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Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Vita. / Bibliography: leaves 324-329. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaves 227-236. / by Mary Josephine Richardson. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 92-98. / by Eric Arthur D'Asaro. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1981. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 95-96. / by Peter Reid Daifuku. / M.S.

Huge amounts of anthropogenic 129I have been and still are released to the environment through liquid and gaseous discharges from the nuclear fuel reprocessing facilities worldwide and in particular the ones in Europe. Most of this 129I signal has been accumulated in the marine environment which plays a major role in the iodine natural pool.  In this thesis, an overview of available 129I concentrations in waters of the oceans and marginal seas together with new data about 129I and 127I spatial distribution in surface seawater along a transect between the North Sea and the northeastern Atlantic Ocean are presented. After comprehensive chemical separation, the concentrations of iodine isotopes (127I and 129I) and their species (iodide and iodate) were analysed using accelerator mass spectrometry and inductively-coupled plasma mass spectrometry. The results show that, generally, changes in the 127I and 127I-/127IO3- are comparable to data from other marine waters which are related to natural distribution patterns. A considerable variation of 129I along the transect is observed with the highest values occurring in the eastern English Channel and relatively low values obtained in the northeastern Atlantic Ocean. Inventory estimations of 129I in the North Sea and the English Channel are 147 kg and 78 kg, respectively, where more than 90% resides in the Southern Bight and the eastern English Channel. Iodate is the dominant iodine species for both 127I and 129I in most seawater samples from the North Sea to the Atlantic Ocean. 129I species variability suggests a slow process of 129I- oxidation in the open sea. It takes at least 10 years for the 129I-/129IO3- pair to reach their natural equilibrium as the water is transported from the English Channel. The results suggest a main transport of 129I from the western English Channel via the Biscay Bay into the northeastern Atlantic Ocean. Further, high 129I/127I and distinctive 129I-/129IO3- values south of 40°N indicate possible contribution of 129I through Mediterranean Outflow Water. The environmental radioactive impact of 129I and possible applications in ecosystem studies are also discussed.

Zooplankton assemblages were examined from waters off the west coast of Scotland encompassing the Firths of Lorn and Clyde, the North Channel, and the Malin Shelf. Size fractionated samples (coarse, >1000μm; medium, 1000μm-330μm; fine, 330μm-180μm) were collected with a submersible pump from 10m and 30m depth in March (1987) and May (1986) providing a composite picture of the fauna in early and late spring conditions, respectively. The feasibility of using image analysis as a method for processing zooplankton samples was examined. Although a programme was successfully operated to obtain individual measurement data, much work is still required before a fully automated programme for routine use by planktologists is available. Total zooplankton numbers and biomass, and species distributions and relative abundances were examined. Species assemblages were identified using multivariate analyses. Biomass and abundance spectra by size were examined for the major station groupings. In general, meroplankton dominated the fauna in the Firth of Lorn while large numbers of Calanus spp. occurred in the Firth of Clyde. Small copepods such as Oithona spp. were characteristic of the assemblage on the Malin Shelf. Salinity, followed by temperature, showed the strongest association with the observed station clusters. Chlorophyll a and depth did not generally appear to influence station groupings. The potential for the mixing and exchange of zooplankton between the regions of the study area was evaluated. The results suggest that zooplankton may be entrained from the Firth of Clyde by the Scottish Coastal Current during the spring period. The Malin Shelf may also be an important source of zooplankton for the Firth of Lorn during winter months when an onshore flow of Atlantic water occurs.

L’objectif de ce travail était d’étudier la variabilité de la circulation océanique méridienne aux échelles de temps pluri décennales dans l’océan Atlantique nord au cours des deux mille dernières années, ainsi que son lien avec la variation de l’extension des gyres subtropicales et subpolaires. J’ai donc étudié, à partir de carottes de sédiments marins à fort taux de sédimentation, l’évolution de la température des eaux de surface et de la stratification de la colonne d’eau en lien avec le fonctionnement des gyres subpolaire et subtropicale.Compte tenu des difficultés spécifiques à la période de temps considérée, la première partie de mon travail a consisté à contraindre le milieu et la période de calcification des principaux foraminifères utilisés, à partir de la composition isotopique de l’oxygène analysée dans la coquille des foraminifères planctoniques. J’ai également précisé la calibration en Magnésium et en Calcium en fonction de la température. La deuxième partie de mon travail a consisté à reconstruire les conditions hydrologiques dans des zones clés de l’océan Atlantique Nord sur les deux mille dernières années. J’ai ainsi construit un index de la gyre subpolaire à partir d’un gradient de température Est-Ouest, qui traduit l’intensité dynamique de la gyre subpolaire et de la gyre subtropicale. L’apport de l’analyse des foraminifères planctoniques profonds a permis de reconstituer les variations de la colonne d’eau supérieure. La stratification plus ou moins marquée de la colonne d’eau est reliée directement à l’intensité des vents d’Ouest. Les similitudes entre les vents et l’index de gyre m’ont amené à proposer un couplage entre l’océan et l’atmosphère aux échelles de temps pluri décennales.La dernière partie de ma thèse s’est focalisée sur les conséquences des variations de la dynamique des gyres océaniques sur le transport de chaleur vers les hautes latitudes ainsi que sur l’impact des variations des vents d’Ouest sur le climat européen. / The purpose of this thesis was to study the surface oceanic circulation in the North Atlantic Ocean during the last 2,000 years, and its link with the intensity of the subpolar and the subtropical gyres. To fulfill these objectives, I studied sediment cores with a high sedimentation rate to reconstruct the multidecadal variability of the temperature and the water column stratification, controlled by the dynamic of oceanic gyres. To improve the marine paleoclimatic signal recorded from planktonic foraminifera, I constrained their growing season and their calcification depth by analyzing the oxygen isotopic composition of their calcitic shells. I also established calibrations between Mg/Ca ratio and temperature for the main species used.I applied these calibrations to reconstruct the hydrological conditions in key areas of the North Atlantic Ocean. I constructed an index of the subpolar gyre that traduces the dynamic intensity of the subpolar gyre and the subtropical gyre. I also studied the variability of the upper water column based on the analysis of deep-dwelling foraminifera. I interpret past changes in the water column stratification as resulting from changes in the intensity of Westerly winds. The similarities between the wind forcing evolution and the index of the subpolar gyre dynamics led me to propose a coupling between the ocean and the atmosphere on the multidecadal time scale. The consequences of the gyres dynamic on heat transport and the impacts of the change in westerly wind strength on European climate are studied in the last part of the manuscript.

