L’Ordovicien (485–444 Ma) est une période géologique caractérisée par laconcomitance d’une glaciation majeure et de l’une des 5 plus grandes extinctions de masse del’histoire de la Terre. Cette thèse avait pour objectif d’améliorer la compréhension de l’évolutiondu climat à cette époque à l’aide de la modélisation numérique, ain de fournir une imagecohérente de la glaciation. Nous avons d’abord démontré que la coniguration continentaleordovicienne induit une dynamique océanique particulière, à l’origine d’une instabilité climatiquepermettant un refroidissement brutal du climat global sans variation importante de laconcentration atmosphérique en CO2 (pCO2). Dans un deuxième temps, un modèle innovantcouplé climat-calotte a permis de produire la première simulation de la mise en place de la glaciationsupportée par les données géologiques, sous un scénario cohérent de baisse de la pCO2.Les résultats indiquent que les premières glaces continentales se seraient mises en place dèsl’Ordovicien Moyen (465 Ma), quelque 20 millions d’années plus tôt qu’initialement envisagé.Dans ce scénario, le franchissement de l’instabilité climatique ordovicienne marque la miseen place du maximum glaciaire au cours de l’Ordovicien terminal Hirnantien (445–444 Ma).Des expériences réalisées avec un modèle de végétation primitive montrent que le développementdes plantes non-vasculaires a pu constituer le mécanisme à l’origine de la chute de lapCO2, via une intensiication de l’altération des surfaces continentales. Enin, les interactionsentre climat et biosphère marine ont été envisagées selon 2 axes complémentaires. (i) De nouvellescontraintes ont été fournies pour comprendre la paléobiogéographie des communautésmarines, par la publication de cartes de la circulation océanique de surface modélisée sousdiférentes pCO2 au cours de l’Ordovicien Inférieur, Moyen et Supérieur. (ii) Les relationsentre variations climatiques et état redox de l’océan ont été étudiées avec un modèle d’océanrécent bénéiciant d’un module de biogéochimie marine (MITgcm). Les simulations suggèrentdes anoxies partielles (durant le Katien) ou globales (durant le Silurien inférieur) au cours dela transition Ordovicien–Silurien. Elles démontrent également que l’extinction de l’Ordovicienterminal ne serait pas liée à un évènement d’anoxie. / The Ordovician (485–444 Ma) is a geological period characterized by theconcomitance of a major glaciation and one of the “Big Five” mass extinction events thatpunctuated the Earth’s history. This dissertation aimed at developing a better understandingof the climatic evolution at that time through numerical modeling, in order to providea consistent picture of the glaciation. First, it was shown that the Ordovician continentalconiguration leads to a particular ocean dynamics, which induces in turn the development ofa climatic instability that allows global climate to cool suddenly in response to subtle changesin the atmospheric partial pressure of CO2 (pCO2). Secondly, an innovative climate-ice sheetcoupled model produced the irst simulation of the glaciation that is supported by geologicaldata, in the context of a decrease in pCO2. Results show that glacial onset may have occurredas early as the Mid Ordovician (465 Ma), i.e., some 20 million years earlier than thoughtinitially. In this scenario, the climatic instability is reached during the latest Ordovician andaccounts for the onset of the Hirnantian glacial maximum (445–444 Ma). Experiments conductedwith a non-vascular vegetation model reveal that the origination and expansion of theirst land plants signiicantly intensiied continental weathering during the Ordovician andpotentially drove the drop in atmospheric CO2. Finally, the interactions between climate andthe marine biosphere were investigated based on 2 complementary axes. (i) News constraintson the paleobiogeography of marine living communities were brought through the publicationof maps showing the ocean surface circulation modeled at various pCO2 levels during theEarly, Middle and Late Ordovician. (ii) The relationships between climatic variations andthe redox state of the ocean were studied using a recent ocean model with biogeochemical capabilities(MITgcm). The simulations suggest partial and global oceanic anoxic events duringthe Katian and the early Silurian respectively. They also show that anoxia is probably notresponsible for the latest Ordovician mass extinction event.

