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Chuxian Li, Jeroen E. Sonke, Gaël Le Roux, Nathalie Van der Putten, Natalia Piotrowska, Catherine Jeandel, Nadine Mattielli, Mathieu Benoit, Giles F. S. Wiggs, François De Vleeschouwer |
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Title |
Holocene dynamics of the southern westerly winds over the Indian Ocean inferred from a peat dust deposition record |
Type |
Journal |
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Year |
2020 |
Publication |
Quaternary Science Reviews |
Abbreviated Journal |
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Volume |
231 |
Issue  |
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Pages |
106169 |
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Keywords |
Amsterdam Island Anthropogenic activities Dust sources Peat Southern westerly winds |
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Abstract |
The southern westerly winds (SWW) play a major role in climate variability in Southern Hemisphere mid- and high-latitudes, regulating rainfall, ocean circulation, and the Southern Ocean carbon sink. Despite their importance, little is known about millennial scale changes in the SWW and how they have influenced the climate system in the past and interacted with the Earth’s surface elements, such as dust, nutrients and carbon. Here we present a dust record from a 6.6 kyr old peat core in Amsterdam Island (AMS) situated at the northern edge of the SWW (37°S) in the Southern Indian Ocean. Mineral dust flux was used to track atmospheric dust production, long-distance transport and subsequent deposition. Dust provenance was determined from rare earth element (REE) and Nd isotopic signatures (εNd) in the peat core, compared with a reference dataset of Southern Hemisphere dust sources. Using a multi-proxy mixing model, the εNd and REE ratios show a relatively uniform mixture of ca. 40% local, 15% Southern African and 45% Southern South American dust sources since 6.6 cal kyr BP. However, from 1910 AD onwards, there is a doubling in the contribution from Southern Africa (32%). Two mineral dust flux minima occur at 6.2–4.9 cal kyr BP and 3.9–2.7 cal kyr BP, interpreted as periods with equatorward-shifted and/or strengthened SWW at the northern edge of the wind belt. Conversely, periods of higher dust flux at 6.6–6.2 cal kyr BP, 4.9–3.9 cal kyr BP, and 1.4 cal kyr BP onwards are interpreted as poleward-shifted and/or weakened SWW. These interpretations are based on the findings that higher (lower) wind speeds lead to enhanced (less) removal of distal dust on the way to AMS, by wet deposition and turbulence. Published Holocene SWW records at the northern edge of the wind belt (33–41°S) covering South-America, Southern-Africa and Australia, show much variability over the last 6.6 kyr. We suggest this reflects complex regional climate variability in the different SH longitudinal sectors, indicating that SWW are not zonally homogeneous at the northern edge of the wind belt. The recent shift in dust provenance is not accompanied by enhanced total dust deposition at AMS. We therefore suggest that human impact (e.g., land use changes) and drier climate conditions in Southern Africa have led to enhanced dust mobilization. |
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1065,1133 |
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Bachelor's thesis |
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0277-3791 |
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yes |
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Call Number |
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Serial |
8193 |
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Author |
Héloïse Barbel, Dominique Todisco, Najat Bhiry |
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Title |
A geochemical investigation of an Early Inuit semi-subterranean winter dwelling in a periglacial context |
Type |
Journal |
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Year |
2020 |
Publication |
Journal of archaeological science: reports |
Abbreviated Journal |
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Volume |
33 |
Issue |
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Pages |
102552 |
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Keywords |
C-N analysis Cryosolic soils geochemistry FTIR ICP-AES Inuit archaeology Nunavik Semi-subterranean house |
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Abstract |
Geochemical investigations using FTIR, ICP-AES and C-N analyses were carried out on a single-family semi-subterranean Inuit house in order to assess the contribution of Inuit domestic activities in the formation of cryosolic soils in a periglacial archaeological context (Kuuvik Bay, Nunavik, Canada). The geochemical elements data were analyzed using box plots and enrichment factors. The information was also summarized and visualized through principal component analysis (PCA). These complementary statistical approaches provided evidence of a moderate but identifiable and significant imprint of Inuit domestic activities on soil geochemistry. The box plots indicate moderate Ca, Mn, Cu and P enrichments and more noticeable Mg, Fe and S enrichments. These enrichment factors and the ICP-AES data show that samples from the peripheral wall and the tunnel entrance of the house and its vicinity are significantly enriched. While FTIR analysis highlighted the main soil element contents (e.g., organic and mineral components), ICP-AES analysis was used to further document variations in the background elements throughout the site. However, the obtained results do not allow us to undertake a spatial analysis of Inuit activities or to describe them in detail. In addition, the data highlight the difficulty of documenting the natural variability of element contents in cryosolic soils, especially in archaeological contexts. Cryo-pedological processes in the active layer as well as house cleaning and nutrient inputs resulting from Inuit occupations may have attenuated chemical signatures of previous Inuit domestic activities. |
