Dissertations / Theses on the topic 'Oceanic carbonate system'

La mer Méditerranée est souvent considérée comme un océan laboratoire pour comprendre les changements globaux liés à l’augmentation de CO2 atmosphérique. Ce travail, basé sur l’étude de données recueilles dans trois régions méditerranéennes, étudie les variations du CO2 océanique dans ce bassin. À l’échelle de la saison, outre les changements de température, le contenu en alcalinité influe sur le contenu en CO2 en Méditerranée orientale, tandis que les changements en carbone total sont responsables des variations dans le bassin occidental. En zone côtière urbanisée, l’émission de CO2 anthropique conditionne les échanges air-mer de CO2. Cette étude montre que l’augmentation de carbone et l’acidification à l’échelle de plusieurs années ne sont pas seulement dues à l’augmentation du CO2 atmosphérique : le contenu en alcalinité module ces tendances dans le bassin oriental, tandis que, dans le bassin occidental, ces tendances sont vraisemblablement influencées par la dynamique des courants
The Mediterranean Sea is often considered as a laboratory ocean for understanding global changes related to the atmospheric CO2 increase. This work, based on the study of data collected in three Mediterranean regions, investigates the variations of oceanic CO2 in this basin. On a seasonal timescale, in addition to temperature changes, alkalinity content influences the CO2 content in the Eastern Mediterranean, while total carbon changes are responsible for variations in the Western Basin. In urbanised coastal areas, anthropogenic CO2 emission’ influences air-sea CO2 exchanges. This study shows that the carbon increase and the acidification on a multi-year timescale is not only due to the increase in atmospheric CO2: the alkalinity content modulates these trends in the eastern basin, while, in the western basin, these trends are likely influenced by current dynamics

L’alcalinité de l’océan (Alk) est essentielle dans l’absorption de carbone atmosphérique et offre une capacité tampon contre l’acidification. Dans le cadre des prévisions de l’absorption de carbone par les océans et des impacts potentiels sur les écosystèmes, la représentation de l’Alk et du principal facteur de sa distribution dans l’océan profond, le cycle du carbonate de calcium (CaCO3), ont souvent été négligés. Cette thèse aborde le manque de considération accordé à l’Alk et au cycle du CaCO3 dans les modèles du système terrestre (ESM) et explore les implications pour le cycle du carbone dans un océan pré-industriel ainsi que dans des scénarios de changement climatique. À travers une intercomparaison des ESMs, une réduction des biais simulés de l’Alk dans la 6ème phase du Projet d’Intercomparaison de Modèles Couplés (CMIP6) est rapportée. Cette réduction peut s’expliquer partiellement par une calcification pélagique accrue, redistribuant l’Alk en surface et renforçant son gradient vertical dans la colonne d’eau. Une revue des modèles de biogéochimie marine utilisés dans les ESMs actuels révèle une représentation diverse du cycle du CaCO3 et des processus affectant l’Alk. Les schémas de paramétrisation de la production, de l’exportation, de la dissolution et de l’enfouissement du CaCO3 varient considérablement, avec une prise en compte généralement limitée à la seule calcite, et sans calcification benthique. Cette diversité entraîne des projections contrastées de l’export de carbone associé au CaCO3 depuis l’océan de surface vers l’océan profond dans les scénarios futurs. Cependant, des simulations de sensibilité effectuées avec le modèle de biogéochimie marine NEMO-PISCES indiquent que la rétroaction associée sur le flux de carbone anthropique et l’acidification des océans reste limitée. À travers un ensemble de simulations NEMO-PISCES, il est démontré qu’une attention particulière au bilan d’Alk est cruciale pour estimer le dégazage de carbone océanique pré-industriel dû aux apports fluviaux ainsi qu’à l’enfouissement de matière organique et de CaCO3. De telles estimations sont fondamentales pour évaluer le flux de carbone air-mer anthropique en utilisant des données d’observation, et mettent en évidence la nécessité de mieux contraindre le bilan d’Alk de l’océan. Enfin, fidèle au message qu’elle véhicule sur le changement climatique, cette thèse offre une perspective nouvelle et radicale sur les sciences du climat et le système de la recherche actuel
Ocean alkalinity (Alk) is critical for the uptake of atmospheric carbon and provides buffering capacity against acidification. Within the context of projections of ocean carbon uptake and potential ecosystem impacts, the representation of Alk and the main driver of its distribution in the ocean interior, the calcium carbonate (CaCO3) cycle, have often been overlooked. This thesis addresses the lack of consideration given to Alk and the CaCO3 cycle in Earth system models (ESMs) and explores the implications for the carbon cycle in a pre-industrial ocean as well as under climate change scenarios. Through an ESM intercomparison, a reduction in simulated Alk biases in the 6th phase of the Coupled Model Intercomparison Project (CMIP6) is reported. This reduction can be partially explained by increased pelagic calcification, redistributing Alk at the surface and strengthening its vertical gradient in the water column. A review of the ocean biogeochemical models used in current ESMs reveals a diverse representation of the CaCO3 cycle and processes affecting Alk. Parameterization schemes for CaCO3 production, export, dissolution, and burial vary substantially, with no benthic calcification and generally only calcite considered. This diversity leads to contrasting projections of carbon export associated with CaCO3 from the surface ocean to the ocean interior in future scenarios. However, sensitivity simulations performed with the NEMO-PISCES ocean biogeochemical model indicate that the feedback of this on anthropogenic carbon fluxes and ocean acidification remains limited. Through an ensemble of NEMO-PISCES simulations, careful consideration of the Alk budget is shown to be critical to estimating pre-industrial ocean carbon outgassing due to riverine discharge and the burial of organic matter and CaCO3. Such estimates are fundamental to assessing anthropogenic air-sea carbon fluxes using observational data and highlight the need for greater constraints on the ocean Alk budget

Three years of carbonate system measurements from Ryder Bay on the West Antarctic Peninsula are presented. The strong, asymmetric seasonal cycle of surface water Dissolved Inorganic Carbon (DIC) is quantitatively attributed to four processes:mixing of water masses, air-sea CO2 flux, calcium carbonate precipitation/dissolution and photosynthesis/respiration. In summer, reduced mixing with deeper water, net photosynthesis, and melting glacial ice and sea ice reduce DIC. In winter, mixing with deeper water and net heterotrophy increase DIC, resulting in aragonite saturation states close to 1. Ryder Bay is a net annual sink of atmospheric CO2 of 0.90-1.39 mol C m-2 yr-1. The observed variability demonstrates that future climatic changes may significantly affect carbon cycling in this dynamic environment. Carbonate system measurements from the Drake Passage and A23 sections are compared. Lower Circumpolar Deep Water (LCDW) becomes colder and fresher from Drake Passage to A23 due to mixing in the Scotia Sea. The coincident decrease in Total Alkalinity (TA) increases the fugacity of CO2, potentially reducing CO2 uptake in the Weddell Sea through the influence of upwelling LCDW on surface waters. Ventilation of Upper Circumpolar Deep Water (UCDW) in the south of Drake Passage suggests that this region is an important source of CO2 to the atmosphere. The zonal variability of the carbonate system in deep water masses around the Antarctic Circumpolar Current is assessed. Zonal variability, caused by the inflow of North Atlantic Deep Water in the Atlantic sector and UCDW in the Indian and Pacific sectors, has implications for regional air-sea CO2 flux in the high-latitude Southern Ocean. Temporal variability in Sub-Antarctic ModeWater is investigated. Most of the observed DIC increase is attributed to rising atmospheric CO2. There is also weak evidence for increasing remineralised organic carbon, possibly relatedto changes in the strength and location of ventilation.