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration. / October 2008

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration.

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration.

The Late Rhaetian (Late Triassic) extinction event is characterised by shelled species showing a reduction in size, and thickness, which together with changed mineralogy is thought to be as a result of increased atmospheric pCO2 levels. Similar morphological changes have been demonstrated for extant species exposed experimentally to high CO2 leading to the hypothesis that Late Triassic extinctions were linked with global ocean acidification and increased oceanic palaeotemperatures. Consequently, the aim of this present work was to test this ocean acidification hypothesis by investigating morphological changes in selected shelled fossil species across this extinction event, and attempt to correlate them with changes in environmental temperature and pCO2. The abundance, size, shell thickness and mineralogy was determined for three common species, the bivalves Liostrea hisingeri and Plagiostoma gigantea and the ostracod Ogmoconchella aspinata collected from Triassic and Jurassic rocks from two locations in southwest England. Palaeotemperature was reconstructed from examination of these fossils and from the literature and atmospheric pCO2 estimated from published accounts. The shell size of bivalves increased during periods of high pCO2 and high palaeotemperature at both locations. Ostracod carapace sizes increased at St Audrie’s Bay but decreased at Lyme Regis during periods of high pCO2, while ostracod carapace size decreased during periods of high palaeotemperature at St Audrie’s Bay. However, ostracod shell thickness increased and decreased as pCO2 increased but shows no relationship with palaeotemperature at either location. Laboratory experiments on the effect of elevated pCO2 and elevated temperature on three modern species of ostracod was carried out. Modern species Leptocythere sp. and L. castanea subjected to either elevated pCO2 or elevated temperature showed increased dissolution, however size and thickness did not significantly change. In the same experimental conditions L. lacertosa showed increased dissolution however size continued to increase, while thickness was maintained. Comparison of fossil bivalve and ostracod data to modern high pCO2 and high temperature experiments illustrates some correlations to the modern experiments results indicating high pCO2 and high palaeotemperature conditions could have been occurring during the Triassic-Jurassic boundary interval. From the evidence presented, combined with an appropriate trigger (CAMP volcanism), it can be concluded that both ocean acidification and palaeotemperature were contributing to the species adaptations identified across the Triassic-Jurassic boundary interval.

