the strongest ambient noise, and it is observed everywhere on Earth. We introduce a new approach which permits us to detect polarized signals in the time-frequency domain and which we use to characterize the microseismic noise. We analyze 7 years of continuous seismograms from the global GEOSCOPE network. Microseisms are dominated by Rayleigh waves, and we therefore focus on elliptically polarized signals. The polarized signals are detected in the time-frequency domain through a degree of polarization measure. We design polarization spectra and show that microseismic noise is more strongly polarized than noise in other frequency bands. This property is used to measure the directions of the polarized noise at individual stations as a function of time and frequency. Seasonal variations are found for the back azimuths and for the number of polarized signals at many stations. We show that the back azimuth directions are robust measurements that point toward the source areas computed from ocean wave models.
Keywords: microseismic noise, polarization, primary and secondary microseisms, seismology, 7255 Surface waves and free oscillations, 7299 General or miscellaneous,
Programme: 133
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. (2012). Comparative phylogeography of three trematomid fishes reveals contrasting genetic structure patterns in benthic and pelagic species
. Marine Genomics, 8, 23–34.
Abstract: Population genetics patterns of marine fish in general and of Southern Ocean fish in particular range from virtual panmixia over ocean-wide scale to deeply fragmented populations. However the causes underlying these different patterns are not properly understood. In this paper, we tested the hypotheses that population connectivity is positively related to a combination of life history traits, namely duration of pelagic larval period and the tendency towards pelagic life style in the adulthood. To do so, we analysed the variability of six microsatellite and one mitochondrial marker (cytochrome b) in three Southern Ocean fish species (Trematomus newnesi, Trematomus hansoni and Trematomus bernacchii). They share a recent common ancestor but notably differ in their duration of pelagic larval period as well as pelagic versus benthic lifestyle. We sampled over a range of more than 5000 km for all three species and used a number of population genetics tools to investigate past and contemporary levels of connectivity. All species experienced population fluctuations, but coalescent simulations suggested that contemporary populations are in migration-drift equilibrium. Although global FST values were rather low, a significant population structure separated the High-Antarctic from the Peninsular regions in all species. The level of genetic differentiation was much lower in the pelagic versus benthic species. Present data suggest that past and present genetic structuring in the Southern Ocean are indeed related with the ecological traits of Antarctic fish, however the relative importance of individual factors remains unclear.
Keywords: Microsatellite markers, Mitochondrial, Larval duration, Glaciations, Notothenioidei, Life history,
Programme: 1142
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Dewar Meagan L, Arnould John P Y, Dann Peter, Trathan Phil, Groscolas Rene, Smith Stuart, . (2013). Interspecific variations in the gastrointestinal microbiota in penguins
. MicrobiologyOpen, 2(1), 195–204.
Abstract: Despite the enormous amount of data available on the importance of the gastrointestinal (GI) microbiota in vertebrate (especially mammals), information on the GI microbiota of seabirds remains incomplete. As with many seabirds, penguins have a unique digestive physiology that enables them to store large reserves of adipose tissue, protein, and lipids. This study used quantitative real-time polymerase chain reaction (qPCR) and 16S rRNA gene pyrosequencing to characterize the interspecific variations of the GI microbiota of four penguin species: the king, gentoo, macaroni, and little penguin. The qPCR results indicated that there were significant differences in the abundance of the major phyla Firmicutes, Bacteroides, Actinobacteria, and Proteobacteria. A total of 132,340, 18,336, 6324, and 4826 near full-length 16S rRNA gene sequences were amplified from fecal samples collected from king, gentoo, macaroni, and little penguins, respectively. A total of 13 phyla were identified with Firmicutes, Bacteroidetes, Proteobacteria, and Fusobacteria dominating the composition; however, there were major differences in the relative abundance of the phyla. In addition, this study documented the presence of known human pathogens, such as Campylobacter, Helicobacter, Prevotella, Veillonella, Erysipelotrichaceae, Neisseria, and Mycoplasma. However, their role in disease in penguins remains unknown. To our knowledge, this is the first study to provide an in-depth investigation of the GI microbiota of penguins.
Keywords: Microbiota, penguins, pyrosequencing, qPCR,
Programme: 119
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. (2010). ASTEP South: an Antarctic Search for Transiting ExoPlanets around the celestial south pole (Vol. 511).
Abstract: Context. The Concordia base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3-month long night during the Antarctic winter, favorable weather conditions, and low scintillation. Aims. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project to discover transiting planets and understand the limits of visible photometry from the Concordia site. Methods. ASTEP South is the first phase of the ASTEP project. The instrument is a fixed 10 cm refractor with a 4k $\times $ 4k CCD camera in a thermalized box, pointing continuously a $3.88\times 3.88\ensuremath{^{\circ}} $2 field of view centered on the celestial south pole. We describe the project and report results of a preliminary data analysis. Results. ASTEP South became fully functional in June 2008 and obtained 1592 hours of data during the 2008 Antarctic winter. The data are of good quality but the analysis has to account for changes in the PSF (point spread function) due to rapid ground seeing variations and instrumental effects. The pointing direction is stable within 10 arcsec on a daily timescale and drifts by only 34 arcsec in 50 days. A truly continuous photometry of bright stars is possible in June (the noon sky background peaks at a magnitude $R \approx 15~\rm arcsec^{-2}$ on June 22), but becomes challenging in July (the noon sky background magnitude is $R \approx 12.5~\rm arcsec^{-2}$ on July 20). The weather conditions are estimated from the number of stars detected in the field. For the 2008 winter, the statistics are between 56.3% and 68.4% of excellent weather, 17.9% to 30% of veiled weather (when the probable presence of thin clouds implies a lower number of detected stars) and 13.7% of bad weather. Using these results in a probabilistic analysis of transit detection, we show that the detection efficiency of transiting exoplanets in one given field is improved at Dome C compared to a temperate site such as La Silla. For example we estimate that a year-long campaign of 10 cm refractor could reach an efficiency of 69% at Dome C versus 45% at La Silla for detecting 2-day period giant planets around target stars from magnitude 10 to 15. The detection efficiency decreases for planets with longer orbital periods, but in relative sense it is even more favorable to Dome C. Conclusions. This shows the high potential of Dome C for photometry and future planet discoveries.