In this study, we investigate the role that the solubility and biological pumps have on CO₂ variability across the Agulhas Current system ( Agulhas Current and the Agulhas Return Current). The Agulhas Current system transports heat and salt from the Indian Ocean into the South Atlantic Ocean via the Agulhas leakage, which influences the Atlantic Meridional Overturning Circulation (AMOC). This study presents for the first time a characterization of the role the Agulhas Current system (Agulhas and Agulhas Return Currents) has on the uptake of anthropogenic CO₂. Fugacity of carbon dioxide (fCO₂ ) values were obtained from a ship-based underway pCO₂ (partial pressure of carbon dioxide) system and the air-sea CO₂ fluxes were computed using 6-hourly wind speeds from the NOAA Blended Sea Winds. An experiment was conducted during the Crossroads scientific monitoring line in May 2013, where surface dissolved inorganic carbon, total alkalinity and CO₂ flux were compared between the Agulhas and Agulhas Return Currents and the region directly south over the Agulhas Plateau. Our findings highlighted that the solubility and biological pumps played minimal to no role in the drawdown of carbon across the sub-Tropical zone and the Agulhas Current system (Agulhas and Agulhas Return Currents), due to opposing effect between chlorophyll and temperature on pCO₂ that explained why although there was carbon drawdown by primary production in the Agulhas and Agulhas Return Current regions, this does not play a role in enhancing the air-sea exchange of CO₂. The solubility pump was responsible for CO₂ in the sub-Antarctic zone. The biological and solubility pumps were responsible for CO₂ sink in the Agulhas Plateau eddy. The highest CO₂ flux in the study was observed in the Agulhas Plateau eddy at a flux value of -8.12 mmolC.m-².day-¹ due to the cooler mean sea surface temperature of ~16.5 °C. This is the first time that such as study has been undertaken and aims to provide a better understanding of the role of Western Boundary Currents such as the Agulhas Current has in the uptake of CO₂.

Since the industrial revolution, CO sub 2 has increased in the atmosphere and about 40% of the increase has been taken up by the ocean. An artifact of increasing CO sub 2 in the ocean is ocean acidification; it changes the calcium carbonate saturation state, which in turn alters the calcification rate of shelled organisms. The purpose of this dissertation is to estimate the changes in the carbonate system in the oceans, and whether these changes are due to natural (biological activity, chemical transformation or mixing of water masses) or anthropogenic (human activities) perturbations. The first hypothesis states that the presence of boric acid (B(OH) sub 3) in seawater changes the thermodynamic constants of CO sub 2, pK sup * sup 1 and pKsup * sup 2. Due to experimental limitations, the solubility of B(OH) sub 3 was determined in electrolyte solutions (LiCl, NaCl, KCl, RbCl and CsCl) instead of real or artificial seawater. The results can be used to estimate the B(OH) sub 3 activity coefficients gamma sub B and solubility [B] in natural mixed electrolyte solutions. The second hypothesis states that filtering seawater sampled in the open ocean is necessary for the determination of total alkalinity (TA). Measurement of 180 samples of surface, oxygen minimum, and deep waters in the Pacific and Indian oceans revealed that the at- sea measured TA of filtered and unfiltered samples were not statistically different. Finally, a synthesis and analysis of the carbonate parameters in the Atlantic and Indian oceans is undertaken. Results from repeat hydrographic cruises in these oceans were used for this task. Parameters TA and total CO sub 2 (TCO sub 2) are predicted using hydrographic properties and a multi-linear regression method to obtain a more homogenous dataset. The results of the predicted TA prove to be successful, which is not the case for TCO sub 2 at the surface of the ocean. Finally, it is found that the increase in anthropogenic CO sub 2 signal remineralization and mixing of water masses increase the acidity of the ocean at the surface and in deep waters, respectively. This causes the aragonite saturation horizon to shoal. Recommendations for further studies are provided in the "Summary and conclusion" chapter.

The surface ocean plays an important role in the marine carbon cycle linking the atmosphere and the deep ocean. There are substantial variations in the surface ocean carbonate system in different environments and on various time scales, resulting from the interactions of various physical and biogeochemical processes. In this study, the use of Ships of Opportunity (SOO, as carriers of automatic underway measuring systems and platforms for sample collections) was promoted to enhance the surface ocean observing capacity to provide in-situ observations with better temporal resolution and spatial coverage in a cost- effective way (Chapter 2). The functionality, reliability and accuracy of an automatic pCO2 sensor were assessed extensively under various field and laboratory conditions (Chapter 3). The sensor proved to be suitable for long-term onboard and in-situ measurements, while its uncertainty is largely determined by the reference used for calibration. Observations made from two SOOs were examined to better understand the variability and control of the surface ocean carbonate system (Chapter 4, 5). The spatial variability of alkalinity in different marine environmental settings were investigated focusing on the influences of physical and biogeochemical processes on the alkalinity-salinity relationship (Chapter 4). By using salinity-normalized alkalinity as an indicator, the TA addition or removal processes were examined in the open ocean regime in the Atlantic, Pacific and Indian Ocean (mainly controlled by precipitation and evaporation), in the western North Atlantic margin, eastern North Pacific and Mediterranean Sea (additional alkalinity inputs from rivers, currents or the Black Sea), and in the Red Sea (alkalinity removal by CaCO3 precipitation). In coastal regions, a regional-specific term for zero salinity end member should be considered in salinity normalization practice, and care should be taken when use the abstract intercept of alkalinity-salinity regression to estimate the river water end member (only works reliably in river-dominated systems). The temporal variations of the surface carbonate system and air-sea CO2 flux in the Northeast Atlantic (Bay of Biscay) were examined on seasonal to interannual time scales (Chapter 5). The seasonal variability of DIC (single annual peak in winter, shaped by the winter increase due to deep convection followed by the spring biological drawdown) is different to the seasonal cycle of pCO2 (double annual peaks in winter and summer, determined by the competing effects of temperature and nonthermal processes on pCO2). A comparative study shows a latitudinal transition of pCO2 seasonality in the North Atlantic: from the temperature-dominated oligotrophic subtropical gyre to the subpolar region where pCO2 is dominated by changing concentrations of DIC. Located in the transition zone, pCO2 in the mid-latitude Bay of Biscay shows a double-peak distribution in its annual cycle: the summer peak is dominated by temperature increase while the winter peak results from the dominant convection effect. The interannual biogeochemical changes in the Bay of Biscay were found to be closely related to the varying intensity of winter mixing, with higher seasonal amplitudes of DIC and nutrients observed in cold years in response to negative phases of the North Atlantic Oscillation. An increase in annual mean seawater pCO2 was observed from 2002 to 2010 associated with decreased rates of oceanic CO2 uptake.

