This thesis investigates the influence of predator movements upon habitat selection and foraging success. It deals with two very distinct datasets one from a marine system, the snow crab (Chionoecetes opilio) fishery, and the second from a freshwater system, an experimental rainbow trout (Oncorhynchus mykiss) aquaculture operation. Deriving a standardized measure of catch from logbook data is important because catch per unit effort (CPUE) is used in fisheries analysis to estimate abundance, but it some cases CPUE is a biased estimate. For the snow crab fishery, a relative abundance measure was developed using fisher movements and logbook data that reflected commercially available biomass and produced an improved relative abundance estimate. Results from the aquaculture dataset indicate that escaped farmed rainbow trout continue to use the cage site when waste feed is available, while native lake trout do not interact with the cage. Once access to waste feed is removed, both lake trout and escaped rainbow trout do not use the cage site. This thesis uses methods to identify patterns and behaviours using movement tracks to increase our understanding of predator habitat usage.

Although the air-ice interface is atmospherically important, it is difficult to model accurately because exclusion and precipitation of solutes during freezing, deposition of atmospheric species, and heterogeneous/photochemical processes all affect its properties. In this thesis, glancing-angle spectroscopic methods were developed to study ice surfaces. Glancing-angle Raman spectroscopy showed that nitrate is not strongly excluded to the ice surface during freezing, in contradiction with expectations based on equilibrium thermodynamics. Glancing-angle laser-induced fluorescence showed that hydronium ions are not strongly excluded when dilute acidic solutions (HNO3 or HCl) are frozen. These results suggest that solutes are not universally excluded and that care should be taken in modelling surface concentrations on ice. Deposition of HCl(g) was found to result in different pH responses at the "pure" vs. "salty" ice surfaces. Changes at the "salty" ice surface were consistent with the existence of a brine layer at the air-ice interface while changes at the "pure" ice surface were distinctly different, indicating that it may not be appropriate to model it as a cold, liquid layer. Significantly, results also suggest that the sea ice surface is buffered against pH changes, with important implications for interpreting pH-dependent chemistry. The conversion of sea-salt derived halides to reactive halogen species can lead to dramatic changes in the oxidative capacity of the overlying atmosphere. At ambient pH and naturally occurring halide concentrations, the dark ozonation of NaBr and NaI solutions was found to proceed more quickly on frozen vs. aqueous substrates, consistent with a freeze-concentration enhancement in halide concentration at the surface. A photochemical mechanism for halogen release from artificial saline snow was evidenced. The presence of ozone and light in the actinic region leads to accelerated production of Br2 and BrCl and the release of Cl2, in a process enhanced by high surface area, acidity and additional gas phase Br2. The results provide strong evidence for snowpack "halogen explosion" chemistry in which gas phase halogens are recycled back into a concentrated brine layer at the snow grain surface.

Although the air-ice interface is atmospherically important, it is difficult to model accurately because exclusion and precipitation of solutes during freezing, deposition of atmospheric species, and heterogeneous/photochemical processes all affect its properties. In this thesis, glancing-angle spectroscopic methods were developed to study ice surfaces. Glancing-angle Raman spectroscopy showed that nitrate is not strongly excluded to the ice surface during freezing, in contradiction with expectations based on equilibrium thermodynamics. Glancing-angle laser-induced fluorescence showed that hydronium ions are not strongly excluded when dilute acidic solutions (HNO3 or HCl) are frozen. These results suggest that solutes are not universally excluded and that care should be taken in modelling surface concentrations on ice. Deposition of HCl(g) was found to result in different pH responses at the "pure" vs. "salty" ice surfaces. Changes at the "salty" ice surface were consistent with the existence of a brine layer at the air-ice interface while changes at the "pure" ice surface were distinctly different, indicating that it may not be appropriate to model it as a cold, liquid layer. Significantly, results also suggest that the sea ice surface is buffered against pH changes, with important implications for interpreting pH-dependent chemistry. The conversion of sea-salt derived halides to reactive halogen species can lead to dramatic changes in the oxidative capacity of the overlying atmosphere. At ambient pH and naturally occurring halide concentrations, the dark ozonation of NaBr and NaI solutions was found to proceed more quickly on frozen vs. aqueous substrates, consistent with a freeze-concentration enhancement in halide concentration at the surface. A photochemical mechanism for halogen release from artificial saline snow was evidenced. The presence of ozone and light in the actinic region leads to accelerated production of Br2 and BrCl and the release of Cl2, in a process enhanced by high surface area, acidity and additional gas phase Br2. The results provide strong evidence for snowpack "halogen explosion" chemistry in which gas phase halogens are recycled back into a concentrated brine layer at the snow grain surface.

