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Hajo Eicken, Finn Danielsen, Josephine-Mary Sam, Maryann Fidel, Noor Johnson, Michael K Poulsen, Olivia A Lee, Katie V Spellman, Lisbeth Iversen, Peter Pulsifer, Martin Enghoff. (2021). Connecting Top-Down and Bottom-Up Approaches in Environmental Observing (Vol. 71). Bachelor's thesis, , .
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Guillot T. (2021). Science of temperate exoplanets: The lessons from Juno. Bachelor's thesis, , .
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. (2021). Exploring the Microdiversity Within Marine Bacterial Taxa: Toward an Integrated Biogeography in the Southern Ocean (Vol. 12).
Abstract: Most of the microbial biogeographic patterns in the oceans have been depicted at the whole community level, leaving out finer taxonomic resolution (i.e., microdiversity) that is crucial to conduct intra-population phylogeographic study, as commonly done for macroorganisms. Here, we present a new approach to unravel the bacterial phylogeographic patterns combining community-wide survey by 16S rRNA gene metabarcoding and intra-species resolution through the oligotyping method, allowing robust estimations of genetic and phylogeographic indices, and migration parameters. As a proof-of-concept, we focused on the bacterial genus Spirochaeta across three distant biogeographic provinces of the Southern Ocean; maritime Antarctica, sub-Antarctic Islands, and Patagonia. Each targeted Spirochaeta operational taxonomic units were characterized by a substantial intrapopulation microdiversity, and significant genetic differentiation and phylogeographic structure among the three provinces. Gene flow estimations among Spirochaeta populations support the role of the Antarctic Polar Front as a biogeographic barrier to bacterial dispersal between Antarctic and sub-Antarctic provinces. Conversely, the Antarctic Circumpolar Current appears as the main driver of gene flow, connecting sub-Antarctic Islands with Patagonia and maritime Antarctica. Additionally, historical processes (drift and dispersal limitation) govern up to 86% of the spatial turnover among Spirochaeta populations. Overall, our approach bridges the gap between microbial and macrobial ecology by revealing strong congruency with macroorganisms distribution patterns at the populational level, shaped by the same oceanographic structures and ecological processes.
Programme: 1044
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Guillaume Hubert. (2021). Analyses of the Secondary Cosmic Ray using CCD camera in high-altitude observatories and Antarctica stations (Vol. 395).
Abstract: Charge-Coupled Device (CCD) and Array Pixel Sensors (APS) can be used to image radiation-induced energy deposition. The high sensitivity of depleted silicon to ionizing radiation constitutes an opportunity to investigate radiation effects while it is a nuisance to astronomer activities. CCD and APS provide a better combination of spatial and intensity resolution for radiation events than other available types of detector. This paper proposes to analyze radiation events observed in the CCD camera and more specifically analyses of charge deposition spectra and spatially extensive events. Measurements were performed in the Pic du Midi from 2011 to 2015 and in the Concordia Antarctica station since 2018. Coupled transport models (i.e. particle transport and charge transport in semiconductors) allow investigating contributions to charge collection spectra as a function of the particle nature, i.e. neutron, proton and muon. Coupled measurements and simulations allow to access to the detected secondary CR flux and the charge deposition pattern. Results showed that high charge level events seen on atmospheric sites can be considered as hadronic component (mainly neutrons and protons) while low charge levels and punctual events are induced by muons which are able to generate up to 3 fC in the CCD camera. Hence, thanks to double level of measurement sites, muon discrimination from other secondary particles has been investigated. Cross-comparison analyses based on CCD and neutron spectrometers operated in both station/observatory investigate secondary CR dynamic.
Keywords: Array Pixel Sensors (APS) Charge-Coupled Device (CCD)
Programme: 1112
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Guillaume Hubert. (2021). Continuously Measurements of Energy Spectra of Cosmic-Ray-induced-neutrons on the Concordia Antarctic Station for the period 2015-2021 (Vol. 395).
