Alkenone unsaturation index and alkenones in ODP Hole 161-977A

A number of essential elements closely related to each other are involved in the Earth's climatic system. The temporal and spatial distribution of insolation determines wind patterns and the ocean's thermohaline pump. In turn, these last two are directly linked to the extension and retreat of marine and continental ice and to the chemistry of the atmosphere and the ocean. The variability of these elements may trigger, amplify, sustain or globalize rapid climatic changes. Paleoclimatic oscillations have been identified in this thesis by using fossil organic compounds synthesized by marine and terrestrial flora. High sedimentation rate deposits at the Barents and the Iberian peninsula continental margins were chosen in order to estimate the climatic changes on centennial time resolution. At the Barents margin, the sediment recovered was up to 15,000 years old (unit ''a'', from latin ''annos'') (M23258; west of the Bjørnøya island). At the Iberian margin, the sediment cores studied covered a wide range of time spans: up to 115,000 a (MD99-2343; north of the Minorca island), up to 250,000 a (ODP-977A; Alboran basin) and up to 420,000 a (MD01-2442, MD01-2443, MD01-2444, MD01-2445; close to the Tagus abyssal plain). At the northern site, inputs containing marine, continental and ancient reworked organic matter provided a detailed reconstruction of climate history at the time of the final retreat of the Barents ice sheet. At the western Barents continental slope, warm climatic conditions were observed during the early Holocene (~from 8,650 a to 5,240 a ago); in contrast, an apparent long-term cooling trend occurred in the late Holocene (~from 5,240 a to 760 a ago), in consistence with other paleoarchives from northern and southern European latitudes. The Iberian margin sites, which were never covered with large ice sheets, preserved exceptionally complete sequences of rapid events during ice ages hitherto not studied in such great detail: during the last glacial (~from 70,900 a to 11,800 a ago), the second glacial (~from 189,300 a to 127,500 a ago), the third ice age (~from 278,600 a to 244,800 a ago) and the fourth (~from 376,300 a to 337,500 a ago). In this thesis, crucial research questions were brought up concerning the severity of different glacial periods, the intensity and rates of the recorded oscillations and the long distance connections related to rapid climate change. The data obtained provide a sound basis to further research on the mechanisms involved in this rapid climate variability. An essential point of the research was the evidence that, over the past 420,000 a, at the whole Iberian margin, warm and stable long periods similar to the Holocene always ended abruptly in few centuries after a gradual deterioration of climate conditions. The detailed estimate of past climate variability provides clues to the natural end of the present warm period. Returning to an ice age in European lands would be exacerbated by a number of factors: a lack of differential solar heating between northern and southern north Atlantic latitudes, enhanced evaporation at low latitudes, and an increase in snowfall or iceberg discharges at northern regions. It must be emphasized that all climatic oscillations observed in this thesis were caused by forces of nature, i.e. the last two centuries were not taken into consideration.

