This thesis deals with the use of geochemical proxies on foraminifera for paleoceanographical, paleoecological and paleoenvironmental interpretations in the fossil epicontinental sea - the Central Paratethys during the Langhian. It discusses the used methodologies and approaches that were specially chosen to fit the problematic of the studied area such as the single test analysis of carbon and oxygen stable isotopes on foraminifera. Other geochemical methods were represented by Mg/Ca based paleothermomethry and by several organic geochemistry proxies on whole rock samples (n-alkane indices, δ13 Corg, and carbon ratios - TOC/TIC/TC). These were further combined with foraminiferal paleoecological data, which allowed identification of particular water masses in the studied region as well as the prevailing circulation patterns/regimes during the studied interval in the Paratethyan marine realm. Additionally, there were interpreted various regional paleoenvironmental and paleoecological consequences. The Paratethys had similar hydrography of surficial waters with the Mediterranean, conversely to the bottom waters that were different, probably of a regional origin with their own evolution during the studied time interval. The anti-estuarine circulation regime, which was probably linked with the closure...

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 117-126). / In this thesis, I present high-resolution stable-isotope and planktonic-fauna records from Bering Sea sediment cores, spanning the time period from 50,000 years ago to the present. During Marine Isotope Stage 3 (MIS3) at 30-20 ky BP (kiloyears before present) in a core from 1467m water depth near Umnak Plateau, there were episodic occurrences of diagenetic carbonate minerals with very low 13C (-22.4%), high 18O (6.5%), and high [Mg]/[Ca], which seem associated with sulfate reduction of organic matter and possibly anaerobic oxidation of methane. The episodes lasted less than 1000 years and were spaced about 1000 years apart. During MIS3 at 55-20 ky BP in a core from 2209m water depth on Bowers Ridge, N. pachyderma (s.) and Uvigerina 18O and 13C show no coherent variability on millennial time scales. Bering Sea sediments are dysoxic or laminated during the deglaciation. A high sedimentationrate core (200 cm/ky) from 1132m on the Bering Slope is laminated during the Blling warm phase, Allerd warm phase, and early Holocene, where the ages of lithological transitions agree with the ages of those climate events in Greenland (GISP2) to well within the uncertainty of the age models. The subsurface distribution of radiocarbon was estimated from a compilation of published and unpublished North Pacic benthic-planktonic 14C measurements (475{2700 m water depth). There was no consistent change in 14C probles between the present and the Last Glacial Maximum, Blling-Allerd, or the Younger Dryas cold phase. N. pachyderma (s.) 18O in the Bering Slope core decreases rapidly (in less than 220 y) by 0.7-0.8h at the onset of the Blling and the end of the Younger Dryas. These isotopic shifts are accompanied by transient decreases in the relative abundance of N. pachyderma (s.), suggesting that the isotopic events are transient warnings and sustained freshenings. / by Mea S. Cook. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2000. / Includes bibliographical references. / Benthic foraminiferal δ13C, Cd/Ca, and Ba/Ca are important tools for reconstructing nutrient distributions, and thus ocean circulation, on glacial-interglacial timescales. However, each tracer has its own "artifacts" that can complicate paleoceanographic interpretations. It is therefore advantageous to measure multiple nutrient proxies with the aim of separating the various complicating effects. Zn/Ca is introduced as an important aid toward this goal. Benthic (Hoeglundina elegans) Cd/Ca ratios from the Bahama Banks indicate that the North Atlantic subtropical gyre was greatly depleted in nutrients during the last glacial maximum (LGM). A high-resolution Cd/Ca record from 965 m water depth suggests that Glacial North Atlantic Intermediate Water formation was strong during the LGM, weakened during the deglaciation, and strengthened again during the Younger Dryas cold period. Comparison of Cd/Ca and δ13C data reveals apparent short-term changes in carbon isotopic air-sea signatures. Benthic foraminiferal Zn/Ca could be a sensitive paleoceanographic tracer because deep water masses have characteristic Zn concentrations that increase about ten-fold from the deep North Atlantic to the deep North Pacific. A "core top calibration" shows that Zn/Ca is controlled by bottom water dissolved Zn concentration and, like Cd/Ca and BalCa, by bottom water saturation state with respect to calcite Since Zn/Ca responds to a different range of saturation states than Cd/Ca, the two may be used together to evaluate changes in deep water carbonate ion (CO32- ) concentration. Zn/Ca and Cd/Ca ratios in the benthic foraminifer Cibicidoides wuellerstorfi exhibit large fluctuations over the past 100,000 years in a deep (3851 m) eastern equatorial Pacific sediment core. The data imply that bottom water CO32- concentrations were lowest during glacial Marine Isotope Stage 4 and highest during the last deglaciation. LGM CO32- concentrations appear to have been within a few μmol kg-1 of modern values. Deep North Atlantic Cd/Ca ratios imply much higher nutrient concentrations during the LGM. Although such data have usually been explained by a northward penetration of Southern Ocean Water (SOW), it has been suggested that they could result from increased preformed nutrient levels in the high-latitude North Atlantic or by increased aging of lower North Atlantic Deep Water (NADW). Glacial Zn/Ca data, however, require a substantially increased mixing with SOW and thus a reduction in NADW formation. Large changes in carbon isotopic air-sea exchange are invoked to reconcile benthic δ13C and trace metal data. / by Thomas Mathew Marchitto, Jr. / Ph.D.

