Dissertations / Theses on the topic 'Seasonal cycle'

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.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press.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.

Both physical circulation and biogeochemical characteristics are unique in the Southern Ocean (SO) region, and are fundamentally different from those of the northern hemisphere. Moreover, according to previous research, the oceanic response to the trend of the Southern Annual Mode (SAM) has profound impacts on the future oceanic uptake of carbon dioxide in the SO. In other words, the climate and circulation of the SO are strongly coupled to the overlying atmospheric variability. However, while we have understanding on the SO physical circulation and have the ability to predict the future changes of the SO climate and physical processes, the link between the SO physical processes, the air-sea carbon flux, and correlated climate variability remains unknown. Even though scientists have been studying the spatial and temporal variability of the SO carbon flux and the associated biogeochemical processes, the spatial patterns and the magnitudes of the air-sea carbon flux do not agree between models and observations. Therefore, in this study, we utilized a modified version of a general circulation model (GCM) to performed realistic simulations of the SO carbon on seasonal to interannual timescales, and focused on the crucial physical and biogeochemical processes that control the carbon flux. The spatial pattern and the seasonal cycle of the air-sea carbon dioxide flux is calculated, and is broadly consistent with the climatological observations. The variability of air-sea carbon flux is mainly controlled by the gas exchange rate and the partial pressure of carbon dioxide, which is in turn controlled by the compensating changes in temperature and dissolved inorganic carbon. We investigated the seasonal variability of dissolved inorganic carbon based on different regional processes. Furthermore, we also investigated the dynamical adjustment of the surface carbon flux in response to the different gas exchange parameterizations, and conclude that parameterization has little impact on spatially integrated carbon flux. Our simulation well captured the SO carbon cycle variability on seasonal to interannual timescales, and we will improve our model by employ a better scheme of nutrient cycle, and consider more nutrients as well as ecological processes in our future study.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59-60).
A recent article by Kidston et al. [8] demonstrates that the length of atmospheric eddies increases in simulations of future global warming. This thesis expands on Kidston et al.'s work with additional studies of eddy length in the NCEP2 reanalysis (a model-data synthesis that reconstructs past atmospheric circulation) and general circulation models (GCMs) from the Coupled Model Intercomparison Project phase 3. Eddy lengths are compared to computed values of the Rossby radius and the Rhines scale, which have been hypothesized to set the eddy length. The GCMs reproduce the seasonal variation in the eddy lengths seen in the reanalysis. To explore the effect of latent heating on the eddies, a modification to the static stability is used to calculate an effective Rossby radius. The effective Rossby radius is an improvement over the traditional dry Rossby radius in predicting the seasonal cycle of northern hemisphere eddy length, if the height scale used for calculation of the Rossby radius is the depth of the free troposphere. There is no improvement if the scale height is used instead of the free troposphere depth. However, both Rossby radii and the Rhines scale fail to explain the weaker seasonal cycle in southern hemisphere eddy length. In agreement with Kidson et al., the GCMs robustly project an increase in eddy length as the climate warms. The Rossby radii and Rhines scale are also generally projected to increase. Although it is not possible to state with confidence what process ultimately controls atmospheric eddy lengths, taken as a whole the results of this study increase confidence in the projection of future increases in eddy length.
by Todd A. Mooring.
S.B.

Animals and plants in temperate regions must adapt their life cycle to pronounced seasonal variation. The research effort that has gone into studying these cyclical life history events, or phenological traits, has increased greatly in recent decades. As phenological traits are often correlated to temperature, they are relevant to study in terms of understanding the effect of short term environmental variation as well as long term climate change. Because of this, changes in phenology are the most obvious and among the most commonly reported responses to climate change. Moreover, phenological traits are important for fitness as they determine the biotic and abiotic environment an individual encounters. Fine-tuning of phenology allows for synchronisation at a local scale to mates, food resources and appropriate weather conditions. On a between-population scale, variation in phenology may reflect regional variation in climate. Such differences can not only give insights to life cycle adaptation, but also to how populations may respond to environmental change through time. This applies both on an ecological scale through phenotypic plasticity as well as an evolutionary scale through genetic adaptation. In this thesis I have used statistical and experimental methods to investigate both the larger geographical patterns as well as mechanisms of fine-tuning of phenology of several butterfly species. The main focus, however, is on the orange tip butterfly, Anthocharis cardamines, in Sweden and the United Kingdom. I show a contrasting effect of spring temperature and winter condition on spring phenology for three out of the five studied butterfly species. For A. cardamines there are population differences in traits responding to these environmental factors between and within Sweden and the UK that suggest adaptation to local environmental conditions. All populations show a strong negative plastic relationship between spring temperature and spring phenology, while the opposite is true for winter cold duration. Spring phenology is shifted earlier with increasing cold duration. The environmental variables show correlations, for example, during a warm year a short winter delays phenology while a warm spring speeds phenology up. Correlations between the environmental variables also occur through space, as the locations that have long winters also have cold springs. The combined effects of these two environmental variables cause a complex geographical pattern of phenology across the UK and Sweden. When predicting phenology with future climate change or interpreting larger geographical patterns one must therefore have a good enough understanding of how the phenology is controlled and take the relevant environmental factors in to account. In terms of the effect of phenological change, it should be discussed with regards to change in life cycle timing among interacting species. For example, the phenology of the host plants is important for A. cardamines fitness, and it is also the main determining factor for oviposition. In summary, this thesis shows that the broad geographical pattern of phenology of the butterflies is formed by counteracting environmental variables, but that there also are significant population differences that enable fine-tuning of phenology according to the seasonal progression and variation at the local scale.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

In the terrestrial biosphere forests have a significant role as a carbon sink. Under recent climate change, it is increasingly important to detect seasonal change or ‘phenology’ that can influence the global carbon cycle. Monitoring canopies using camera systems has offered an inexpensive means to quantify the phenological changes. However, the reliability is not well known. In order to examine the usefulness of cameras to observe forest phenology, we analysed canopy images taken in two deciduous forests in Japan and England and investigate which colour index is best for tracking forest phenology and predict carbon uptake by trees. A camera test using model leaves under controlled conditions has also carried out to examine sensitivity of colour indices for discriminating leaf colours. The main findings of the present study are: 1) Time courses of colour indices derived from images taken in deciduous forests showed typical patterns throughout the growing season. Although cameras are not calibrated instrument, analysis of images allowed detecting the timings of phenological events such as leaf onset and leaf fall; 2) The strength of the green channel (or chromatic coordinate of green) was useful to observe leaf expansion as well as damage by spring late frost. However, the results of the camera test using model leaves suggested that this index was not sufficiently sensitive to detect leaf senescence. Amongst colour indices, Hue was the most robust metric for different cameras, different atmospheric conditions and different distances. The test also revealed Hue was useful to track nitrogen status of leaves; 3) Modelling results using a light use efficiency model for GPP showed a strong relationship between GPP and Hue, which was stronger than the relationships using alternative traditional indices.

La banquise antarctique a subi une réduction brutale en 2016, après plus de quatre décennies d'une lente augmentation. Une telle évolution pourrait avoir de larges conséquences, compte tenu de l'importance de la banquise antarctique pour le climat, l'océan et l'écosystème marin polaire local. Pourtant, les modèles climatiques ne parviennent pas à reproduire les changements observés, laissant planer une incertitude considérable quant à leur origine et à leurs conséquences. Cette déficience des modèles est en partie due à une mauvaise compréhension des processus fondamentaux liés à la banquise antarctique. Dans cette thèse, nous contribuons à faire progresser cette compréhension, en adoptant une perspective saisonnière. Les processus moteurs de l'avancée et du retrait saisonniers de la banquise sont explorés. En particulier, les rôles possibles d'un préconditionnement thermodynamique, des flux de chaleur air-glace-mer et de la dynamique de la banquise sont étudiés. Nous montrons, dans l'état moyen, que les dates d'avancée et de retrait de la banquise sont largement contrôlées par des processus thermodynamiques, à travers un préconditionnement respectif du contenu thermique de la couche de mélange et de l'épaisseur de la banquise. Les variations des flux de chaleur air-glace-mer et la dynamique de la banquise ont une importance significative mais secondaire. Ces conclusions sont étayées par un modèle thermodynamique simple, des analyses d'observations et un modèle glace-océan (NEMO). Nous montrons également que les changements récents dans la saisonnalité de la banquise sont principalement dus à des processus thermodynamiques, comme pour l'état moyen. La réduction de la banquise antarctique suivant l'année 2016 coïncide avec un recul plus précoce et une avancée plus tardive de la banquise, à l'échelle quasi-circompolaire. Notre analyse relie ces changements à une glace plus fine en hiver, une fonte plus rapide au printemps et un océan de surface plus chaud en été, en accord avec les processus de la rétroaction glace-albédo. L'empreinte circumpolaire de ces changements leur suggère une cause océanique
Antarctic sea ice has undergone an abrupt reduction in 2016, following more than four decades of a slow increase. This could have wide-ranging consequences given the importance of Antarctic sea ice for climate, ocean, and local ecosystem. Yet, climate models fail to capture this observed evolution, leaving considerable uncertainty regarding its origin, impacts and future evolution. Models failure relates, but not only, to a poor understanding of fundamental Antarctic sea ice processes. In this thesis, we contribute to progress understanding of Antarctic sea ice, adopting a seasonal perspective. We investigate the drivers of seasonal sea ice edge advance and retreat, analyzing the roles of thermodynamic preconditioning, air-ice-sea heat fluxes and sea ice dynamics. We show that, in the mean state, timings of ice edge advance and retreat are largely controlled by thermodynamics, via preconditioning from mixed layer heat content and sea ice thickness, respectively. Variations in air-ice-sea heat fluxes and sea ice dynamics have a significant but secondary importance. This conclusion is supported by a simple thermodynamic model, observational analyses and the NEMO ice-ocean model. We also show that recent changes in sea ice seasonality are mainly driven by thermodynamics, similar to the mean state. The reduction in Antarctic sea ice following 2016 coincides with nearly circumpolar earlier retreat and later advance of the ice edge. Our analysis links these changes to thinner ice in winter, faster melt in spring and warmer upper ocean in summer, in line with ice-albedo feedback processes. Based on the circumpolar footprint of these changes, we argue that they likely have an oceanic origin

In Canada, the residential building sector consumes 17% of the total energy and contributes 15% of the total GHG emissions. Predominantly, the energy demand for cooling in the residential sector is increasing due to large occupancy floor area and high usage of air-conditioning. Minimizing energy use and GHG emissions is one of the highest priority goals set for national energy management strategies in developed countries including Canada. In this research, a sustainability assessment framework is developed to evaluate the techno-economic and environmental performance of different building cooling systems, namely conventional snow storage system, watertight snow storage system, high-density snow storage system, and the conventional chiller cooling system. The framework is implemented in a low-rise residential building in Kelowna (BC, Canada) to appraise its practicality. The Life cycle assessment (LCA) approach is used to assess the environmental impacts of different building cooling systems. LCA results revealed that the systems have varying energy requirements and associated environmental impacts during the different life cycle phases (extraction and construction, utilization, and end of life). The annual cooling energy demands for different cooling systems are also estimated. The LCA is carried out using SimaPro 8.1 software and the TRACI 2.1 method. Multi-criteria decision analysis is employed using the ‘Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE-II)’ to evaluate the sustainability of different cooling systems over their life cycle. The results showed that the snow storage systems tend to reduce the greenhouse gas emissions and associated environmental impacts more than the conventional cooling system. A probabilistic feasibility evaluation tool is developed to evaluate the techno-economic performance of different cooling systems. The incremental economic performance of alternatives is estimated in terms of the total cooling cost per kWh at the facility. Monte-Carlo simulation was performed to consider the uncertainty factors involved in the techno-economic parameters of cooling systems. Results of this analysis verified that the snow storage systems are more energy efficient and low-cost options for building cooling systems. The developed frameworks will support decision-makers in evaluating the sustainability of building cooling systems. Moreover, socio-economic benefits, i.e. improving affordability, equity, and enhancing energy sustainability, could be achieved.
Applied Science, Faculty of
Engineering, School of (Okanagan)
Graduate