Pollen and macrofossil profiles from six cores in Illinois, U.S.A

Pollen analysis of Wisconsinan sediments from eleven localities in northern and central Illinois, combined with the results of older studies, allows a first general survey of the vegetational changes in Illinois during the last glaciation. In the late Altonian (after 40,000 B.P.), pine was already the most prevalent tree type in northern Illinois. Probably because of the influence of the last Altonian ice advance to northern Illinois, pine migrated to the south and reached south-central Illinois, which was at that time a region of prairie, with oak and hickory trees in favorable sites. Likewise in the late Altonian, spruce appeared in northern Illinois. Spruce also expanded its area to the south during the Wisconsinan, reaching south-central Illinois only after 21,000 B.P., in the early Woodfordian. Deciduous trees (predominantly oak) were present in south-central Illinois throughout the Wisconsinan. Their prevalence decreased to the north. The vegetation during the different subdivisions of the last glacial period in Illinois was approximately as follows: Late Altonian: Pine/spruce forest with some deciduous trees in northern and central Illinois; prairie and oak/hickory stands in south-central Illinois; immigration of pine. Farmdalian: Pine/spruce forest in central Illinois; deciduous trees and pine in south-central Illinois, with areas of open vegetation, perhaps similar to the present-day transition of prairie to forest in the northern Great Plains. Woodfordian: Northern and central Illinois ice covered; in south central Illinois, spruce and oak as dominant tree types, but also pine and grassland. During the Woodfordian, pine and spruce disappeared again from south-central Illinois, and oak/hickory forest and prairie again prevailed. The ice-free areas of northern Illinois become populated temporarily with spruce, but later there is proof of deciduous forest in this region. Pollen investigations in south-central Illinois have shown convincingly that deciduous trees could survive relatively close (less than 60 km) to the ice margin. Therefore the frequently presented view that arctic climatic conditions prevailed in North America during the last glaciation far south of the ice margin can be refuted for the Illinois area, confirming the opinion of other authors resulting from investigations of fossil mollusks and frost-soil features. The small number of localities investigated still permits no complete reconstruction of the vegetation zones and their possible movements in Illinois. During the Altonian and Farmdalian in Illinois, a vegetational zonation probably existed similar to that of today in North America. As the ice pushed southward as far as 39° 20' N. lat in the early Woodfordian, this zonation was apparently broken up under the influence of a relatively moderate climate. In any case, the Vandalia area, which was only about 60 km south of the ice, was at that time neither in a tundra zone nor in a zone of boreal coniferous forest.

(Table 1) Nd isotope ratios of ODP Leg 208 samples

We present new Nd isotope records from Walvis Ridge Ocean Drilling Program (ODP) sites 1262-1264 (southeastern Atlantic) spanning the past 24 Ma to investigate the Neogene evolution of Atlantic thermohaline circulation. The new data indicate that deepwater epsilon-Nd(t) values from ODP Site 1262 decrease from -11.0 at 10.6 Ma to -12.5 by 7.3 Ma. This decrease parallels the Nd isotope trends contained in Fe-Mn crust records from the northwestern Atlantic; however, the shift at ODP Site 1262 (4755 m water depth) occurred up to ~6 Ma earlier than the corresponding changes in crust records from the Atlantic and earlier than any Atlantic site shallower than 2700 m paleowater depth. Recent interpretations of the rapid decrease in Fe-Mn crust Nd epsilon-Nd(t)ss values invoke changes in weathering inputs to the Labrador Sea region rather than a fundamental change in deepwater convection in the Labrador Sea. However, the new evidence for significant depth stratification of the Nd isotope signal in the southeastern Atlantic between 10.6 and 7.3 Ma suggests that the onset of deepwater convection in the Labrador Sea may have played a role in the deepwater decrease in Nd isotopic composition. Climatic conditions during the middle to late Miocene likely favored an increase in the importance of glacially induced mechanical weathering, while at the same time promoting deep convection in the Labrador Sea.

(Table 1) Major element composition of core 5022-2CP, Laguna Potrok Aike, southern Patagonia