Abstract: The CHINSTRAP (Continuous High-altitude Investigation of the Neutron Spectra for Terrestrial Radiation Antarctic Project) supported by the French Polar Agency (IPEV) aims at recording cosmic-ray (CR) induced-neutron spectra at the Concordia station since December 2015. The neutron spectrometer measures the neutron spectrum over a wide energy range from meV up to tens of GeV with a short time resolution. Several parameters can influence the measurement, including systematic and environmental effects such as the atmospheric pressure, the hydrometric environment close to the instrument and the atmospheric water vapor. This paper presents CR induced neutrons measurements analyses from 2015 to 2021 in Concordia, integrating corrections to take into account environmental and systematic effects. Long-term and short-term analyses are proposed, applied to count rate, fluxes and spectra. A last part investigates the contribution of modelling to data analyses and the ability to deduce the solar modulation from neutron spectra and the radiation field extrapolation using nuclear transport in atmosphere. An underlying objective is also to improve physical models allowing analyses of continuous and simultaneously measurements of CR induced neutrons spectra.
Programme: 1112
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. (2021). Food source diversity, trophic plasticity, and omnivory enhance the stability of a shallow benthic food web from a high-Arctic fjord exposed to freshwater inputs (Vol. 66).
Abstract: Under climate change, many Arctic coastal ecosystems receive increasing amounts of freshwater, with ecological consequences that remain poorly understood. In this study, we investigated how freshwater inputs may affect the small-scale structure of benthic food webs in a low-production high-Arctic fjord (Young Sound, NE Greenland). We seasonally sampled benthic invertebrates from two stations receiving contrasting freshwater inputs: an inner station exposed to turbid and nutrient-depleted freshwater flows and an outer station exposed to lower terrestrial influences. Benthic food web structure was described using a stable isotope approach (?13C and ?15N), Bayesian models, and community-wide metrics. The results revealed the spatially and temporally homogeneous structure of the benthic food web, characterized by high trophic diversity (i.e., a wide community isotopic niche). Such temporal stability and spatial homogeneity mirrors the high degree of trophic plasticity and omnivory of benthic consumers that allows the maintenance of several carbon pathways through the food web despite different food availability. Furthermore, potential large inputs of shelf organic matter together with local benthic primary production (i.e., macroalgae and presumably microphytobenthos) may considerably increase the stability of the benthic food web by providing alternative food sources to locally runoff-impacted pelagic primary production. Future studies should assess beyond which threshold limit a larger increase in freshwater inputs might cancel out these stability factors and lead to marked changes in Arctic benthic ecosystems.
Programme: 1158
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. (2021).
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Grégoire Mureau. (2021). Étude des impacts des événements extrêmes sur le massif dunaire de la plage de Sanvík (Islande) (Vol. https://www-iuem.univ-brest.fr/pops/attachments/26).
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. (2021). (Vol. 118).
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. (2021). Comparison of interferometer calibration techniques for improved SuperDARN elevation angles (Vol. 28).
Abstract: The high frequency radars in the Super Dual Auroral Radar Network (SuperDARN) estimate the elevation angles of returned backscatter using interferometric techniques. These elevation angles allow the ground range to the scattering point to be estimated, which is crucial for the accurate geolocation of ionospheric measurements. For elevation angles to be accurately estimated, it is important to calibrate the interferometer measurements by determining the difference in the signal time delays caused by the difference in the electrical path lengths from the main array and the interferometer array to the point at which the signals are correlated. This time delay is known as tdiff. Several methods have been proposed to estimate tdiff using historical observations; these methods are summarised in this paper. Comparisons of the tdiff estimates from the different calibration methods are presented and sources of uncertainty discussed. The effect of errors in the estimated tdiff value on the accuracy of geolocation is evaluated and discussed. The paper concludes with a series of recommendations for both scientific SuperDARN data users and SuperDARN radar operators.
Keywords: Geolocation HF radar Interferometer calibration Ionosphere SuperDARN
Programme: 312
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