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Programme |
1080 |
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Campaign |
LOTECHAIN |
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Corporate Author |
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Thesis |
Bachelor's thesis |
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Edition |
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ISSN |
2352-409X |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
8206 |
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Author |
Samuel Veilleux, Najat Bhiry, Armelle Decaulne |
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Title |
Talus slope characterization in Tasiapik Valley (subarctic Québec): Evidence of past and present slope processes |
Type |
Journal |
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Year |
2020 |
Publication |
Geomorphology |
Abbreviated Journal |
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Volume |
349 |
Issue |
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Pages |
106911 |
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Keywords |
Morphometry Nunavik Periglacial Slope dynamics Snow avalanches |
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Abstract |
Topographic, granulometric, morphometric, petrographic and vegetation surveys were conducted on the slopes of Tasiapik Valley, near Umiujaq (Nunavik), to document mass wasting processes and their geomorphological impact. Talus slopes, widespread at the foot of the steep rockwalls of Tasiapik Valley, are an important landscape feature in the area. The lithology of the slope deposits attest their local origin, namely the result of rockfalls coming from the adjacent wall. Locally, poor vegetation covering the clasts exhibits recently fallen debris; elsewhere, dense shrub cover has colonized the slopes demonstrating the low activity nowadays. On-going periglacial processes have led to extensive dismantling of the rockface, enabling for debris supply. Following the last deglaciation, paraglacial processes have potentially favoured slope instabilities. The use of automatic cameras during the winter 2017–2018 resulted in the observation of many snow-avalanche events; however few rockfall events have been observed. Spring snow avalanches have carried rock debris to the talus at the foot of the slope; snow also enabled debris redistribution on the slopes. |
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Programme |
1148 |
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Edition |
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ISSN |
0169-555X |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
8261 |
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| Permanent link to this record |
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Author |
Renac Christophe, Moine Bertrand, Goudour Jean-Pierre, LeRomancer Marc, Perrache Chantal |
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Title |
Stable isotope study of rainfall, river drainage and hot springs of the kerguelen archipelago, SW Indian Ocean |
Type |
Journal |
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Year |
2020 |
Publication |
Geothermics |
Abbreviated Journal |
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Volume |
83 |
Issue |
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Pages |
101726 |
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Keywords |
Geothermal springs Kerguelen archipelago Stable isotope composition Water-Rock interaction |
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Abstract |
This study is the first synthesis of chemical composition and stable isotopes values for the Kerguelen archipelago waters. The stable isotope values for rainfall and river waters in the Kerguelen archipelago allow a calculation of the Local Meteoric Water Line (δD rainfall = 8.43 x δ18O rainfall + 11) and a summer runoff line (δD river drainage = 7.45 x δ18O river drainage + 6). Surface waters with low- ion concentrations, chlorine facies and stable isotope values infiltrate through fractures and lava flows recharging deeper groundwaters. Thermal groundwater with low- (7 to 50 °C) and high- (50 to 100 °C) temperatures emerges in different localities in the volcanic archipelago. The low-temperature thermal waters might represent a mixture of high-temperature water with rainfall, thermal gradient changes or shallower infiltration compared to that for high-temperature thermal waters. The Rallier du Baty and Val Travers areas contain geothermal fluids with high-temperature springs, fumaroles and a large water flow. In the Rallier du Baty, the major ion chemistry and O, H, C and S stable isotope ratio of low (7 to 50 °C) temperature spring waters in Rallier du Baty area demonstrate a geothermal-system recharged by meteoric water (δD H2O liquid = 7.0 x δ18O H2O liquid + 0.5) rather than sea water. The chemical and isotopic compositions of elevated temperature spring waters (50 to 100 °C) have a long and complex history of meteoric water interacting with cooling magmas (δD H2O liquid = 1.78 x δ18O H2O liquid – 23). Surficial precipitation of aragonite, kaolinite, pyrite, native sulfur attest to a long livied geothermal system. A temperature of the geothermal reservoir has been estimated between 193 and 259 °C by cation geothermometry. The combination of minerals observed, major ion composition of water with thermodynamic modeling and stable isotope data suggest a geothermal system with a series of water/rock interactions from 50 to 250 °C. The conductive cooling of rising of H2O−CO2-rich fluids have produced a H2O−CO2 phase separation with the precipitation of secondary minerals. |
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Programme |
408,444 |
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Thesis |
Bachelor's thesis |
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ISSN |
0375-6505 |
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Approved |
yes |
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Call Number |
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Serial |
8262 |