The purpose of this thesis is to analyse the spatial and temporal variability of the aragonite saturation state (ΩAR), commonly used as an indicator of ocean acidification, in the North-East Atlantic. When the aragonite saturation state decreases below a certain threshold, ΩAR <1, calcifying organisms (i.e. molluscs, pteropods, foraminifera, crabs, etc.) are subject to dissolution of shells and aragonite structures. This objective agrees with the challenge 'Ocean, climate change and acidification' of the EU COST Ocean Governance for Sustainability project, which aims to combine the information collected on the state of health of the oceans. Two open-sources data products, EMODnet and GLODAPv2, have been integrated and analysed for the first time in the North-East Atlantic region. The integrated dataset contains 1038 ΩAR vertical profiles whose time distribution spans from 1970 to 2014. The ΩAR has been computed from CO2SYS software considering different combinations of input parameters, pH, Total Alkalinity (TAlk) and Dissolved Inorganic Carbon (DIC), associated with Temperature, Salinity and Pressure at in situ conditions. A sensitivity analysis has been performed to better understand the data consistency of ΩAR computed from the different combinations of pH, Talk and DIC and to verify the difference among observed TAlk and DIC parameters and their output values from the CO2SYS tool. Maps of ΩAR have been computed with the best data coverage obtained from the two datasets, at different levels of depth in the area of investigation and they have been compared to the work of Jiang et al. (2015). The results are consistent and show similar horizontal and vertical patterns. The study highlights some aragonite undersaturated values (ΩAR <1) below 500 meters depth, suggesting a potential effect of acidification in the considered time period. This thesis aims to be a preliminary work for future studies that will be able to design the ΩAR variability on a decadal distribution based on the extended time-series acquired in this work.

Depuis la révolution industrielle, les activités humaines libèrent de grandes quantités de dioxyde de carbone (CO2) dans l'atmosphère. Une partie de cet excès de CO2 est captée par les océans et a provoqué des perturbations et des changements dans le cycle du système carbonaté. Ces perturbations du système carbonaté sont désormais connues pour altérer l'état d'acidification des océans. Dans l'océan Atlantique Sud, les grands tourbillons des Aiguilles, sont parmi les plus grandes structures à méso-échelle des océans. Parce qu'ils sont des structures anticycloniques, ces tourbillons sont associés à des régions où l'océan perd de la chaleur vers l'atmosphère, mais leurs rôles par rapport au système carbonaté sont encore mal connus. Ainsi, l'objectif principal de cette recherche doctorale était d'étudier la relation entre les tourbillons des Aiguilles et la capture et le transport du CO2/Cant tout au long de leur vie ainsi que le rôle que ces structures jouent dans l'état d'acidification de l'océan Atlantique Sud.Lors de cette thèse, nous avons pu démontrer que les tourbillons des Aiguilles sont capables non seulement de capter plus de CO2 que les eaux environnantes, mais aussi de transférer ce carbone en profondeur dans la colonne d'eau et peuvent transporter plus de Cant le long de leur trajectoires. Etant donné que les observations indiquent que 30% de ces structures libérées dans le courant des Aiguilles atteignent la côte ouest de l'océan Atlantique Sud et interagissent même avec le courant du Brésil, nous pouvons les désigner comme l'un des déclencheurs susceptibles d'intensifier l'acidification observée pour les couches centrales de cette région
​Human activities have been releasing large amounts of carbon dioxide (CO2) into the atmosphere since the Industrial Revolution. Part of this excess CO2 is captured by the oceans and has been causing perturbations and changes in the carbonate system cycle. These changes in the carbonate system are now known to alter the acidification state of the oceans.In the South Atlantic Ocean are observed the Agulhas eddies, which are among the largest mesoscale structures in the oceans. Because they are anticyclonic structures, these eddies are associated with regions where the ocean loses heat to the atmosphere, but its role in relation to the carbonate system is still poorly studied. Thus, the main objective of this doctoral research was to investigate the relationship between the Agulhas eddies and CO2/Cant uptake and transport throughout their lives and which role these structures play in the acidification state in the South Atlantic Ocean.As a main conclusion of this thesis, we have been able to demonstrate that the Agulhas eddies are able not only to capture more CO2 than the surrounding waters, but also to transfer into the water column and can carry more Cant along their trajectories. As studies show that 30% of these structures released in the Agulhas leakage reach the west coast of the South Atlantic Ocean and even interact with the Brazilian Current, we can indicate them as one of the triggers that may be intensifying the acidification observed for the central layers of this region
Atividades humanas vêm liberando grandes quantidades de dióxido de carbono (CO 2 ) na atmosfera desde a Revolução Industrial. Parte desse excesso de CO 2 é capturado pelos oceanos (carbono antropogênico, C ant ) e vêm causando perturbações e alterações no ciclo do sistema carbonato. Essas alterações no sistema carbonato alteram o estado de acidificação dos oceanos.No oceano Atlântico Sul observa-se os vórtices das Agulhas, que estão entre as maiores estruturas de mesoescala dos oceanos. Por serem estruturas anticiclônicas, estes vórtices estão associados às regiões em que o oceano perde calor para a atmosfera, porém seu papel em relação ao sistema carbonato ainda é pouco estudado. Dessa forma, o objetivo principal dessa pesquisa de doutorado foi investigar a relação dos vórtices das Agulhas com a captura e transporte de CO 2 /C ant ao longo de suas vidas e qual o papel dessas estruturas no estado de acidificação no oceano Atlântico Sul. Como conclusão principal dessa tese, pudemos demonstrar que os vórtices das Agulhas são capazes não só de capturar mais CO 2 do que as águas ao seu redor, como também de transferir para o interior da coluna d’água, podendo carregar mais C ant ao longo de suas trajetórias. Como estudos mostram que 30% dessas estruturas liberadas no vazamento das Agulhas atingem a costa Oeste do Oceano Atlântico Sul e chegam a interagir com a Corrente do Brasil, podemos indicá-los como um dos gatilhos que podem estar intensificando a acidificação observada para as camadas centrais dessa região

Human activities have contributed to the increase in atmospheric greenhouse gases such as carbon dioxide (CO2). This anthropogenic gas emission has led to a rise in the average Earth temperature. Moreover, the ocean constitutes the major sink for anthropogenic CO2 and its dissolution in surface waters has already resulted in an increase of seawater acidity since the beginning of the industrial revolution. This is commonly called ocean acidification. The increase in water temperature could induce modifications of the physical and chemical characteristics of the ocean. Also, the structure and the functioning of marine ecosystems may be altered as a result of ocean acidification.

