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Sacré N. (2020). Modélisation des réseaux trophiques dans les environnements marins côtiers des Iles Kerguelen.
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D. B. Green, S. Bestley, R. Trebilco, S. P. Corney, P. Lehodey, C. R. McMahon, C. Guinet, Mark A. Hindell. (2020). Modelled mid-trophic pelagic prey fields improve understanding of marine predator foraging behaviour (Vol. 43). Bachelor's thesis, , .
Abstract: Biophysical interactions are influential in determining the scale of key ecological processes within marine ecosystems. For oceanic predators, this means foraging behaviour is influenced by processes shaping the distribution of prey. However, oceanic prey is difficult to observe and its abundance and distribution is regionally generalised. We use a spatiotemporally resolved simulation model to describe mid-trophic prey distribution within the Southern Ocean and demonstrate insights that this modelled prey field provides into the foraging behaviour of a widely distributed marine predator, the southern elephant seal. From a five-year simulation of prey biomass, we computed climatologies of mean prey biomass (average prey conditions) and prey biomass variability (meso-scale variability). We also compiled spatially gridded metrics of seal density and diving behaviour from 13 yr of tracking data. We statistically modelled these metrics as non-linear functions of prey biomass (both mean and variability) and used these to predict seal distribution and behaviour. Our predictions were consistent with observations (R2adj = 0.23), indicating that seals aggregate in regions of high mesoscale activity where eddies concentrate prey. Here, seals dived deeper (R2marg = 0.12, R2cond = 0.51) and spent less time hunting (R2marg = 0.05, R2cond = 0.56), likely targeting deep but profitable prey patches. Seals generally avoided areas of low eddy activity where prey was likely dispersed. Most seals foraged south of the Subantarctic Front, despite north of the front exhibiting consistently high simulated prey biomasses. This likely reflects seal prey or habitat preferences, but also emphasises the importance of mesoscale prey biomass variability relative to regionally high mean biomass. This work demonstrates the value of coupling mechanistic representations of prey biomass with predator observations to provide insight into how biophysical processes combine to shape species distributions. This will be increasingly important for the robust prediction of species’ responses to rapid system change.
Keywords: ecosystem modelling kerguelen plateau micronekton predators prey interaction southern elephant seal Southern Indian Ocean
Programme: 109,1201
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Stefano Santini, Michele Dragoni. (2020). Moment rate of the 2018 Gulf of Alaska earthquake (Vol. 298).
Abstract: The 2018 Gulf of Alaska earthquake (Mw 7.9) occurred in a region of the Pacific plate southwest of the Alaskan subduction zone. The earthquake was a strike-slip event, with the hypocenter located at a depth of about 25 km and a seismic moment equal to 0.96 × 1021 Nm. Two observed moment rates have been obtained by the Geoscope Observatory, France, and by the United States Geological Survey (USGS). Both of them can be interpreted as due to the failure of two asperities on the fault surface. We consider a discrete fault model, with two asperities of different areas and strengths, and show that the observed moment rates can be reproduced by appropriate values of the model parameters, as inferred from the available data. A good fit to the observed moment rates is obtained by a sequence of three dynamic modes of the system, including a phase of simultaneous slip of the asperities. The two moment rates are however characterized by different initial conditions, in terms of different initial shear stress distributions on the fault. Shear stresses on the asperities are calculated as functions of time during the event and show a similar evolution in the two cases, but with different final values. The model results show that the presence of simultaneous asperity motion can significantly increase the seismic moment of a large earthquake.
Keywords: Asperity models Fault mechanics Nonlinear dynamical systems Seismic moment rates Theoretical seismology
Programme: 133
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Lorène Julia Marchand, Michèle Tarayre, Thomas Dorey, Yann Rantier, Françoise Hennion. (2020). Morphological variability of cushion plant Lyallia kerguelensis (Caryophyllales) in relation to environmental conditions and geography in the Kerguelen Islands: implications for cushion necrosis and climate change (Vol. 44). Bachelor's thesis, , .