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Author |
Kévin Fourteau, Fabien Gillet-Chaulet, Patricia Martinerie, Xavier Faïn |
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Title |
A Micro-Mechanical Model for the Transformation of Dry Polar Firn Into Ice Using the Level-Set Method |
Type |
Journal |
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Year |
2020 |
Publication |
Frontiers in Earth Science |
Abbreviated Journal |
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Volume |
8 |
Issue |
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Pages |
101 |
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Keywords |
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Abstract |
Interpretation of greenhouse gas records in polar ice cores requires a good understanding of the mechanisms controlling gas trapping in polar ice, and therefore of the processes of densification and pore closure in firn (compacted snow). Current firn densification models are based on a macroscopic description of the firn and rely on empirical laws and/or idealized geometries to obtain the equations governing the densification and pore closure. Here, we propose a physically-based methodology explicitly representing the porous structure and its evolution over time. In order to handle the complex geometry and topological changes that occur during firn densification, we rely on a Level-Set representation of the interface between the ice and the pores. Two mechanisms are considered for the displacement of the interface: (i) mass surface diffusion driven by local pore curvature and (ii) ice dislocation creep. For the latter, ice is modeled as a viscous material and the flow velocities are solutions of the Stokes equations. First applications show that the model is able to densify firn and split pores. Using the model in cold and arid conditions of the Antarctic plateau, we show that gas trapping models do not have to consider the reduced compressibility of closed pores compared to open pores in the deepest part of firns. Our results also suggest that the mechanism of curvature-driven surface diffusion does not result in pore splitting, and that ice creep has to be taken into account for pores to close. Future applications of this type of model could help quantify the evolution and closure of firn porous networks for various accumulation and temperature conditions. |
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Programme |
1153 |
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ISSN |
2296-6463 |
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Approved |
yes |
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Call Number |
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Serial |
8268 |
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Author |
Agnès Lewden, Batshéva Bonnet, Andreas Nord |
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Title |
The metabolic cost of subcutaneous and abdominal rewarming in king penguins after long-term immersion in cold water |
Type |
Journal |
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Year |
2020 |
Publication |
Journal of Thermal Biology |
Abbreviated Journal |
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Volume |
91 |
Issue |
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Pages |
102638 |
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Keywords |
Metabolism Normothermia Rewarming Subcutaneous temperature |
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Abstract |
Marine endotherms in the polar regions face a formidable thermal challenge when swimming in cold water. Hence, they use morphological (fat, blubber) adjustment and peripheral vasoconstriction to reduce demands for heat production in water. The animals then regain normothermia when resting ashore. In the king penguin (Aptenodytes patagonicus) metabolic rate is lower in fed than in fasted individuals during subsequent rewarming on land. This has been suggested to be a consequence of diversion of blood flow to the splanchnic region in fed birds, which reduces peripheral temperatures. However, peripheral temperatures during recovery have never been investigated in birds with different nutritional status. The aim of this study was, therefore, to measure subcutaneous and abdominal temperatures during the rewarming phase on land in fasted and fed king penguins, and investigate to which extent any different rewarming were reflected in recovery metabolic rate (MRR) after long term immersion in cold water. We hypothesized that fed individuals would have a slower increase of subcutaneous temperatures compared to fasted penguins, and a correspondingly lower MRR. Subcutaneous tissues reached normothermia after 24.15 (back) and 21.36 min (flank), which was twice as fast as in the abdomen (46.82 min). However, recovery time was not affected by nutritional condition. MRR during global rewarming (4.56 ± 0.42 W kg−1) was twice as high as resting metabolic rate (RMR; 2.16 ± 0.59 W kg−1). However, MRR was not dependent on feeding status and was significantly elevated above RMR only until subcutaneous temperature had recovered. Contrary to our prediction, fed individuals did not reduce the subcutaneous circulation compared to fasted penguins and did not show any changes in MRR during subsequent recovery. It seems likely that lower metabolic rate in fed king penguins on land reported in other studies might not have been caused primarily by increased circulation to the visceral organs. |
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Programme |
394 |
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ISSN |
0306-4565 |
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Approved |
yes |
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Call Number |
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Serial |
8271 |
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Author |
Alexander Winterl, Sebastian Richter, Aymeric Houstin, Anna P. Nesterova, Francesco Bonadonna, Werner Schneider, Ben Fabry, Céline Le Bohec, Daniel P. Zitterbart |
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Title |