The Southern Ocean forms a vital component of the earth system as a sink of CO2 and heat, taking over 40% of the annual oceanic CO2 uptake (75% of global heat uptake), slowing down the accumulation of CO2 in the atmosphere and thus the rate of climate change. However, recent studies based on the Coupled Model Intercomparison Project version 5 (CMIP5) Earth System Models (ESMs) show that CMIP5 ESMs disagree on the phasing of the seasonal cycle of the CO2 flux (FCO2) and compare poorly with available observation estimates in the Southern Ocean. Notwithstanding these differences, the seasonal cycle is a dominant mode of CO2 variability in the Southern Ocean, and hence this is an important bias. Previous studies suggest that these biases of FCO2 in ESMs might be a significant limitation to the long-term simulation of CO2 characteristics in the Southern Ocean. Consequently, this study has three primary objectives: first, to develop a process-based diagnostic method to analyze and isolate key biases and their underlaying mechanisms in the model-observations seasonal cycle of FCO2 differences for forced ocean models and ESMs. Second, to use this framework to examine sources of biases responsible for the limited skill of CMIP5 models in simulating the seasonal cycle of FCO2 with respect to observed estimates. Thirdly, to investigate how these present-day biases in the seasonality and drivers of CO2 in CMIP5 ESMs affect modelled longterm changes in the mechanisms of CO2 uptake in the Southern Ocean. In the first part of the dissertation, an objective diagnostic framework was established to analyze model-observation biases in the seasonal scale of FCO2 using the NEMO PISCES ORCA2LP model output, and Takahashi et al. (2009) observed estimates. The diagnostic framework focuses on examining the relative contributions of the competing drivers (SST and DIC) and related processes (solubility, biological and mixing) to instantaneous monthly changes in surface pCO2 (and FCO2) at the seasonal scale. In the second part of the dissertation, this approach is applied to 10 CMIP5 models in the Southern Ocean, to investigate the mechanistic basis for the seasonal cycle of FCO2 biases. It was found that FCO2 biases in CMIP5 models can be grouped into two main categories, i.e. group-SST and group-DIC. Group-SST models are characterized by an exaggeration of the seasonal rates of change of Sea Surface Temperature (SST) in autumn and spring during the cooling and warming peaks, respectively. These faster-than-observed rates of change of SST tip the control of the seasonal cycle of pCO2 and FCO2 towards SST and result in divergence between the observed and modelled seasonal cycles, particularly in the Sub-Antarctic Zone. While almost all analyzed models show these SST-driven biases, 3 out of 10 (namely NorESM1-ME, HadGEM2-ES and MPI-ESM, collectively the group-DIC models) compensate the solubility bias because of their exaggerated primary production, such that biologically-driven DIC changes become the regulators of the seasonal cycle of FCO2. It was also found that despite significant differences in the spatial characteristics of the mean annual fluxes, CMIP5 models show a zonal homogeneity in the seasonal cycle of FCO2 at the basin-scale in contrast to observed estimates. In the final third of the dissertation, using five CMIP5 ESMs from the RCP8.5 scenario, it was found that CMIP5 models present climate biases in the seasonality and drivers of FCO2 are fundamental to how models simulate long-term changes in the mechanisms of CO2 uptake in the Southern Ocean. Although all five analyzed models show an increased annual mean CO2 uptake by the end of the century, they show significant differences in the mechanisms. The present-day temperature biased models (group-SST) generally maintain the dominance of the temperature driver in the seasonal variability of FCO2 to end of the century. But show enhanced CO2 uptake due to increased anthropogenic atmospheric CO2 and decreased surface CO2 buffering capacity but they display a weak to null role of biological activity in the increased CO2 sink. On the other hand, the increased CO2 uptake at the end of the century in group-DIC models is explained increased biological driven CO2 uptake in spring, linked to increased Revelle factor and solubility driven CO2 uptake in winter. Increased Revelle factor at the end of the century enhance pCO2 changes for even smaller DIC changes.

Central Africa is, climatologically speaking, a poorly studied region (Clivar, 2000; Dezfuli and Nicholson, 2012; Nicholson and Dezfuli, 2012; Todd and Washington, 2004). It is considered as a knowledge gap in the understanding of the tropical climate system (Todd and Washington, 2004). Drivers of Central Africa rainfall are not well documented and deserve more attention. The aims of thesis are to enhance our fundamental understanding of Central Africa rainfall and the mechanisms involved in its seasonal and interannual variability as well as to assess how an atmospheric general circulation model forced by observed sea surface temperature (SST), the ECHAM5.3 model, does represent the main features of Central Africa hydroclimate variability. The seasonal cycle of Central Africa rainfall is primarily driven by change in the atmospheric low-pressure system of Central Africa landmass, water vapor and latent heat release rather than change of local temperature. From October to April, over Central Africa and its neighbouring regions, we highlight the existence in the mid-lower troposphere, between 1000 and 500 hPa of a dominant cyclonic and quasipermanent circulation pattern that drives the atmospheric large-scale circulation and its associated water vapor transports, namely the Central Africa Low. The Central Africa Low, with its variation strongly modulated by El Niño Southern Oscillations (ENSO), is characterized by strong convective activity due to an unstable atmosphere over central Africa, leading to high rainfall with less variance. Nevertheless, when the Central Africa Low prevails, Central Africa is a sink of water vapor, with the Indian Ocean as the main supplier. The weakening of the Central Africa Low, in May to September, is associated with the reversal of the water vapor transport at the northern boundary channel, leading Central Africa to become a source of moisture. During this season, both surrounding oceans are suppliers of moisture, with some additional contribution from the Congo basin rainforest. Central Africa rainfall variability is controlled by large-scale circulation variation, rather than variation in tropospheric water vapor. Year-round, the large-scale circulation is characterized by dominant easterly jets at middle (African easterly jets, AEJs) and upper (tropical easterly jets, TEJ) levels, owed by the Central Africa Low. At low-levels, there is a shallow zonal overturning circulation thermally direct, namely the Congo Basin Cell, driven by near-surface land-ocean thermal contrast between the warm central Africa landmass and the relatively cold Atlantic Ocean. The Congo Basin Cell, characterizes by eastward flow, persists year-round, with a maximum strength (-196.92±32.89 Sv) and width (30o degree) in August/September and minimum strength (-24.80± 17.83 Sv) and width (~6o degree) in May. The Congo Basin Cell does not play any crucial role in modulating Central Africa rainfall but it does regulate the rainfall distribution, through the seasonal position of the ITCZ. At midlevel, the atmospheric convective instability over Central Africa is controlled by the southward import of high moist static energy from the warmer Sahel associated with the AEJ over Central Africa. The saturation of the rising moist air at midlevel determines the location of high rainfall over central Africa year-round. Nevertheless, the absence of significant trend (- 0.013 mm per decade) of the Central Africa rainfall is associated with the weakening of the Central Africa Low in recent decades (1979 to 2015), consistent with Lau and Wu (2006). Further investigations on physical mechanisms affecting the Central Africa hydroclimate reveals that the Central Africa Low and land-ocean thermal contrasts are the main drivers of Central Africa rainfall variability at seasonal and interannual time scale, through the control of AEJs and the Congo Basin Cell strength and width. The analysis of ECHAM5.3 experiments provide a support to these mechanisms. Finally, to unravel what are the physical mechanisms shaping the rainfall anomalies patterns associated with the interannual variability of Central Africa rainfall, we found out that the Central Africa does reflect the regional-scale response of the atmosphere to the variation of the interbasin SST anomalies gradient (ΔSST) between tropical Atlantic and Indian Oceans. Likely, the zonal contrast of central Africa rainfall is owed by the Central Africa Low, which separates central Africa in two distinct regions of opposite polarity by regulating the strength of the low-level westerly and mid-upper easterly jets and their associated water vapor transports. This east-west dipole-like pattern of Central Africa rainfall is similar to the second leading mode obtained by empirical orthogonal functions (EOF) analysis of rainfall anomalies during the long rainy season. Thus, during the positive phase of ΔSST, the Central Africa Low area change induces an anomalous clockwise zonal overturning cell over Central Africa, with ascending branch over Atlantic, indicative of deep convection leading to rainfall surplus, and sinking branch over Indian Ocean, indicative of subsistence, which suppress convection and lead to rainfall deficit, consistent with the mechanism proposed by Dezfuli et al. (2015). However, the impact of ΔSST on Central Africa rainfall variability is asymmetrical during positive and negative phases of ΔSST.

Seventeen Earth system models (ESMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were evaluated, focusing on the seasonal sensitivities of net biome production (NBP), net primary production (NPP), and heterotrophic respiration (Rh) to interannual variations in temperature and precipitation during 1982-2005 and their changes over the twenty-first century. Temperature sensitivity of NPP in ESMs was generally consistent across northern high-latitude biomes but significantly more negative for tropical and subtropical biomes relative to satellite-derived estimates. The temperature sensitivity of NBP in both inversion-based and ESM estimates was generally consistent in March-May (MAM) and September-November (SON) for tropical forests, semiarid ecosystems, and boreal forests. By contrast, for inversion-based NBP estimates, temperature sensitivity of NBP was nonsignificant for June-August (JJA) for all biomes except boreal forest; whereas, for ESM NBP estimates, the temperature sensitivity for JJA was significantly negative for all biomes except shrublands and subarctic ecosystems. Both satellite-derivedNPP and inversion-based NBP are often decoupled from precipitation, whereas ESM NPP and NBP estimates are generally positively correlated with precipitation, suggesting that ESMs are oversensitive to precipitation. Over the twenty-first century, changes in temperature sensitivities of NPP, Rh, and NBP are consistent across all RCPs but stronger under more intensive scenarios. The temperature sensitivity of NBP was found to decrease in tropics and subtropics and increase in northern high latitudes in MAM due to an increased temperature sensitivity of NPP. Across all biomes, projected temperature sensitivity of NPP decreased in JJA and SON. Projected precipitation sensitivity of NBP did not change across biomes, except over grasslands in MAM.

A climatological field is a mean gridded field that represents the monthly or seasonal trend of an ocean parameter. This instrument allows to understand the physical conditions and physical processes of the ocean water and their impact on the world climate. To construct a climatological field, it is necessary to perform a climatological analysis on an historical dataset. In this dissertation, we have constructed the temperature and salinity fields on the Mediterranean Sea using the SeaDataNet 2 dataset. The dataset contains about 140000 CTD, bottles, XBT and MBT profiles, covering the period from 1900 to 2013. The temperature and salinity climatological fields are produced by the DIVA software using a Variational Inverse Method and a Finite Element numerical technique to interpolate data on a regular grid. Our results are also compared with a previous version of climatological fields and the goodness of our climatologies is assessed, according to the goodness criteria suggested by Murphy (1993). Finally the temperature and salinity seasonal cycle for the Mediterranean Sea is described.

The purple sandpipers (Calidris maritima) are the most common waders in the high arctic archipelago of Svalbard, Norway. There they have to cope with a very short summer season and high metabolic costs of migrating far north and breeding in an arctic environment. The food on land is usually scarce, whereas there are rich feeding grounds in the littoral zone, such as in the intertidal zone of river flats. These feeding grounds are though only available to the purple sandpipers during low tide and as long as the estuary is not covered by sea ice. One of these intertidal flats was used as the fieldwork area in this study. To study when the birds are coming to this intertidal flat for feeding, a count study was performed during the entire stay of the purple sandpipers in Svalbard in summer 2010. Point counts were performed at low tide during 118 different days. Additionally, point counts were performed at twenty days during the six hours of the entire low tide period, to study when during the tidal cycle most sandpipers were feeding at the estuary. Most sandpipers were counted at the intertidal flat at the beginning of June with the highest number, 921 individuals, on 8th June. When the tundra was free of snow and the birds could start breeding, numbers where rapidly declining with very few sandpipers left in the estuary in July and the first part of August. From the end of August numbers were increasing again with a second but lower peak in the end of September and beginning of October. By the end of October all sandpipers had left the estuary. The study on the appearance of purple sandpipers at the estuary at the different periods of low tide showed that there were significantly more sandpipers between low tide and half an hour later than at the rest of the low tide period. This might be due to better access to their prey at that time. This knowledge could be used in future studies aiming at recording the maximum numbers. The result of the phenologic study could be included in a long term monitoring to see if the numbers and the timing of purple sandpipers are stable in this area or not: Are the peak numbers differing significantly? Is the timing of the arrival, the stay on the tundra and the timing of leaving the archipelago in the fall changing? Long-term monitoring would be especially interesting in the view of possible influences of the climate change on the purple sandpipers. Rising sea level as a result of the climate change would change the morphology of the estuaries and thereby influence the food resources available for sandpipers.