Phytoplankton productivity is one of the primary controls in regulating our climate, for instance via impact on atmospheric CO2 levels. Coccolithophores, of which Emiliania huxleyi is the most abundant species, are considered to be the most important pelagic calcifying organisms on Earth. Coccolithophores are characterized by calcium carbonate platelets (coccoliths) covering the exterior of the cells. They form massive blooms in temperate and sub-polar oceans and in particular along continental margin and in shelf seas. The intrinsic coupling of organic matter production and calcification in coccolithophores underlines their biogeochemical importance in the marine carbon cycle. Both processes are susceptible to change with ocean acidification and warming. Coccolithophores are further known to produce transparent exopolymer particles (TEP) that promote particle aggregation and related processes such as marine snow formation and sinking. Thus, the impact of ocean warming and acidification on coccolithophores needs to be studied and this can be carried out through a transdisciplinary approach.

The first part of this thesis consisted of laboratory experiments on E. huxleyi under controlled conditions. The aim was to estimate the effect of increasing water temperature and acidity on E. huxleyi and especially on the calcification. Cultures were conducted at different partial pressures of CO2 (pCO2); the values considered were 180, 380 and 750 ppm corresponding to past, present and future (year 2100) atmospheric pCO2. These experiments were conducted at 13°C and 18°C. The cellular calcite concentration decreases with increasing pCO2. In addition, it decreases by 34 % at 380 ppm and by 7 % at 750 ppm with an increase in temperature of 5°C. Changes in calcite production at future pCO2 values are reflected in deteriorated coccolith morphology, while temperature does not affect coccolith morphology. Our findings suggest that the sole future increase of pCO2 may have a larger negative impact on calcification than its interacting effect with temperature or the increase in temperature alone. The evolution of culture experiments allows a better comprehension of the development of a bloom in natural environments. Indeed, in order to predict the future evolution of calcifying organisms, it is required to better understand the present-day biogeochemistry and ecology of pelagic calcifying communities under field conditions.

The second part of this dissertation was dedicated to results obtained during field investigations in the northern Bay of Biscay, where frequent and recurrent coccolithophorid blooms were observed. Cruises, assisted by remote sensing, were carried out along the continental margin in 2006 (29 May – 10 June), 2007 (7 May – 24 May) and 2008 (5 May – 23 May). Relevant biogeochemical parameters were measured in the water column (temperature, salinity, dissolved oxygen, Chlorophyll-a and nutrient concentrations) in order to determine the status of the bloom at the time of the different campaigns. Calcification has been shown to be extremely important in the study area. In addition, TEP production was significant at some stations, suggesting that the northern Bay of Biscay could constitute an area of important carbon export. Mortality factors for coccolithophores were studied and the first results of lysis rates measured in this region were presented.

Results obtained during culture experiments and comparison with data reported in the literature help to better understand and to predict the future of coccolithophores in a context of climate change. Data obtained during either culture experiments or field investigations allowed a better understanding of the TEP dynamics. Finally, the high lysis rates obtained demonstrate the importance of this process in bloom decline. Nevertheless, it is clear that we only begin to understand the effects of global change on marine biogeochemistry, carbon cycling and potential feedbacks on increasing atmospheric CO2. Thus, further research with a combination of laboratory experiments, field measurements and modelling are encouraged.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Over the last 800 ky the Earth’s climate system has been triggered by orbitally- forced oscillations, referred to as glacial- interglacial cycles. However, the detailed dynamics of these cycles, specifically the transition between glacial into interglacial phase, are still to be completely understood. An interesting feature of these phases is that atmospheric CO2 and CH4 concentrations are better correlated with Antarctica and Greenland rather than with North Hemisphere temperatures, and this suggests the hypothesis that greenhouse gases are important amplifiers of the orbital forcing in the glacial-interglacial cycles. The cyclicity of biological marine productivity on glacial-interglacial scale observed both in the Pacific and further supports the idea that climate changes are cyclic and control the global carbon dynamics. Here, we investigate the role played by coccolithophores, a group of calcifying phytoplankton tightly connected to the global climate through the carbon cycle, during the last deglaciation in the Southern Ocean and Eastern Equatorial Pacific. The present thesis focuses on Termination I (TI), the latest warming event that the Earth has experienced, with the final aim to provide new insights on climate dynamics that are not still completely understood. In this PhD thesis, the response of calcareous phytoplankton to increased temperatures (global warming), shifts in the carbonate system (ocean acidification) and enhanced water column stratification (as a response to the increase in temperatures) have been analyzed. Our results are based on sediment samples recovered from two sites located in the South Atlantic area of the Southern Ocean (ODP1089 and PS2498-1; Chapters 2,3,4) and one in the Eastern Equatorial Pacific Ocean, off the coast of Ecuador (Site ODP1238; Chapter 5). These three case studies allowed an evaluation of the repeatability of our analyses (Chapter 2) and, more importantly, a better comprehension on several aspects related to coccolithophore community evolution and coccolith carbonate production such as: 1) the coccolith absolute abundances, 2)the components of the nannoplankton assemblages, the changes in coccolith mass and calcification dynamics of Emiliania huxleyi and 3) the main morphological / environmental control factors at high latitudes (Chapter 3 and 4) and low latitudes (Chapter 5). Overall, the results presented in this thesis suggest that coccolith assemblages at high latitudes are mainly composed by Emiliania huxleyi and Calcidiscus leptoporus. We propose an enhanced carbonate counter pump as a trigger mechanism increasing the deep ocean alkalinity in the last glacial at Site ODP1089, and increased pCO2sw during the interglacial at Site PS2498-1. At low latitudes (Site ODP1238), we have observed an increase in calcification is more active in compared to photosynthesis activity during the deglaciation. Finally, the mass and calcification of E. huxleyi seem to be controlled by the carbonate system of the entire water column.
L'evoluzione del clima terrestre, durante gli ultimi 800.000 anni è caratterizzata dacicli climatici glaciale - interglaciale (freddo/caldo) forzati da oscillazioni dei parametri orbitali. Tuttavia, la dinamica della transizione tra la fase glaciale e la fase interglaciale rimane non è ancora completamente chiara. Un’importante peculiarità riguardante queste specifiche fasi di transizione è che le concentrazioni atmosferiche di anidride carbonica e metano sono correlate con le temperature registrate in Antartide e Groenlandia piuttosto che con quelle dell’emisfero settentrionale. Questa osservazione supporta l’ ipotesi che i gas serra possano giocare un ruolo fondamentale come amplificatori della forzante orbitale per il sistema climatico. A favore di questa ciclicità climatica esistono evidenze legate alla variazioni di produttività osservate sia in Atlantico che Pacifico. In questa tesi di dottorato abbiamo investigato il ruolo dei coccolitoforidi, un gruppo di alghe unicellulari che influenzano il clima attraverso il ciclo globale del carbonio, durante l’ultima deglaciazione nell’Oceano Meridionale e Oceano Pacifico equatoriale orientale. Questo studio si è concentrato sull’ultima Terminazione (TI), che rappresenta l’ultimo evento di riscaldamento climatico che la Terra abbia sperimentato, con lo scopo di cercare di fornire maggiori informazioni sulle possibili dinamiche che si attivano alla transizione tra glaciale e interglaciale.è. Si è quindi considerato questo intervallo per analizzare le possibili risposte del fitoplancton ai processi quali l’ aumento delle temperature (riscaldamento globale), la variazione degli equilibri nel sistema carbonatico (acidificazione delle acque) e l’incremento della stratificazione delle acque (come risposta all’aumento di temperature delle acque). I nostri risultati si basano su campioni di sedimento provenienti da due siti localizzati nell’area del sud Atlantico nell’Oceano Meridionale (ODP1089 e PS2498-1; Capitoli 2,3,4) e uno nell’area dell’Oceano Pacifico equatoriale orientale, a largo dell’ Ecuador (Capitolo 5). Questi tre casi studio ci hanno permesso di valutare la ripetibilità dei nostri risultati (Capitolo 2) e, sopratutto, di comprendere molteplici aspetti della comunità a coccolitoforidi e delle dinamiche di questo gruppo nella produzione carbonatica, come ad esempio: 1) le abbondanze assolute dei coccoliti, 2) le loro abboandanze relative, 3) le dinamiche della massa e della calcificazione di Emiliania huxleyi e 4) i principali controlli morfologici/ ambientali alle alte latitudini (Capitoli 3 e 4) e basse latitudini (Capitolo 5). In generale, i risultati presentati in questa tesi suggeriscono che l’associazione a coccoliti alle alte latitudini risulta principalmente composta da E. huxleyi e Calcidiscus leptoporus. Inoltre, si ipotizza che la pompa carbonatica abbia funzionato come fattore d’innesco per aumento di alcalinità della parte piu profonda dell’oceano durante l’ ultimo glaciale (ODP1089), e abbia prodotto un aumento della pressione dell’anidride carbonica discolta in acqua durante la fase interglaciale (PS2498-1). Alle basse latitudini (ODP1238), abbiamo osservato un aumento dell’attività di calcificazione rispetto a quella fotosintetica durante la deglaciazione. Infine, l’analisi della massa e del grado di calcificazione di E. huxleyi sembra indicare questi due parametri sono controllati dalla chimica delle acque superficiali e profonde.