Total organic carbon, total inorganic carbon, biogenic silica content and total organic carbon/total nitrogen ratios of the Laguna Potrok Aike lacustrine sediment record are used to reconstruct the environmental history of south-east Patagonia during the past 51 ka in high resolution. High lake level conditions are assumed to have prevailed during the Last Glacial, as sediments are carbonate-free. Increased runoff linked to permafrost and reduced evaporation due to colder temperatures and reduced influence of Southern Hemispheric Westerlies (SHW) may have caused these high lake levels with lake productivity being low and organic matter mainly of algal or cyanobacterial origin. Aquatic moss growth and diatom blooms occurred synchronously with southern hemispheric glacial warming events such as the Antarctic A-events, the postglacial warming following the LGM and the Younger Dryas chronozone. During these times, a combination of warmer climatic conditions with related thawing permafrost could have increased the allochthonous input of nutrients and in combination with warmer surface waters increased aquatic moss growth and diatom production. The SHW were not observed to affect southern Patagonia during the Last Glacial. The Holocene presents a completely different lacustrine system because (a) permafrost no longer inhibits infiltration nor emits meltwater pulses and (b) the positioning of the SHW over the investigated area gives rise to strong and dry winds. Under these conditions total organic carbon, total organic carbon/total nitrogen ratios and biogenic silica cease to be first order productivity indicators. On the one hand, the biogenic silica is influenced by dissolution of diatoms due to higher salinity and pH of the lake water under evaporative stress characterizing low lake levels. On the other hand, total organic carbon and total organic carbon/total nitrogen profiles are influenced by reworked macrophytes from freshly exposed lake level terraces during lowstands. Total inorganic carbon remains the most reliable proxy for climatic variations during the Holocene as high precipitation of carbonates can be linked to low lake levels and high autochthonous production. The onset of inorganic carbon precipitation has been associated with the southward shift of the SHW over the latitudes of Laguna Potrok Aike. The refined age-depth model of this record suggests that this shift occurred around 9.4 cal. ka BP.

Age model and chemistry of sediment core STK7 from Steisslinger See

Stable isotope records for carbon and oxygen in bulk carbonates, carbon in bulk organic matter, and for total and chromium-reducible sulfur in a lacustrine sediment core from Lake Steisslingen (Southwest Germany) show several distinct and abrupt shifts during the last 15,000 years. Variations in the isotopic composition of authigenic carbonates indicate two major phases in the lake history. In the pre-Holocene, the hydrological budget of the lake was apparently stable. Variations of delta18O values of authigenic carbonates were, therefore, dominantly controlled by temperature changes. A decrease in the delta18Ocarb values of about 2 per mil at the Allerød/Younger Dryas transition is interpreted as a drop in mean annual air temperatures of approximately 5°C. An abrupt temperature increase of a similar magnitude is inferred at the Younger Dryas/Preboreal boundary. Throughout most of the Holocene, the isotopic composition of authigenic carbonates was influenced by marked changes in the hydrological budget of the lake. A major positive excursion in the delta13Ccarb and delta18Ocarb values at the beginning of the Atlantic and a smaller one in the Preboreal were related to evaporation effects, which indicate that dry climatic conditions must have prevailed at that time. A simultaneous increase in delta13C values of bulk organic matter at the beginning of the Atlantic suggests a high level of productivity in the lake. As a consequence, aqueous sulfate became limited as indicated by variations in the delta34S values of total and chromium-reducible sedimentary sulfur. Therefore, we conclude that the beginning of the Atlantic was characterized not only by dry but also by warm climatic conditions, which triggered a higher productivity in the lake. In the Subatlantic sediments, large variations in carbon, oxygen, and sulfur isotope ratios were observed as a result of human activities, causing considerable perturbations in the biogeochemical element cycling of Lake Steisslingen. Results obtained by the study of the continuous 15 ka record of Lake Steisslingen document clearly that isotopic proxy data from lacustrine sediments can provide useful information on environmental and climatic changes of local, regional, and in the case of the Younger Dryas event, of even hemispherical significance.

Late Pleistocene sedimentation in the Western Mediterranean Sea

Sediment cores from the Western Mediterranean Sea (WMS) have been analyzed for their bulk element composition, delta18O values of planktic foraminiferal tests, and 87Sr/86Sr and 143Nd/144Nd ratios of their bulk lithogenic components. The investigated time interval comprises the last 215 kyr. Si/Al and Ti/Al ratios as well as radiogenic isotope compositions indicate changes in the provenance of the lithogenic components between glacial intervals and interglacial phases. Comparison with modern data indicates that detrital input from the northwestern and northeastern Sahara may have dominated during interglacial phases. In contrast, during glacial periods the accumulation rate of terrigenous sediment is high and changes in the sediment source areas are evident that may be related to changes in the prevailing atmospheric circulation over the basin and its source areas. A productivity reconstruction based on bio-mediated barium accumulation rates reveals increased surface productivity during glacial phases. Intervals time-equivalent to sapropel formation in the Eastern Mediterranean Sea (EMS) show no changes in surface productivity compared to the intervening intervals. Comparison of the productivity patterns between the WMS and EMS suggests a decoupling during Late Pleistocene sapropel formation and highlights the importance of more localized factors such as the freshwater drainage basin.