Includes bibliographical references
A recent study by Lenton et al., 2013, compared the mean seasonal cycle of air-sea CO₂ flux in the Southern Ocean(SO) over 1990 – 2009 period using five ocean biogeochemical models(BGMs) and atmospheric and ocean inversion models with monthly mean observations for the year 2000. This was done using a set of geographic boundaries to defined sub-domains of the SO consistent with the Regional Carbon Cycle and Assessment and Processes (RECCAP) protocol. Lenton et al., 2013 found that the seasonal cycle anomaly of the five BGMs better resolved observations of the air-sea CO₂ flux seasonal cycle in the SAZ, but was generally out phase with observations in the polar zone. In this study two setups of the ocean biogeochemical model NEMO PISCES was used to investigate the characteristics of the air-sea CO₂ flux seasonal cycle in the Southern Ocean in the period 1993- 2006. The study focused on two aspects i.e. (i) the sensitivity of air-sea CO₂ flux seasonal cycle to model resolution: comparing the ORCA2-LIM-PISCES (2° x 2° cos Ø) and PERIANT05 (NEMO-PISCES) (0.5° x 0.5° cos Ø) model configurations relative to climatological mean observations for the year 2000 (Takahashi et al., 2009) , and (ii) the sensitivity of air-sea CO₂ flux seasonal cycle to zonal boundary definition: comparing the air-sea CO₂ flux seasonal cycle and annual fluxes for three different boundaries i.e. Lenton 2013 RECCAP boundaries (44°S – 58°S and south of 58°S), geographic boundaries (40°S -50°S and south of 50°S) and dynamic boundaries (Sub-Antarctic Zone and Antarctic Zone, defined using climatological frontal positions). The seasonal cycle of the air-sea CO₂ flux in ORCA2 was found to be out of phase and overestimated the CO₂ flux compared to observations in almost all the sub-regions considered. The use of dynamic boundaries was found not to improve resolving observations seasonal cycle of air-sea CO₂ flux in both ORCA2 and PERIANT05. Boundary definition was found to affect the magnitude of ORCA2 annual air-sea CO₂ fluxes surface area based, where sub-regions of larger surface area gave larger annual CO₂ uptake and vice versa. This was mainly because ORCA2 air-sea CO₂ fluxes were found to show a general CO₂ in-gassing bias and spatially uniform in most parts of the SO and hence integration over a larger surface area gave larger annual fluxes. On the contrary PERIANT05 air-sea CO₂ fluxes spatial variability was not uniform in most parts of the SO however influenced by regional processes and hence annual fluxes were found not surface area based. The poor spatial representation and seasonal cycle sensitivity of ORCA2 air-sea CO₂ fluxes was found to be primarily due to lack or weak winter CO₂ entrainment and biological CO₂ draw down during the summer season. PERIANT05 on the contrary showed the effect of winter CO₂ entrainment, however maintains lack of or weak biological CO₂ draw down in the seasonal cycle. PERIANT05 was also found to show major weakness in the spatial representation of air-sea CO₂ fluxes north of the polar front with relative to T09 observations.

Data recorded from annual tagging and regular tag resightings of southern elephant seals at Marion Island, permitted the investigation of temporal variation in the terrestrial haulout cycle of this species, and estimation of participation levels in the little understood resting haulout phase, that could be related to age, sex, and sexual status. Primigravid females moulted later, and were less inclined to rest, than nulligravid females of the same age, but moulted earlier than mature females, among which the mean moulting dates of respective age-classes were practically the same. It is proposed that earlier implantation among primigravid females, as a function of their returning to sea and regaining condition before parous females, resulted in the earlier mean breeding haulout date of primiparous females. The mean haulout dates of breeding and moulting males were negatively and postively correlated with ascending age, respectively. More than half of the surviving individuals of each immature age- and sex-class were observed to haul out to rest, with participation levels generally consistent from year to year, indicating chat the autumn-winter haulout represents more than simple random haulout events. It is suggested that elephant seals are faced with a trade-off between maximising their time spent foraging, and gaining valuable experience at terrestrial functioning, in their immature years.
Dissertation (MSc (Zoology))--University of Pretoria, 2006.
Zoology and Entomology
unrestricted

Biofilm communities were cultivated in rotating annular bioreactors using water from the South Saskatchewan River. The impacts of seasonal variations, nutrients, pollutants and dissolved oxygen on the activity and composition of the biofilms were assessed by using a combination of microcosm assays and molecular biology techniques.
The seasonal pattern in nitrification, denitrification and hexadecane mineralization, and in the occurrence of nirK in the South Saskatchewan River biofilms was: fall greater than winter, which was equivalent to spring. Hexadecane mineralization was higher in fall 1999 than in fall 2001, denitrification was similar in these two years, and no seasonal pattern of nitrification was observed.
The addition of combined nutrients (C, N, and P) resulted in significant increases in the measured bacterial activities and in the predominance of alkB, nirS and nirK in all seasons and years. The addition of individual nutrients did not stimulate hexadecane mineralization, denitrification, and the PCR amplification of nirS and nirK. In fall 1999, CNP and, to a lesser extent P, stimulated nitrification, whereas in fall 2001, no pattern was observed. The results showed that nutrients, especially P, were limiting for bacterial activities, and that the biofilm activities and composition varied with nutrient availability and time of year.
At the concentration assessed (1 ppb), hexadecane partially inhibited denitrification to similar extents in both years, had a negative impact on nitrification and hexadecane mineralization in fall 1999, and a positive impact on these two latter activities in fall 2001. Nickel (0.5 mg liter-1 ) negatively affected denitrification but had no effect on hexadecane mineralization. The alkB and nirS genes were less predominant and absent, respectively, in biofilms grown in the presence of nickel. DGGE analyses indicated that nickel reduced the biofilm bacterial diversity.
The results presented herein provide much needed information on the microbial ecology of river biofilms, and on the impact and interactive effects of pollutant and nutrient inputs on these biofilms. These results and the techniques used in this project can be applied to monitor environmental effects of anthropogenic activities on aquatic biofilms, and can contribute to establish or revise environmental regulations.

This study investigated the effects of a seasonally variable forage resource on herbivore population dynamics. This involved estimating the relative importance of environmental conditions, and the accessible and used forage resources, at different stages of the seasonal cycle to herbivores in different life-stages and at different points in the reproductive cycle. This study was carried out in the Richtersveld region in South Africa, using goats kept by semi-nomadic Nama pastoralists. In the main study site, the Richtersveld National Park (RNP), herd movements follow a general seasonal migratory pattern: herds are based in the riparian zone of the Orange River during the dry season, and on plains away from the river in the wet season. Over 800 uniquely marked female goats in three life-stages (adults, yearlings and kids) were monitored over a three year period (2007 to 2009). These goats were weighed at 2 - 3 month intervals to provide an estimate of body condition. Browse availability in the riparian zone was estimated using measurements at an individual branch-level and a whole tree-level. FPAR satellite imagery was used to estimate forage abundance outside the riparian zone. Goat density was mapped for each week of the study using census data and the herd positions. Goat body condition, survival rates and fecundity rates for each life-stage were modelled as a response to forage availability, density and climatic conditions. The riparian zone in the RNP was found to function as the key resource of the RNP goat population. Forage depletion by goat browsing resulted in a negative feedback on goat body condition. This decline in body condition was directly related to lower adult survival over the dry season. Fecundity was also most influenced by dry season conditions through the negative effect of poor body condition on pregnancy rates and birth rates. Asymmetric competition between life-stages, resulting from the riparian browse profile being depleted from the bottom-up, was predicted to have a strong effect on goat demography by contributing to differences in body condition and survival rates between life-stages. Wet season conditions appeared to have little effect on goat population dynamics, either through increased neonate survival or through a mass carry-over effect influencing dry season survival. Goat body condition and vital rates were compared between the RNP and the neighbouring Kuboes rangeland, which does not have access to the Orange River, to assess the impact of differences in their dry season forage resource. The long-term size and variability of the livestock population in the RNP was also compared with livestock dynamics in Paulshoek, a rangeland 250 km south east of the RNP. The a priori predictions of relative population dynamics in each region, based on perceived differences in the nature of the key resource in each region, were largely supported.

Precipitation (P) and precipitable water (W) are important components of the hydrological cycles in the earth system, and their seasonal cycles are closely related to monsoon circulations over monsoon regions. Through theoretical analyses and extensive analysis of data from in-situ measurements, satellite remote sensing, and regional reanalysis, significant progress has been made (via four peer-reviewed publications) in four areas related to P, W, and monsoon onset and retreat. First, based on the normalized W index, a novel unified method is proposed to determine global monsoon onset and retreat dates. The results are consistent with those obtained from different local criteria. Second, theoretical and data analyses demonstrate that, because of the large annual range of temperature, W can increase from winter to summer anywhere except in the tropics, including both monsoon and nonmonsoon regions. Third, while the seasonal variation of P is, in general, caused by complex processes (e.g., atmospheric circulations), thermodynamic derivations and data analysis demonstrate that the variation of P from winter to summer can be easily understood from the comparative strength between the change of water vapor and the change of temperature. In monsoon regions, the change of water vapor from winter to summer is much greater than the change of temperature, so P has an in-phase relation with W. While in some of the nonmonsoon regions, where winter is the rainy season, the change of temperature is much greater than the change of water vapor, leading to an out-of-phase relation between P and W, and, relative to summer, the coldness of the winter air is much more significant than its dryness. Finally, the satisfactory performance of the globally unified monsoon index can be understood by comparing the seasonal cycles of P and W. The significant positive correlations between P and W at seasonal and synoptic scales imply that W has the ability to indicate both the means and the interannual variations of the monsoon onset and retreat. Since large increase of W from winter to summer can occur in both monsoon and nonmonsoon regions, the global monsoon regions cannot be obtained from the seasonal change of W.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2011.
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Exemplares de Illex argentinus capturados pela pesca comercial ao longo do sul do Brasil foram amostrados mensalmente de Março de 2007 a Janeiro de 2008, para comprimento dorsal do manto (ML), sexo, idade e maturidade e para comparação entre ‘estação fria’ (Junho-Novembro) e ‘estação quente’ (Dezembro-Maio). Os machos foram 51.5% da amostra, 106-330 mm, 96-275 dias; enquanto que as fêmeas foram 48.5%, 114-341 mm, 124-257 dias. A distribuição de freqüência de ML mostrou que exemplares pequenos ocorreram durante todo o ano enquanto que os machos e a fêmeas grandes ocorreram apenas na ‘estação fria’. O retro-cálculo da data de eclosão mostrou uma desova anual, sendo mais intensa nos meses frios. 131-330 mm ML e 147-275 dias foram os mínimos e os máximos encontrados para os machos maturos, enquanto que para as fêmeas foram 166-341 mm e 146-257 dias. A média do ML na maturidade foi de 181,2 mm e 156,3 mm para fêmeas e machos, respectivamente, e, 79,8% das fêmeas maturas estavam acasaladas. A fase paralarval teve uma média de 28,4 dias e não houve diferença sazonal e no sexo. O crescimento (incremento médio diário ML) dos calamares eclodidos na ‘estação quente’ e que cresceram como juvenis e maturos na ‘estação fria’ foi maior do que aqueles eclodiram na ‘estação fria’. O oposto foi observado para os calamares que eclodiram na ‘estação fria’. De acordo com estes resultados, Illex argentinus pquenos e maturos, desovam e eclodem no sul do Brasil em todas as estações e têm uma fase paralarval menor do que os exemplares de latitudes mais altas. A mistura de calamares pequenos eclodidos por todo o ano e calamares maiores desovantes de inverno é sugerido.
Specimens of Illex argentinus from commercial trawl catches along Southern Brazil were sampled monthly for dorsal mantel length (ML), sex, age and maturity from March 2007 to January 2008 in order to compare the cold season (June to November) and the warm season (December to May). Males (51.5%, 106-330 mm, 96-275 days) and females (48.5%, 114-341 mm, 124-257 days) were sampled. ML frequency distributions showed that small specimens occurred year round while larger males and females occurred only in the cold season. Back-calculated hatching dates showed year-round spawning, which is more intense in cold months. Mature males were 131-330mm and 147-275 days and females were 166-341 mm and 146-257 days. Mean ML’s at maturity were 181.2 mm and 156.3 mm for females and males, respectively, and 79.8% of the mature females was mated. The mean paralarval phase was 28.4 days without seasonal and sex differences. Growth (daily mean ML increment) of squids hatched in the warm season that grew as juveniles and matured in the cold season was higher than the growth of the ones hatched in the cold season. The opposite was observed in squids that hatched in the cold season. According to these results, small sized Illex argentinus that mature, spawn and hatch in southern Brazil in all seasons have a shorter paralarval phase than specimens in higher latitudes. The mixture of small sized squids hatching year round and large sized squid spawning in winter is suggested.

