No description available.

Comprendre de quelle façon les populations animales répondent aux conditions qui prévalent dans leur environnement revêt une grande importance. Les conditions climatiques et météorologiques sont une source importante de variabilité dans l'environnement et celles-ci ont des répercussions sur les espèces sauvages, en affectant leur physiologie, leur comportement et leurs ressources. Les ongulés alpins et nordiques font face à une succession annuelle de conditions environnementales favorables et défavorables, entraînant chez ceux-ci d'importants changements de masse saisonniers. Chez ces grands herbivores, la masse est importante puisqu'elle est positivement corrélée à la survie et à la reproduction. C'est pourquoi il est essentiel d'investiguer les paramètres affectant les changements de masse saisonniers. L'objectif principal de ma maîtrise était donc d'identifier et de mieux comprendre l'effet des conditions climatiques et météorologiques sur les changements de masse estivaux et hivernaux d'un ongulé alpin: le mouflon d'Amérique (Ovis canadensis). Pour atteindre cet objectif, j'ai utilisé les données du suivi à long terme de la population de mouflons de Ram Mountain, Alberta. Les mesures de masse répétées prises lors des captures permettent d'estimer la masse printanière et automnale des individus, ainsi que leur gain de masse estival et leur changement de masse hivernal. En affectant les coûts énergétiques de la thermorégulation et des déplacements et en influençant la végétation, les conditions climatiques et météorologiques peuvent avoir d'importantes conséquences sur les changements de masse des ongulés alpins. La température, les précipitations et un indice de climat global (le «Pacific Decadal Oscillation»; PDO) ont donc été utilisés afin de caractériser les conditions environnementales et d'investiguer les effets de ces variables sur les changements de masse saisonniers des individus de différentes classes d'âge et de sexe. Des températures froides au printemps ont engendré de plus grands gains de masse estivaux. Des printemps froids peuvent ralentir la maturation des plantes, engendrant une plus grande période où il est possible de s'alimenter de jeunes plantes nutritives, ce qui explique probablement cet effet positif des printemps froids. Cet effet doit toutefois être nuancé puisque les changements de masse hivernaux étaient également influencés par la température printanière, avec des printemps chauds menant à de plus faibles pertes de masse. Il semble que cet effet était dû à une apparition hâtive de la végétation, menant à une prise de masse des mouflons avant qu'ils ne soient capturés au printemps. Cela suggère qu'en affectant la disponibilité et la qualité de la végétation, les conditions printanières ont des répercussions à la fois sur le gain de masse estival, mais également sur les changements de masse hivernaux des mouflons. Le PDO au printemps a un effet positif important sur le gain de masse des adultes mâles lorsque la densité est faible. Des températures chaudes à l'automne engendrent de plus grands gains de masse pendant l'hiver chez les agneaux mâles (la plupart des agneaux gagnent de la masse l'hiver), potentiellement en augmentant la période possible de prise de masse pour ces jeunes individus. Les femelles de deux ans et les mâles adultes ont perdu plus de masse lors d'hivers avec beaucoup de précipitations et des températures froides, respectivement. Finalement, ce projet de recherche a permis d'identifier les variables climatiques et météorologiques clés affectant les changements de masse saisonniers d'un ongulé alpin. Cette étude a également mis en évidence des effets du PDO sur les changements de masse saisonniers, soulignant que de tels indices peuvent s'avérer utiles afin de les mettre en lien avec la variation phénotypique chez les espèces sauvages, et ce sans qu'il n'y ait nécessairement de fortes corrélations entre ces indices et les variables météorologiques locales.

Over the 1951-2009 time period, 47% of all tropical systems in the Atlantic Basin transitioned to post-tropical storms. These storms are capable of producing hurricaneforce winds, torrential, flooding rains and storm surge that floods coastal areas. This study adds to previous climatological work by completing a case-study of Hurricane Ike (2008) and examining how teleconnections such as the El Niño Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) contribute to the strength of a transitioning post-tropical storm. T-tests performed show strong statistical relationships between an increase (decrease) in post-tropical storm frequency and warm PDO – La Niña (cold PDO – La Niña), cold PDO – ENSO neutral (warm PDO – ENSO neutral), and warm (cold) AMO conditions. Moreover, nearly significant results were found for the same increase (decrease) and La Niña seasons since (pre) 1980 and for cold (warm) PDO conditions. Modeling the MJO suggests that increased (decreased) relative humidity associated with the wet (dry) phase could increase (decrease) precipitation output from the storm and decrease (increase) forward speed of the storm, decreasing (increasing) wind speeds observed at the surface.