2013/2014
Since the beginning of Industrial Revolution a massive amount of atmospheric carbon dioxide, produced by human activity, has been absorbed by the World’s Oceans. This process has led to an acidification of marine waters on a global scale and is one of the most serious threats facing marine ecosystems in this century. The negative impacts of ocean acidification could be much more relevant in coastal ecosystems, where marine life is concentrated and biogeochemical processes are more active. However, future projections of pH reduction in these areas are difficult to estimate because result from multiple physical and biological drivers, including watershed weathering, river-born nutrient inputs, and changes in ecosystem structure and metabolism. In order to assess the sensibility of the Gulf of Trieste to the ocean acidification, high quality determination of the marine carbonate system (pHT, total alkalinity, dissolved inorganic carbon-DIC, buffer capacity) and other related biogeochemical parameters were carried out along a transect from the Isonzo River mouth to the centre of the gulf and at the coastal Long Term Ecological Research station C1. At the same time the biological influence of organic matter production and decomposition on the marine CO2 system was estimated using 14C primary production and heterotrophic prokaryote production (by 3H-leucine incorporation). The two years long measurements revealed a complex dynamic of the marine carbonate system, due to the combined effects of local freshwater inputs, biological processes, and air-sea CO2 exchange. However, it was possible to estimate the influence of the different drivers on a seasonal time scale. In winter the very low seawater temperature (minima = 2.88 °C) and strong Bora events determined a marked dissolution of atmospheric CO2 and elevated DIC concentration. During warm seasons the DIC concentration gradually decreased in the surface layer, due to biological drawdown (primary production) and thermodynamic equilibria (CO2 degassing), whereas under the pycnocline the respiration and remineralisation of organic matter prevailed, causing a temporary acidification of bottom waters. The winter seawater invasion of atmospheric CO2 was balanced by high riverine AT input (maxima ∼ 2933 µmol kg-1), derived mainly from chemical weathering of carbonate rocks of the surrounding karstic area, which increased the buffer capacity of this system and probably could mitigate the effect of ocean acidification. The marine carbonate system was also analysed in the Middle and Southern Adriatic Sea, in order to estimate the concentration of anthropogenic carbon dioxide currently present in this area. The results suggested that the entire water column was contaminated by a large amount of anthropogenic CO2 and very high concentration was detected near the bottom, in correspondence of the North Adriatic Dense Waters. This finding supported the hypothesis that during dense water formation events the very low seawater temperature can favour the physical dissolution of atmospheric carbon dioxide, and also revealed the active role of the North Adriatic Sea in sequestering and storing anthropogenic CO2 into the deep layers of Mediterranean Sea.
Dall’inizio della Rivoluzione Industriale ad oggi, una grande quantità di anidride carbonica antropogenica presente in atmosfera è stata assorbita dagli Oceani di tutto il mondo. Questo processo ha portato all’acidificazione del mare su scala globale e rappresenta una delle più gravi minacce per gli ecosistemi marini in questo secolo. L’impatto negativo di tale fenomeno, noto come ocean acidification, potrebbe essere maggiore soprattutto negli ecosistemi costieri, poiché è qui che si concentrano gli organismi marini ed è qui che i cicli biogeochimici risultano più attivi. Tuttavia è difficile stimare il futuro abbassamento del pH in queste aree a causa della loro complessità e della moltitudine dei processi fisici, chimici e biologici coinvolti (cambiamenti dello stato trofico e del metabolismo dell’ecosistema, input fluviale di nutrienti, materia organica e prodotti di dissoluzione delle rocce, ecc.). Allo scopo di valutare la vulnerabilità del Golfo di Trieste rispetto al processo di ocean acidification, per due anni sono state eseguite misure di elevata precisione del sistema carbonatico marino (pHT, alcalinità totale, carbonio inorganico disciolto-DIC, capacità tamponante) e di altri parametri biogeochimici correlati lungo un transetto che congiunge la foce del fiume Isonzo al centro del Golfo e nella stazione C1 sito LTER (Long Time Ecological Research C1). Inoltre, per valutare in maniera più approfondita l’influenza dei processi biologici sulla variabilità del sistema carbonatico, è stata stimata la produzione primaria, attraverso il metodo dell’incorporazione di 14C, e la produzione procariotica eterotrofa, attraverso l’incorporazione di 3H-leucina. I risultati hanno evidenziato una complessa dinamica del sistema carbonatico dovuta all’effetto e all’interazione degli apporti fluviali, dei processi biologici e dello scambio di CO2 tra atmosfera e mare. Su scala stagionale, tuttavia, è stata stimata l’influenza e il contributo dei diversi processi. In inverno, la bassa temperatura dell’acqua, che in un caso estremo ha raggiunto i 2.88 °C, e i forti venti di Bora hanno favorito la dissoluzione della CO2 atmosferica, determinando un incremento della concentrazione di DIC. Durante la primavera e l’estate i livelli di DIC sono diminuiti gradualmente negli strati superficiali, grazie all’effetto combinato della produzione primaria e alla perdita di CO2 verso l’atmosfera per degassamento. Nel periodo tardo estivo-autunnale, invece, al di sotto del picnoclino i processi di respirazione e remineralizzazione della materia organica sono risultati predominanti determinando, a causa dell’elevata concentrazione di CO2 prodotta, una temporanea acidificazione delle acque di fondo. Il forte assorbimento di CO2 atmosferica stimato durante l’inverno era, però, controbilanciato dall’apporto fluviale di alcalinità totale, derivante dal processo di dissoluzione delle rocce calcaree presenti nell’area carsica. Tale fenomeno ha determinato un aumento della capacità tamponante del sistema, mitigando probabilmente il processo di ocean acidification in quest’area. Parallelamente alle analisi nel Golfo di Trieste, il sistema carbonatico marino è stato analizzato anche nel Medio e Sud Adriatico, con lo scopo di stimare la concentrazione di anidride carbonica antropogenica attualmente presente in questi sottobacini. I risultati hanno dimostrato come tutta la colonna d’acqua avesse assorbito una grande quantità di CO2 antropica. In particolare elevate concentrazioni sono state individuate sul fondo, in corrispondenza delle acque dense di origine nord adriatica. Tali risultati hanno confermato l’ipotesi secondo la quale in inverno, durante il processo di formazione di acque dense nel Nord Adriatico, le basse temperature raggiunte dalle acque possono favorire la dissoluzione fisica della CO2 atmosferica. Hanno dimostrato, inoltre, l’importante ruolo svolto da tutto il bacino nord adriatico nel sequestrare e trasportare la CO2 antropica nelle profondità del mare, estendendo il processo di ocean acidification anche ad aree meno contaminate.
XXVII Ciclo
1982