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O objetivo deste trabalho foi analisar a estrutura da comunidade e estimar produção dos copépodes pelágicos do ambiente recifal em diferentes escalas temporais. As amostras foram coletadas em uma estação fixa dentro da baía Tamandaré durante a maré vazante, ao longo de quatro ciclos lunares, durante os períodos seco (novembro/dezembro de 2010) e chuvoso (julho/agosto 2010) e durante os períodos diurnos e noturnos. Foram coletados dados de pluviometria, temperatura, salinidade, material particulado em suspensão e clorofila-a. As amostras de plâncton foram obtidas através da utilização de arrastos subsuperfíciais horizontais usando uma rede cônica (malha de abertura de 200 μm). O material coletado foi fixado e as amostras foram analisadas por contagem, identificação, classificação por estágio de desenvolvimento, sexo e medição das espécies de copépodes presentes nas subamostras. Foram realizados cálculos de densidade, diversidade, riqueza e a frequência de ocorrência para todas as espécies de copépodes pelágicos. A partir das medidas do prossomo dos copépodes foi calculado o peso dos organismos e subsequentemente foram feitos os cálculos de biomassa e das taxas de crescimento e finalmente dos dados de produtividade. As análises realizadas sugerem que a comunidade de copépodes pelágicos do mesozooplâncton associada aos recifes de Tamandaré é regida por fatores ambientais totalmente associados a variações sazonais, principalmente pela pluviosidade, MPS e também pela salinidade. Foram identificados 22 espécies para região, e as espécies que mais frequentes e abundantes ao longo de todo estudo foram: Acartia lilljeborgi, Paracalanus quasimodo, Temora turbinata, Pseudodiaptomus acutus e Calanopia americana. Os valores densidade (694,6 ± 239,4 e 260,7 ± 481,2 ind.m-3 seco e chuvoso), biomassa (1452,02 ± 1072,40 e 200,43 ± 200,27 μg C m-3 seco e chuvoso) e produção (360,640 ± 261,60 e 50,147 ± 50,12 μg C m-3 dia-1 seco e chuvoso) foram significativamente diferentes entre os períodos seco e chuvoso, com maiores valores observados no período seco. Em relação aos turnos diurno/noturmo também existe diferenças significativas para os valores de densidade, biomassa e produção, e os maiores valores foram registrados durante a noite. Portanto, pode-se concluir que assim como a estrutura da comunidade, a produção estimada das principais espécies de copépodes pelágicos de um ambiente recifal é influenciada pelas variações sazonais e nictemeral. Existe influencia das fases da lua, sobre a estrutura da comunidade considerando cada período individualmente e estes dados foram corroborados pelas análises estatísticas ANOVA e PERMANOVA aplicados aos dados de densidade total e das espécies, respectivamente. Em relação aos dados de biomassa e produção, analisados de forma geral, as variações dos ciclos lunares não parecem influenciar de forma significativa a produtividade das espécies de copépodes da região.
The aim of this study was to analyze the community structure and to estimate the production of pelagic copepods on the reef environment at different time scales. Samples were taken at one station in the Tamandaré bay at ebb tide, along four lunar cycles, during dry (November and December 2010) and rainy periods (July and August 2010) and during the days and nights. Data of rainfall, temperature, salinity, suspended particulate matter (SPM) and chlorophyll-a were collected. The plankton samples were obtained through the use of subsurface horizontal hauls with a plankton net (mesh size of 200 μm). The material was fixed and the samples were analyzed by counting, identification, classification by stage of development, sex and measurement of copepod species present in the subsamples. Calculations of density, diversity, richness and frequency of occurrence were performed for all species of pelagic copepods. From the measurements of the copepod prosome, the weight of the organisms was obtained and subsequently the biomass and growth rates, and ultimately the productivity data, were calculated. The performed analysis suggest that the pelagic copepods community of the mesozooplankton associated with the reefs of Tamandaré is regulated by environmental factors entirely associated with seasonal variations, mainly rainfall, SPM and also by salinity. For the region, 22 species were identified, and the most frequent and abundant species throughout the study were: Acartia lilljeborgi, Paracalanus quasimodo, Temora turbinata, Pseudodiaptomus acutus and Calanopia americana. The values of density (694.60 ± 239.40 and 260.70 ± 481.20 ind. m-3 dry and rainy seasons), biomass (1,452.02 ± 1,072.40 and 200.43 ± 200.27 μg C m-3 dry and rainy seasons) and production (360.64 ± 261.60 and 50.14 ± 50.12 μg C m-3 day-1 dry and rainy seasons) were significantly different between the dry and rainy seasons, with higher values being observed in the dry season. Regarding the period of the day, there are also significant differences in the values of density, biomass and production, and the highest values were recorded during the night. Therefore, it can be concluded that, as well as the community structure, the estimated production of the main species of pelagic copepods on a reef environment is influenced by seasonal and nictemeral variations. There is influence of the moon phases on the structure of the community, considering each period individually. This result was corroborated by the ANOVA and PERMANOVA statistical analysis applied to the data of total and species density, respectively. Regarding biomass and production data, analyzed in general, the variations of lunar cycles do not seem to significantly influence the productivity of copepod species in the region.

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This paper examines the multi-level, primitive equation, global ocean circulation model of Semtner and Chervin for its ability to simulate the seasonal cycle in the tropical Pacific Ocean. The result of a 20-year integration of this model using annual mean wind forcing was reported in Semtner and Chervin (1988). This was the first global eddyresolving ocean calculation and it showed many realistic features of ocean circulation. The phase of the simulation analyzed in this report incorporates seasonally varying wind forcing from the Hellerman and Rosenstein (1983) global data set. These wind stress values were defined on a grid with 2° spacing which have been interpolated to the onehalf degree grid points of the Semtner and Chervin model. There is no interannual variability in the wind fields of this data set. The results presented here are from the fourth year of a 10-year seasonal cycle run.

Thesis (M.S.)--University of Nevada, Reno, 2006.
"May, 2006." Includes bibliographical references (leaves 92-98). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2008]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.

Climate models have projected that arid and semiarid lands will experience warmer and drier conditions for the next 100 years. For the last twenty years, the Southwestern US has been experiencing one of the worst droughts over the last century, not only threatening ecological systems but also the water security of its population. Understanding the environmental processes that affect arid and semiarid forests are essential to better understand the water and carbon cycles, and tree-ring research has contributed valuable knowledge in this regard. There is a common understanding that moisture-stress has significant impacts on forested ecosystems and thereby on the global carbon and water cycles. Under persistent moisture deficit, a decline in growth, an increased proportion of wildfires, insect outbreaks, and mass-tree-mortality are often observed in arid and semi-arid forests, having large impacts on their carbon budgets and their capacity to act as a carbon sink. This study addresses the seasonal and regional climatic influences on the water-carbon relations in the ponderosa pine forests of the southwestern US (SW). This region is characterized by a complex climatology related to the North American Monsoon system (NAMS). A topic of interest in this dissertation is the role of the summer rainfall after the early-summer hyper-arid period in the region, providing a unique seasonal condition for these ecosystems to thrive. While these forests clearly rely on winter snowpack to drive much of their annual net primary productivity, the temporal and regional extent to which they supplement winter moisture with summer monsoon moisture needs to be clarified. The core of this dissertation is a study of the spatial and temporal variability of the stable carbon and oxygen isotopes in the cellulose of subsections of the tree rings (e.g., earlywood and latewood) collected from a network of thirteen sites along a latitudinal gradient extending from southern Arizona and New Mexico, through southwest Colorado, and up to northern Utah. The analysis is based on biological and physical processes and their close relationships with isotope effects to infer eco-physiological responses to climate variations over the last century. The stable carbon isotopes are used to derive intrinsic Water-Use Efficiency (iWUE) defined by the molar ratio of carbon gain to water loss. The stable oxygen isotope ratio is used to infer the variations on evaporative flux at the leaf level, which depend on stomatal conductance, atmospheric vapour pressure deficit at the leaf surface, and variations in the isotopic ratio of the source water. Both isotopic ratios are used to document variations in tree productivity and hydrologic vulnerability within the context of climate change impacts on this region. During the study, it was found that climate change in the SW has impacted the carbon and water cycles of these forests for at least the past twenty years. Additionally, seasonality influence the eco-physiology of ponderosa pine change along the latitudinal gradient, as shown by significant differences between EW and LW. These differences are explained by the large shifts in seasonal VPD, which are more evident in the southern part of our study region due to the mid-summer arrival of monsoon rains. These findings will be useful for regional natural resource managers and improves our understanding of seasonal influences on forest water–carbon relationships. This approach will also be useful to develop seasonally resolved paleoclimate and paleo-ecophysiological reconstructions to characterize the long-term influence of winter versus summer moisture on carbon-water relations in forested ecosystems.

A climate controlled, dynamic chamber was used to measure carbon dioxide (CO$ sb2$) and methane (CH$ sb4$) exchange on an ombrotrophic peatland. The study periods were July to early November 1995, and early May to July 1996. Five sample sites, showing ecological and hydrological contrast, were investigated. Measurements of Net Ecosystem Exchange showed peak photosynthetic capacity (GP$ sb{ max})$ ranging from 0.52 $ pm$ 0.04 mg C m$ sp{-2}$ s$ sp{-1}$ (June 1996) to 0.03 $ pm$ 0.02 mg C m$ sp{-2}$ s$ sp{-1}$ (early November 1995). Dark respiration measurements ranged from $-$0.21 $ pm$.02 mg C m$ sp{-2}$ s$ sp{-1}$ (June 1996) to $-$0.02 $ pm$.01 mg C m$ sp{-2}$ s$ sp{-1}$ (late May 1996), and showed significant relationships to soil temperature at all sites. Site average methane measurements ranged from 29-72 mg m$ sp{-2}$ d$ sp{-1}$, and showed a strong relationship to water table on a seasonal basis, but a poor correlation to simultaneous NEE. Modelled Net Ecosystem Productivity (NEP) among sites ranged from 17.1 to 115 gC over the entire study period. The CO$ sb2$ exchanges in late spring and early fall made a large contribution to the figure due to the imbalance in the photosynthetic and dark respiration components of the carbon budget. No discernible relationship was found between seasonal NEP and methane release. The results suggest a large importance of the extreme ends of the growing season in an analysis of the carbon budget of peatlands, periods hitherto little investigated. They also suggest that NEP/methane connections may be restricted in their significance to mainly flooded mires.