Modern major element concentrations and ratios measured in Atlantic surface sediments (36°N-49°S)

Numerous studies use major element concentrations measured on continental margin sediments to reconstruct terrestrial climate variations. The choice and interpretation of climate proxies however differ from site to site. Here we map the concentrations of major elements (Ca, Fe, Al, Si, Ti, K) in Atlantic surface sediments (36°N-49°S) to assess the factors influencing the geochemistry of Atlantic hemipelagic sediments and the potential of elemental ratios to reconstruct different terrestrial climate regimes. High concentrations of terrigenous elements and low Ca concentrations along the African and South American margins reflect the dominance of terrigenous input in these regions. Single element concentrations and elemental ratios including Ca (e.g., Fe/Ca) are too sensitive to dilution effects (enhanced biological productivity, carbonate dissolution) to allow reliable reconstructions of terrestrial climate. Other elemental ratios reflect the composition of terrigenous material and mirror the climatic conditions within the continental catchment areas. The Atlantic distribution of Ti/Al supports its use as a proxy for eolian versus fluvial input in regions of dust deposition that are not affected by the input of mafic rock material. The spatial distributions of Al/Si and Fe/K reflect the relative input of intensively weathered material from humid regions versus slightly weathered particles from drier areas. High biogenic opal input however influences the Al/Si ratio. Fe/K is sensitive to the input of mafic material and the topography of Andean river drainage basins. Both ratios are suitable to reconstruct African and South American climatic zones characterized by different intensities of chemical weathering in well-understood environmental settings.

Clay-mineral composition and biogenic opal content of Late Neogene to Quaternary sediments of the Antarctic Peninsula region

Clay-mineral composition and biogenic opal content in upper Miocene to Quaternary drift sediments recovered at two Ocean Drilling Program (ODP) sites from the continental rise in the Bellingshausen Sea had been analyzed in order to reconstruct the climatic and glacial history of the Antarctic Peninsula. The clay mineral composition at both sites is dominated by smectite, illite, and chlorite, and alternates between a smectite-enriched and a chlorite-enriched assemblage throughout the last 9.3 my. The spatial distribution of clay minerals in Holocene sediments west of the Antarctic Peninsula facilitates the identification of particular source areas, and thus the reconstruction of transport pathways. The similarity to clay mineral variations reported from upper Quaternary sequences suggests that the short-term clay-mineralogical fluctuations in the ODP cores reflect glacial-interglacial cyclicity. Thus, repeated ice advances and retreats in response to a varying size of the Antarctic Peninsula ice cap are likely to have occurred throughout the late Neogene and Quaternary. The clay minerals in the drift sediments exhibit only slight long-term variations, which are caused by local changes in glacial erosion and in supply of source rocks, rather than by major climatic changes. The opal records at the ODP sites are dominated by long-term variations since the late Miocene. We infer that the opal content in the drift sediments, although it is influenced by dissolution in the water column and the sediment column and by the burial with lithogenic detritus, provides a signal of paleoproductivity. Because the annual sea-ice coverage is regarded as the main factor controlling biological productivity, the opal signal helps to reconstruct paleoceanographic changes in the Bellingshausen Sea. Slightly enhanced opal deposition during the late Miocene indicates slightly warmer climatic conditions in the Antarctic Peninsula area than at present. During the early Pliocene, enhanced opal deposition in the Pacific sector of the Southern Ocean and coinciding high opal concentrations in sedimentary sequences from the Atlantic and Indian sectors document a strong reduction of sea-ice cover and relatively warm climatic conditions. Thereby, the early onset of the Pliocene warmth in the Bellingshausen Sea points to a positive feedback of regional Antarctic climate on the global thermohaline circulation. A decrease of opal deposition between 3.1 and 2.6 Ma likely reflects sea-ice expansion in response to reduced supply of northern-sourced deep-waters to the Southern Ocean, caused by the onset of Northern Hemisphere glaciation. Throughout the Quaternary, a relatively constant level of opal deposition on the Antarctic continental margin indicates relatively stable climatic conditions.

