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Author |
R. Olmi, M. Bittelli, G. Picard, L. Arnaud, A. Mialon, S. Priori |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Investigating the influence of the grain size and distribution on the macroscopic dielectric properties of Antarctic firn |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Cold Regions Science and Technology |
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Volume |
185 |
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Pages |
103254 |
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Keywords |
Antarctica Close−off Dielectric measurements Dielectric model Firn Full wave EM simulations Ice cores |
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Abstract |
This study is based on the analysis of detailed measurements of firn dielectric properties performed in Antarctica through coring down to 106 m. Dielectric measurements in the frequency band (0.4–2.5 GHz) have been carried out using an open−resonator probe. Density was also measured for the same samples. The experimental results confirmed the well−known dependence of the real part of permittivity ε′ on depth and density, showing an increase of ε′ with density. The imaginary part also increases with depth with a rather complex dependence on frequency, probably due to the presence of salts or impurities. The analysis of the experimental data was performed by implementing 3D and 2D full wave numerical models, to simulate a mixture of firn crystals at prescribed densities, corresponding to the measured densities on the ice cores. The numerical analysis of the ensemble of inclusions showed that the usual symmetric formulae used for modeling ice dielectric properties agree with the average results of the simulation, but they are not able to explain the spreading of the measured data at given density. A dielectric model was then developed allowing for quantification of the dependence of dielectric properties on density, by combining two models: one consisting in firn crystals into an air host, the other assuming the presence of air inclusions into a homogeneous firn host. The weighted equation is based on the volume fraction. A simple geometric shape (ellipsoidal) is assumed for both ice crystals and air inclusions. This kind of shape is reasonable for the purpose of the dielectric study. The result is a mixture, smoothly changing from firn particles in air (low density) to air bubbles in an ice matrix (high density). A statistical analysis has been accomplished to investigate the dependence of the dielectric properties on the geometrical arrangement of the inclusions. For that purpose, a large number of simulations with different arrangements (micro−states) giving rise to the same average density (macro−states) has been carried out. The permittivity change due to micro−state variability appears to be at least two−three times the model variation due to density alone, and comparable to the measured variability at a given depth, suggesting that firn structure has a significant effect on the dielectric properties. |
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0165-232X |
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7995 |
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Author |
A. Baranov, R. Tenzer, A. Morelli |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Updated Antarctic crustal model |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Gondwana Research |
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Volume |
89 |
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Pages |
1-18 |
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Keywords |
Antarctica Crustal structure Gondwana Sediments |
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Abstract |
We use seismic data together with a subglacial bedrock relief from the BEDMAP2 database to obtain a new three-layer model of the consolidated (crystalline) crust of Antarctica that locally improves the global seismic crustal model CRUST1.0. We collect suitable data for constructing crustal layers, analyse them and build maps of the crustal layer thickness and seismic velocities. We use the subglacial relief according to a tectonic configuration and then interpolate data using a statistical kriging method. The P-wave velocity information from old seismic profiles have been supplemented with the new shear-wave velocity models. We adjust the thickness of crustal layers by multiplying a total crustal thickness by a percentage ratio of each individual layer at each point. Our results reveal large variations in seismic velocities between different crustal blocks forming Antarctica. The most pronounced differences exist between East and West Antarctica. In East Antarctica, a high P-wave velocity (vP > 7 km/s) layer in the lower crust is absent. The P-wave velocity in the lower crust changes from 6.1 km/s beneath the Lambert Rift to 6.9 km/s beneath the Wilkes Basin. In West Antarctica, a thick mafic lower crust is characterized by large P-wave velocities, ranging from 7.0 km/s under the Ross Sea to 7.3 km/s under the Byrd Basin. In contrast, velocities in the lower crust beneath the Transantarctic and Ellsworth-Whitmore Mountains are ~6.8 km/s. The P-wave velocities in the upper crust in East Antarctica are within the range 5.5–6.4 km/s. The upper crust of West Antarctica is characterized by the P-wave velocities of 5.6–6.3 km/s. The P-wave velocities in the middle crust vary within 5.9–6.6 km/s in East Antarctica and within 6.3–6.5 km/s in West Antarctica. A low-velocity layer (5.8–5.9 km/s) is detected at depth of ~20–25 km beneath the Princes Elizabeth Land. |