Les mares forestières temporaires sont de petites zones humides d’eau douce, sujettes à de fortes dégradations. Le fonctionnement des mares naturelles et restaurées a été étudié en se basant sur les taux de décomposition de la matière organique (MO) et sur l’effet de facilitation d’une plante vasculaire (Molinia caerulea, molinie) sur la croissance des sphaignes (Sphagnum palustre). Les taux de décomposition de la MO dans l’eau ne différaient pas entre les mares naturelles et restaurées mais ils étaient influencés par la teneur en carbone organique du sol, l’ouverture de la canopée forestière et le couvert en sphaignes. Dans le sol de la zone de transition mare-forêt, ces taux étaient réduits par la saturation en eau et par un couvert molinie-sphaignes. La présence de la molinie diminuait la croissance des sphaignes, suggérant une compétition. Les résultats de cette étude contribuent à l’écologie de la restauration de ces mares et questionnent leur devenir dans un contexte de changement climatique
Vernal pools are small freshwater wetlands, subject to strong degradations. The functioning of natural and restored vernal pools was studied, based on organic matter (OM) decomposition rates and the facilitation effect of a vascular plant (Molinia caerulea, purple-moor grass) on Sphagnum growth (Sphagnum palustre). The rates of OM decomposition in water were not different between natural and restored pools, but they were influenced by soil organic carbon content, tree canopy openness and Sphagnum cover. In the soil of the pool-forest transition zone, these rates were reduced by water logging and by a Molinia-Sphagnum cover. The presence of Molinia decreased Sphagnum growth, suggesting a competition relationship. The results of this study contribute to the restoration ecology of vernal pools and raise the question of their fate in the climate change context

This study explored the effects of seasonal variability on the geochemistry of sinking pthesiss and on the nitrogen cycle of the Cariaco Basin. Pthesis fluxes were measured at the base of the euphotic zone (the depth of 1% of photosynthetically active radiation - PAR) with drifting sediment traps during months of upwelling and non-upwelling regimes from March 2007 to November 2009. Flux estimates were analyzed in the context of seasonal variations in sea surface temperature, primary productivity, and chlorophyll a concentrations using data generated by the CARIACO Time-series Program as well as satellite data. Additionally, nine years (1996-2000 and 2004-2007) of nutrients, phytoplankton taxonomy and δ15N of sinking pthesis data within the twilight zone (225 m) from the CARIACO Time-series Program were examined. Results showed that the flux of organic matter responded to changes in surface chlorophyll a but not to primary production. Sinking organic matter decreased by an order of magnitude from the base of the euphotic zone to the oxic-anoxic interface; most of the organic matter produced in surface waters was remineralized before leaving the upper 50-100 m. Lithogenic material often represented a large fraction of the flux. Isotopic analyses showed that 13C/12C ratios of sinking organic carbon were enriched (~-19‰) during the upwelling period and depleted during relaxation (~-23‰). This reflects seasonal changes in inorganic carbon utilization by phytoplankton and suggests that the δ13C of organic carbon in Cariaco sediments can be used as a proxy for carbon fixation by primary producers. The δ15N of the settling flux was influenced by the strength of the upwelling and the presence of the nitrogen fixer Trichodesmium thiebautii in the basin in different seasons; the 15N/14N ratio of sinking nitrogen reflects both imported and local nitrogen fixation signals. This result argues against previous interpretations of the δ15N from the basin's sedimentary record, which suggested that the nitrogen isotopic composition of flux is influenced by denitrification at the oxic-anoxic interface. Dissolved gas samples from the Cariaco eastern and western sub-basins from September 2008 (non-upwelling) and March 2009 (upwelling) were studied to assess the production of biogenic nitrogen gas through mass spectrometric N2/Ar ratiometry. Excess nitrogen gas indicated that upwelling affects the intensity of denitrification at the oxic-anoxic interface. In four of the six stations the concentration of biogenic nitrogen gas at the oxic-anoxic interface was 2.7-6.1 µM N higher during the upwelling period than during the relaxation season (p< 0.001), implying that denitrification in the basin was stimulated by the vertical flux of organic matter and/or the ventilation of the oxic-anoxic interface by oxygenated and nutrient-rich intermediate Caribbean waters.

Cette thèse étudie les cycles économiques provinciaux chinois durant la période 1989-2009. Dans un premier temps, Nous utilisons une variété de techniques afin d'examiner la nature et le degré de comouvement entre les cycles de croissance provinciaux chinois. Nous détectons différentes propriétés des cycles de croissance provinciaux. En utilisant une méthodologie de classification basée sur un modèle, nous constatons que les provinces peuvent être classées parmi cinq classes en fonction des mesures standards des caractéristiques cycliques. Bien que la majorité des provinces a connu la récession qui a eu lieu autour de la crise asiatique, la nation dans son ensemble a connu une phase d'expansion. En outre, toutes les provinces, ont connu la récession liée à la crise financière internationale qui a eu lieu en 2007/2008 à l'exception du Jiangsu et Tianjin. Toutes les provinces côtières, sauf Hainan, sont significativement synchronisées avec le cycle national. En outre, nous constatons que les quatre principales récessions nationales sont bien diffusées dans tout le pays. Ensuite, nous analysons la co-cyclicité entre les provinces dans chacune des six régions définies par Groenewold et al. (2008). Nous nous basons sur la décomposition tendance-cycle en utilisant le modèle à composantes inobservables univarié et multivarié. Nous trouvons que La majorité des cycles provinciaux reflètent des chocs de la demande plutôt que des chocs de l'offre. En examinant si des cycles communs existent au sein de chaque région, nous pouvons formuler des conclusions sur la pertinence de la définition de ces régions
This thesis deals with the Chinese provincial growth cycles over the period 1989-2009. First, we use a variety of techniques to examine the nature and degree of comovement among Chinese provincial growth cycles. We detect different properties of the provincial growth cycles. Using a model-based clustering methodology, we find that provinces can be classified among five major clusters as a function of standard measures of cyclical characteristics. Although the majority of provinces experienced the recession that occurred around the Asian crisis, the nation as whole experienced an expansionary phase. Moreover, all the provinces experienced the recession related to the subprime crisis that occurred in 2007/2008 except Jiangsu and Tianjing. However, All coastal provinces except Hainan are significantly synchronized with the national cycle. Furthermore, we find that the main four national recessions are well diffused across the country. Then, we analyse the co-cyclicality between provinces in each of the six regions defined by Groenewold et al. (2008). We rely on trend-cycle decomposition by using both univariate and multivariate unobserved component model. The majority of provincial cycles reflect demand rather than supply-side shocks. By examining the commonality of provincial growth cycles within each region, we ask whether the definition of these regions is supported by statistical analysis. We find mixed results. Finally, we use a Markov switching model that allow for the identification of business/seasonal cycle interaction

This thesis gives an experiential account of notions of the home in contemporary rural China. Based on a year of fieldwork in a mountain village in rural Shanxi Province, the thesis explores everyday and ritual practices to investigate how people make themselves at home under conditions of political economic transformation. Villagers accommodate and resist conflicts of interest by negotiating boundaries of insiders and outsiders through the home. Differences of gender and generation come to the fore as people compromise between aspiration and pragmatism within the home under conditions of resurgent market competition. The theoretical concern of the thesis lies in connecting wider social processes to personal life projects through the intimate sphere of the home. The rhythm of the seasons patterns the thesis into spring, summer, autumn and winter chapters, as the seasons were pivotal in ordering people’s everyday practices and ritual activities within a shared social and ecological environment. The opening chapter on the autumn harvest coincided with my arrival in the village. The chapter explores how labour, and particularly women’s labour, transforms the earth into affective belonging, and how women negotiate conflicts over food consumption between the agricultural and market economy. The winter chapter parallels tales of personal life history with wider kinship networks across various generations, while simultaneously tracing bodily pathways from the domain of the hot stove in the home to the cold grave in the fields. The next chapter begins with the celebratory periods of springtime during the New Year Festival, a time of ritual renewal in the home when women partook in a local domestic ritual of propitiating the little spirits of the house. At Qingming Festival villagers’ practices of worshipping the ancestors in the fields were juxtaposed with a tour company’s staging of an elaborate ritual revival of star worship in the village. Conflicting aspirations over the future of the past thereby tore fissures into the emerging ritual terrain between outside spectacle and inside convergence. The last ethnographic chapter looks at the summer as a time for regenerating life, particularly through marriage and children. Reciprocal caring cycles between different generations of women are central to balancing domestic and occupational aspirations in negotiation with the local implementation of the family planning policy. House-based rituals at children’s birthday parties and bridal farewell ceremonies formally celebrate the roles of matrilateral relatives.

ENGLISH:

The natural nitrogen cycle has been and is significantly perturbed by anthropogenic emissions of reactive nitrogen (Nr) compounds into the atmosphere, resulting from our production of energy and food. In the last century global ammonia (NH3) emissions have doubled and represent nowadays more than half of total the Nr emissions. NH3 is also the principal atmospheric base in the atmosphere and rapidly forms aerosols by reaction with acids. It is therefore a species of high relevance for the Earth's environment, climate and human health (Chapter 1). As a short-lived species, NH3 is highly variable in time and space, and while ground based measurements are possible, they are sparse and their spatial coverage is largely heterogeneous. Consequently, global spatial and temporal patterns of NH3 emissions are poorly understood and account for the largest uncertainties in the nitrogen cycle. The aim of this work is to assess distributions and saptiotemporal variability of NH3 using satellite measurements to improve our understanding of its contribution to the global nitrogen cycle and its related effects.

Recently, satellite instruments have demonstrated their abilities to measure NH3 and to supplement the sparse surface measuring network by providing global total columns daily. The Infrared Atmospheric Sounding Interferometer (IASI), on board MetOp platforms, is measuring NH3 at a high spatiotemporal resolution. IASI circles the Earth in a polar Sun-synchronous orbit, covering the globe twice a day with a circular pixel size of 12km diameter at nadir and with overpass times at 9:30 and 21:30 (local solar time when crossing the equator). An improved retrieval scheme based on the calculation of Hyperspectral Range Index (HRI) is detailed in Chapter 2 and compared with previous retrieval methods. This approach fully exploits the hyperspectral nature of IASI by using a broader spectral range (800-1200 cm-1) where NH3 is optically active. It allows retrieving total columns from IASI spectra globally and twice a day without large computational resources and with an improved detection limit. More specifically the retrieval procedure involves two steps: the calculation of a dimensionless spectral index (HRI) and the conversion of this index into NH3 total columns using look-up tables (LUTs) built from forward radiative transfer simulations under various atmospheric conditions. The retrieval also includes an error characterization of the retrieved column, which is of utmost importance for further analysis and comparisons. Global distributions using five years of data (1 November 2007 to 31 October 2012) from IASI/MetOp-A are presented and analyzed separately for the morning and evening overpasses. The advantage of the HRI-based retrieval scheme over other methods, in particular to identify smaller emission sources and transport patterns over the oceans is shown. The benefit of the high spatial sampling and resolution of IASI is highlighted with the regional distribution over China and the first four-year time series are briefly discussed.

We evaluate four years (1 January 2008 to 31 December 2011) of IASI-NH3 columns from the morning observations and of LOTOS-EUROS model simulations over Europe and Western Russia. We describe the methodology applied to account for the variable retrieval sensitivity of IASI measurements in Chapter 3. The four year mean distributions highlight three main agricultural hotspots in Europe: The Po Valley, the continental part of Northwestern Europe, and the Ebro Valley. A general good agreement between IASI and LOTOS-EUROS is shown, not only over source regions but also over remote areas and over seas when transport is observed. The yearly analyses reveal that, on average, the measured NH3 columns are higher than the modeled ones. Large discrepancies are observed over industrial areas in Eastern Europe and Russia pointing to underestimated if not missing emissions in the underlying inventories. For the three hotspots areas, we show that the seasonality between IASI and LOTOS-EUROS matches when the sensitivity of the satellite measurements is taken into account. The best agreement is found in the Netherlands, both in magnitude and timing, most likely as the fixed emission timing pattern was determined from experimental data sets from this country. Moreover, comparisons of the daily time series indicate that although the dynamic of the model is in reasonable agreement with the measurements, the model may suffer from a possible misrepresentation of emission timing and magnitude. Overall, the distinct temporal patterns observed for the three sites underline the need for improved timing of emissions. Finally, the study of the Russian fires event of 2010 shows that NH3 modeled plumes are not enough dispersed, which is confirmed with a comparison using in situ measurements.