micrObs – A customizable time-lapse camera for ecological studies |
Type |
Journal |
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Year |
2020 |
Publication |
HardwareX |
Abbreviated Journal |
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Volume |
8 |
Issue |
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Pages |
e00134 |
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Keywords |
Automated camera system Collective behavior Ecology Image processing Remote sensing Wildlife monitoring |
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Abstract |
Camera traps for motion-triggered or continuous time-lapse recordings are readily available on the market. For demanding applications in ecology and environmental sciences, however, commercial systems often lack flexibility to freely adjust recording time intervals, suffer from mechanical component wear, and can be difficult to combine with auxiliary sensors such as GPS, weather stations, or light sensors. We present a robust time-lapse camera system that has been operating continuously since 2013 under the harsh climatic conditions of the Antarctic and Subantarctic regions. Thus far, we have recorded over one million images with individual cameras. The system consumes 122 mW of power in standby mode and captures up to 200,000 high-resolution (16 MPix) images without maintenance such as battery or image memory replacement. It offers time-lapse intervals between 2 s and 1 h, low-light or night-time power saving, and data logging capabilities for additional inputs such as GPS and weather data. |
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Programme |
137 |
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ISBN |
2468-0672 |
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yes |
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Serial |
8302 |
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Author |
Le Bourg Baptiste |
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Title |
Ecologie trophique des étoiles de mer de l’Océan Austral : Influence des facteurs environnementaux sur la diversité trophique // Trophic ecology of Southern Ocean sea stars: Influence of environmental drivers on trophic diversity |
Type |
Thesis |
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Year |
2020 |
Publication |
Thèse de doctorat. université de liège |
Abbreviated Journal |
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Issue |
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Pages |
287 pp. |
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Abstract |
[fr] Comme le reste du monde, l’Océan Austral est impacté par le changement climatique. Néanmoins, ces changements varient en fonction des différentes régions de cet océan. Les modifications de la couverture par la glace de mer autour du continent Antarctique en sont une des manifestations les plus visibles. Ainsi, la couverture glaciaire a fortement diminué en Péninsule Antarctique Occidentale, tandis qu’elle tend à légèrement augmenter sur le reste de la façade du continent. Ces modifications des conditions environnementales influencent le fonctionnement des écosystèmes de cet océan. Notamment, la disparition ou la persistance de la couverture glaciaire dans une région où elle avait une présence saisonnière peut empêcher l’apparition des efflorescences estivales du phytoplancton, impactant ainsi la dynamique des populations de krill et de leurs prédateurs dans le milieu pélagique. Le milieu benthique sera lui aussi perturbé par les modifications environnementales résultant du changement climatique, puisque les flux de matière organique vers ce compartiment seront affectés. Les étoiles de mer (Echinodermata : Asteroidea) sont un élément clé du benthos de l’Océan Austral, avec 12% des espèces d’étoiles de mer connues y vivant. En milieu tempéré, ce taxon peut, au travers d’interactions trophiques, jouer un rôle important dans le fonctionnement des écosystèmes en contrôlant les populations d’autres organismes qui ont eux-mêmes un effet conséquent sur les écosystèmes. Ce groupe est considéré comme assez résistant aux changements de température de l’eau de mer en milieu Antarctique. Il est cependant susceptible d’être affecté par les modifications des conditions environnementales et leur influence sur le fonctionnement des réseaux trophiques. En effet, la réduction de l’abondance ou la disparition de proies communes peut entraîner un risque accru compétition dans les assemblages d’étoiles de mer. Afin de déterminer le rôle écologique des étoiles de mer dans l’Océan Austral, et de comprendre comment elles pourraient être impactées par le changement climatique, une étude de leur écologie trophique et des facteurs qui la contrôlent est nécessaire. Par conséquent, les objectifs de cette thèse de doctorat étaient de déterminer quelle est la place des étoiles de mer dans l’Océan Austral, et comment des facteurs environnementaux comme la turbidité, la profondeur et la glace de mer impactent leur diversité trophique. Pour ce faire, les rapports isotopiques du carbone (δ13C), de l’azote (δ15N) et du soufre (δ34S) ont été analysés dans des tissus d’étoiles de mer prélevées dans l’ensemble de l’Océan Austral (n = 2454 individus, auxquels s’ajoutent des données sur 204 individus issues de la littérature ou partagées par des collègues). Une proportion importante des échantillons d’étoiles de mer est issue de collections archivées dans des institutions et/ou des muséums, ce qui a permis de significativement augmenter la couverture spatiale et temporelle de l’échantillonnage. Cependant, ces échantillons ont pour la plupart été conservés dans de l’éthanol, et certains ont été préalablement fixés avec du formaldéhyde. Or, les liquides de préservation peuvent altérer les rapports isotopiques des tissus biologiques. Par conséquent, l’impact de la méthode de préservation sur les rapports isotopiques dans les tissus d’étoiles de mer a été étudié (chapitre 3) lors d’une expérience à long terme (deux ans). Celle-ci a montré qu’il était possible de corriger mathématiquement l’effet des liquides de préservation sur les rapports isotopiques des étoiles de