Haptophyta

Haptophyta are predominantly planktonic and phototrophic organisms that have their main distribution in marine environments worldwide. They are a major component of the microbial ecosystem, some form massive blooms and some are toxic. Haptophytes are significant players in the global carbonate cycle through photosynthesis and calcification. They are characterized by the haptonema, a third appendage used for attachment and food handling, two similar flagella, two golden-brown chloroplasts, and organic body scales that serve in species identification. Coccolithophores have calcified scales termed coccoliths. Phylogenetically Haptophyta form a well-defined group and are divided into two classes Pavlovophyceae and Coccolithophyceae (Prymnesiophyceae). Currently, about 330 species are described. Environmental DNA sequencing shows high haptophyte diversity in the marine pico- and nanoplankton, of which many likely represent novel species and lineages. Haptophyte diversity is believed to have peaked in the past and their presence is documented in the fossil record back to the Triassic, approximately 225 million years ago. Some biomolecules of haptophyte origin are extraordinarily resistant to decay and are thus used by geologists as sedimentary proxies of past climatic conditions.

Haptophyta

Haptophyta are predominantly planktonic and phototrophic organisms that have their main distribution in marine environments worldwide. They are a major component of the microbial ecosystem, some form massive blooms and some are toxic. Haptophytes are significant players in the global carbonate cycle through photosynthesis and calcification. They are characterized by the haptonema, a third appendage used for attachment and food handling, two similar flagella, two golden-brown chloroplasts, and organic body scales that serve in species identification. Coccolithophores have calcified scales termed coccoliths. Phylogenetically Haptophyta form a well-defined group and are divided into two classes Pavlovophyceae and Coccolithophyceae (Prymnesiophyceae). Currently, about 330 species are described. Environmental DNA sequencing shows high haptophyte diversity in the marine pico- and nanoplankton, of which many likely represent novel species and lineages. Haptophyte diversity is believed to have peaked in the past and their presence is documented in the fossil record back to the Triassic, approximately 225 million years ago. Some biomolecules of haptophyte origin are extraordinarily resistant to decay and are thus used by geologists as sedimentary proxies of past climatic conditions.

Agua y desarrollo urbano en la Castilla medieval: aportaciones a su estudio en la ciudad de Guadalajara

Uno de los elementos críticos del urbanismo castellano en la Edad Media era el acceso a recursos hídricos que pudieran servir para el abastecimiento humano. En función del clima, la orografía, y las infraestructuras heredadas de épocas anteriores, cada ciudad y villa del reino trató de buscar la mejor manera de asegurar el suministro de agua para sus vecinos. A lo largo de este trabajo se analiza la forma en la que el concejo de Guadalajara, así como los principales poderes religiosos y nobiliarios de la ciudad, fueron trazando la red de abastecimiento urbano durante la Baja Edad Media, a partir de las fuentes del paraje conocido como El Sotillo, y cómo realizaron la explotación económica del cauce del río Henares en las cercanías del municipio. El agua, bien escaso en la Alcarria, fue durante los siglos bajomedievales un elemento de gran importancia económica y símbolo de prestigio social, que despertó el interés de todos los grupos de la sociedad arriacense.

