Given its crucial role in atmospheric chemistry and its global warming potential, methane(CH4) deserves to be accurately budgeted. However, the recent renewed rise in atmosphericCH4 growth rates from 2007 on, after a few years of slow-down, attests that sources are notcompensated anymore by sinks, and calls for a better assessment of the processes contributingto the global CH4 budget. Among natural sources, oceanic emissions are still subject tomany uncertainties, due to the lack of sampling. This is particularly relevant in polar regions,where the role of sea ice on CH4 sea-air fluxes is largely unknown.In an effort to contribute to a better characterisation of CH4 dynamics in oceanic environments,we investigated very contrasted settings during a journey from temperate to polarregions and applied the concentration and stable isotope approach.We start by evaluating the performance of a commercially available in situ CH4 sensor(CONTROS HydroC® CH4 from Kongsberg Contros) in controlled and natural environments,with the hope of using it in the framework of our various field campaigns. Although thissensor has the potential to significantly increase the spatial and temporal resolution comparedto discrete sampling, the long response time prevents from using its measurements as absolutevalues in dynamic natural environments and calls for progress in the field of technologies forcontinuous in situ dissolved CH4 measurements. However, the sensor turns out to be veryuseful during cruises to observe relative changes in dissolved CH4 concentrations and guidethe discrete sampling episodes.Our journey starts in the Scheldt estuary, at the transition between land and sea. Stableisotope analyses reveal that the unusual enrichment of dissolved CH4 in 13C and D in theupper estuary could result from intense microbial oxidation or an unknown source upstream.In the lower part of the estuary, this enriched CH4 mixes with depleted CH4 produced bymethanogenesis in the sediments, before entering the North Sea.In the shallow coastal Wadden Sea, we highlight the dominant contribution of coastal areasto oceanic CH4 emissions. The progressive increase in dissolved CH4 concentrations coincidedwith a 2°C warming of seawater. Submarine groundwater discharge, controlled by thespring-neap tide cycle, and tidal pumping might also have contributed to temporal variationsin dissolved CH4 concentrations and isotopic composition.In the Barents Sea, sailing towards polar latitudes, we find that the fractional sea-ice coverdid not induce a significant change in CH4 concentration nor isotopic composition at theocean-atmosphere interface. Local CH4 seepages at the seafloor might be a relict of gashydrate dissociation after the retreat of the Scandinavian Ice Sheet from the continental shelfafter the Last Glacial Maximum.Trapped in landfast sea ice at Barrow (Arctic) and Cape Evans (Antarctic), we find thatthe processes governing CH4 dynamics in sea ice happen to be dependent on the season andthe regional setting, and can be unravelled thanks to stable isotope analyses. At Barrow,the range of delta-13C values points towards in-ice microbial oxidation of CH4 produced bymethanogenesis in the underlying sediments. At Cape Evans, the much higher delta-13C valuessuggest a hydrothermal origin of CH4 trapped in sea ice and/or aerobic production withinsea ice.The journey ends in the Ross Sea, where the high variability and supersaturation observed indissolved CH4 concentrations, as well as carbon isotope signatures typical of a thermogenicorigin, suggest that gas seepages on the continental shelf might be the main source of CH4 tothe water column.This unique dataset of CH4 concentration and stable isotope composition in seawater, in seaice and in the atmosphere, highlights the spatial and temporal variability of the processesgoverning CH4 dynamics across the various oceanic environments investigated. This thesisprovides an example of how the isotopic approach can be successfully applied to disentanglethe biogeochemical cycle of CH4. To better constrain oceanic emissions, we recommend theimplementation of an extensive monitoring network to measure dissolved CH4 continuously,particularly in shallow coastal regions, which contribute the most. Eventually, further studiesshould focus on the Southern Ocean, which has yet to reveal its secrets with regard to CH4dynamics. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Despite high taxonomic diversity elsewhere in North America during the Pleistocene, vertebrate faunas are exceedingly rare in the region of northern Mexico. Térapa, a unique fossil site located in the present-day desert of Northcentral Sonora, Mexico (29°41́N, 109°39́W, 605. m elevation), contributes to our understanding of the paleoecology and paleoclimate of the region during the Late Pleistocene, ca. 43,000-40,000. cal.yr BP. At least 60 vertebrate taxa, including amphibians, turtles, a crocodilian, snakes, birds and many mammals, have been recovered from an 11-m thick sequence of fossiliferous sediments. The diversity and tropical affinity of these taxa suggest a more-forested environment than the thornscrub desert habitat present in this region today.Isotopic analyses of tooth enamel carbonate from ancient mammalian herbivores suggest that the Sonoran desert has undergone considerable climate change since the Late Pleistocene. Bulk carbon (́13C) and oxygen (́18O) isotopes from nine mammalian fossils indicate a habitat mosaic with variations in diet that include browsers, mixed feeders and C4 hyper-grazers (́13C range of -10‰ to 2‰). Unique to this site are 13C tooth enamel values of -6.1 and -5.6 ‰ for the deer Odocoileus, which suggest a more variable diet than strict browsing, including possibly feeding on CAM and/or C4 plants. Serial sampling of carbon (δ13C) and oxygen (δ18O) isotopes for ancient mammal teeth with hypsodont dentitions (fossil Equus and Bison,) as well as δ18O meteroric water estimates from well-supported climatic models suggest a cooler and more equable environment at Térapa during the Late Pleistocene. These results also support previous habitat reconstructions inferred from the macrobotanical and packrat midden records of northern Sonora (Mexico). High-resolution stable isotope geochemistry indicates that: 1) ancient Térapa was covered with forest and grassland habitats that extended northward into Mexico by about 350km relative to their present-day northern limits during the Late Pleistocene; and 2) an Amount Effect (AE) is demonstrated in the fossil record at Térapa even though the climate was less seasonal compared to the modern desert habitat.