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133 |
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1342-937X |
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7994 |
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Author |
Fanny Larue, Ghislain Picard, Jérémie Aublanc, Laurent Arnaud, Alvaro Robledano-Perez, Emmanuel LE Meur, Vincent Favier, Bruno Jourdain, Joel Savarino, Pierre Thibaut |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Radar altimeter waveform simulations in Antarctica with the Snow Microwave Radiative Transfer Model (SMRT) |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Remote Sensing of Environment |
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Volume |
263 |
Issue |
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Pages |
112534 |
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Keywords |
Antarctic ice sheet Field measurements Modeling Radar altimetry Remote sensing SMRT Waveform |
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Abstract |
Radar altimeters are important tools to monitor the volume of the ice sheets. The penetration of radar waves in the snowpack is a major source of uncertainty to retrieve surface elevation. To correct this effect, a better understanding of the sensitivity of the radar waveforms to snow properties is needed. Here, we present an extension of the Snow Model Radiative Transfer (SMRT) to compute radar waveforms and conduct a series of simulations on the Antarctic ice sheet. SMRT is driven by snow and surface roughness properties measured over a large latitudinal range during two field campaigns on the Antarctic Plateau. These measurements show that the snowpack is rougher, denser, less stratified, warmer, and has smaller snow grains near the coast than on the central Plateau. These simulations are compared to satellite observations in the Ka, Ku, and S bands. SMRT reproduces the observed waveforms well. For all sites and all sensors, the main contribution comes from the surface echo. The echo from snow grains (volume scattering) represents up to 40% of the amplitude of the total waveform power in the Ka band, and less at the lower frequencies. The highest amplitude is observed on the central Plateau due to the combination of higher reflection from the surface, higher scattering by snow grains in the Ka and Ku bands, and higher inter-layer reflections in the S band. In the Ka band, the wave penetrates in the snowpack less deeply on the central Plateau than near the coast because of the strong scattering caused by the larger snow grains. The opposite is observed in the S band, the wave penetrates deeper on the central Plateau because of the lower absorption due to the lower snow temperatures. The elevation bias caused by wave penetration into the snowpack show a constant bias of 10 cm for all sites in the Ka band, and a bias of 11 cm, and 21 cm in the Ku band for sites close to the coast and the central Plateau, respectively. Now that SMRT is performing waveform simulations, further work will address how the snowpack properties affect the parameters retrieved by more advanced retracking algorithms such as ICE-2 for different snow cover surfaces. |
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1110 |
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0034-4257 |
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yes |
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7997 |
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Author |
Pierre-Yves Pascal, Yann Reynaud, Elie Poulin, Chantal De Ridder, Thomas Saucede |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Feeding in spatangoids: the case of Abatus Cordatus in the Kerguelen Islands (Southern Ocean) |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Polar Biology |
Abbreviated Journal |
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Volume |
44 |
Issue |
4 |
Pages |
795-808 |
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Abstract |
Irregular urchins exclusively live in marine soft bottom habitats, dwelling either upon or inside sediments and selectively picking up sediment grains and organic particles, or swallowing bulk sediment to feed on the associated organic matter. The exact food source and dietary requirements of most irregular echinoids, however, remain incompletely understood. The schizasterid species Abatus cordatus (Verrill, 1876) is a sub-Antarctic spatangoid that is endemic to the Kerguelen. The feeding behaviour of A. cordatus was investigated using simultaneously metabarcoding and stable isotope approaches. Comparison of ingested and surrounding sediments by metabarcoding revealed a limited selective ingestion of prokaryotes and eukaryotes by the urchin. Compared to surrounding sediments, the gut content had (i) higher carbon and nitrogen concentrations potentially due to selective ingestion of organic matter and/or the sea urchin mucus secretion and (ii) δ15N enrichment due to the selective assimilation of lighter isotope in the gut. Feeding experiments were performed using 13C and 15 N-enriched sediments in aquariums. The progression of stable isotope enrichment in proximal and distal parts of the digestive track of A. cordatus revealed that all particles are not similarly transported likely due to siphon functioning. Ingestion of water with associated dissolved and particulate organic matter should play an important role in urchin nutrition. A. cordatus had a gut resident time fluctuating between 76 and 101 h and an ingestion rate of 36 mg dry sediment h−1 suggesting that dense populations of the species may play a key ecological role through bioturbation in soft bottom shallow-water habitats of the Kerguelen Islands. |