Abstract: In recent decades, climate change has been faster in various parts of the world. Within species, to counter rapid climate changes shift of geographical area, individuals’ plastic responses or populations’ genetic adaptation might occur. The sub-Antarctic islands are subject to one of the most rapid climate changes on earth, with already visible impacts on native vegetation. Such might be the case of Lyallia kerguelensis a cushion plant strictly endemic to the Kerguelen Islands. In L. kerguelensis, necrotic parts were observed in cushions these last decades and possibly related to water stress. We analysed morphological variability of L. kerguelensis, including necrosis extent, across 19 populations spanning a wide range of environments across the Kerguelen Islands. Inter-population variations in the cushion surface area, shape and compactness were well explained by topography, degree of wind exposure, slope aspect, proportions of coarse sand and bare soil, and geographical distance between populations. All these variables are related to wind intensity and water availability. Moreover, in cushions with less than 10% necrosis in surface area, necrosis extent was positively correlated to soil sodium. Sodium availability might reduce the plant’s capacity for osmotic adjustment in face of other abiotic stresses, such as water stress. We conclude that cushion morphology may have the capacity to adjust to environmental variation, including aspects of climate change, but that cushion necrosis may be accelerated in the driest and most saline environments.
Programme: 1116
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Adam T. Devlin, Jiayi Pan, Hui Lin. (2020). Multi-Timescale Analysis of Tidal Variability in the Indian Ocean Using Ensemble Empirical Mode Decomposition (Vol. 125).
Abstract: Ocean tides have been observed to be changing worldwide for nonastronomical reasons, which can combine with rising mean sea level (MSL) to increase the long-term impact to coastal regions. Tides can also exhibit variability at shorter timescales, which may be correlated with short-term variability in MSL. This short-term coupling may yield higher peak water levels and increased impacts of exceedance events that may be equally significant as long-term sea level rise. Previous studies employed the tidal anomaly correlation (TAC) method to quantify the sensitivity of tides to MSL fluctuations at long-period (>20 years) tide gauges in basin-scale surveys of the Pacific and Atlantic Ocean, finding that TACs exist at most locations. The Indian Ocean also experiences significant sea level rise and tidal variability yet has been less studied due to a sparse network of tide gauges. However, since the beginning of the 21st century, more tide gauges have been established in a wider geographical range, bringing the possibility of better estimates of tidal and MSL variability. Here, we improve the TAC approach, using the ensemble empirical mode decomposition (EEMD) method to analyze tidal amplitudes and sea level at multiple frequency bands, allowing a more effective use of shorter record tide gauges and better understanding of multiple timescales of tidal variability. We apply this approach to 73 tide gauges in the Indian Ocean to better quantify tidal variability in these under-studied regions, finding that the majority of locations exhibit significant correlations of tides and MSL.
Keywords: Coastal risks Ensemble Empirical Mode Decomposition Indian Ocean Sea level variability Tidal evolution Tidal variability
Programme: 688
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J Mathurin, E Dartois, C Engrand, J Duprat, A Deniset- Besseau, A Dazzi, Y Kebukawa, T Noguchi, D Troadec. (2020). Nanometre-scale infrared chemical imaging (AFM-IR) of organic matter in ultra-carbonaceous Antarctic micrometeorites (UCAMMS) and future analyses of Hayabusa 2 samples..
Abstract: Introduction: The chemical composition of organic matter (OM) in interplanetary samples (meteorites and micrometeorites) is suitably characterized by the distribution of the different chemical bonds using infrared (IR) vibrational spectroscopy (see e.g. [1]). Classical IR microscopy provides a global view of the dust grain chemical structure content but remains limited by the diffraction, with typical spot sizes sampling a few micrometers in the mid-IR range. This spatial resolution limitation is well above that of complementary techniques such as isotopic imaging with NanoSIMS or transmission electron or X-ray microscopy techniques. These techniques reveal mineralogical, chemical and isotopic heterogeneities at the sub-micron scale but do not give full access to the distribution of the various chemical bonds. The IR diffraction limitation can be circumvented by using AFM-IR microscopy. This technique opens a new window for studies of OM at ten to tens of nanometer scales and will be of importance for studies of the samples from carbonaceous asteroid Ryugu, returned by the Hayabusa 2 space probe in December 2020. AFM-IR is now a well-established microscopy technique in the vibrational field. It combines an atomic force microscope (AFM) and a tunable IR source to detect photo-thermal effect and access chemical information down to a nanoscale resolution [2]. This technique is now applied in a wide diversity of scientific fields [3], and was recently used to analyze extraterrestrial OM [4, 5]. We report here on recent results obtained on imaging two UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) using AFM-IR [5]. A small fraction of the Antarctic micrometeorites from the Concordia collection consists in UCAMMs, particles with extreme concentrations in OM, most of them exhibiting large deuterium excesses [6]. UCAMMs are also found in Japanese interplanetary dust collections [7-9]. These UCAMMs most likely originate from the surface of small icy bodies in the outer regions of the solar system [1,6,7,10]. The large OM fraction of UCAMMs (considerably higher than in the most carbon-rich meteorites) enables direct analyses without the pre-treatment generally applied to extract the OM from other meteoritic samples, and give access to unaltered chemical maps of the intimate association of minerals and organics.