The seasonal cycle of snow and sea ice is a fundamental feature of the Arctic climate system. In the Northern Hemisphere, about 55 million km2 of sea ice and snow undergo complete melt and freeze processes every year. Because snow and sea ice are much brighter (higher albedo) than the underlying surface, their presence reduces absorption of incoming solar energy at high latitudes. Therefore, changes of the sea-ice and snow cover have a large impact on the Arctic climate and possibly at lower latitudes. One of the most important determining factors of the seasonal snow and sea-ice cover is the timing of the seasonal melt-freeze transitions. Hence, in order to better understand Arctic climate variability, it is key to continuously monitor these transitions. This thesis presents an algorithm for obtaining melt-freeze transitions using scatterometers over both the land and sea-ice domains. These satellite-borne instruments emit radiation at microwave wavelengths and measure the returned signal. Several scatterometers are employed: QuikSCAT (1999–2009), ASCAT (2009–present), and OSCAT (2009–present). QuikSCAT and OSCAT operate at Ku-band (λ=2.2 cm) and ASCAT at C-band (λ=5.7 cm), resulting in slightly different surface interactions. This thesis discusses these dissimilarities over the Arctic sea-ice domain, and juxtaposes the time series of seasonal melt-freeze transitions from the three scatterometers and compares them with other, independent datasets. The interactions of snow and sea ice with other components of the Arctic climate system are complex. Models are commonly employed to disentangle these interactions. But this hinges upon robust and well-formulated models, reached by perpetual testing against observations. This thesis also presents an evaluation of how well eleven state-of-the-art global climate models reproduce the Arctic sea-ice cover and the summer length—given by the melt-freeze transitions—using surface observations of air temperature. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 4: Submitted.</p>

Electric mobility scooters are increasing in popularity and are used extensively by individuals with mobility impairments to conduct activities of daily living. Scientific literature on the safety and efficacy of scooters in winter conditions is sparse and the current technical standards for scooters do not mandate testing in these conditions. This study paves the way for more rigorous standard testing by: 1) Describing a novel, motion-capture based method to quantify the tractive performance of scooters; 2) Describing methods to create a wide variety of simulated winter conditions; 3) Presenting pilot-test results of a scooter driven in these winter conditions. The outcomes of this study are significant because it is the first study to evaluate the performance of a scooter in winter conditions. Furthermore, it constitutes the first phase of a broader initiative to develop a rigorous, new winter test method for scooters and drive improvements in safety, performance and design.

Measurements of the key aerosol properties including light scattering and backscattering coefficients (σsp and σbsp), light absorption coefficient (σap), and particle concentration were made at Summit, Greenland, in the summer of 2011. From these quantities, the single scattering albedo (ω) and angstrom scattering and absorption exponents (åsp, åap) were calculated. In conjunction with these measurements, aerosol optical depth (AOD or τ) and the spectral surface albedo, Rs, were measured. Additionally, the aerosol chemical composition was characterized through snow and air filter analyses. A radiative transfer model was used to estimate the direct aerosol radiative forcing and radiative forcing efficiency using the measurements as inputs. Taken as a whole, this project allowed for the first ever measurement-based characterization of aerosol radiative forcing over central Greenland.

“Original Sin”—evocative and powerful words, but what if they were applied to one of the world’s most popular fairy tales? This thesis explores Snow White in the context of the Seven Deadly Sins and the grand fall of Adam and Eve. The forbidden fruit manifests itself in different ways, pulling the prim and proper princess into places she never could have imagined. But what of the Wicked Queen, here known as Lilith? She too feels the bite of the world’s sick sense of humor, exacting revenge on those who have wronged her. Are these poems about them? Or are they about the author? Perhaps they are both: the innocent children learn quickly of life’s cruelty, handling it with equal parts grace and selfishness. Dive into the minds of Lilith and Snow White as they explore what it means to be themselves in a world that doesn’t care if they end up happy.