mer, et donc d’utiliser des échantillons archivés pour des études d’écologie trophique. Afin de mieux connaître l’importance potentielle des étoiles de mer dans les écosystèmes de l’Océan Austral, le réseau trophique des forêts de Macrocystis pyrifera (Phaeophycées, Laminariales ; ou “kelp”) subantarctiques a été reconstitué grâce à l’analyse des rapports isotopiques dans des tissus d’invertébrés (19 taxa, dont 6 d’étoiles de mer) et de producteurs primaires échantillonnés dans les îles Kerguelen (chapitre 4). L’utilisation de modèles de mélange isotopique a démontré qu’il n’y a pas de consommateur majeur de Macrocystis pyrifera dans ces forêts de kelp, et que le réseau trophique est alimenté par la matière organique pélagique et du micro/macrophytobenthos vivant (à l’exception du kelp) ou sous forme de détritus (incluant probablement des détritus de kelp). Ceci suggère que les étoiles de mer n’ont pas les mêmes fonctions écologiques dans les forêts à Macrocystis pyrifera des régions subantarctiques que dans celles des régions plus tempérées où elles contrôlent partiellement les populations d’herbivores. Nos résultats démontrent également que les étoiles de mer subantarctiques ne se limitent pas à être des prédateurs au sommet des chaînes alimentaires. D’une part, certaines espèces occupent d’autres positions trophiques plus basales. D’autre part, leurs niches trophiques ne se recouvrent pas nécessairement : certaines exploitent plus la partie du réseau trophique soutenu par la production pélagique et d’autres la partie du réseau trophique soutenue par la production benthique (y compris détritique). Après cette analyse d’un réseau trophique entier, nous avons réalisé une comparaison des niches isotopiques d’étoiles de mer à une échelle locale, et étudié les liens possibles entre changements ontogénétiques, c’est-à-dire au cours de la vie et de la croissance, et écologie trophique (chapitre 5). L’analyse des rapports isotopiques dans des étoiles de mer prélevées dans l’anse d’Ezcurra (baie de l’Amirauté, île du Roi-George, îles Shetland du sud) a montré que la taille, et plus particulièrement le rayon du disque central, peut être reliée aux rapports isotopiques chez certaines espèces, indiquant des changements ontogénétiques de l’alimentation chez ces dernières. Cette observation n’est cependant valable que pour certaines espèces, en particulier des espèces omnivores, où on observe une élévation de la position trophique en fonction de la taille de l’étoile de mer. La relation entre le rayon du disque et l’alimentation peut notamment s’expliquer par le fait que les étoiles de mer les plus grandes peuvent dévaginer leur estomac sur de plus grandes surfaces et donc consommer des proies plus grandes et/ou de niveau trophique plus élevé. Chez les étoiles de mer consommant du sédiment ou potentiellement suspensivores, cette relation entre la taille et les rapports isotopiques n’est généralement pas observée, ce qui suggère qu’il y a probablement moins de variabilité du régime alimentaire en fonction de la taille des individus chez ces espèces. L’analyse des rapports isotopiques dans les étoiles de mer prélevées dans l’anse d’Ezcurra indique également que certaines espèces d’étoiles de mer présentent une variabilité de régime alimentaire importante qui détermine en partie leurs interactions trophiques interspécifiques. La turbidité générée par l’apport de matière terrigène par les eaux de ruissellement issues de la fonte des glaciers terrestres crée un gradient environnemental important de l’intérieur vers l’extérieur de l’anse d’Ezcurra, qui détermine les conditions d’habitat et la nature des ressources disponibles pour les étoiles de mer. Certaines espèces adaptent leurs régimes alimentaires en fonction de ces conditions variables. Les interactions entre espèces sont également affectées. A l’intérieur de l’anse, sujet à une importante turbidité, les espèces Diplasterias brandti et Odontaster validus ont des valeurs de δ13C plus différenciées (i.e. des sources de nourriture plus différentes) et des niches isotopiques se recouvrant moins, qu’à l’extérieur, sujet à une turbidité moindre. De même, la taille de la niche isotopique d’Odontaster validus est plus réduite vers l’intérieur de l’anse que vers l’extérieur. Ceci correspond probablement à une situation moins favorable en termes de disponibilité et de diversité des ressources à l’intérieur de l’anse. Ceci pourrait conduire à une constriction de la niche isotopique d’Odontaster validus ainsi qu’à une ségrégation des ressources accrue qui pourrait limiter la compétition interspécifique entre les quelques espèces capables de survivre à ces conditions défavorables. Dans le chapitre 6, nous avons étudié l’impact du groupe trophique, de la profondeur, de la concentration de glace et de la durée de la saison glaciaire sur l’alimentation des étoiles de mer par l’intermédiaire d’une analyse globale de notre jeu de données à l’échelle de l’Océan Austral. De plus, l’Océan Austral a été subdivisé en différentes écorégions benthiques d’après des données environnementales (température au fond, glace de mer, bathymétrie) et biologique (distribution des espèces) afin d’étudier les variations biogéographiques de l’alimentation des étoiles de mer. Cette subdivision a notamment mis en évidence la séparation des environnements antarctique et subantarctique, la différence des valeurs de δ13C de la matière organique dans les eaux de surface entre les écorégions subantarctiques et antarctiques étant reflétée dans les tissus d’étoiles de mer benthiques. Dans ce chapitre, la compilation des informations disponibles sur leur régime alimentaire a permis de procéder à une classification des taxa d’étoiles de mer de l’Océan Austral en groupes trophiques, allant des suspensivores aux prédateurs de proies mobiles. Les différences de rapports isotopiques entre ces groupes trophiques et leur variabilité dans certains d’entre eux suggèrent une diversité des sources de nourriture et/ou des stratégies d’alimentation entre et au sein des groupes trophiques. Ces résultats confirment bien que, contrairement à ce qui est parfois dit