Programme: 1120
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Nicolas Meyer, Loïc Bollache, François-Xavier Dechaume-Moncharmont, Jérôme Moreau, Eve Afonso, Anders Angerbjörn, Joël Bêty, Dorothée Ehrich, Vladimir Gilg, Marie-Andrée Giroux, Jannik Hansen, Richard B. Lanctot, Johannes Lang, Nicolas Lecomte, Laura McKinnon, Jeroen Reneerkens, Sarah T. Saalfeld, Brigitte Sabard, Niels M. Schmidt, Benoît Sittler, Paul Smith, Aleksandr Sokolov, Vasiliy Sokolov, Natalia Sokolova, Rob van Bemmelen, Olivier Gilg. (2020). Nest attentiveness drives nest predation in arctic sandpipers (Vol. 129).
Abstract: Most birds incubate their eggs to allow embryo development. This behaviour limits the ability of adults to perform other activities. Hence, incubating adults trade off incubation and nest protection with foraging to meet their own needs. Parents can either cooperate to sustain this tradeoff or incubate alone. The main cause of reproductive failure at this reproductive stage is predation and adults reduce this risk by keeping the nest location secret. Arctic sandpipers are interesting biological models to investigate parental care evolution as they may use several parental care strategies. The three main incubation strategies include both parents sharing incubation duties (‘biparental’), one parent incubating alone (‘uniparental’), or a flexible strategy with both uniparental and biparental incubation within a population (‘mixed’). By monitoring the incubation behaviour in 714 nests of seven sandpiper species across 12 arctic sites, we studied the relationship between incubation strategy and nest predation. First, we described how the frequency of incubation recesses (NR), their mean duration (MDR), and the daily total duration of recesses (TDR) vary among strategies. Then, we examined how the relationship between the daily predation rate and these components of incubation behaviour varies across strategies using two complementary survival analysis. For uniparental and biparental species, the daily predation rate increased with the daily total duration of recesses and with the mean duration of recesses. In contrast, daily predation rate increased with the daily number of recesses for biparental species only. These patterns may be attributed to two independent mechanisms: cryptic incubating adults are more difficult to locate than unattended nests and adults departing the nest or feeding close to the nest can draw predators’ attention. Our results demonstrate that incubation behaviour as mediated by incubation strategy has important consequences for sandpipers’ reproductive success.
Keywords: Arctic shorebirds breeding behaviour incubation recesses incubation strategy nest survival parental care
Programme: 1036
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M. Belke-Brea, F. Domine, S. Boudreau, G. Picard, M. Barrere, L. Arnaud, M. Paradis. (2020). New Allometric Equations for Arctic Shrubs and Their Application for Calculating the Albedo of Surfaces with Snow and Protruding Branches (Vol. 21).