A interação entre troposfera e estratosfera tem grande influência e é de grande importância nos processos de ciclogênese em superfície. Entretanto, não se conhece exatamente a frequência destas interações e nem como podem influenciar na intensidade de ciclones em geral. Este trabalho tem como objetivo geral estudar como os altos níveis da atmosfera afetam o desenvolvimento de ciclones em superfície na América do Sul e Oceano Atlântico Sul, utilizando o conceito de vorticidade potencial (VP). Através de dados de ciclones rastreados em superfície e VP em 300 hPa desenvolveu-se um algoritmo que associa automaticamente os ciclones em superfície com anomalias de vorticidade potencial (AVP). Para o período 1998-2003, fez-se então a separação dos ciclones em associados (AAVP) e não-associados (NAVP) a AVP. De forma geral, observou-se que a maior parte dos ciclones AAVP concentra-se na região oceânica extratropical e os NAVP preferencialmente na região continental próximo de 30°S e em latitudes subtropicais. Para todo o período analisado, o número total de ciclones AAVP (55%) superou o número de NAVP (45%), sendo o ano de 2002 o único que apresentou número maior de eventos NAVP. Quanto à distribuição sazonal, os ciclones AAVP são mais frequentes nos meses de inverno e primavera, enquanto que os NAVP nos meses de verão. O tempo de vida dos NAVP é menor que dos AAVP, além de possuírem menor intensidade (de acordo com a pressão central média). Além destes fatores, a distância percorrida e a velocidade médias dos ciclones NAVP são menores do que dos AAVP. As composições dos campos sinóticos mostram que nos eventos NAVP, independente da estação do ano, a troposfera é mais quente que nos AAVP. Nos NAVP a forçante térmica é essencial para a formação do ciclone, enquanto que nos AAVP a AVP induz vorticidade ciclônica primeiro em altos níveis, que então se propaga para baixos níveis. Através da análise dos campos sinóticos, notou-se maior baroclinia nos casos NAVP, pois tanto os cavados em altos e médios níveis quanto a corrente de jato permanecem favorecendo o desenvolvimento do ciclone em superfície, enquanto que nos AAVP o centro do ciclone em superfície está verticalmente quase alinhado ao cavado. Centros de vorticidade relativa ciclônica em 500 hPa desprendem-se do escoamento de oeste em todas as estações para os casos AAVP, porém, no verão, isto também é visto nos NAVP. / The process of troposphere-stratosphere interaction has influence and is very important on surface cyclogenesis. However, the frequency of these interactions and how they influence the intensity of cyclones is not known exactly. The main objective of this work is to study how the upper levels affect the development of surface cyclones in South America and South Atlantic Ocean using the concept of potential vorticity (PV). Cyclone tracking data and 300 hPa PV were used to develop an algorithm that automatically associates the surface cyclones with potential vorticity anomaly (PVA). For the period 1998-2003, the cyclones were separated as associated (APVA) and non-associated (NPVA) with PVA. In general, it was observed that most of the APVA cyclone was concentrated in extratropical oceanic region, while NPVA cyclones form over the continent preferably around 30°S and subtropics. The total number of APVA cyclones (55%) exceeds the number of NPVA (45%), except for 2002. In regard to seasonal distribution, the APVA cyclones are more frequent in winter and spring months while NPVA in summer months. The lifetime of NPVA cyclones is shorter and they are less intense than APVA (according to the average central pressure). In addition to these factors, the mean traveled distance and mean velocity are smaller in the NPVA than in APVA. The composites of the synoptic fields show that in NPVA events, regardless of the season, the troposphere is warmer than in APVA. In NPVA cases the thermal forcing is essential to the cyclogenesis, while in the APVA the cyclonic vorticity induced by PVA at upper levels propagating to low levels is more important. The NPVA cases present more baroclinic characteristics which the upper and mid-level troughs accompanied by the jet stream favoring the surface cyclone development, whereas in the APVA the surface cyclone center remains almost vertically aligned with these troughs. For APVA cases, the centers of cyclonic vorticity at 500 hPa detach from westerly flow in all seasons however in summer this is also seen in NPVA.