dans la littérature, les étoiles de mer de l’Océan Austral font preuve d’une grande diversité trophique. La profondeur est apparue comme un facteur influençant fortement l’écologie trophique des étoiles de mer, aussi bien à l’échelle de tout l’Océan Austral que des écorégions. En effet, les étoiles de mer côtières semblent exploiter des réseaux trophiques soutenus par une diversité de producteurs primaires pélagiques et benthiques tandis que les étoiles de mer plus profondes paraissent dépendre de la sédimentation de la production primaire de surface. Ainsi, les étoiles de mer côtières sont caractérisées par l’exploitation d’un plus grand nombre de sources de matière organique. Par contre, il est également apparu que les étoiles de mer plus profondes ont une plus grande diversité de positions trophiques que les côtières. La plus faible diversité et la plus faible disponibilité des ressources trophiques en milieu profond pourraient favoriser la diversification des comportements alimentaires (e.g. omnivorie, prédation, consommation de sédiment) des étoiles de mer, ce qui pourrait permettre de réduire la compétition entre espèces. L’impact de la glace de mer sur l’alimentation des étoiles de mer antarctiques a également été étudié. En cas de forte concentration en glace de mer, les communautés sympagiques semblent être utilisées comme ressources trophiques par les étoiles de mer. De même, pour certains groupes trophiques, une dépendance croissante à l’égard de phytodetritus dégradés semble exister dans les stations où la durée de la saison glaciaire est la plus élevée. Ce mécanisme pourrait permettre d’atténuer les impacts de la glace de mer sur la disponibilité des ressources trophiques pendant les plus longues périodes de couverture de glace de mer. Nos résultats suggèrent aussi que les liens entre glace de mer et alimentation des consommateurs benthiques sont multiples mais complexes à interpréter. En outre, ils ne sont pas tous consistants d’une écorégion à l’autre, vraisemblablement en lien avec les caractéristiques océanographiques très variées que l’on peut y rencontrer. Enfin, les impacts des différents paramètres environnementaux peuvent varier d’un groupe trophique à l’autre, illustrant la nécessité de prendre en compte la diversité trophique pour prédire la susceptibilité des étoiles de mer aux changements environnementaux futurs, qu’ils soient d’origine naturelle ou anthropique. En résumé, les travaux présentés dans cette thèse montrent que l’écologie trophique des étoiles de mer de l’Océan Austral est influencée par un ensemble de facteurs intrinsèques (taille, groupe trophique) et extrinsèques (turbidité, profondeur, glace de mer). Les informations sur l’influence des facteurs environnementaux permettent d’établir des hypothèses sur les possibles impacts du changement climatique sur les étoiles de mer et leur rôle dans les réseaux trophiques benthiques de l’Océan Austral. En effet, les paramètres environnementaux influencent, au travers de la disponibilité en ressources, l’écologie trophique des étoiles de mer, et notamment les interactions entre espèces. Ainsi, la plus faible diversité et la plus faible disponibilité des ressources trophiques en milieu turbide et en milieu profond ont été considérées comme pouvant favoriser la diversification des comportements alimentaires pour éviter la compétition entre espèces. Au contraire, leur plus grande disponibilité en milieu peu turbide et côtier permet la consommation de proies similaires avec un risque limité de compétition. La glace de mer a des impacts plus variés sur la disponibilité en ressources trophiques, servant d’habitat aux communautés sympagiques et favorisant les efflorescences de phytoplancton lors de sa débâcle, mais les inhibant en cas de persistance. Par conséquent, les modifications de la couverture glaciaire et de sa dynamique à cause du changement climatique vont induire des changements dans la disponibilité des ressources trophiques pour le benthos de l’Océan Austral. De même, des modifications de la turbidité en milieu côtier suite à la modification de la dynamique des glaciers terrestres pourraient avoir des conséquences sur la disponibilité en ressources dans ce type d’environnement. Ces changements vont probablement modifier la nature des interactions trophiques entre les taxa d’étoiles de mer, avec une hausse ou une baisse de l’importance de la compétition, ce qui pourrait entraîner des modifications dans la structure des assemblages d’étoiles de mer dans l’Océan Austral. [en] Like in the rest of the world, climate change impacts the Southern Ocean, but not in the same way in all regions of this ocean. Changes in sea ice cover around the Antarctic continent are one of the most visible manifestations. For example, sea ice cover has decreased significantly in the Western Antarctic Peninsula while it tends to increase slightly on the rest of the coastline of the continent. These changes in environmental conditions influence the functioning of the ecosystems of this ocean. In particular, the disappearance or persistence of sea ice in a region where it was seasonally present may prevent the appearance of summer phytoplankton blooms, thus impacting the dynamics of krill populations and their predators in the pelagic environment. The benthic environment will also be disturbed by environmental modifications resulting from climate change, as organic matter fluxes toward this compartment will be affected. Sea stars (Echinodermata: Asteroidea) are a key component of Southern Ocean benthos, with 12% of the known sea star species living there. In temperate environments, this taxon may play an important role in the functioning of ecosystems with its trophic interactions controlling the populations of other organisms, which themselves have a large effect on the ecosystems. This group is considered to be quite resistant to changes of seawater temperature in the Antarctic environment. However, it will likely be affected by changes of environmental conditions and functioning of food webs. Indeed, a reduction in the abundance or disappearance of common prey can lead to an increased