Herd management and livestock productivity in the Altai region of Western Mongolia

This thesis analyses the influence of qualitative and quantitative herbage production on seasonal rangelands, and of herd and pasture use strategies on feed intake, body mass development and reproductive performance of sheep and goats in the Altai mountain region of Bulgan county (soum) in Khovd province (aimag). This westernmost county of Mongolia is characterized by a very poor road network and thus very difficult access to regional and national markets. The thesis explores in this localized context the current rural development, the economic settings and political measures that affect the traditional extensive livestock husbandry system and its importance for rural livelihoods. Livestock management practices still follow the traditional transhumant mode, fully relying on natural pasture. This renders animal feeding very vulnerable to the highly variable climatic conditions which is one of many reasons for gradually declining quantity and quality of pasture vegetation. Small ruminants, and especially goats, are the main important species securing economic viability of their owners’ livelihood, and they are well adapted to the harsh continental climate and the present low input management practices. It is likely that small ruminants will keep their vital role for the rural community in the future, since the weak local infrastructure and slow market developments currently do not allow many income diversification options. Since the profitability of a single animal is low, animal numbers tend to increase, whereas herd management does not change. Possibilities to improve the current livestock management and thus herders’ livelihoods in an environmentally, economically and socially sustainable manner are simulated through bio-economic modelling and the implications are discussed at the regional and national scale. To increase the welfare of the local population, a substantial infrastructural and market development is needed, which needs to be accompanied by suitable pasture management schemes and policies

Analysis of the Market Potential of Syrian Organic Fruit and Vegetables for Exports to Germany

Syria has been a major producer and exporter of fresh fruit and vegetables (FFV) in the Arabic region. Prior to 2011, Syrian FFV were mainly exported to the neighbouring countries, the Gulf States and Northern Africa as well as to Eastern European countries. Although the EU is potentially one of the most profitable markets of high quality FFV (such as organic ones) in the world, Syrian exports of FFV to Western European countries like Germany have been small. It could be a lucrative opportunity for Syrian growers and exporters of FFV to export organic products to markets such as Germany, where national production is limited to a few months due to climatic conditions. Yet, the organic sector in Syria is comparatively young and only a very small area of FFV is certified according to EU organic regulations. Up to the author’s knowledge, little was known about Syrian farmers’ attitudes towards organic FFV production. There was also no study so far that explored and analysed the determining factors for organic FFV adoption among Syrian farmers as well as the exports of these products to the EU markets. The overarching aim of the present dissertation focused on exploring and identifying the market potential of Syrian exports of organic FFV to Germany. The dissertation was therefore concerned with three main objectives: (i) to explore if German importers and wholesalers of organic FFV see market opportunities for Syrian organic products and what requirements in terms of quality and quantity they have, (ii) to determine the obstacles Syrian producers and exporters face when exporting agricultural products to Germany, and (iii) to investigate whether Syrian farmers of FFV can imagine converting their farms to organic production as well as the underlying reasons why they do so or not. A twofold methodological approach with expert interviews and a farmer survey were used in this dissertation to address the abovementioned objectives. While expert interviews were conducted with German and Syrian wholesalers of (organic) FFV in 2011 (9 interviews each), the farmer survey was administrated with 266 Syrian farmers of FFV in the main region for the production of FFV (i.e. the coastal region) from November 2012 till May 2013. For modelling farmers’ decisions to adopt organic farming, the Theory of Planned Behaviour as theoretical framework and Partial Least Squares Structural Equation Modelling as the main method for data analysis were used in this study. The findings of this dissertation yield implications for the different stakeholders (governmental institutions and NGOs, farmers, exporters, wholesalers, etc.) who are interested in prompting the Syrian export of organic products. Based on the empirical results and a literature review, an action plan to promote Syrian production and export of organic products was developed which can help in the post-war period in Syria at improving the organic sector.