Abstract: Arctic shrubs reduce surface albedo in winter when branches protrude above the snow. To calculate the albedo of those mixed surfaces, the branch area index (BAI) of Arctic shrubs needs to be known. Moreover, an exposed-vegetation function is required to determine the BAI for protruding branches only. This study used a structural analysis of 30 Betula glandulosa shrubs, sampled near Umiujaq, northern Quebec, to (i) establish an allometric relationship between shrub height and BAI and (ii) determine a specific exposed-vegetation function for Arctic shrubs. The spectral albedo (400–1080 nm) of mixed surfaces was then simulated with the equations derived from this study and validated with in situ measured spectra. Shrubs were sampled from two sites, one along the coast and the other in a nearby valley. The shrub height–BAI relationship varied between both sites. BAI values of shrubs growing in the wind-sheltered valley were 30%–50% lower. The exposed-vegetation function obtained here differed from the linear functions found in the literature. The linear functions strongly overestimated the BAI of exposed branches. Albedo was well simulated with an accuracy of 3% when using an allometric relationship adapted to the environmental conditions of our study site. However, simulated albedo values were consistently higher than field measurements, probably because radiation absorbed by impurities and buried branches was neglected in the model. We conclude that specific exposed-vegetation and allometric equations need to be implemented in models to accurately simulate the albedo of mixed snow–shrub surfaces.
Programme: 1042
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L. T. Ellis, M. Kh. Alikhadzhiev, R. S. Erzhapova, H. H. Blom, H. Bednarek-Ochyra, M. Burghardt, M. J. Cano, I. V. Czernyadjeva, E. Yu. Kuzmina, A. D. Potemkin, G. Ya. Doroshina, D. Dagnino, C. Turcato, L. Minuto, P. Drapela, M. V. Dulin, E. Fuertes, A. Graulich, K. Hassel, L. Hedenäs, T. H. Hofton, T. Høitomt, I. Jukonienė, M. Kırmacı, N. E. Koroleva, Ł. Krajewski, M. Kropik, H. Kürschner, E. V. Kushnevskaya, J. Larraín, M. Lebouvier, A. I. Maksimov, O. Yu. Pisarenko, V. Plášek, Z. Skoupá, S. Yu. Popov, V. E. Fedosov, M. Puglisi, A. Stebel, S. Ştefănut, G. Vončina, M. Wierzgoń, S.-L. Guo. (2020). New national and regional bryophyte records, 64 (Vol. 42).
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Barbero A. Grilli R., Blouzon C., Caillon N., Savarino, J. (2020). New Observations to Better Constrain NOx (NO + NO2) Concentrations on the Antarctic Plateau and to Resolve the Ambiguity in the NO2:NO Ratio.
Abstract: High southern latitude regions present specificities that are highly relevant for studying the climate in connection with the atmospheric chemistry. Contrary to regions of the rest of the world, Antarctica is still considered as a pristine environment not yet influenced by predominant anthropogenic emissions (with the notable exceptions of GHG) and thus represents the last continental-size natural laboratory. Polar snow-air-radiation interactions and the specific oxidant character of the polar atmosphere are key in order to decipher the right information buried in the ice and the current chemical stability of the polar atmosphere. Previous Antarctic campaigns have shown atmospheric similarities between the Antarctic Plateau (at Dome C, Concordia) and other regions. However, several differences are yet to be explained: the large NO2:NO ratios previously found in ambient air indicates the existence of an unknown source of NO2 above the Antarctic Plateau. These observations question either the reliability of previous measurements or the lack of our understanding of the NOx chemistry. Novel optical instruments based on the incoherent broadband cavity enhanced absorption spectroscopy technique (IBBCEAS) were developed. The instruments can measure simultaneously NO2, NOx and NO with detection limits of 11, 10 and 21 ppt, respectively (1σ) within 22 minutes of measurements. The two compact and transportable instruments were deployed during the 2019/20 Dome C summer campaign. Atmospheric measurements together with flux chamber experiments were performed for determining the snowpack NOx emissions and the NO2:NO ratio. The observations seem to differ from the conclusions of the previous Antarctic campaigns. Assuming steady state and maximum radiations, the theoretical NO2:NO ratio from the period observed in December was calculated to be 0.38 ± 0.15 and 0.31 ± 0.12 in January. The instruments measured a ratio close to steady state in December (0.25 ± 0.25) while the ratio observed in January (1.248 ± 0.792) indicates the presence of a strong NO oxidant or an unknown source of NO2. Flux chamber experiments on different types of snow were done during this campaign, and the results will help deepen our knowledge of Antarctic atmospheric chemistry.
Programme: 1177
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