Corals combine photosynthesis and calcification in an intricate and delicately balanced relationship to form large biomineralized structures that are dominant features of tropical coastlines worldwide. Coral reefs have great scientific and economic importance but have recently experienced widespread decline attributed to increasing anthropogenic pressure on reef systems. Physical damage events, such as ship groundings, when coupled with existing nutrient stress and changing global climate present a poor outlook for successful natural recovery of reef communities. The main goal of the proposed research is to better understand how environmental factors, both local and global, affect the coral holobiont and influence overall coral fitness. The target species of this research, Montastraea cavernosa and Porites astreoides, are important and widespread Caribbean reef-builders. While it has been shown that nutrient and pCO2 stress affect coral growth and calcification, study of specific effects on coral tissue and reproductive success has not received significant attention in the literature despite considerable current interest. This study addresses this data gap in quantitatively examining the effect of elevated nutrients and pCO2 on 1) P. astreoides recruit survivorship, development, early calcification, and symbiotic zooxanthellae morphology; 2) M. cavernosa and P. astreoides wound regeneration, tissue characteristics over time at the histological and ultrastructural level, and trends in symbiotic zooxanthellae morphology; and 3) survival, growth and histological/ultrastructural characteristics of M. cavernosa and P. astreoides fragments transplanted to the field and in the laboratory. Histological and ultrastructural observations from corals transplanted to the field are then compared to ex-situ laboratory experimental corals. In the fleshy and large-polyped faviid M. cavernosa, healing of a linear wound was characterized by granulation of new tissue across the wound site, facilitated by coalescent granular amoebocytes. The wound healing strategy of this species appears to progress with wound closure and re-epithelialization before calcification resumes, as actively calcifying calicodermis was generally not observed at the healing front. Tissue regeneration in the small-polyped P. astreoides was characterized by formation of multiple islands of eosinophilic healing fronts along the depth of the wound track, and an accumulation of granular amoebocyte cells in regenerating tissue. The wound healing strategy of this species appeared to result in re-epithelialization of exposed body wall without necessarily closing the wound. Elevated pCO2 significantly reduced survivorship in P. astreoides recruits, and both nutrient enrichment and elevated pCO2 significantly reduced wound regeneration rate in M. cavernosa and P. astreoides. In both species, phosphate enrichment had the greatest deleterious effect on wound repair. A significant application of this study is the identification of possible zooxanthellar morphological indices of elevated nutrients and ocean acidification. The similarity in starch, lipid and uric acid accumulation patterns in Symbiodinium sp. from P. astreoides recruits and coral fragments of both species indicate a correlation between these anthropogenic stressors and the intracellular accumulation of excess carbon and nitrogen by the symbiont. Zooxanthellar carbon accumulation, in the form of starch and/or lipid, was the greatest under elevated nitrate. Zooxanthellar nitrogen accumulation, in the form of uric acid, was the greatest under elevated CO2. Comparison of zooxanthellar metrics between the field corals (P. astreoides, and M. cavernosa) and ex-situ corals and recruits indicated that carbon accumulation in Symbiodinium from field corals was consistently significantly less than in the ex-situ experimental P. astreoides recruits and M. cavernosa fragments exposed to elevated nitrate. This indicates that the field corals were likely not exposed to elevated nitrate at the time of collection. Both M. cavernosa and P. astreoides adults in the field accumulated significantly less uric acid than their counterparts in the tissue repair experiment, indicating that the field corals were exposed to higher pH and lower CO2 than the ex-situ corals. These results suggest that the field corals were not exposed to nutrient concentration profiles similar to the experimental treatments, particularly elevated nitrate. However, histological metrics indicated that the transplanted corals were subjected to increasing sedimentation stress over time. Overall, nitrate was found to affect recruits and adults on a similar scale, while phosphate and pCO2 affected carbon and nitrogen storage more in recruits compared to adults. While nutrients and pCO2 had no mechanistic effect on regeneration at histological level, ultrastructural metrics indicate an impact on the mutualistic energy exchange between the symbiotic partners, partially decoupling symbiosis. Effects were generally found to be greater in P. astreoides compared to M. cavernosa, and the unique life history strategy of the subject species and differences in their endosymbiont physiology reveal distinct responses to elevated nutrients and pCO2. Although the laboratory findings were not necessarily applicable to field observations, they provide insight into factors that may influence fragment success in the field. Quantitative assessment of the effect of elevated nutrients and pCO2 is thus useful in management decisions involving water quality standards, and is essential in the prediction of future coral condition and resilience.

Climate change has, in recent decades, warmed the climate and changed carbondynamics in land and water systems. For example, temperature and precipitation canchange carbon dynamics and cause largely unknown consequences. This researchuses data from a unique measuring station near Kattestrupeforsen, Jämtland, Sweden, in order to answer the question of how the pCO2 (ppm) concentration of the water in the local area reacts to changes in the factors of air/water temperature, solar irradiation, precipitation, turbidity, water level and water inflow into the area. This was analysed using a visual analysis of the peaks that occur in the pCO2 and a statistical regression analysis of peak pCO2 events and for each yearly quarter as well as for the identified peak events. Moreover, the limited amount of available turbidity data was visually analysed to comprehend how it correlates with the pCO2 values. The results indicate that the turbidity data available has no visible correlation, possibly due to a lack in data. Temperature data appeared to be responsible for some of the variation seen, although likely more as a conditional value. Irradiation and precipitation data gave inconsequent results and are not deemed likely to influence the peaks in pCO2 in the time scale analysed. Water level and streamflow showed the most stable and significant correlation of all parameters analysed, although they remained relatively inconsistentin their ability to explain pCO2 peaks seen. / <p>2024-03-06</p>