No description available.

The recent, rapid decline in Arctic summer sea ice extent has prompted questions as to the rates and magnitude of previous sea ice decline and the affect of this physical change on icerelated ecosystems. However, satellite data of sea ice only extends back to 1978, and mapped observations of sea ice prior to the 1970s are sparse at best. Inventories of boreal ecosystems are likewise hampered by a paucity of investigations spanning more than the past few decades. Paleoclimate records of sea ice and related primary productivity are thus integral to understanding how sea ice responds to a changing climate. Here I examine modern sedimentation, decadal-scale climate change in the recent past, and centennial- to millennial-scale changes of the past 400 ka using both qualitative and quantitative diatom data in concert with sedimentology and organic geochemistry. Diatom taxonomy and corresponding ecological affinities are compiled in this study and updated for the Bering Sea region and then used as recorders of past climate changes. In recent decades, the Pacific Decadal Oscillation and the strength of the Aleutian Low are reflected by subtle changes in sediment diatom assemblages at the Bering Sea shelf-slope break. Farther back in time, the super-interglacial, marine isotope stage (MIS) 11 (428-390ka), began in Beringia with extreme productivity due to flooding of the Bering Land Bridge. A moisture-driven advance of Beringian glaciers occurred while eustatic sea level was high, and insolation and seasonality both decreased at the global peak of MIS 11. Atlantic/Pacific teleconnections during MIS 11 include a reversal in Bering Strait throughflow at 410 ka and a relationship between North Atlantic Deep Water Formation and Bering Sea productivity. Finally, concentrations of the biomarker-based sea ice proxy, IP25, are compared to sea ice concentration across the Bering and Chukchi seas. Changes in the concentration of IP25 in the sediments may be driven by the length of time that the epontic diatom bloom lasts. When combined with a sediment-based proxy for sea surface temperatures, IP25 can be used to reconstruct spring ice concentration.

The occurrence of wildfire is influenced by a suite of factors ranging from "top-down" influences (e. g., climate) to "bottom-up" localized influences (e. g., ignitions, fuels, and land use). We carried out the first broad-scale assessment of wildland fire patterns in northern Mexico to assess the relative influence of top-down and bottom-up drivers of fire in a region where frequent fire regimes continued well into the 20th century. Using a network of 67 sites, we assessed (1) fire synchrony and the scales at which synchrony is evident, (2) climate drivers of fire, and (3) asynchrony in fire regime changes. We found high fire synchrony across northern Mexico between 1750 and 2008, with synchrony highest at distances < 400 km. Climate oscillations, especially El Nino-Southern Oscillation, were important drivers of fire synchrony. However, bottom-up factors modified fire occurrence at smaller spatial scales, with variable local influence on the timing of abrupt, unusually long fire-free periods starting between 1887 and 1979 CE. Thirty sites lacked these fire-free periods. In contrast to the neighboring southwestern United States, many ecosystems in northern Mexico maintain frequent fire regimes and intact fire-climate relationships that are useful in understanding climate influences on disturbance across scales of space and time.

Decadal variations in climate are important, because the magnitude of sustained decadal change is often much larger than the often discussed background trends. Climate variability at interannual and longer periods is most often discussed in the context of climate modes defined by sea level pressure (SLP) and sea surface temperature (SST) patterns. However, SLP and SST are not capable descriptors of ocean dynamics. The approximately two decades of global sea surface height (SSH) measurements from satellite altimetry reveal substantial low-frequency redistributions of heat and salt in the ocean, which may or may not be related to defined climate modes. In addition, coastal sea level responds directly to synoptic variability in the atmosphere, providing long records of weather events in coastal areas. The unifying idea in the following analyses is the value and versatility of SSH from altimetry and sea level from tide gauges for investigations of decadal climate variability. Three applications of SSH and coastal sea level to the study of decadal change demonstrate the merits of using sea level for investigations of oceanic and atmospheric, episodic and continuous processes. The analyses concern a multidecadal change in storminess along the coast of the Southeast U.S., basin-scale coherent sea level variations in the western boundary of the North Atlantic, and the low-frequency response of the ocean to atmospheric forcing in the Northeast Pacific.