Anticipating future risk in social-ecological systems using fuzzy cognitive mapping: the case of wildfire in the Chiquitania, Bolivia

Understanding complex social-ecological systems, and anticipating how they may respond to rapid change, requires an approach that incorporates environmental, social, economic, and policy factors, usually in a context of fragmented data availability. We employed fuzzy cognitive mapping (FCM) to integrate these factors in the assessment of future wildfire risk in the Chiquitania region, Bolivia. In this region, dealing with wildfires is becoming increasingly challenging because of reinforcing feedbacks between multiple drivers. We conducted semistructured interviews and constructed different FCMs in focus groups to understand the regional dynamics of wildfire from diverse perspectives. We used FCM modelling to evaluate possible adaptation scenarios in the context of future drier climatic conditions. Scenarios also considered possible failure to respond in time to the emergent risk. This approach proved of great potential to support decision making for risk management. It helped identify key forcing variables and generate insights into potential risks and trade-offs of different strategies. The “Hands-off” scenario resulted in amplified impacts driven by intensifying trends, affecting particularly the agricultural production under drought conditions. The “Fire management” scenario, which adopted a bottom-up approach to improve controlled burning, showed less trade-offs between wildfire risk reduction and production compared with the “Fire suppression” scenario. Findings highlighted the importance of considering strategies that involve all actors who use fire, and the need to nest these strategies for a more systemic approach to manage wildfire risk. The FCM model could be used as a decision-support tool and serve as a “boundary object” to facilitate collaboration and integration of different perceptions of fire in the region. This approach also has the potential to inform decisions in other dynamic frontier landscapes around the world that are facing increased risk of large wildfires.

Influence du climat, de la disponibilité des ressources et de la taille des populations sur la phénologie et les patrons de migration du caribou migrateur, "Rangifer tarandus"

De nombreuses populations migratrices sont actuellement en déclin. Les changements climatiques entrainent des modifications dans les habitats des espèces migratrices et la phénologie des processus naturels, lesquels se répercutent sur la migration, une période critique pour ces espèces. Comprendre comment les variables environnementales et climatiques affectent la phénologie et les patrons de migration est donc crucial. Ma thèse s’intéresse à l’impact du climat, des ressources alimentaires et de la compétition sur les migrations printanières et automnales des caribous migrateurs, Rangifer tarandus, des troupeaux Rivière-George (TRG) et Rivière-aux-Feuilles (TRF) du Nord-du-Québec et du Labrador. Le premier volet de ma thèse propose une approche objective, basée sur la détection des changements dans la structure des déplacements saisonniers, pour identifier les dates de départ et arrivée en migration. Validée à l’aide de trajets simulés, elle a été appliquée aux migrations printanières et automnales de femelles caribous. Le second volet porte sur l’impact des conditions environnementales sur la phénologie des migrations de printemps et d’automne. Il montre que la phénologie de la migration est principalement affectée par les conditions climatiques rencontrées lors de la migration, les conditions d’enneigement affectant notamment les coûts des déplacements. Au printemps, les caribous subissent des conditions défavorables lorsque la fonte des neiges est précoce. À l’automne, ils semblent ajuster leurs déplacements et migrent plus vite quand la neige débute tôt pour limiter les coûts de déplacement dans une neige profonde. Le troisième volet porte sur les patrons de migration à l’automne et montre que ceux-ci sont affectés essentiellement par une compétition intra- et inter-troupeaux pour les aires d’hivernages. Les caribous du TRG répondent à une augmentation de la compétition sur les aires les plus proches de l’aire de mise bas, liée à une taille de population élevée, en migrant préférentiellement vers les aires les plus éloignées. L’utilisation des aires hivernales par les caribous du TRF est, quant à elle, contrainte par la présence et l’abondance du TRG, cette contrainte diminuant à mesure que le TRG décline et abandonne les migrations vers les aires d’hivernages communes aux deux troupeaux. Cette thèse améliore notre compréhension de l’influence des facteurs environnementaux sur la phénologie et les patrons de migration du caribou migrateur. Ces connaissances sont très utiles pour comprendre l’impact des changements climatiques et établir les plans de conservation pour les espèces migratrices.