Kangaroos are the world's most diverse group of herbivorous marsupials. Following late-Miocene intensification of aridity and seasonality, they radiated across Australia, becoming the continent's ecological equivalents of the artiodactyl ungulates elsewhere. Their diversity peaked during the Pleistocene, but by approximately 45,000 years ago, 90% of larger kangaroos were extinct, along with a range of other giant species. Resolving whether climate change or human arrival was the principal extinction cause remains highly contentious. Here we combine craniodental morphology, stable-isotopic, and dental microwear data to reveal that the largest-ever kangaroo, Procoptodon goliah, was a chenopod browse specialist, which may have had a preference for Atriplex (saltbushes), one of a few dicots using the C4 photosynthetic pathway. Furthermore, oxygen isotope signatures of P. goliah tooth enamel show that it drank more in low-rainfall areas than its grazing contemporaries, similar to modern saltbush feeders. Saltbushes and chenopod shrublands in general are poorly flammable, so landscape burning by humans is unlikely to have caused a reduction in fodder driving the species to extinction. Aridity is discounted as a primary cause because P. goliah evolved in response to increased aridity and disappeared during an interval wetter than many it survived earlier. Hunting by humans, who were also bound to water, may have been a more decisive factor in the extinction of this giant marsupial.

Neogene land-mammal localities are very rare in the northeastern U.S.; therefore, the late Miocene/early Pliocene Gray Fossil Site in eastern Tennessee can clarify paleoecological dynamics during a time of dramatic global change. In particular, the identification of ancient forests and past climate regimes will better our understanding of the environmental context of mammalian evolution during the late Cenozoic. Stable isotope analyses of bulk and serial samples of fossil tooth enamel from all ungulates present at the Gray site elucidate paleoecological reconstructions. The herbivorous megafauna include taxa of likely North American and Eurasian ancestry including: the tapir Tapirus polkensis, rhino Teleoceras cf. T. hicksi, camel cf. Megatylopus sp., peccary Tayassuidae, and proboscidean Gomphotheriidae. The tapir, rhino, camel, and peccary yield mean stable carbon isotope (δ13C) tooth enamel values of - 13.0‰, - 13.3‰, - 13.8‰, and - 13.1‰, respectively, suggesting forest-dwelling browsers. This range of δ13C values indicates the presence of a C3 dominated ancient local flora. Because δ13C values decline with increasing canopy density, the ancient temperate forests from the Gray site were moderately dense. The lack of significant C4 plant consumption (i.e., tooth enamel δ13C values < - 9‰) suggests the presence of forests large enough to independently support the continued browsing of sustainable populations of browsers from the Gray site. In contrast, bulk and serial δ13C values ranging from - 0.7‰ to 0.3‰ from a gomphothere tusk support a diet consisting of C4 grasses, suggesting the presence of C4 grasslands within the individuals home range. The rare earth element (REE) analyses of the gomphothere tusk and the teeth of Tapirus and Teleoceras indicates that these individuals shared similar depositional environments; thus, demonstrating the concurrent presence of C3 forests and C4 grasslands in the northeast. Stable carbon and oxygen serial sample variation of the tapir, rhino, peccary, and gomphothere is less than 1.5‰, suggesting minor differences in seasonal temperature and/or precipitation. These data support the possibility of a North American forest refugium in the southern Appalachians during a time typified by more open environments.

Stable isotopes of mammoths and mastodons have the potential to illuminate ecological changes in late Pleistocene landscapes and megafaunal populations as these species approached extinction. The ecological factors at play in this extinction remain unresolved, but isotopes of bone collagen (δ13C, δ15N) and tooth enamel (δ13C, δ18O, 87Sr/86Sr) from midwestern North America are leveraged to examine ecological and behavioral changes that occurred during the last interglacial-glacial cycle. Both species had significant C3 contributions to their diets and experienced increasing levels of niche overlap as they approached extinction. A subset of mastodons after the last glacial maximum exhibit low δ15N values that may represent expansion into a novel ecological niche, perhaps densely occupied by other herbivores. Stable isotopes from serial and microsampled enamel show increasing seasonality and decreasing temperatures as mammoths transitioned from Marine Isotope Stage (MIS) 5e to glacial conditions (MIS 4, MIS 3, MIS 2). Isotopic variability in enamel suggests mobility patterns and life histories have potentially large impacts on the interpretation of their stable isotope ecology. This study further refines the ecology of midwestern mammoths and mastodons demonstrating increasing seasonality and niche overlap as they responded to landscape changes in the final millennia before extinction.