Methane (CH4) and carbon dioxide (CO2) are two greenhouse gases and main drivers of global climate change. Lakes are known to be a source of CH4 and CO2 to the atmosphere. While the importance of these emissions is clear, their magnitudes and regulation are still uncertain due to the scarcity of flux measurement data from lakes. Most previous flux measurements have been carried out on lakes &lt;10 km2 and the extrapolations are not representative of large lakes directly. Recent research has led to a growing recognition of the great importance of lakes as a source of emissions. Still, the relationship between environmental variables, lake properties and seasonal changes and the variability between and within lakes raises several question marks. Larger scale studies of greenhouse gases are needed to determine the spatial and temporal dynamics that exist. In this study, a floating chamber method and manual sampling was used to investigate the spatiotemporal variability and influencing variables of CH4 flux and concentration, as well as dissolved inorganic carbon (DIC) and pCO2aq (partial pressure of CO2 in the water). The sampling was conducted during five weeks in September and October 2020 in three large Swedish lakes. Our results generally showed varying CH4 values between the three lakes, indicating that nutrients affect the amount and emission of CH4. A pattern was found where the CH4 was higher near the shore and at a shallower depth. There was a correlation between CH4 concentration and the environmental variables wind speed and air- and water temperatures. Our DIC values were high in two of the lakes and low in one, all lakes’ DIC differed significantly from each other. The pCO2 did not have any difference within the lakes, and there was no difference between the lakes except in one case. Both DIC and pCO2 correlated with air- and water temperature. This study displays the large spatiotemporal variability within and between large lakes and that representative values for large lakes require more measurements under different conditions to distinguish how greenhouse gases emit and flux between lakes and atmosphere. / Metan (CH4) och koldioxid (CO2) är två växthusgaser och stora drivkrafter för globala klimatförändringar. Sjöar är kända för att vara en källa för CH4 och CO2 till atmosfären. Trots att betydelsen av dessa utsläpp är tydlig är deras storlek och reglering fortfarande osäker på grund av brist på flödesmätdata från sjöar. De flesta tidigare flödesmätningarna har utförts på sjöar &lt;10 km2 och det har påvisats att extrapoleringar inte är direkt representativa för stora sjöar. Ny forskning har lett till ett mer allmänt erkännande av sjöars stora betydelse som källa till utsläpp. Trots detta väcker förhållandet mellan miljövariabler, sjöegenskaper, säsongsförändringar och variationen mellan och inom sjöar flera frågetecken. Storskaliga studier om växthusgaser behövs för att bestämma den rumsliga och tidsmässiga dynamiken som finns. I denna studie användes en kammarmetod och manuell provtagning för att undersöka spatiotemporal variabilitet och miljövariabler som kan påverka CH4 flöde och koncentration, samt upplöst oorganiskt kol (DIC) och pCO2aq (partial trycket av CO2 i vattnet). Provtagningen genomfördes under fem veckor i september och oktober 2020 i tre stora svenska sjöar. Våra resultat visade generellt varierande CH4 värden mellan de tre sjöarna, vilket indikerade att näringsämnen påverkar mängd och utsläpp av CH4. Ett mönster noterades där CH4 var högre nära stranden och på ett grundare djup. Det fanns ett samband mellan CH4 koncentration och miljövariablerna vindhastighet och luft- och vattentemperatur. DIC-värdena var höga i två av sjöarna och låga i en, alla sjöarnas DIC skiljde sig signifikant från varandra. pCO2 hade ingen skillnad inom sjöarna, och det fanns ingen skillnad mellan sjöarna utom i ett fall. Både DIC och pCO2 korrelerade med luft- och vattentemperatur. Studien visar den stora spatiotemporala variationen inom och mellan stora sjöar och att representativa värden för stora sjöar kräver fler mätningar under olika förhållanden för att urskilja hur växthusgaser emitterar och flödar mellan sjöar och atmosfär.