Chapter 4 describes the comparisons of IASI-NH3 measurements with several independent ground-based and airborne data sets. Even though the in situ data are sparse, we show that the yearly distributions are broadly consistent. For the monthly analyzes we use ground-based measurements in Europe, China and Africa. Overall, IASI-derived concentrations are in fair agreement but are also characterized by less variability. Statistically significant correlations are found for several sites, but low slopes and high intercepts are calculated in all cases. At least three reasons can explain this: (1) the lack of representativity of the point surface measurement for the large IASI pixel, (2) the use of a single profile shape in the retrieval scheme over land, which does therefore not account for a varying boundary layer height, (3) the impact of the averaging procedure applied to satellite measurements to obtain a consistent quantity to compare with the in situ monthly data. The use of hourly surface measurements and of airborne data sets allows assessing IASI individual observations. Much higher correlation coefficients are found in particular when comparing IASI-derived volume mixing ratio with vertically resolved measurements performed from the NOAA WP-3D airplane during CalNex campaign in 2010. The results demonstrate the need, for validation of the satellite columns, of measurements performed at various altitudes and covering a large part of the satellite footprint.

The six-year of IASI observations available at the end of this thesis are used to analyze regional time series for the first time (Chapter 5). More precisely, we use the IASI measurements over that period (1 January 2008 to 31 December 2013) to identify seasonal patterns and inter-annual variability at subcontinental scale. This is achieved by looking at global composite seasonal means and monthly time series over 12 regions around the world (Europe, Eastern Russia and Northern Asia, Australia, Mexico, South America, 2 sub-regions for Northern America and South Asia, 3 sub-regions for Africa), considering separately but simultaneously measurements from IASI morning and evening overpasses. The seasonal cycle is inferred for the majority of these regions. The relations between the NH3 atmospheric abundance and emission processes is emphasized at smaller regional scale by extracting at high spatial resolution the global climatology of the month of maxima columns. In some region, the predominance of a single source appears clearly (e.g. agriculture in Europe and North America, fires in central South Africa and South America), while in others a composite of source processes on small scale is demonstrated (e.g. Northern Central Africa and Southwestern Asia).

Chapter 6 presents the achievements of this thesis, as well as ongoing activities and future perspectives.

FRANCAIS:

Le cycle naturel de l'azote est fortement perturbé suite aux émissions atmosphériques de composés azotés réactifs (Nr) résultant de nos besoins accrus en énergie et en nourriture. Les émissions d'ammoniac (NH3) ont doublé au cours du siècle dernier, représentant aujourd'hui plus de la moitié des émissions totales de Nr. De plus, le NH3 étant le principal composé basique de notre atmosphère, il réagit rapidement avec les composés acides pour former des aérosols. C'est dès lors un constituant prépondérant pour l'environnement, le climat et la santé publique. Les problématiques environnementales y étant liées sont décrites au Chapitre 1. En tant que gaz en trace le NH3 se caractérise par une importante variabilité spatiale et temporelle. Bien que des mesures in situ soient possibles, elles sont souvent rares et couvrent le globe de façon hétérogène. Il en résulte un manque de connaissance sur l'évolution temporelle et la variabilité spatiale des émissions, ainsi que de leurs amplitudes, qui représentent les plus grandes incertitudes pour le cycle de l'azote (également décrites au Chapitre 1).

Récemment, les sondeurs spatiaux opérant dans l'infrarouge ont démontré leurs capacités à mesurer le NH3 et par là à compléter le réseau d'observations de surface. Particulièrement, l'Interféromètre Atmosphérique de Sondage Infrarouge (IASI), à bord de la plateforme MetOp, mesure le NH3 à une relativement haute résolution spatiotemporelle. Il couvre le globe deux fois par jour, grâce à son orbite polaire et son balayage autour du nadir, avec un temps de passage à 9h30 et à 21h30 (temps solaire local quand il croise l'équateur). Une nouvelle méthode de restitution des concentrations basée sur le calcul d'un index hyperspectral sans dimension (HRI) est détaillée et comparée aux méthodes précédentes au Chapitre 2. Cette méthode permet d'exploiter de manière plus approfondie le caractère hyperspectral de IASI en se basant sur une bande spectrale plus étendue (800-1200 cm-1) au sein de laquelle le NH3 est optiquement actif. Nous décrivons comment restituer ces concentrations deux fois par jour sans nécessiter de grandes ressources informatiques et avec un meilleur seuil de détection. Plus spécifiquement, la procédure de restitution des concentrations consiste en deux étapes: le HRI est calculé dans un premier temps pour chaque spectre puis est ensuite converti en une colonne totale de NH3 à l'aide de tables de conversions. Ces tables ont été construites sur base de simulations de transfert radiatif effectuées pour différentes conditions atmosphériques. Le processus de restitution des concentrations comprend également le calcul d'une erreur sur la colonne mesurée. Des distributions globales moyennées sur cinq ans (du 1 novembre 2007 au 31 Octobre 2012) sont présentées et analysées séparément pour le passage diurne et nocturne de IASI. L'avantage de ce nouvel algorithme par rapport aux autres méthodes, permettant l'identification de sources plus faibles de NH3 ainsi que du transport depuis les sources terrestres au-dessus des océans, est démontré. Le bénéfice de la haute couverture spatiale et temporelle de IASI est mis en exergue par une description régionale au-dessus de la Chine ainsi que par l'analyse de premières séries temporelles hémisphériques sur quatre ans.

Au Chapitre 3, nous évaluons quatre ans (du 1 janvier 2008 au 31 décembre 2011) de mesures matinales de IASI ainsi que de simulations du modèle LOTOS-EUROS, effectuées au-dessus de l'Europe et de l'ouest de la Russie. Nous décrivons une méthodologie pour prendre en compte, dans la comparaison avec le modèle, la sensibilité variable de l'instrument IASI pour le NH3. Les comparaisons montrent alors une bonne concordance générale entre les mesures et les simulations. Les distributions pointent trois régions sources: la vallée du Pô, le nord-ouest de l'Europe continentale et la vallée de l'Ebre. L'analyse des distributions annuelles montre qu'en moyenne, les colonnes de NH3 mesurées sont plus élevées que celles simulées, à part pour quelques cas spécifiques. Des différences importantes ont été identifiées au-dessus de zones industrielles en Europe de l'est et en Russie, ce qui tend à incriminer une sub-estimation voire une absence de ces sources dans les inventaires d'émissions utilisés en entrée du modèle. Nous avons également montré que la saisonnalité est bien reproduite une fois la sensibilité des mesures satellites prise en compte. La meilleure concordance entre le modèle et IASI est observée pour les Pays-Bas, ce qui est certainement dû au fait que le profil temporel des émissions utilisé pour les simulations LOTOS-EUROS est basé sur des études expérimentales réalisées dans ce pays. L'étude des séries temporelles journalières indique que la dynamique du modèle est raisonnablement en accord avec les mesures mais pointe néanmoins une possible mauvaise représentation du profil temporel ainsi que de l'ampleur des émissions. Finalement, l'étude des importants feux ayant eu cours en Russie à l'été 2010 a montré que les panaches modélisés sont moins étendus que ceux observés, ce qui a été confirmé grâce à une comparaison avec des mesures sols.

Le chapitre 4 est dédié à la confrontation des mesures IASI avec différents jeux de données indépendants acquis depuis le sol et par avion. Les distributions globales annuelles sont concordantes, bien que la couverture spatiale des mesures sols soit limitée. Des mesures effectuées à la surface en Europe, en Chine et en Afrique sont utilisées pour les comparaisons mensuelles. Ces dernières révèlent une bonne concordance générale, bien que les mesures satellites montrent une plus faible amplitude de variations de concentrations. Des corrélations statistiquement significatives ont été calculées pour de nombreux sites, mais les régressions linéaires sont caractérisées par des pentes faibles et des ordonnées à l'origine élevées dans tous les cas. Au minimum, trois raisons contribuent à expliquer cela: (1) le manque de représentativité des mesures ponctuelles pour l'étendue des pixels IASI, (2) l'utilisation d'une seule forme de profil vertical pour la restitution des concentrations, qui ne prend dès lors pas en compte la hauteur de la couche limite, (3) l'impact de la procédure utilisée pour moyenner les observations satellites afin d'obtenir des quantités comparables aux mesures sols mensuelles. La prise en compte de mesures en surface effectuées à plus haute résolution temporelle ainsi que de mesures faites depuis un avion permet d'évaluer les observations IASI individuelles. Les coefficients de corrélation calculés sont bien plus élevés, en particulier pour la comparaison avec les mesures effectuées depuis l'avion NOAA WP-3D pendant la campagne CalNex en 2010. Ces résultats démontrent la nécessité de ce type d'observations, effectuées à différentes altitudes et couvrant une plus grande surface du pixel, pour valider les colonnes IASI-NH3.

Les six ans de données IASI disponibles à la fin de cette thèse sont utilisées pour tracer les premières séries temporelles sub-continentales (Chapitre 5). Plus spécifiquement, nous explorons les mesures IASI durant cette période (du 1 janvier 2008 jusqu'au 31 décembre 2013) pour identifier des structures saisonnières ainsi que la variabilité inter-annuelle à l'échelle sous-continentale. Pour arriver à cela, des moyennes saisonnières composites ont été produites ainsi que des séries temporelles mensuelles au-dessus de 12 régions du globe (Europe, est de la Russie et nord de l'Asie, Australie, Mexique, Amérique du Sud, 2 sous-régions en Amérique du nord et en Asie du sud et 3 sous-régions en Afrique), considérant séparément mais simultanément les mesures matinales et nocturnes de IASI. Le cycle saisonnier est raisonnablement bien décrit pour la plupart des régions. La relation entre la quantité de NH3 atmosphérique et ses sources d'émission est mise en exergue à l'échelle plus régionale par l'extraction à haute résolution spatiale d'une climatologie des mois de colonnes maximales. Dans certaines régions, la prédominance d'un processus source apparait clairement (par exemple l'agriculture en Europe et en Amérique du nord, les feux en Afrique du Sud et en Amérique du Sud), alors que, pour d'autres, la diversité des sources d'émissions est démontrée (par exemple pour le nord de l'Afrique centrale et l'Asie du sud-ouest).

Le Chapitre 6 reprend brièvement les principaux aboutissements de cette thèse et présente les différentes recherches en cours et les perspectives associées.

Doctorat en Sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished

I conducted an integrative field study on male cottonmouths (Agkistrodon piscivorus), a common pitviper of the southeastern United States, to investigate the evolution of contrasting mating patterns in North American pitvipers (bimodal and unimodal annual patterns) and resolve conflicting information about the pattern exhibited by the cottonmouth. I determined a unimodal late summer peak of testosterone (T) and a muted unimodal seasonal cycle of the sexual segment of the kidney (a secondary sexual characteristic), both of which were correlated with the single peak of spermatogenesis in late summer. I also conducted a study to determine diel and seasonal variation of corticosterone (CORT), the effect of captive handling on CORT, and the relationship between CORT and T after captive handling, and detected a significant elevation of CORT and a significant decrease of T after capture in male cottonmouths, as well as a significant negative correlation between CORT and T.