Keywords: methods: observational – methods: data analysis – site testing – techniques: photometri
Programme: 1066
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Philippe Ricaud, Paolo Grigioni, Romain Roehrig, Pierre Durand, Dana E. Veron. (2020). Trends in Atmospheric Humidity and Temperature above Dome C, Antarctica Evaluated from Observations and Reanalyses (Vol. 11). Bachelor's thesis, , .
Keywords: meteorological reanalyses microwave radiometer precipitable water radiosondes SAM index temperature trends
Programme: 910
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. (2011). Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells (Arctica islandica) and their function as paleotemperature proxies
. Palaeogeography, Palaeoclimatology, Palaeoecology, 302(12), 52–64.
Abstract: The Sr/Ca and Mg/Ca ratios of many biogenic skeletons provide useful paleotemperature estimates. As yet however, it has remained largely impossible to obtain such information from bivalve shells. In the present study, metal-to-calcium values in the hinge plate (aragonite, outer shell layer) of four ontogenetically old (85 to 374 year-old) specimens of the long-lived bivalve, Arctica islandica, were measured on a LAICPMS. The shells were collected alive in 1868, 1986 and 2003 from three different localities around Iceland. With increasing ontogenetic age and decreasing growth rate, a distinct trend toward increasing Sr/Ca (max. 5.17 mmol/mol) and Mg/Ca values (max. 0.89 mmol/mol) and greater variance were observed. Three potential explanations for these trends include a reduced capacity for element selection due to cell ageing, changing metabolism and/or a relative increase in the number of organic-rich (= Mg-rich) and organic-poor (= Sr-rich) shell portions through ontogeny. Partition coefficients however, remained far below 1, indicating that physiology exerted a strong control over the element partitioning between the shells and the ambient water. After mathematical elimination of these vital effects, residuals exhibited a highly significant negative correlation (e.g., age-detrended Sr/Ca data: R = 0.64, R2 = 0.41, p < 0.0001, growth rate-detrended Mg/Ca data: R = 0.52, R2 = 0.27, p < 0.0001) with sea surface temperature. These results are in good agreement with results obtained from the precipitation of abiogenic aragonite. The results of the present study can help to develop new techniques to extract environmental signals from the metal-to-calcium ratios of bivalve shells.
Keywords: Metal-to-calcium ratio, Bivalve shell, Vital effect, Sea surface temperature, Longevity,
Programme: 1090
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. (2020). Snow microbiome functional analyses reveal novel aspects of microbial metabolism of complex organic compounds (Vol. 9).
Abstract: Microbes active in extreme cold are not as well explored as those of other extreme environments. Studies have revealed a substantial microbial diversity and identified cold-specific microbiome molecular functions. We analyzed the metagenomes and metatranscriptomes of 20 snow samples collected in early and late spring in Svalbard, Norway using mi-faser, our read-based computational microbiome function annotation tool. Our results reveal a more diverse microbiome functional capacity and activity in the early- vs. late-spring samples. We also find that functional dissimilarity between the same-sample metagenomes and metatranscriptomes is significantly higher in early than late spring samples. These findings suggest that early spring samples may contain a larger fraction of DNA of dormant (or dead) organisms, while late spring samples reflect a new, metabolically active community. We further show that the abundance of sequencing reads mapping to the fatty acid synthesis-related microbial pathways in late spring metagenomes and metatranscriptomes is significantly correlated with the organic acid levels measured in these samples. Similarly, the organic acid levels correlate with the pathway read abundances of geraniol degradation and inversely correlate with those of styrene degradation, suggesting a possible nutrient change. Our study thus highlights the activity of microbial degradation pathways of complex organic compounds previously unreported at low temperatures.
Keywords: metagenome metatranscriptome mi-faser snow microbiome
Programme: 1192
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. (2020). The metabolic cost of subcutaneous and abdominal rewarming in king penguins after long-term immersion in cold water (Vol. 91).
Keywords: Metabolism Normothermia Rewarming Subcutaneous temperature
Programme: 394
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Koubbi Philippe, Hulley Percy-Alexander, Pruvost Patrice, Henri Pauline, Labat Jean-Philippe, Wadley Victoria, Hirano Daisuke, Moteki Masato, . (2011). Size distribution of meso- and bathypelagic fish in the Dumont dUrville Sea (East Antarctica) during the CEAMARC surveys
. Polar Science, 5(2), 195–210.
Keywords: Mesopelagic, Bathypelagic, Southern Ocean, Myctophids, East Antarctica,
Programme: 1142
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