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ
Os oceanos funcionam como um reservatório natural de carbono, no qual sua solubilidade na superfície dos oceanos varia de acordo com a temperatura. Antes do período industrial, as variações na concentração de CO2 atmosférico estavam fortemente associadas às transições glacial-interglacial (G-IG), onde os menores valores de CO2 na atmosfera foram registrados nos períodos glaciais, decorrente do aumento da solubilidade do CO2 nos oceanos. Nesses períodos, o aumento da solubilidade do CO2 na coluna d’água estimulou a produção de íons carbonato, beneficiando organismos que calcificam carbonato de cálcio (CaCO3) em suas conchas e esqueletos. O processo inverso, ou seja, menor solubilidade do CO2 e, consequentemente, menor disponibilidade de íons carbonatos nos oceanos marcou os períodos interglaciais. O presente estudo teve como objetivo avaliar os efeitos das variações no peso-normalizado pelo tamanho (do inglês, size-normalized weight, SNW) de foraminíferos planctônicos durante os últimos 70.000 anos no Sudoeste do Atlântico visando compreender os efeitos da calcificação e/ou dissolução do carbonato e da microestrutura das testas de foraminíferos planctônicos que viviam na porção superior da coluna d'água (G. ruber-white e G. sacculifer-sem saco). Para tanto, foi utilizado um testemunho coletado na Bacia de Santos a 2225 m de profundidade, que compreende os últimos 185 mil anos, dos quais os primeiros 70 mil anos foram estudados. Os resultados mostraram que ambas as espécies apresentaram um aumento do SNW na transição entre os períodos G-IG, associado com indícios de dissolução nas testas do período glacial, quando observada a microestrutura. Esses resultados demonstram a ação corrosiva das águas de fundo durante os glaciais e diferem dos obtidos em outros estudos realizados no Atlântico Norte que registram características menos corrosivas durante o último glacial em profundidades de até 3500 metros. A redução no peso das testas durante o período glacial foi atribuída à ação da dissolução dos carbonatos. A dissolução pode ocorrer abaixo da camada denominada lisoclina, porém apesar da grande mudança na profundidade da lisoclina durante os glaciais no Atlântico Sul, o testemunho, ainda assim, estaria 800 m acima da influência da lisoclina. Acima da lisoclina, a dissolução dos carbonatos pode ocorrer por diversos outros fatores, tais como pelo aumento da geração de CO2 pela atividade bentônica durante eventos de aumento de produtividade. Essa atividade bentônica tornaria a camada da interface água-sedimento corrosiva às estruturas carbonáticas. Nesse sentido, foram registrados no testemunho estudado um aumento nos teores de sílica e ferro, nutrientes que poderiam estimular um aumento da produtividade primaria, o que se refletiria nos altos níveis de carbono orgânico também registrados no testemunho durante o período glacial, estimulando, assim, a atividade bentônica. Outra possibilidade que explicaria a dissolução observada é decorrente de mudança na geometria das massas d’água durante os glaciais, o qual promoveria o contato do sedimento com massas d’água Antárticas (Águas de Fundo Antárticas-AFA), que são mais corrosivas. Entretanto, estudos anteriores realizados com o mesmo testemunho e baseados em isótopos de neodímio não corroboram a ocorrência de mudanças na geometria das massas d’água na região, pelo menos para os últimos 25 mil anos.
Oceans work as a natural reservoir of carbon, where the solubility in the surface varies with temperature. Before the industrial period, variations in the atmospheric CO2 concentration were strongly associated with the glacial-interglacial (G-IG) transitions, where the lowest atmosphere CO2 values were recorded in the glacial periods, due to the increase in the CO2 solubility. In these periods, the increase of the CO2 solubility in the water column stimulated the production of carbonate ions, benefiting organisms that calcify calcium carbonate (CaCO3) in their shells. The inverse process, that is, the lower CO2 solubility and, consequently, lower carbonate ions availability in the oceans marked the interglacial periods. The objective of this study was to evaluate the effects of size-normalized weight during the last 70.000 years in the Southwest Atlantic to understand the effects of calcification and/or dissolution of carbonate and microstructure analysis of the Planktonic foraminifera that lived in the upper portion of the water column (G. ruber-white) and G. sacculifer). For that, a core collected in the Santos Basin at 2225 m depth was used, which includes the last 185 thousand years, of which the first 70 thousand years were studied. The results showed that both species showed an increase in SNW at the transition between the G-IG periods, associated with evidence of dissolution in the glacial period, when the microstructure was observed. These results demonstrate the corrosive action of the bottom waters during the glaciers and differ from those obtained in other studies conducted in the North Atlantic that record less corrosive characteristics during the last glacial in depths of up to 3500 meters. The reduction in the weight of the shells during the glacial period was attributed to the action of the carbonate dissolution. The dissolution may occur below the lysoclin layer, but despite the large change in lysoclin depth during the glaciers in the South Atlantic, the corer would still be 800 m above the influence of lysoclin. Above lysoclin, the carbonate dissolution can occur due to several other factors, such as the increase of CO2 generation by benthic activity during productivity increase events. This benthic activity would make the water-sediment interface layer corrosive to carbonate structures. In this sense, an increase in silica and iron contents was recorded in the studied corer, nutrients which could stimulate an increase in primary productivity, which would be reflected in the high levels of organic carbon also recorded in the corer during the glacial period, stimulating benthic activity. Another possibility that would explain the observed dissolution is due to a change in the geometry of the water masses during the glaciers, which would promote the contact of the sediment with Antarctic water masses (Antarctic Bottom Water-ABW), which are more corrosive. However, previous studies carried out with the same evidence and based on neodymium isotopes do not corroborate the occurrence of changes in the geometry of water masses in the region, at least 25 ka years