Le Système Nord du Courant de Humboldt (SNCH) est le lieu d’une forte activité biologique due à un upwelling côtier intense. Il abrite l’une des plus grandes populations de l’anchois du Pérou soumis à la plus grande pêcherie monospécifique au monde. Le SNCH héberge aussi de grandes et variables, populations d’oiseaux, composées de trois espèces sympatriques productrices de guano : le cormoran guanay (Phalacrocorax bougainvillii), le fou péruvien (Sula variegata) et le pélican péruvien (Pelecanis thagus), qui se nourrissent principalement d’anchois. Dans ce travail, nous examinons les fluctuations de ces trois populations d’oiseaux marins, en nous concentrant sur le cycle saisonnier de leur reproduction, pour aborder les questions suivantes : Dans quelle mesure les saisonnalités de reproduction diffèrent elles entre espèces ? Dans quelle mesure sont-elles plastiques dans le temps et dans l’espace ? Qu’est ce qui, des conditions environnementales et des activités anthropogéniques affecte le plus la reproduction des oiseaux marins ? Nous abordons ces questions en utilisant des données de présence de reproducteurs (1) dans 30 sites péruviens répartis entre 06°S-18°S (2003-2014) ; et (2) dans un site, pendant trois périodes (1952-1968, 1972-1989, 2003-2014). Nous utilisons des covariables environnementales décrivant les conditions océanographiques, l’abondance, l’accessibilité et la condition des proies, ainsi que des covariables décrivant la pression de pêche. Nous utilisons des modèles d’occupation multi-saisonniers pour caractériser la saisonnalité de la reproduction et la relier aux covariables environnementales. Nous utilisons aussi des analyses en composantes principales fonctionnelles pour classifier les différences de saisonnalité entre sites, et des forêts aléatoires de régression pour analyser la contribution relative des covariables à la variabilité de la saisonnalité de reproduction.Nous mettons en évidence qu’en moyenne, la reproduction démarre au cours de l’hiver austral / début de printemps et prend fin en été / début d’automne, ce patron étant plus marqué chez les fous et pélicans que chez les cormorans. La reproduction est calée dans le temps de telle sorte à ce que les jeunes prennent leur indépendance lorsque les conditions de production primaire, d’abondance et d’accessibilité des proies sont maximales. Ce patron est unique en comparaison avec les autres écosystèmes d’upwelling et peut être expliqué par les fortes abondances absolues de proies disponibles tout au long de l’année dans le SNCH.La saisonnalité de reproduction diffère entre les sites de nidification. Les oiseaux se reproduisent plus tôt et avec de plus fortes probabilités lorsque les colonies sont plus grandes, situées sur des îles à moins de 20 km des côtes, aux plus basses latitudes, et présentant une production primaire plus élevée. Alors, la saisonnalité de la reproduction est davantage influencée par les conditions environnementales locales que par les gradients environnementaux de grande échelle.Les oiseaux marins adaptent aussi la saisonnalité de leur reproduction aux changements drastiques causés dans l’écosystème par les changements de régime. Les cormorans font preuve de la plus grande plasticité, en modulant la date te l’amplitude de la saisonnalité de leur reproduction, cela est probablement permis par leur plus grande flexibilité de fourragement. Les dates et amplitudes fixes observées chez les fous peuvent être liées aux spécificités de leur stratégie de fourragement et à des changements de proies lorsque le stock d’anchois est bas. Les différences spécifiques dans les adaptations de la saisonnalité de reproduction permettent aux oiseaux de profiter différemment des conditions locales de proies, et de faire face aux changements de régime avec des stratégies différentes. Une méthodologie de capture-recapture en parallèle des comptages mensuels est proposée pour élargir les horizons de l’évaluation des dynamiques d’une population
The Northern Humboldt Current System (NHCS) is a place of a high biological activity due to an intense coastal upwelling. It supports one of the biggest forage fish populations, the Peruvian anchovy, and the world-leading monospecific fishery in terms of landings. The NHCS also hosts large, although variable, seabird populations, composed among others by three guano-producing sympatric species: the Guanay cormorant (Phalacrocorax bougainvillii), the Peruvian booby (Sula variegata) and the Peruvian pelican (Pelecanus thagus), which all feed primarily on anchovy.In this work we reviewed the fluctuations of these three seabird populations, focusing on the seasonal cycle of their breeding, to address the following questions: How different are the seasonality of reproduction among species? To what extent may they be plastic in space and time? What from the natural environment and the anthropogenic activities impact more the breeding of seabirds?We addressed these questions using the monthly occupancy of breeders (1) in >30 Peruvian sites between 06°S and 18°S and from 2003 to 2014; and (2) in one site during three decadal periods (1952-1968, 1972-1989, 2003-2014). We also used environmental covariates from satellite and at-sea monitoring such as oceanographic conditions, prey abundance, availability and body conditions, and fisheries pressure covariates. We used multiseason occupancy models to characterize the seasonality of breeding and relate it with environmental covariates. We also used functional principal component analysis for classifying the differences in seasonality among sites, and random forest regression for analyzing the relative contribution of covariates in the variability of the seasonal breeding.We found that in average seasonal breeding mainly started during the austral winter/ early spring and ended in summer/ early fall, this pattern being stronger in boobies and pelicans than in cormorants. The breeding onset of seabirds is timed so that fledging independence occurs when primary production, prey conditions and availability are maximized. This pattern is unique compared with other upwelling ecosystems and could be explained by the year-round high abundances of anchovy in the NHCS.The average seasonal breeding may differ among nesting sites. Seabirds breed earlier and are more persistent when colonies are larger, located on islands, within the first 20km of the coast, at lower latitudes and with greater primary production conditions. These results suggest that in the NHCS, the seasonality of breeding is more influenced by local environmental conditions than by large-scale environmental gradients. These results provides critical information to a better coordination of guano extraction and conservancy policies.Seabirds may also adapt the seasonality of their breeding to drastic ecosystem changes caused by regime shifts. We found that the three study species exhibited a gradient of plasticity regarding the seasonality of their breeding. Cormorants showed a greater plasticity, modulating the timing and magnitude on their breeding seasonality. This is probably authorized by the greater foraging flexibility offered its great diving capacities. Fixed onset and magnitudes of breeding in boobies may be related to their specific foraging strategy and/or to changes of prey items when anchovy stock was low. We also suggested that boobies may adapt other fecundity traits as growth rate of chicks to lower abundance of anchovy.The specific differences in the adaptation of seasonal breeding allow seabirds to take profit differently from local prey conditions or to face differently regime shifts. Further researches, implementing a large-scale capture-recapture methodology in parallel with monthly census, are proposed in order to fulfill gaps in the basic knowledge on vital traits (adult survival, first age at reproduction, and juvenile recruitment) which are critical parameters to evaluate the dynamic of a population

Les dépôts saisonniers de glace de CO2 et de H2O jouent un rôle ma jeur dans le climat actuel de Mars. Leur cycle de condensation/sublimation contrôle en grande partie les variations de la pression atmosphérique et de l'humidité. Le but de cette thèse est d'apporter de nouvelles contraintes observationnelles aux interactions surface/atmosphère pendant la phase de retrait des dépôts saisonniers nord. A partir des données proche infrarouge de l'imageur hyperspectral OMEGA (Mars Express), l'extension des glaces saisonnières de CO2 et H2O a été cartographiée du solstice d'hiver au solstice d'été. Un anneau de glace d'eau entoure systématiquement les dépôts saisonniers riches en CO2 et constitue une source importante de vapeur d'eau lors de sa sublimation. Une couche de glace d'eau recouvre progressivement la glace de CO2 , résultat de deux processus : l'accumulation de la glace d'eau contenue dans la glace de CO2 et restant en surface lorsque le CO2 se sublime, et la condensation de vapeur d'eau issue de la sublimation de l'anneau de glace d'eau. Des remontées soudaines de la signature de la glace de CO2 sont observées dans les dépressions spirales et escarpements de la calotte permanente nord, et dans le champ de dunes circumpolaires, conséquence probable d'un renforcement ponctuel des vents catabatiques par le passage de systèmes dépressionnaires. Le résultat de ces processus dynamiques est une accumulation inhomogène de givre d'eau sur la calotte permanente nord au début de l'été qui participe à l'évolution actuelle de la calotte. La connaissance de la localisation des sources de vapeur d'eau et des interactions surface/atmosphère pendant l'hiver et le printemps nord permettra d'améliorer les modèles climatiques et notre compréhension du cycle actuel de l'eau sur Mars.

Ce travail étudie l'impact de la température de surface, principalement océanique, sur la mousson ouest africaine, pendant la saison où les précipitations sont les plus importantes autour de de la côte guinéenne (au nord du golfe de Guinée), de fin mai à début juillet. Les données utilisées sont principalement les réanalyses ECMWF ERA5, mais également des produits de données observées : température de surface océanique, précipitations, couverture de différents types de nuages, et vent à la surface de l'océan.Une première partie expose les méthodes adoptées et le contexte saisonnier dans lequel s'inscrit cette phase côtière de la mousson, avant la migration des précipitations vers le nord du continent (Sahel) en été.Une étude climatologique tenant compte de la variabilité interannuelle est ensuite réalisée sur la période 2008-2015 : on retrouve le rôle déterminant de la langue d'eau froide (upwelling équatorial qui apparaît en mai) sur le début de la saison des pluies côtières. De plus, on met en évidence le rôle probable de l'upwelling côtier, qui se forme en juillet le long des côtes guinéennes entre 8W et 5E, sur la fin de ces précipitations côtières, via la diminution de la convergence côtière du transport d'humidité.On s'intéresse ensuite au cycle diurne, qui est important près de la côte et suit complètement la modulation de la convergence de basse couche par l'alternance brise de mer / brise de terre : là encore, l'upwelling côtier semble renforcer la brise de mer et diminuer l'intensité de la brise de terre, donc diminuer les précipitations côté océan (qui constituent la majeure partie des précipitations côtières).Pour finir, une étude à l'échelle intrasaisonnière sur la période 2000-2018 montre que l'influence océanique sur les précipitations côtières (plus précisément sur leur latitude) diminue progressivement vers la fin de la saison pour laisser le régime d'ondes d'est vers 700 hPa prendre le contrôle des précipitations, même si nos analyses suggèrent que ces deux modes interagissent entre eux. On retrouve de plus en intrasaisonnier un signal correspondant à ce qu'on trouve à l'échelle saisonnière : une intensification (diminution) de l'upwelling côtier aurait bien pour effet de diminuer (augmenter) les précipitations côtières
This work, concerning the West African monsoon, studies the role of surface temperature, mainly over the ocean, during the Spring Guinean coast rainfall season (north of the Gulf of Guinea), from May to July. The data used are mainly ECMWF ERA5 reanalyses, but also satellite observation data : ocean surface temperature, precipitation, cover of different types of clouds, and ocean surface wind.The first part describes the methods developed and the seasonal context in which this coastal phase of the monsoon occurs, before the migration of precipitation towards the Sahel latitude in summer.A climatological study taking into account the inter-annual variability is then carried out over the period 2008-2015. It evidences the determining role of the cold tongue (equatorial upwelling, which appears in May) on the beginning of the coastal rainy season. In addition, highlight is put on the probable role of coastal upwelling, which occurs in July along the Guinean coast between 8W and 5E. This occurence coincides with the end of this coastal precipitation, through the decrease of moisture transport coastal convergence. Then we study the diurnal cycle. Near the coast, it mainly consists in the modulation of the low layer convergence by the sea breeze / land breeze alternation. Again, the coastal upwelling seems to strengthen the sea breeze and decrease the intensity of the land breeze, thus reducing precipitation on the ocean side (which constitutes the major part of coastal precipitation).This work is completed by a study of intra-seasonal variability over the period 2000-2018. Main results are that the oceanic influence on coastal precipitation latitude gradually decreases towards the end of the coastal monsoon season, leaving then the regime of easterly waves around 700 hPa take control of precipitation. Our statistical results, nevertheless, suggest that these two synoptic « modes » interact with each other. Moreover, we find, at the intra-seasonal scale, a signal corresponding to what is found at the seasonal scale: an intensification (decrease) of coastal upwelling would indeed have the effect of reducing (increasing) coastal precipitation