Feedbacks between the climate system and the high-latitude carbon cycle will substantially influence the intensity of future climate change. It is therefore crucial that the net ecosystem exchange of CO2 (NEE) between the high-latitude land surface and the atmosphere is accurately quantified, where NEE refers to the difference between ecosystem respiration (R) and photosynthesis (gross ecosystem exchange, GEE): NEE=-GEE+R in umol/m^2/s. NEE can only be directly measured over areas of 1 km^2 through eddy covariance, and modeling approaches such as the Vegetation Photosynthesis Respiration Model (VPRM) are required to upscale NEE. VPRM is a remote sensing based model that calculates R as a linear function of air temperature (Ta) when air temperature is above a given threshold (Tlow), and sets respiration to a constant value when Ta<Tlow. GEE is estimated according to remote sensing observations of vegetation indices, shortwave radiation, air temperature, and soil moisture. Although in situ findings have shown that snow and Arctic species composition have a substantial influence on high-latitude NEE, model estimates of high-latitude NEE have typically been generated without Arctic-specific vegetation classes, and without using remote sensing observations to represent the effects of snow on NEE. The hypothesis driving this work was therefore that uncertainty in estimates of high-latitude NEE could be reduced by representing the influences of Arctic vegetation classes and snow. The central objectives were to determine feasible approaches for reducing uncertainty in VPRM estimates of NEE by representing the influences of snow and Arctic vegetation, create PolarVPRM accordingly, and analyze inter-annual variability in PolarVPRM estimates of high-latitude North American NEE (2001-2012). The associations between snow and NEE, and the potential to describe these influences on NEE using remote sensing observations, were examined using time lapse camera observations of snow cover area (SCA) and eddy covariance measurements of NEE from Daring Lake, Northwest Territories, Canada. Analyses indicated good agreement between SCA derived from camera, Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) observations. SCA was also found to influence the timing and magnitude of NEE. MODIS SCA was therefore incorporated into VPRM, and VPRM was calibrated using eddy covariance and meteorological observations collected in 2005 at Daring Lake. VPRM was run through years 2004-2007 over both Daring Lake and Ivotuk, Alaska, USA, using four model formulations, three of which represented the effects of SCA on respiration and/or photosynthesis, and another which did not use MODIS SCA. Comparisons against eddy covariance observations indicated that uncertainty was reduced in VPRM estimates of NEE when respiration was calculated as a linear function of soil temperature when SCA>50%, and as a linear function of air temperature when SCA<50%, thereby reflecting the influence of snow on decoupling soil/air temperatures. Representing the effect of SCA on NEE therefore reduced uncertainty in VPRM estimates of NEE. In order to represent spatial variability in high-latitude estimates of NEE due to vegetation type, Arctic-specific vegetation classes were created for PolarVPRM by combining and aggregating two existing vegetation classifications: the Synergetic Land Cover Product and the Circumpolar Arctic Vegetation Map. Levene's test indicated that the PolarVPRM vegetation classes divided the pan-Arctic region into heterogeneous distributions in terms of net primary productivity, and passive microwave derived estimates of snow and growing season influences on NEE. A non-parametric statistical approach of Alternating Conditional Expectations found significant, non-linear associations to exist between passive microwave derived estimates of snow and growing season drivers of NEE. Furthermore, the shape of these associations varied according to the vegetation class over which they were examined. Further support was therefore provided to the idea that uncertainty in model estimates of NEE could be reduced by calculating snow and growing season NEE separately within each vegetation class. PolarVPRM estimates of NEE in 2001-2012 were generated at a three hourly and 1/6 x 1/4 degree resolution across polar North America (55-170 W, 55-83 N). Model calibration was conducted over three sites: Daring Lake, Ivotuk, and Atqasuk, Alaska, USA. Model validation was then conducted by comparing PolarVPRM estimates of year-round daily average NEE to non-gap-filled eddy covariance observations of daily average NEE acquired over the three calibration sites, as well as six other Arctic sites. PolarVPRM performed well over all sites, with an average mean absolute error (MAE) of 0.20 umol/m^2/s, and had diminished error rates when the influence of SCA on respiration was explicitly represented. Error analysis indicated that peak growing season GEE was underestimated at Barrow because GEE at this site showed a stronger response to the amount of incoming shortwave radiation than at the calibration site, suggesting that PolarVPRM may underestimate GEE over wetland and barren vegetated regions. Despite these uncertainties, PolarVPRM was found to generate more accurate estimates of monthly and three-hourly NEE relative to eddy covariance observations than two established models, FLUXNET Model-Tree Ensemble (MTE) and CarbonTracker. Relative to eddy covariance observations and PolarVPRM estimates, MTE tended to overestimate snow season respiration, and CarbonTracker tended to overestimate the amount of midday photosynthesis. Analysis of PolarVPRM output across North America (north of 55 N) found an increase in net annual carbon efflux over over time (2001-2012). Specifically, increased rates of respiration are estimated when soil and air temperatures are warmer. Although increases in growing season vegetation indices and air temperature enable greater photosynthetic uptake by Arctic vegetation, forests and shrublands uptake less CO2 in the middle of the growing season when air temperatures rise above the physiological optima for photosynthesis. As a result, PolarVPRM estimated a decline in net photosynthetic uptake over time. Overall, PolarVPRM output indicates that North American regions north of 55 N are losing strength as a carbon sink in response to rising air temperatures.