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1044 |
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ISSN |
1432-2056 |
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yes |
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8000 |
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Author |
Margot Arnould-Pétré, Charlène Guillaumot, Bruno Danis, Jean-Pierre Féral, Thomas Saucède |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Individual-based model of population dynamics in a sea urchin of the Kerguelen Plateau (Southern Ocean), Abatus cordatus, under changing environmental conditions |
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2021 |
Publication |
Ecological Modelling |
Abbreviated Journal |
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Volume |
440 |
Issue |
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Pages |
109352 |
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Keywords |
Climate change Dynamic energy budget Ecological modelling Endemic echinoderm Individual-based model Kerguelen Model sensitivity |
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Abstract |
The Kerguelen Islands are part of the French Southern Territories, located at the limit of the Indian and Southern oceans. They are highly impacted by climate change, and coastal marine areas are particularly at risk. Assessing the responses of species and populations to environmental change is challenging in such areas for which ecological modelling can constitute a helpful approach. In the present work, a DEB-IBM model (Dynamic Energy Budget – Individual-Based Model) was generated to simulate and predict population dynamics in an endemic and common benthic species of shallow marine habitats of the Kerguelen Islands, the sea urchin Abatus cordatus. The model relies on a dynamic energy budget model (DEB) developed at the individual level. Upscaled to an individual-based population model (IBM), it then enables to model population dynamics through time as a result of individual physiological responses to environmental variations. The model was successfully built for a reference site to simulate the response of populations to variations in food resources and temperature. Then, it was implemented to model population dynamics at other sites and for the different IPCC climate change scenarios RCP 2.6 and 8.5. Under present-day conditions, models predict a more determinant effect of food resources on population densities, and on juvenile densities in particular, relative to temperature. In contrast, simulations predict a sharp decline in population densities under conditions of IPCC scenarios RCP 2.6 and RCP 8.5 with a determinant effect of water warming leading to the extinction of most vulnerable populations after a 30-year simulation time due to high mortality levels associated with peaks of high temperatures. Such a dynamic model is here applied for the first time to a Southern Ocean benthic and brooding species and offers interesting prospects for Antarctic and sub-Antarctic biodiversity research. It could constitute a useful tool to support conservation studies in these remote regions where access and bio-monitoring represent challenging issues. |
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1044 |
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ISSN |
0304-3800 |
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yes |
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Call Number |
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Serial |
8002 |
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Author |
Benjamin Pohl, Thomas Saucède, Vincent Favier, Julien Pergaud, Deborah Verfaillie, Jean-Pierre Féral, Ylber Krasniqi, Yves Richard |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Recent Climate Variability around the Kerguelen Islands (Southern Ocean) Seen through Weather Regimes |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Journal of Applied Meteorology and Climatology |
Abbreviated Journal |
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Volume |
60 |
Issue |
5 |
Pages |
711-731 |
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Keywords |
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Abstract |
Daily Weather Regimes Are Defined Around The Kerguelen Islands (Southern Ocean) On The Basis Of Daily 500-hpa Geopotential Height Anomalies Derived From The Era5 Ensemble Reanalysis Over The Period 1979–2018. Ten Regimes Are Retained As Significant. Their Occurrences Are Highly Consistent Across Reanalysis Ensemble Members. Regimes Show Weak Seasonality And Nonsignificant Long-term Trends In Their Occurrences. Their Sequences Are Usually Short (1–3 Days), With Extreme Persistence Values Above 10 Days. Seasonal Regime Frequency Is Mostly Driven By The Phase Of The Southern Annular Mode Over Antarctica, Midlatitude Dynamics Over The Southern Ocean Such As The Pacific–south American Mode, And, To A Lesser Extent, Tropical Variability, With Significant But Weaker Relationships With El Niño–southern Oscillation. At The Local Scale Over The Kerguelen Islands, Regimes Have A Strong Influence On Measured Atmospheric And Oceanic Variables, Including Minimum And Maximum Air Temperature, Mostly Driven By Horizontal Advections, Seawater Temperature Recorded 5 M Below The Surface, Wind Speed, And Sea Level Pressure. Relationships Are Weaker For Precipitation Amounts. Regimes Also Modify Regional Contrasts Between Observational Sites In Kerguelen, Highlighting Strong Exposure Contrasts. The Regimes Allow Us To Improve Our Understanding Of Weather And Climate Variability And Interactions In This Region; They Will Be Used In Future Work To Assess Past And Projected Long-term Circulation Changes In The Southern Midlatitudes. |