Feeding ecology and trophic interactions of six species of wading birds were explored through a combined analysis of stable isotope profiles and endoparasite communities. Stable isotopes broadly characterize the feeding preferences and geographic information, while parasite communities reflect long-term trends in feeding ecology. Deceased birds were obtained from four South Florida wildlife rehabilitation organizations. Of the 81 birds dissected, 73 contained parasites. Parasites were predominately found within the gastrointestinal tract. Host and range extensions were noted for several parasite taxa. Bird host species had a significant effect on the parasite community (P=0.001) while wildlife center location and maturity status did not. Stable nitrogen (δ15N) values for pectoral muscle tissues, representing approximately 24 days, ranged from 6.44 to 13.48‰ while stable carbon (δ13C) values ranged from -33.39 to -11.66‰. δ13C varied significantly among location (P=0.0002) and δ15N varied significantly among species (P15N and δ13C was analyzed in combination; bird species (P=0.001) and location (P=0.001) were significantly different. By using this combined approach of stable isotope analysis and parasite identification, it was possible to elucidate more components of bird feeding ecology. Stable isotope analysis provided knowledge on trophic interactions based on δ15N values, while δ13C was used to determine the differences in geographic foraging location. As endoparasites are acquired trophically via food-web interactions, identifying the parasite community allowed for trophic links to be drawn between organisms present within the same environment. Combining these two techniques allows for an abundance of information on feeding ecology and trophic interactions to be obtained.

Indiana University-Purdue University Indianapolis (IUPUI) / Drylands cover 40% of the earth’s terrestrial surface supporting over 2 billion people, the majority of whom reside in developing nations characterised by high population growth rates. This imposes pressure on the already limited water resources and in some dryland regions such as southern Africa, the origins and dynamics of rainfall are not well understood. Research has also tended to focus on factors limiting (e.g., rainfall) than sustaining productivity in drylands. However, non-rainfall water (NRW) e.g., fog and dew can supplement and/or exceed rainfall in these environments and could potentially be exploited as potable water resources. Much remains unknown in terms of NRW formation mechanisms, origins, evolution, potability and potential impact of global climate change on these NRW dependent ecosystems. Using Namibia as a proxy for drylands and developing nations, this dissertation applies stable isotopes of water (δ2H, δ18O, δ17O and d-excess), cokriging and trajectory analysis methods to understand ecohydrological processes. Results suggest that locally generated NRW may be a regular occurrence even in coastal areas such as the Namib Desert, and that what may appear as a single fog event may consist of different fog types co-occurring. These results are important because NRW responses to global climate change is dependent on the source, groundwater vs. ocean, and being able to distinguish the two will allow for more accurate modelling. I also demonstrate, that fog and dew formation are controlled by different fractionation processes, paving the way for plant water use strategy studies and modelling responses to global climate change. The study also suggests that current NRW harvesting technologies could be improved and that the potability of this water could raise some public health concerns related to trace metal and biological contamination. At the same time, the dissertation concludes that global precipitation isoscapes do not capture local isotope variations in Namibia, suggesting caution when applied to drylands and developing nations. Finally, the dissertation also reports for the first time, δ17O precipitation results for Namibia, novel isotope methods to differentiate synoptic from local droughts and suggests non-negligible moisture contributions from the Atlantic Ocean due to a possible sub-tropical Atlantic Ocean dipole.

No description available.

The brown bear (Ursus arctos) is a generalist omnivore that occupies diverse habitats and displays high levels of behavioral plasticity. Plasticity in foraging behavior can result in variable diets across a population, and allow individuals to use a greater variety of resources. The distribution of food in space and time may also be an important factor in determining brown bear resource selection as it can greatly influence foraging efficiency. Our objectives were to determine if seasonal brown bear home ranges were influenced by temporal availability and spatial distribution of resources and if deviation from an optimal diet influenced brown bear body condition. Understanding how the spatial and temporal distribution of food influences brown bear space use and the relationships between behavioral plasticity and the ability of populations to persist in dynamic environments could provide additional insights into the eco-evolutionary advantages of variable foraging behavior and ultimately population resilience.

Managed loblolly pine (Pinus taeda) stands are common in the southeastern United States and provide young forest conditions for early successional breeding birds. Common pine management practices (e.g. hardwood control) and novel practices (e.g. switchgrass [Panicum virgatum] intercropping), may influence breeding bird use. I evaluated breeding bird abundance, diversity, and resource use within loblolly stands treated to control hardwood species, intercropped with switchgrass, and with no additional management. Hardwood control and switchgrass intercropping both decreased hardwoods and shrubs, and increased forbs. Switchgrass intercropping increased some early successional bird abundances. However, diversity was not different among treatments. Switchgrass intercropping increased 13C:12C in birds and vegetation; both hardwood control and switchgrass intercropping increased 15N:14N in birds and vegetation. Birds moved freely among stands of different ages and management practices. My results suggest these practices improve conditions for some early successional birds and may help maintain ecological value of loblolly stands for birds.