Cette étude a été motivée par la nécessité de pouvoir décrire la variabilité biogéochimique avec la même résolution que les paramètres physiques. Des profileurs optiques ont permis de mesurer à haute fréquence les propriétés optiques inhérentes dans la colonne d'eau. Par comparaison avec des données discrètes acquises simultanément à nos mesures, les coefficients optiques à des longueurs d'onde précises ont été convertis en grandeurs biogéochimiques quantitatives. Nous avons estimé la concentration en chlorophylle a et en carbone particulaire total ainsi que la répartition verticale de la matière organique dissoute colorée (CDOM). La nature qualitative du matériel particulaire et dissous a été abordée en combinant différents coefficients optiques ainsi qu'en analysant leur dépendance spectrale. En préalable aux campagnes dans l'Atlantique nord (campagnes POMME), une expérience en milieu contrôlé a été menée sur une population d'organismes phytoplanctoniques calcifiants (Emiliania huxleyi) afin de caractériser ses propriétés biooptiques ainsi que leurs modifications consécutives à une augmentation de la pCO2 atmosphérique du niveau actuel (360 ppm) au niveau prévu pour la fin du siècle (700 ppm). Lors des campagnes entre le Portugal continental et les Açores nous avons effectué le suivi biooptique de la variabilité à méso-échelle à trois périodes clés de l'année : fin de l'hiver, printemps et fin de l'été. L'observation à haute résolution de la colonne d'eau a permis de mettre en évidence certaines relations entre les caractéristiques hydrologiques et biogéochimiques. Le déploiement de nos instruments le long de radiales avec un système tracté autorisant une résolution de 2 milles (Tow-Yo) a conduit à préciser l'influence des structures tourbillonnaires de moyenne échelle.

<p>Systemic infection, major surgery, trauma and many other causes can lead to impaired organ function. Compensated shock is not detected by global hemodynamic and oxygen measurements, as they take no account for regional variations. Focus has therefore gradually turned from looking at systemic changes to selective investigations of regional blood flow and ischemia. This thesis presents a series of experiments evaluating new application and validation of various monitoring techniques.</p><p>An experimental porcine model with anesthetized and invasively monitored animals was used. The circulatory interventions included endotoxin infusion (septic shock), aortic constriction and selective clamping of splanchnic arteries. The aim was to compare air with saline tonometry, to validate the intraperitoneal use of tonometry and to reexamine the use of endoluminal reflectance pulse oxymetry. To investigate the relative contributions of regional blood flow and detection of ischemia, measurements of hepatic venous oxygen saturation (ShvO₂), lactate concentrations and PCO₂ gap were used.</p><p>Our findings support the use of air instead of saline as the preferred technique for tonometric measurements. With the intraperitoneal application of tonometry we gain more information on regional aspects of the splanchnic circulation, and it appears to be a reliable monitoring option for early detection of ischemia in the small intestine. Measurements of ShvO₂will give an overall reflection of the intestinal circulation. The sigmoid colonic pulse oximetry showed a non-linear response in relation to regional blood flow, and will therefore not be able to detect gradual changes in oxygen saturation. Determination of the regional to endtidal PCO₂ gap might prove valuable for monitoring of the intestinal circulation.</p><p>Because of sophisticated interactions between portal and hepatic arterial blood flow and hepatic compensation for regional ischemia, a combination of monitoring techniques might be needed. The results of this study will hopefully encourage clinical evaluation of intraperitoneal tonometry and endtidal PCO₂ gap recordings for non-invasive, semi-continuous, trend monitoring of the splanchnic circulation.</p>