This thesis investigates the influence of predator movements upon habitat selection and foraging success. It deals with two very distinct datasets one from a marine system, the snow crab (Chionoecetes opilio) fishery, and the second from a freshwater system, an experimental rainbow trout (Oncorhynchus mykiss) aquaculture operation. Deriving a standardized measure of catch from logbook data is important because catch per unit effort (CPUE) is used in fisheries analysis to estimate abundance, but it some cases CPUE is a biased estimate. For the snow crab fishery, a relative abundance measure was developed using fisher movements and logbook data that reflected commercially available biomass and produced an improved relative abundance estimate. Results from the aquaculture dataset indicate that escaped farmed rainbow trout continue to use the cage site when waste feed is available, while native lake trout do not interact with the cage. Once access to waste feed is removed, both lake trout and escaped rainbow trout do not use the cage site. This thesis uses methods to identify patterns and behaviours using movement tracks to increase our understanding of predator habitat usage.

Résumé : Cette recherche présente l'analyse spatio-temporelle de l'évolution conjointe de l'augmentation de la présence arbustive et de la dynamique de la fonte de la neige au Nunavik, Québec, Canada. Cette zone est caractérisée par la complexité de l'interaction de multiples changements simultanés de la température, de la couverture de la neige ainsi que de la pousse végétative. La première partie de ce travail consiste à faire l'analyse de l’évolution temporelle de ces multiples changements. Cette analyse a nécessité la mise en place d’une importante base de données climatiques, satellitaires et de couverture de sol à plusieurs échelles, sur une période allant jusqu'à 60 ans, soit de 1950-2012. La deuxième partie du travail consiste à faire l'analyse spatiale à haute résolution de l’influence de la fraction du couvert arbustif sur la fonte de la neige. L'analyse et l'interprétation des résultats obtenus dans la première partie montrent clairement un changement climatique significatif sur la région étudiée, découpée en 3 bandes de latitude correspondant à la toundra, la taïga ouverte et à la taïga forestière, respectivement du Nord au Sud. Ce changement de climat correspond à un réchauffement marqué, entre 0.75°C et 1.57°C par décade entre les zones 1 (toundra) et 3 (taïga forestière) respectivement. On peut noter que la hauteur de neige maximale annuelle a diminué dans les trois zones alors que les précipitations hivernales ont augmenté en zone 1 et 3 sur les 45 dernières années. Les résultats montrent une nette augmentation de la végétation arbustive dans les zones 2 et 3 (LAI plus élevé de 100% dans la zone 3 par rapport à la zone 1). L'impact de la végétation a été analysé à partir de la durée de fonte relative entre le début de la fonte et la disparition de la neige. Il apparait clairement que la végétation active la fonte précocement, allongeant ainsi significativement la durée de fonte (+600%). Cependant, l'impact de la végétation ne retarde pas la date de fin du couvert nival qui est de plus en plus précoce pour les zones 2 et 3. L'analyse spatiale à haute résolution montre que la présence arbustive entraine une date de fin de neige plus précoce par rapport au sol nu. Cette étude démontre clairement que la croissance de la végétation qui résulte du réchauffement climatique impacte la dynamique du couvert nival, aussi affectée par ce réchauffement. Une étude approfondie des processus en causes avec des mesures in situ appuyées par leur modélisation permettrait de mieux comprendre ces phénomènes. // Abstract : This study presents a spatial-temporal analysis of the joint evolution of the increase of shrubiness and the dynamics of snowmelt in Nunavik, Quebec, Canada. This zone is characterized by the complexity of the interaction of multiple changes of temperature, snow cover and vegetation growth. The first part of this study analyzes the temporal evolution of these changes. The analysis required the use of a large database on climate, satellite data and ground cover at multiple scales over a period of up to 60 years, from 1950 to 2012. The second part of the study consists of a spatial high-resolution analysis of the influence of the fraction of shrub cover on snowmelt. The analysis and interpretation of the results clearly show a significant climate change over the study area, divided into three latitudinal transects corresponding to tundra, open taiga and forested taiga. A significant warming of 0.75 ° C and 1.57 ° C per decade was experienced between zones 1 (tundra) and 3 (forested taiga) respectively. The maximum annual snow depth on the ground decreased over the 3 zones studied while winter precipitations increased in zones 1 and 3 over the last 45 years. The results show a significant increase in shrub vegetation in zones 2 and 3. The impact of the vegetation on snow was analyzed with melt duration (from melt onset to complete melt). It appears clearly that the vegetation triggers the melting process earlier and significantly extends the melt duration (+600%). However, the impact of vegetation does not delay the date of the snow cover disappearance. The high-resolution spatial analysis showed that shrubs cause an earlier snow cover disappearance date than bare soil. This study clearly demonstrates that vegetation growth resulting from global warming impacts the snow cover dynamics, which are also affected by global warming. A thorough study of the processes with in-situ measurements supported by models would help gaining a better comprehension of these phenomena.