Through a discipline termed “comparative sedimentology”, modern carbonate depositional environments have been used extensively as analogs to aid in the interpretation of equivalent fossil systems. Using field samples, GIS and remote sensing data for three isolated carbonate platforms in the Pacific, this thesis seeks to examine relationships between grain texture and grain type and their environment of deposition. The motivation is to highlight relationships that have the potential to better understand facies relations on carbonate platforms, and thereby reduce uncertainty and increase accuracy of subsurface exploration. The results of this study show that on Raivavae, Tubuai, and Bora Bora: French Polynesia grain texture and type of collected sediment samples could be used to predict water depth and relative distance lagoonward from the reef rim with ≥ 73% and ≥ 67% accuracy, respectively. The predictive relationships; however, were largely site specific. The exception being that the same relationship between water depth and the abundance of mud and coral could be used on both Raivavae (accuracy = 81%) and Tubuai (accuracy = 78%). Additionally, the abundance of coral and Halimeda in sediment samples were able to classify samples as belonging to either the platform margin or platform interior environments on Raivavae, Tubuai, and Bora Bora with 75%, 65%, and 65% accuracy, respectively. Overall, the results of this study suggest that the abundance of coral holds potential to be utilized as a proxy for distance from the reef rim on modern and ancient isolated carbonate platforms dating back to the Miocene geological epoch.

L’océan côtier occupe une position clé dans le cycle du carbone et est exposé à l’acidification des océans. Une grande partie de matière organique(MO) marine et continentale est minéralisée dans les sédiments estuariens par des voies aérobies ou anaérobies. Cette minéralisation produit du carbone inorganique dissous (DIC), mais aussi de l’alcalinité totale(TA) pour la partie anoxique, ce qui tamponne les variations de pH du système et augmente la capacitéde l’eau de mer à absorber du CO2. Des mesures dans les sédiments du prodelta du Rhône ont montré que la minéralisation anoxique, surtout la sulfato-réduction, y est dominante et produit des forts flux de TA et de DIC. Proche de l’embouchure, c’est surtout la MO continentale qui est minéralisée et la fraction marine augmente vers le large. Une expérience d’acidification des sédiments de la baie de Villefranche-sur-mer a montré que l’acidification des océans cause la dissolution des carbonates ce qui tamponne le pH dans les sédiments
Continental shelves are key regions for theglobal carbon cycle and particularly exposed to oceanacidification. A large part of organic matter (OM) ofcontinental and marine origin is mineralized in estuarinesediments following oxic and anoxic pathways.This mineralization produces dissolved inorganic carbon(DIC) leading to acidification of the bottom waters.Anoxic mineralization can produce total alkalinity(TA) that can contribute to buffer bottom water pHand increase the CO2 storage capacity of seawater. Measurementsin the sediments of the Rhˆone River prodeltashowed that anoxic mineralization, especially sulfate reduction,are the major pathways of OM mineralizationand create high DIC and TA fluxes. Land derived OMis mineralized close to the river mouth and marine OMtakes over on the shelf. An acidification experiment withsediment cores from the bay of Villefranche evidencedthat acidification causes carbonate dissolution at thesediment surface that buffers porewater pH

L’océan côtier occupe une position clé dans le cycle du carbone et est exposé à l’acidification des océans. Une grande partie de matière organique(MO) marine et continentale est minéralisée dans les sédiments estuariens par des voies aérobies ou anaérobies. Cette minéralisation produit du carbone inorganique dissous (DIC), mais aussi de l’alcalinité totale(TA) pour la partie anoxique, ce qui tamponne les variations de pH du système et augmente la capacitéde l’eau de mer à absorber du CO2. Des mesures dans les sédiments du prodelta du Rhône ont montré que la minéralisation anoxique, surtout la sulfato-réduction, y est dominante et produit des forts flux de TA et de DIC. Proche de l’embouchure, c’est surtout la MO continentale qui est minéralisée et la fraction marine augmente vers le large. Une expérience d’acidification des sédiments de la baie de Villefranche-sur-mer a montré que l’acidification des océans cause la dissolution des carbonates ce qui tamponne le pH dans les sédiments
Continental shelves are key regions for theglobal carbon cycle and particularly exposed to oceanacidification. A large part of organic matter (OM) ofcontinental and marine origin is mineralized in estuarinesediments following oxic and anoxic pathways.This mineralization produces dissolved inorganic carbon(DIC) leading to acidification of the bottom waters.Anoxic mineralization can produce total alkalinity(TA) that can contribute to buffer bottom water pHand increase the CO2 storage capacity of seawater. Measurementsin the sediments of the Rhˆone River prodeltashowed that anoxic mineralization, especially sulfate reduction,are the major pathways of OM mineralizationand create high DIC and TA fluxes. Land derived OMis mineralized close to the river mouth and marine OMtakes over on the shelf. An acidification experiment withsediment cores from the bay of Villefranche evidencedthat acidification causes carbonate dissolution at thesediment surface that buffers porewater pH

Includes bibliographical references.
Ocean Acidification through the uptake of anthropogenic CO₂ is resulting in a decrease in surface water carbonate ion concentration, a critical compound for marine calcifying organisms (Fabry et al., 2008; Orr et al., 2005). Natural seasonal variability is predicted to hasten the effects of Ocean Acidification in the Southern Ocean, resulting in possible surface water wintertime aragonite (the more soluble form of calcium carbonate) undersaturation (Ωarag< 1) south of the Antarctic Polar Front by the year 2030 (McNeil and Matear, 2008). An Ocean Acidification study was conducted to determine the seasonal and interannual variability in aragonite saturation state (Ωarag) at the Antarctic ice shelf between 4°E and 14°W and in the Eastern Weddell Gyre, during the Austral summers of 2008/2009, 2009/2010, 2010/2011 and 2011/2012. This study shows that at the Antarctic ice shelf andin the Eastern Weddell Gyre (EWG), seasonal summertime phytoplankton blooms were a critical factor in the observed decrease in summer surface water CO 2 and the subsequent increase in summer surface water Ωarag.