The present work focused on the interdecadal variability of precipitation in the Western Brazilian Amazon in order to help improve this knowledge and, in addition, to analyze, study and evaluate the low-frequency variability of the hydrological cycle in this region. To this end, we used data collected from conventional rain gauge stations 5, available at the National Climatic Data Center (NCDC), reanalysis data of the following meteorological variables: long-wave radiation emerging (ROLE), temperature of the sea surface (SST) , vertical motion (Omega), zonal wind, as well as data series of the climate index of the Pacific Decadal Oscillation (ODP), and rainfall data of the project at the University of Delaware (UDEL), available at the Climate Diagnostic Center / National Oceanic and Atmospheric Administration (CDC / NOAA). Related to the local climate and the global level, particularly with the El Nino-Southern Oscillation (ENSO) and Pacific Decadal oscillation (ODP). It was noted that at the crucial stage of the ODP was a 8.1% increase in precipitation over the cold phase, mainly in the south-central axis of the western Amazon, while in the northwest basin of Rio Negro, it was noticed that at the hot rained 5.9% less when compared to the cold phase. Evidence indicates that since 1999, the ODP has entered into a new cold phase. Then, we analyzed the SST of the Pacific Ocean for the period 1999-2008 and observed the new configuration should last for 20 years, possibly causing significant changes in rainfall in this region. / Fundação de Amparo a Pesquisa do Estado de Alagoas / No presente trabalho dissertou-se sobre a variabilidade interdecadal da precipitação na Amazônia Ocidental Brasileira com o objetivo de contribuir para melhorar esse conhecimento e, em adição, analisar, estudar e avaliar a variabilidade de baixa freqüência no ciclo hidrológico dessa região. Para tal, foram utilizados dados observados de 5 estações pluviômetricas convencionais, disponíveis no site do National Climatic Data Center (NCDC), dados de reanálises das seguintes variáveis meteorológicas: radiação de ondas longas emergente (ROLE), temperatura da superfície do mar (TSM), movimento vertical (Omega), vento zonal, como também dados da série do índice climático da Oscilação Decadal do Pacífico (ODP), e dados de precipitação do projeto da University of Delaware (UDEL), disponíveis no site do Climate Diagnostic Center/National Oceanic and Atmospheric Administration (CDC/NOAA). Relacionou-se o clima local com o global, em particular com o fenômeno El Nino-Oscilação Sul (ENOS) e a Oscilção Decadal do Pacifico (ODP). Notou-se que na fase quente da ODP houve um aumento de 8,1% na precipitação em relação a fase fria, principalmente no eixo centro-sudoeste da Amazônia ocidental, enquanto no noroeste, bacia do Rio Negro, percebeu-se que na fase quente choveu 5,9% a menos quando comparado a fase fria. Evidências, indicam que desde 1999, a ODP tenha entrado em uma nova fase fria. Então, analisou-se a TSM do Oceano Pacifico para o período 1999-2008 e observou-se a nova configuração que deve perdurar pelos próximos 20 anos, possivelmente provocando mudanças significativas no regime pluviométrico desta região.