competition in sea star assemblages. In order to determine the ecological role of sea stars in the Southern Ocean and to understand how they might be impacted by climate change, a study of their trophic ecology and of the factors controlling it is necessary. Therefore, the objectives of this PhD thesis were to determine the trophic role of sea stars in the Southern Ocean, and how environmental factors such as turbidity, depth and sea ice impact their trophic diversity. To do so, stable isotope values of carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) were analysed in tissues of sea star sampled across the Southern Ocean (n = 2454 individuals, plus data on 204 individuals from the literature or shared by colleagues). A significant proportion of the sea star samples came from collections archived in institutions and/or museums, which significantly increased the spatial and temporal coverage of the study. However, most of these samples were preserved in ethanol, and some have been previously fixed with formaldehyde. Preservative fluids may alter the stable isotope values of biological tissues. Therefore, the impact of the preservation method on the stable isotope values in sea star tissues was studied (chapter 3). A two year-long experiment showed that it was possible to mathematically correct the effect of preservative fluids on stable isotope values in sea stars, making it possible to use archived samples for trophic ecology studies. In order to better understand the potential importance of sea stars in the ecosystems of the Southern Ocean, the food web of subantarctic Macrocystis pyrifera (Phaeophyceae, Laminariales; or “kelp”) forests was reconstructed by analysing stable isotope values in invertebrate (19 taxa, including 6 sea star taxa) and primary producer tissues sampled in the Kerguelen Islands (chapter 4). Mixing models did not highlight major Macrocystis pyrifera consumers and showed that the food web is supported by pelagic organic matter and live (with the exception of kelp) or detrital micro/macrophytobenthos. This suggests that sea stars do not have the same ecological function in Macrocystis pyrifera forests from subantarctic regions than in those from more temperate regions, where they control grazer populations. The results also show that sea stars are not only top predators in the food chain. On the one hand, some species may occupy lower trophic positions. On the other hand, their trophic niches may not overlap: some species rely more on the food chain supported by pelagic production and others on the food chain supported by benthic (including detrital) production. Following this analysis of an entire food web, isotopic niches of sea stars were compared at a local scale, and the possible relationship between ontogenetic changes, i.e. changes during growth, and trophic ecology were studied (chapter 5). The analysis of stable isotope values in sea stars sampled in Ezcurra Inlet (Admiralty Bay, King George Island, South Shetland Islands, chapter 5) showed that the size, and especially the central disc radius, can be linked to stable isotope values in some species, indicating the occurrence of ontogenetic changes in the diet of these species. This was observed only in some species, and notably omnivore species, for which the trophic position increased with body size. The relationship between the disc radius and the trophic ecology may be explained by larger sea stars being able to evert their stomach over larger areas and thus consume larger prey and/or prey with higher trophic level. For sediment feeding and potentially suspension feeding species, the relationship between size and stable isotope values was usually not observed, suggesting lower variability of the trophic ecology between size classes in these species. The analysis of stable isotope values in sea stars sampled in Ezcurra Inlet also indicates that the diet variability of some sea star species may be important, which in part determines their interspecific trophic interactions. The turbidity generated by the terrestrial inputs provided by meltwater run-off from terrestrial glaciers results in an important environmental gradient from the inner to the outer Ezcurra Inlet, which determines the habitat conditions and the characteristics of the resources available for sea stars. Some species may adapt their diet depending on those variable conditions. Interspecific interactions are also impacted. Indeed, the Diplasterias brandti and Odontaster validus species have more different δ13C values (i.e. more different food sources) and lower isotopic niche overlap in the inner inlet, where high turbidity occurs, than in the outer, where turbidity is lower. Similarly, the size of the isotopic niche of Odontaster validus is smaller in the inner Ezcurra Inlet than in the outer. This is probably the result of a more limited availability and diversity of resources in the inner inlet. This may lead to the constriction of Odontaster validus isotopic niche and to resource segregation that may limit interspecific competition between the few species able to survive in these unfavourable conditions. In the chapter 6, the impact of trophic group, depth, sea ice concentration and sea ice season duration on the trophic ecology of sea stars was assessed thanks to a global analysis of the dataset at the scale of the whole Southern Ocean. The Southern Ocean was subdivided into different benthic ecoregions according to environmental (seabed temperature, sea ice, bathymetry) and biotic data (species distribution), to study biogeographic variations in the trophic ecology of sea stars. This subdivision notably highlighted the separation between Antarctic and Subantarctic environments, with the different δ13C values in organic matter from the surface in Subantarctic and Antarctic waters being reflected in tissues from benthic sea stars. In this chapter, the compilation of the available information on their diet allowed to make a classification of sea star taxa from the Southern Ocean into trophic groups, ranging from suspension feeders to predators of active prey. The differences of stable