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Programme |
688,1044,1048 |
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Bachelor's thesis |
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ISSN |
1558-8424 |
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yes |
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Serial |
8003 |
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Author |
Camille Moreau, Quentin Jossart, Bruno Danis, Marc Eléaume, Henrik Christiansen, Charlène Guillaumot, Rachel Downey, Thomas Saucède |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
The high diversity of Southern Ocean sea stars (Asteroidea) reveals original evolutionary pathways |
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Journal |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Progress in oceanography |
Abbreviated Journal |
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Volume |
190 |
Issue |
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Pages |
102472 |
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Keywords |
Antarctica Biodiversity COI mtDNA Echinodermata Evolution Phylogeography |
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Abstract |
Benthic life in the Southern Ocean (SO) features unique life history traits and species assemblages, but the origin and evolution of many of these taxonomic groups is still unclear. Sea stars (Asteroidea) are a diversified and abundant component of benthic ecosystems in the SO, in which they can play key ecological roles. Former studies suggest that the diversity of the entire class is still poorly known and underestimated, hampering the assessment of the origin and evolution of the class in the SO. In the present study, we analyse spatial patterns of SO sea star diversity using an occurrence database of ~14,000 entries. The biogeographic analysis is coupled with the exploration of an extensive molecular phylogeny based on over 4,400 specimen sequences to inform, support and/or question the observed diversity patterns. We show that the current taxonomy of SO asteroids needs revision and that their diversity has generally been overlooked and misinterpreted. Molecular results highlight the recent diversification of most studied taxa, at genus and species levels, which supports an evolutionary scenario referring to successive invasion and exchange events between the SO and adjacent regions, and clade diversification during periods of rapid environmental changes driven by the succession of glacial cycles. Our work advocates for employing, and endorsing the use of extensive genetic barcode libraries for biodiversity studies. |
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Programme |
1044,1124 |
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Thesis |
Bachelor's thesis |
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ISSN |
0079-6611 |
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yes |
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Serial |
8183 |
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Author |
Daniela Levicoy, Sebastián Rosenfeld, Leyla Cárdenas |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Divergence time and species delimitation of microbivalves in the Southern Ocean: the case of Kidderia species |
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Journal |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Polar Biology |
Abbreviated Journal |
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Volume |
44 |
Issue |
7 |
Pages |
1365-1377 |
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Abstract |
The systematics of Subantarctic and Antarctic near-shore marine benthic invertebrates requires major revision and highlights the necessity to incorporate additional sources of information in the specimen identification chart in the Southern Ocean (SO). In this study, we aim to improve our understanding of the biodiversity of Kidderia (Dall 1876) through molecular and morphological comparisons of Antarctic and Subantarctic taxa. The microbivalves of the genus Kidderia are small brooding organisms that inhabit intertidal and shallow subtidal rocky ecosystems. This genus represents an interesting model to test the vicariance and dispersal hypothesis in the biogeography of the SO. However, the description of Kidderia species relies on a few morphological characters and biogeographic records that raise questions about the true diversity in the group. Here we will define the specimens collected with genetic tools, delimiting their respective boundaries across provinces of the SO, validating the presence of two species of Kidderia. Through the revision of taxonomic issues and species delimitation, it was possible to report that the Antarctic species is Kidderia subquadrata and the species recorded in the Subantarctic islands Diego Ramirez, South Georgia and the Kerguelen Archipelago is Kidderia minuta. The divergence time estimation suggests the origin and diversification of Kidderia lineages are related to historical vicariant processes probably associated with the separation of the continental landmasses close to the late Eocene. |