This thesis contributes to the development of dinoflagellate cysts as indicators of past environmental change in the Northeastern Pacific coastal ocean, and investigates past variations in sea-surface temperature, salinity and primary productivity encoded in dinoflagellate cyst sedimentary records from the Santa Barbara Basin (SBB, southern California) and Effingham Inlet (Vancouver Island, British Columbia) over the last millennium. The dinoflagellate cyst records extracted from the SBB and Effingham Inlet predominantly laminated sediments and analysed at sub-decadal resolutions, constitute some of the most detailed records of cyst-producing dinoflagellate populations in the world. A two year-long sediment trap study from the SBB documents the seasonality in dinoflagellate cyst production for the first time on the Pacific coast of the United States. The study shows that dinoflagellate cyst data can be used as indicators of changes in sea-surface temperature and primary productivity associated with seasonal upwelling in the SBB. In particular, several dinoflagellate cyst taxa such as Brigantedinium spp. and Lingulodinium machaerophorum are identified as indicators of “active upwelling” (typically occurring in spring and early summer) and “relaxed upwelling” conditions (fall and early winter) at the site, respectively. Analysis of a dinoflagellate cyst record from the SBB spanning the last ~260 years at biannual resolution documents the response of cyst-producing dinoflagellates to instrumentally-measured warming during the 20th century, and reveals decadal scale variations in primary productivity at the site that are coherent with phases of the Pacific Decadal Oscillation (PDO). The cyst assemblages are dominated by cysts produced by heterotrophic dinoflagellates (in particular Brigantedinium spp.), but the turn of the 20th century is marked by an abrupt increase in concentrations of L. machaerophorum and Spiniferites ramosus, two cyst taxa of autotrophic affinity. Their increasing abundances during the 20th century are interpreted to reflect warmer conditions and possibly stronger stratification during summer and fall. The dinoflagellate cyst data suggest a warming pulse in the early 1900s and provide further evidence that persistently warmer and/or more stratified conditions were established by the late 1920s. The dinoflagellate cyst record from Effingham Inlet, spanning the last millennium, is characterized by the proportionally equal contribution of cysts produced by autotrophic and heterotrophic dinoflagellates in most samples. The cyst data indicate variations in sea-surface temperature, salinity and primary productivity that are associated with local expressions of the Medieval Climate Anomaly (from the base of the record to ~1230), the Little Ice Age (from ~1230 to ~1900) and warming during the second half of the 20th century. Both dinoflagellate cyst records reveal that since the beginning (in the SBB) and mid-20th century (in Effingham Inlet), autotrophic dinoflagellates contribute to a greater portion of the primary production in the region, whereas heterotrophic dinoflagellates, as indicators of diatom populations, decline. Variability in the dinoflagellate cyst data is coherent at both sites and suggest a reduced expression of decadal scale variability associated with the PDO during the 19th century. / Graduate / 0416 / 0427 / mbringue@uvic.ca

Future climate changes will alter disturbance regimes worldwide with important implications for many ecological and social systems. In west central British Columbia, Canada, fire and insect disturbances have shaped the historic character of Douglas-fir (Pseudotsuga menziesii var. glauca Beissn. Franco) dominated forests. However, since AD 1900 fire suppression and other forest management practices have led to denser forests and conifer encroachment into grasslands. Considering climate changes in interior British Columbia are expected to result in warmer and drier conditions, understanding the influence of climate on forest disturbances is crucial for land managers tasked with both mitigating the effects of disturbance and promoting resilience in forest ecosystems. This research focused on developing multi-century, annually-resolved records of fire and western spruce budworm outbreaks to evaluate: the historic climate conditions related to these disturbances; the influence of grassland proximity on disturbance-climate relationships; and, whether western spruce budworm outbreaks were related to fire activity. At the landscape scale, a detailed study in the Churn Creek Protected Area revealed spatially variable stand structure and fire-climate relationships at a low elevation forest-grassland ecotone over the interval AD 1600 to 1900. This finding suggests the site was characterized by fires of mixed-severity dominated by frequent, low-severity, fires related to positive antecedent moisture conditions punctuated by widespread fires of moderate to high severity related to intervals of persistent drought. At the regional scale, the influence of interannual climate variability and large-scale patterns of climate variability (e.g. El Nino Southern Oscillation) was evaluated using new and existing records of fire history and multiple climate pattern reconstructions. Regional fire activity was shown to be significantly related to interannual climate variability, and no consistent patterns between regional fire years and the individual phases or phase combinations of large-scale patterns of climate variability were detected. The findings suggest that the spatial expression of large-scale climate patterns translates into weak and undetectable terrestrial effects related to fire activity in this region. The influence of grassland proximity on disturbance history was investigated using site-level and regional tree-ring reconstructions of western spruce budworm outbreaks and fire activity based on four sites adjacent to grasslands and four sites not adjacent to grasslands between AD 1600 and 1900 (fire) and AD 1600 and 2009 (western spruce budworm). Fires affecting grassland proximal sites were more frequent than fires occurring in forests not adjacent to grasslands, and the character of western spruce budworm outbreaks was generally consistent among all sites. Fire activity was related to both warm, dry and cool, wet conditions in the fire year and/or year(s) preceding the fire depending on proximity to grasslands, suggesting climate conditions associated with both fine fuel growth and drying are key determinants for fire activity. The initiation of western spruce budworm outbreaks was significantly related to drought and this relationship was enhanced at sites adjacent to grasslands. At the site-level and regional scale, no consistent association was found between the initiation of western spruce budworm outbreaks and fire years indicating the historic interaction between these disturbances is weak or non-existent. / Graduate