isotope values between trophic groups and their variability in some of them suggested a diversity of food sources and/or of feeding strategies between and within trophic groups. These results confirm that, contrary to what is sometimes stated in the literature, sea stars in the Southern Ocean show a great trophic diversity. Depth has important effects on the trophic ecology of sea stars, both across the entire Southern Ocean and within ecoregions. Indeed, coastal sea stars may exploit food webs supported by a variety of pelagic and benthic primary producers while deeper sea stars may depend on the sedimentation of the surface primary production. Coastal sea stars are then characterised by a high diversity of food sources, while deeper sea stars have a higher diversity of trophic positions than coastal ones. The lower diversity and availability of food sources in deep waters may induce the diversification of sea star feeding behaviours (e.g. omnivory, predation, sediment feeding), which would reduce competition between species. The impact of sea ice on the trophic ecology of sea stars was also investigated. The sympagic communities may be used as a food source by sea stars in case high sea ice concentrations. Furthermore, increasing reliance on degraded phytodetritus during longer periods of sea ice cover may occur in several trophic groups. This may dampen the impacts of sea ice presence on resource availability during long periods of sea ice cover. Our results also suggest that multiple relationships do exist between sea ice and the diet of benthic consumers, but they are not easy to interpret. Finally, not all of them are consistent across ecoregions, probably as a result of their contrasted oceanographic features. In addition, the impacts of the environmental parameters may differ between trophic groups, highlighting the importance of trophic diversity to predict the sensitivity of sea stars to future environmental changes, whether natural or anthropogenic. To summarise, the studies of this thesis show that the trophic ecology of sea stars from the Southern Ocean is impacted by a combination of intrinsic (body size, trophic group) and extrinsic features (turbidity, depth, sea ice). Information on the influence of environmental parameters may provide hypotheses regarding the possible impacts of climate change on sea stars and on their role in benthic food webs of the Southern Ocean. Indeed, the environmental parameters may influence the trophic ecology of sea stars and the trophic interactions between taxa thanks to their impact on resource availability. The lower diversity and availability of food sources in turbid and deep waters have been considered as potential sources of diversification of feeding behaviours to avoid competition between species. By contrast, their greater availability in less turbid and coastal environments allows the consumption of similar prey with limited risks of competition. Sea ice has more variable impacts on resource availability, being an habitat for sympagic communities and inducing phytoplankton blooms after its break up, but inhibiting them in case of persistence. Consequently, changes in the ice cover and its dynamics because of climate change will induce changes in the resource availability for the Southern Ocean benthos. Similarly, changes in turbidity in coastal areas as a result of modifications in the dynamics of terrestrial glaciers could have consequences on resource availability in this type of environment. These changes are likely to modify the trophic interactions between sea star taxa, with an increase or decrease of the importance of competition, which may result in modifications of the structure of sea star assemblages in the Southern Ocean. |
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Varlamov A., Keptuke G., Lavrillier A. |
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Electronic Devices for Safeguarding Indigenous Languages and Cultures (Eastern Siberia) |
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Routledge Handbook of Indigenous Peoples in the Arctic |
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Le Bohec C. |
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Stratégies adaptatives et dynamique spatio-temporelle des populations de prédateurs marins face aux changements rapides de leur environnement |
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Dans le cadre des changements globaux attendus, il est urgent d’appréhender le devenir des écosystèmes et de la biodiversité qu’ils hébergent. L’étude des conséquences des fluctuations environnementales sur les traits phénotypiques des organismes, ainsi que celle des stratégies adaptatives et de la dynamique des populations qui en découle, sont fondamentales. Grâce au Observatoires du Vivant que je mets en place par le suivi électronique et/ou télémétrique de plusieurs espèces d’oiseaux marins des régions polaires/sub-polaires, mes recherches ont pour principal objectif la compréhension des processus écologiques et évolutifs qui façonnent les populations, et notamment les capacités d’adaptation des organismes face aux contraintes de leur environnement. Je m’intéresse à la plasticité phénotypique et aux mécanismes microévolutifs, deux processus par lesquels les traits phénotypiques au sein d’une population sont capables de s’ajuster aux changements du milieu. La dynamique spatio-temporelle des populations est traitée à différentes échelles, de la colonie aux écosystèmes. A l’interface entre l'écologie évolutive, la génétique et la dynamique des populations, mon projet favorise le développement de modèles mathématiques globaux. Ces derniers permettent de comprendre les liens existants entre les modifications survenant dans l’environnement et les trajectoires spatio-temporelles de ces populations. Les modèles prédictifs obtenus nous informent sur l’évolution de la composante biologique de l’océan Austral. Ils permettront à terme de mettre en place des stratégies de conservation et de gestion durables de la biodiversité et des ressources naturelles. |
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