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1044 |
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ISSN |
1432-2056 |
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yes |
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Call Number |
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Serial |
8004 |
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Permanent link to this record |
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Author |
Zambra López-Farrán, Charlène Guillaumot, Luis Vargas-Chacoff, Kurt Paschke, Valérie Dulière, Bruno Danis, Elie Poulin, Thomas Saucède, Jonathan Waters, Karin Gérard |
![find record details (via OpenURL) openurl](img/xref.gif)
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Title |
Is the southern crab Halicarcinus planatus (Fabricius, 1775) the next invader of Antarctica? |
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Journal |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Global Change Biology |
Abbreviated Journal |
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Volume |
27 |
Issue |
15 |
Pages |
3487-3504 |
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Keywords |
climate change establishment niche modelling non-native species reptant crab Southern Ocean survival thermotolerance |
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Abstract |
The potential for biological colonization of Antarctic shores is an increasingly important topic in the context of anthropogenic warming. Successful Antarctic invasions to date have been recorded exclusively from terrestrial habitats. While non-native marine species such as crabs, mussels and tunicates have already been reported from Antarctic coasts, none have as yet established there. Among the potential marine invaders of Antarctic shallow waters is Halicarcinus planatus (Fabricius, 1775), a crab with a circum-Subantarctic distribution and substantial larval dispersal capacity. An ovigerous female of this species was found in shallow waters of Deception Island, South Shetland Islands in 2010. A combination of physiological experiments and ecological modelling was used to assess the potential niche of H. planatus and estimate its future southward boundaries under climate change scenarios. We show that H. planatus has a minimum thermal limit of 1°C, and that its current distribution (assessed by sampling and niche modelling) is physiologically restricted to the Subantarctic region. While this species is presently unable to survive in Antarctica, future warming under both ‘strong mitigation’ and ‘no mitigation’ greenhouse gas emission scenarios will favour its niche expansion to the Western Antarctic Peninsula (WAP) by 2100. Future human activity also has potential to increase the probability of anthropogenic translocation of this species into Antarctic ecosystems. |
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1044 |
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ISSN |
1365-2486 |
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yes |
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Call Number |
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Serial |
8005 |
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Author |
Christophe Leroy-Dos Santos, Mathieu Casado, Frédéric Prié, Olivier Jossoud, Erik Kerstel, Morgane Farradèche, Samir Kassi, Elise Fourré, Amaëlle Landais |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
A dedicated robust instrument for water vapor generation at low humidity for use with a laser water isotope analyzer in cold and dry polar regions |
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Year ![sorted by Year field, descending order (down)](img/sort_desc.gif) |
2021 |
Publication |
Atmospheric Measurement Techniques |
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14 |
Issue |
4 |
Pages |
2907-2918 |
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Abstract |
Obtaining Precise Continuous Measurements Of Water Vapor Isotopic Composition In Dry Places (Polar Or High-altitude Regions) Is An Important Challenge. The Current Limitation Is The Strong Influence Of Humidity On The Measured Water Isotopic Composition By Laser Spectroscopy Instruments For Low Humidity Levels (Below 3000 Ppmv). This Problem Is Addressed By Determining The Relationships Between Humidity And Measured δ18o And δD Of Known Water Standards. Here, We Present The Development Of A Robust Field Instrument Able To Generate Water Vapor, Down To 70 Ppmv, At Very Stable Humidity Levels (Average 1σ Lower Than 10 Ppmv). This Instrument, Operated By A Raspberry Interface, Can Be Coupled To A Commercial Laser Spectroscopy Instrument. We Checked The Stability Of The System As Well As Its Accuracy When Expressing The Measured Isotopic Composition Of Water Vapor On The Vsmow–slap (Vienna Standard Mean Ocean Water – Standard Light Antarctic Precipitation) Scale. It Proved To Be Highly Stable During Autonomous Operation Over More Than 1 Year At The East Antarctic Concordia And Dumont D'urville Stations. |
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Programme |
1110,1169,1205 |
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Thesis |
Bachelor's thesis |
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ISSN |
1867-1381 |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
8010 |
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Permanent link to this record |