L'intensification de l'effet de serre due à l'augmentation des concentrations de CO 2 dans l'atmosphère pourrait être plus élevée si ce n'est du rôle important de l'océan en tant que puits pour le CO 2 atmosphérique. Malheureusement, une conséquence de la capacité de l'océan à tamponner le CO 2 est l'acidification des eaux de surface des océans. L'océan Austral est particulièrement vulnérable à ces conséquences en raison de ses basses températures et de sa productivité primaire saisonnière élevée. La présente thèse de doctorat a comme objectif d’analyser le système des carbonates, en particulier l'état de l’acidification des océans, dans le détroit de Gerlache et dans la zone polaire de la région de la Terre Adélie. Ces deux régions présentent des hydrodynamiques différents et, par conséquent, devraient présenter des différences dans la variabilité de leur système carbonaté. À partir des données du programme brésilien NAUTILUS et du programme français MINERVE, la dynamique du système des carbonates a été évaluée dans ces régions de 2015 à 2017. Les résultats sont présentés sous la forme d'articles scientifiques qui ont été assemblés pour structurer cette thèse. Le détroit de Gerlache présentait les plus grandes variations spatiales des propriétés du système des carbonates avec des conditions potentiellement acides durant l'été austral. En comparaison, la zone polaire de Terre Adélie présente des variations interannuelles et spatiales plus importantes associées aux zones frontales. En raison de ses conditions géographiques et hydrodynamiques, le détroit de Gerlache est actuellement plus vulnérable à l'acidification des océans que la région de la Terre Adélie
The intensification of the greenhouse effect due to increasing atmospheric CO 2 concentrations could be higher if not for the ocean’s important role as a sink for atmospheric CO 2 . A consequence of the ocean’s capacity for buffering CO 2 is the ocean acidification of sea surface waters. The Southern Ocean is particularly vulnerable to these consequences due to its low temperatures and high seasonal primary productivity. The present Ph.D. thesis focus on the analysis of the carbonate system, particularly the ocean acidification state, in the Gerlache Strait and the polar zone off the Adelie Land region. These two regions present different hydrodynamics and, consequently, are expected to present differences in their carbonate system variability. Using data sets from the Brazilian NAUTILUS programme and the French MINERVE programme, the carbonate system dynamic was assessed in these regions from 2015 to 2017. The results are presented as scientific articles, which were assembled to structure this thesis. The Gerlache Strait showed the largest spatial variations of carbonate system properties with potentially acidic conditions during austral summer. In comparison, the polar zone off Adelie Land larger inter-annual and spatial variations associated with frontal zones. Due to its geographical and hydrodynamic conditions, the Gerlache Strait is currently more vulnerable to ocean acidification than the off Adelie Landregion

The world’s oceans are becoming more acid in a process called ocean acidification. The pH of the ocean have already decreased by 0.1 units from pre-industrial time until today. Scientists predict that by the year of 2100 the pH will decrease by as much as 0.4 units. This is a big potential problem to many marine species, because they have developed in such a stable environment that has not changed for millions of years. It is difficult to predict how they might be affected by such a decrease in pH during a relatively short time period. Several studies have been made on marine species exposed to decreased pH-levels, the results showed changes in their physiology but it is hard to predict how these changes will affect the organism in a long-term scale and if this might change ecosystem dynamics. Our study measured the activity of Littorina littorea and Balanus improvisus when exposed to lower pH, the results of our study showed an increase in activity for the lower pH (pH 6.0-7.5) when compared to the control (~pH8). The area of ocean acidification is a field that requires further studies to fully understand its effects on the marine ecosystems and the species within it.

La synthese des donnees geologiques et structurales du bassin de morondava conduit a modifier la nomenclature stratigraphique des formations sedimentaires du type "karroo". Dans le bassin, le controle tectonique de la sedimentation est realise par un jeu complexe mais permanent de failles en faisceaux denses. La fracturation continentale a permis la mise en place de roches effusives basaltes et gabbros, puis roches granito-syenitiques. L'epaisseur et la nature des formations sedimentaires du bassin de morondava sont propices a la naissance de gisements d'hydrocarbures

Anthropogenic carbon dioxide released into the atmosphere is taken up by the oceans. The most profound change has been the decline in ocean pH as it is likely to impact calcifying marine organisms.. In chapter 2, a method utilising purified Bromophenol Blue (BPB) as an indicator to make simple one-point alkalinity measurements via spectrophotometric detection was developed. Our purified BPB dye was characterised over a range of temperatures and salinities and using the absorbance ratio (R (t) = 25 A590/A436) via equation: pH=pK_a +log[((R_([25])-e_1))/((e_2-R_([25]).e_3))] where e1, = 0.00533, e2 = 2.232, e3 = 0.0319, the pH was calculated. The pKa of purified BPB was also determined as 3.513. The method used for the alkalinity of ANU in-house standard and CRM had an uncertainty of +- 1.5 umol kg-1. Comparing the results to unpurified BPB dye, the uncertainty for alkalinity measured was slightly higher approximately plus minus 3-4 umol kg-1. Thus, for experiments that does not require high precision alkalinity measurements (>=4 umol kg-1), then utilisation of the impure BPB could be suitable. The one-point titration method using purified BPB was tested on seawater samples collected from algal flats at One Tree Island, Australia. The method proved to be suitable for producing accurate and precise alkalinity data i.e. approximately 10-15 samples can be determined per hour. In chapter 3 we present the results of open algal pools and the dome experiments conducted on algal ridges to quantify fluxes of calcium carbonate production and dissolution which are isolated from surrounding ocean waters for approximately 3 - 4 hours. The pH and total alkalinity measurements were made for samples collected from algal pools and the dome experiments. During the day, pH increased from 8.1 to 8.7 pH units while alkalinity decreased from around 2200 to 2000 umol kg-1 this is consistent to photosynthesis and high magnesium- calcite production. During the night the opposite was observed, pH decreased from 7.8 to 7.5 and alkalinity increased from around 2300 to 2500 umol kg-1, via respiration and the dissolution of organic matter. The net production and dissolution rates were half of those observed for a nearby back reef when compared to day and night time periods. An automated spectrophotometric system that monitors changes in ocean pH and alkalinity in culture and field experiments simultaneously was developed in chapter 4. The pH-alkalinity spectrophotometric system was calibrated against multiple certified reference materials (CRM) and the in-house ANU standards. High precision range of pH and total alkalinity that is +- 0.0024 - 0.0059 pH units (n = 10) and +-0.84 - 1.07 umol kg-1 (n=10) were obtained respectively. The system was connected to ANU coral reef culturing tank to measure pH and total alkalinity for three months (mid-July, 2015 to mid-October, 2015). The system was also tested at One Tree Island, Australia. The field deployment of the system reveals significant diurnal variability in both pH and alkalinity at One Tree Island. Carbonate chemistry and metabolic processes on coral reefs over time enables the changes in coral calcification rates to be quantified and often used to predict future changes to calcium carbonate production. The pH and total alkalinity measurements will give an understanding of how ocean acidification and other environmental factors will impact coral reefs. Our new automated spectrophotometric pH-alkalinity system is portable and could be easily adapted for in situ measurements on ships and remote locations.