La réduction du volume des glaciers et la fusion printanière plus précoce de la neige causée par le réchauffement climatique provoquent des variations du cycle hydrologique à la fois pour les têtes de bassin versant, mais aussi pour les zones situées plus à l’aval. Afin de prédire correctement l’amplitude des changements possibles futurs et d’envisager une gestion adaptée, une bonne connaissance de l’interaction entre les glaciers, le climat et les écoulements hydriques est nécessaire. L’objectif de cette étude est d’évaluer l’effet de la variabilité climatique sur le fonctionnement hydro-glaciologique et ses conséquences sur la disponibilité de l’eau du bassin versant de l’Arve (Alpes françaises) depuis 1960. Ce bassin s’étend sur une surface de 1958 km2 et est composé de cinq bassins versants emboités (Arveyron d’Argentière, Arveyron de la Mer de Glace, Arve au Pont des Favrands, à Sallanches and au Bout du Monde), tous influencés par la fusion glaciaire et nivale mais dans différentes proportions étant donnée la large gamme d’extension de couverture glaciaire s’étalant de 5 á 53%. Ce travail est basé sur des longs jeux de données glaciologiques, météorologiques, hydrologiques et de couverture de neige qui sont issues soit de mesures ponctuelles dans l’espace soit de données obtenues par télédétection.L’analyse des tendances a été réalisée sur des données hydrologiques et météorologiques des cinq bassins versants emboités. Pour cela, le cycle saisonnier du débit est ajusté en utilisant une fonction mathématique de type “modèle à pic asymétrique”. Les changements observés des débits ont été reliés aux variables météorologiques ainsi que à l’évolution de la couverture glaciaire. Les résultats indiquent un comportement contrasté entre les bassins versants selon les taux d’englacements, avec une tendance croissante des valeurs de débit dans les bassins versants fortement englacés (couverture de glacier >30%) et une décroissante pour les moins englacés. La sensibilité du cycle hydrologique au changement climatique futur a été évaluée. Pour le milieu du 21e siècle, on prévoit que le volume annuel écoulé serait réduit de 16% pour l’Arveyron d’Argentière et de 31% pour l’Arveyron de la Mer de Glace. Pour la période estivale, la quantification détaillée de chaque terme de l’équation du bilan hydrologique, ainsi que leurs incertitudes, sur les bassins versants de l’Arveyron d’Argentière et de l’Arveyron de la Mer de Glace-Leschaux a permis de souligner l’importance des transferts d’eau souterraine pour représenter et prédire le comportement hydro-glaciologique d’un bassin versant donné. Deux model d’écoulement distribués de type degré-jour couples à un modèle de routage hydrologique à réservoir linéaire ont était utilisé sur le bassin versant de l’Arveyron d’Argentière sur la période 1960–2009. La calibration est effectuée autant sur la base des données de débit qu’avec une approche multicritère avec les données de débit, de couverture neigeuse et du bilan de masse annuel, à pas de temps journalier. Les résultats montrent l’aptitude d’utiliser un modèle classique degré-jour pour simuler le comportement hydro-glaciologique et la production d’eau sous-glaciaire d’un bassin versant fortement glaciaire. Pour la période 1960–2004, une valeur de Kling Gupta Efficiency de 0.85 entre le débit simulé et observe à était obtenu. La calibration multicritère semble réduire les incertitudes des simulations
Glacier recession and the anticipation of spring snow melt driven by a warming climate could lead to changes in the hydrological cycle affecting not only the headwater catchments but also the areas downstream. In order to correctly predict the magnitude of future possible changes and to consider appropriate strategies of water management, a good understanding of the interaction between glaciers, climate and hydrology is needed. The aim of this study is to assess the effect of climate variability on the hydro-glaciological behaviour and its consequence on water availability in the Arve River catchment (French Alps) since 1960. It covers 1958 km2 and is composed by five nested catchments (Arveyron d’Argentière, Arveyron de la Mer de Glace, Arve at Pont des Favrands, Arve at Sallanches and Arve at Bout du Monde), all influenced by glacier and snow melt but characterized by various percentages of glacier cover ranging from 5 to 53%. This research is based on a long dataset of in situ or remote sensing glaciological, meteorological, hydrological and snow cover area data.Trend analyses are performed on the hydrological and meteorological data at all the considered sites. The seasonal cycle of each catchment is fitted using a mathematical function, namely the asymmetric peak model, and changes in the discharge are related to observed changes in the meteorological variables and the glaciers’ evolution. Results point out a contrasting behaviour among the catchments characterized by different glacier covers, showing an increasing trend on the discharge values in highly glacierized catchments (with a glacier cover >30%) and a decrease in the low glacierized ones. The sensitivity of the seasonal cycle to the future climate is evaluated. In the mid-21st century the annual runoff would be reduced by 16% for Arveyron d’Argentière and 31% for Arveyron de la Mer de Glace. Over the summer season, a detailed quantification of each term of the hydrological balance equation, as well as their uncertainties, on the Argentière and Mer de Glace-Leschaux drainage basins allows to underline the importance of considering the groundwater transfers to represent and predict the hydro-glaciological behaviour of a considered catchment. Two different distributed temperature index melt models coupled with a linear reservoir discharge model are used on the Arveron d’Argentière catchment over the 1960–2009 period. The calibration is carried out against discharge only and with a multi- criteria approach considering the discharge, the snow cover area and the glacier-wide annual mass balance values at daily time step. Results demonstrate the suitability of the use of a classical degree day model in simulating the hydro-glaciological behaviour and the subglacial water production of a highly glacierized catchment. A KGE of 0.85 is obtained between the observed and simulate discharge values over the 1960–2004 period. The use of a multi-criteria approach seems to reduce the simulation uncertainties

The Tropical savannas of central Brazil (cerrado) and the Everglades wetland (Florida) ecosystems are ideal systems to study landscape spatial mosaics and their interactions. Both ecosystems show a variety of plant physiognomies distributed within small spatial scales and elevation gradients. Such variety of plant physiognomies provide an opportunity to investigate the roles of climate, topography, nutrient availability and water table dynamics as determinants of plant physiognomic distributions, and their role in shaping regional systems. South Florida Wetlands and the tropical savannas of central Brazil are examples of hydrologically-controlled ecosystems. In hydrologically-controlled ecosystems water sources, the availability of nutrients, and the patterns of water movement play important roles in determining vegetation structure and function. The main objective of this study was to understand ecosystem level processes that shape different physiognomies in two hydrologically-controlled ecosystems. I conducted field work at the IBGE ecological reserve, a field experimental station located in Brasilia, Brazil. I also worked at the Everglades National Park in an area located near the south entrance of the Park in Homestead, Florida. I carried out three interconnected studies investigating water and nutrient dynamics: (1) In a Brazilian savanna I manipulated levels of litter input and measured changes to soil properties, organic matter decomposition and tree growth. I found that changes in litter input affect soil physicochemical properties and soil biochemical processes. I also found that litter dynamics influence tree growth through their effects on soil physicochemical properties. (2) I also studied the effect of water table depth and its temporal variation on spatial patterns of vegetation distribution in the cerrado landscape. I monitored diurnal and seasonal changes in water table depth along two tree-density and topographic gradients. In addition, I measured woody species composition, growth rates of four tree species, litter production, soil nutrients, and nutrient resorption efficiency along those two gradients. I found that water table depth has an important role in determining the spatial distribution of cerrado physiognomies; it also affects tree growth, species composition and nutrient resorption efficiency. (3) In the Everglades I studied patterns of underground water uptake by two vegetation types. I monitored seasonal and diurnal changes in water table depth in a Hammock forest, in a stand dominated by the invasive woody species Schinus terebinthifolius, as well as the water level in an adjacent lake. I estimated stand level transpiration using two different approaches: with sap flow measurements and diurnal oscillations in water table levels. Then, I calculated the total quantity of groundwater withdrawn by evapotranspiration for the wet and dry seasons in the Hammocks and in the exotic invaded site and then compared the results. I found that water uptake by Everglades trees is well coupled to diurnal changes in water table depth and that the amount of water withdrawn from the groundwater was larger during the wet season than during the dry season. Finally, I detected hydrological feedbacks between different vegetation types and nearby bodies of water. Results of this study contributes to the current knowledge of ecosystem level processes in tropical and subtropical ecosystems where water circulation and water availability play a dominant role in shaping vegetation structure and function.

Thesis (Ph. D. in the Field of Hydrology)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2013.
"February 2012." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 155-172).
This thesis addresses the coupling of hydrologic and biogeochemical processes and, specifically, the organization of ecosystem traits with the water, carbon, and nitrogen cycles. Observations from a factorial irrigation-fertilization experiment in a seasonally dry annual grassland are combined with a simple ecosystem model to identify relationships between vegetation, nitrogen availability, and hydrology. Assuming primary productivity is water-limited, data analysis indicates that soil moisture and canopy conductance are insensitive to nitrogen supply, owing to a trade-off between canopy density and leaf conductance that maximizes efficient use of available water. That is, fertilization-induced increases in leaf area index are offset by reduced leaf area-based stomatal conductance. When primary productivity is assumed to be co-limited by water and nitrogen availability, total surface conductance is estimated to be insensitive to nitrogen supply, but added nitrogen increases the ratio of transpiration to evaporation. This coupled water-carbon-nitrogen model is then extended to predict ecosystem sensitivity across independently varied gradients of water and nitrogen supply rates. This analysis reveals two distinct regimes of plant-resource organization. In arid climates, rooting depths decrease with increasing aridity, while in humid climates, rooting depths increase with aridity. In all climates, rooting depths increase with increased nitrogen supply. Further, relative root-carbon allocation always increases with aridity and decreases with nitrogen supply. These resource use strategies result in an efficient use of available water in arid climates and efficient use of available nitrogen in humid climates. The associated ecosystem process rates indicate that nitrogen supply is an important determinant of surface water and carbon fluxes in humid climates, but only of carbon fluxes in arid climates.
by Anthony Joseph Parolari.
Ph.D.in the Field of Hydrology

The relationship between Sertoli cell lipid inclusions and spermatogenic activity was investigated using light microscopy and morphometric analysis of the lipid droplet content of Sertoli cells and spermatids from the seasonal breeding mink. Tissue was obtained and analyzed each month during a twelve month period to establish the presence of seasonal and stage-related cycles of lipid droplet content in these cells. It is concluded that the amount of lipid inclusions in Sertoli cells varies with the degree of spermatogenic activity being lowest after the release of mature spermatids in the lumen during the active spermatogenic phase and at the time of maximal testicular regression. Furthermore, cholesterol esters are a component of these lipid inclusions and the seasonal changes in lipid inclusions of Sertoli cells are reflected by seasonal changes in the amount of Sertoli cell cholesterol esters. (Abstract shortened by UMI.)

In spite of the widely perceived importance of suspended particulate material (SPM) , its distribution in the shelf seas and the processes controlling its variation are little known. This thesis reports an exploratory study of the spatial and time dependant variability of SPM in an area of the northern Irish Sea. SPM was determined both directly by gravimetric methods and via measurements of beam attenuation (c). Spatial distributions were determined from grid surveys using a profiling transmissometer. In addition a six month record of beam attenuation and current velocity was obtained from a site off the north coast of Anglesey. A clear spatial pattern in the surface distribution of c was observed which was similar to the distribution of h/ta, suggesting that concentrations of SPM are determined by the availability of TKE from tidal stirring. A strong seasonal cycle of c was observed in mixed water, with values decreasing in June, July and August which suggested a reduction in the supply of SPM during summer. In stratified water, high concentrations of SPM remained confined to the dense layer below the thermocline. The seasonal cycle was observed in the time series from the mooring, but in addition there was a marked response to tidal currents in the spring and in autumn. Close analysis of the record in April and May-showed signals at M% and M4frequencies. These variations in c were attributed to a local response to tidal currents causing erosion of the sea-bed and to the oscillation of a horizontal gradient in c in the region. A regression model was found to explain 35% of the variance in data from a5 week time series. 70% of the variance was explained for four day time series, near spring tides. The relationship between c and tidal flows was more marked at spring tides than at neaps.