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A contourite drift complex on the J-Anomaly Ridge (JAR) and Southeast Newfoundland Ridge (SENR), offshore eastern Canada, records an extensive archive of North Atlantic circulatory and sedimentary dynamics formed under the influence of the Deep Western Boundary Current (DWBC). Seismic-reflection profiles constrained by drill sites from IODP Expedition 342 are used to map the spatial and temporal distribution of contourite sedimentation and to evaluate the Cenozoic history of the DWBC within a preexisting climatic framework. This study indicates three phases of sedimentation termed here Pre-Contourite-Drift Phase (~115-50 Ma), Active-Contourite-Drift Phase (~50-2.6 Ma), and Post-Contourite-Drift Phase (~2.6-0 Ma). Bottom current controlled sedimentation began at the boundary between Pre-Contourite-Drift Phase and Active-Contourite-Drift Phase (~50 Ma), and correlates to a long-term global cooling trend that initiated at the end of the Early Eocene Climatic Optimum. Within the Active-Contourite-Drift Phase at ~30 Ma depocenters shifted deeper and current energy and focus is interpreted to have increased in association with global oceanographic change at the Eocene-Oligocene transition. The beginning of Post-Contourite-Drift Phase sedimentation (~2.6 Ma) marks a shift in bottom current path towards shallower water depths, and corresponds with the onset of Northern Hemisphere ice sheets. These events of circulatory reorganization correlate with other North Atlantic seismic stratigraphic studies, suggesting that these events occurred throughout the North Atlantic. An improved understanding of long-term (>1000000 yr) dynamics of North Atlantic circulation in response to significant reorganization of Cenozoic climate provides important context towards refining models and prediction of oceanic response to contemporary climate change. / Master of Science

Atlantic Meridional Overturning Circulation (AMOC) is a vital process that transfers heat and nutrients throughout the world's oceans, helping to regulate global climate and support marine ecosystems. The timing and nature of the shift to modern AMOC, and especially to deep-water formation in the North Atlantic, has been a topic of ongoing study, with the Eocene-Oligocene Transition (EOT, ~34 Ma) as a potential focal point of this shift. However, the role played by abrupt EOT cooling and Antarctic glaciation in North Atlantic circulation remains unclear. Improved constraints on Paleogene circulation will provide insight into the sensitivity of AMOC to perturbations in global climate, which is particularly relevant in light of contemporary climate change. To examine deep North Atlantic circulation response to the EOT we obtained grain-size data from the terrigenous fraction of the mud-dominated sediments of the Southeast Newfoundland Ridge contourite drift complex at IODP Site U1411, which is interpreted to have formed under the influence of the Deep Western Boundary Current. We analyzed 195 samples that span 150 m of stratigraphy from 36-26 Ma. The main objective was to use the 'sortable silt' fraction (10-63 µm) to generate a record of relative change in bottom-current intensity. These data are complemented with a record of the abundance and size of lithogenic sand (>63 µm). Here we present the first physical proxy record of abyssal current intensity in the North Atlantic, from late Eocene to mid Oligocene. Invigoration of North Atlantic deep circulation occurred gradually (over Myr timescales), with no significant changes linked temporally to the EOT. We infer that deep circulation in the North Atlantic was not sensitive to the abrupt global cooling and Antarctic glaciation associated with the EOT. Rather, our data suggest that changes in North Atlantic circulation were likely governed by longer-term processes related to the opening of key tectonic gateways, such as the Greenland-Scotland Ridge in the North Atlantic, and the Drake and Tasman Passages in the Southern Ocean. Additionally, we identify a significant mid-Oligocene invigoration of North Atlantic abyssal circulation, which climaxes around 27.9 Ma, and is coeval with a decrease in atmospheric CO2. / Master of Science

Les coccolithophoridés sont des algues marines photosynthétiques et planctoniques qui produisent des plaques micrométriques de carbonate de calcium (CaCO3) appelés coccolithes. Ces algues sont apparues il y 210 Ma et produisent actuellement la majeure partie du CaCO3 dans les océans modernes, jouant ainsi un rôle majeur dans le cycle du carbone. Cependant, l’émergence de la production de CaCO3 océanique par les coccolithophoridés au cours du Jurassique, ainsi que son impact sur le cycle du carbone, restent très mal compris. Cette étude s’est donc focalisée sur une période du Jurassique Moyen (Bajocien inférieur, -170 Ma) enregistrant la diversification de Watznaueria, un genre de coccolithophoridé qui a ensuite dominé la production de CaCO3 océanique pendant plus de 80 Ma. L’analyse des assemblages de coccolithes du Jurassique Moyen du Portugal et du sud de la France, réalisée à l’aide d’une méthode de reconnaissance automatique appliquée pour la première fois aux coccolithes du Jurassique, a permis de quantifier l’importance de cette période de diversification sur la production de CaCO3 pélagique. En outre, la durée de cet intervalle clé a été réévaluée grâce à l’analyse cyclostratigraphique des séries sédimentaires du Sud de la France. Les variations de production de CaCO3 pélagique ainsi reconstituées ont été comparées aux perturbations du cycle du carbone enregistrées par les rapports des isotopes du carbone, et indiquent un lien probable avec une augmentation marquée de la fertilité des océans. Par ailleurs, l’analyse paléontologique montre que cette diversification correspond à l’apparition successive de différentes espèces vraisemblablement opportunistes du genre Watznaueria. Enfin, les flux obtenus de CaCO3 pélagiques, largement inférieurs à ceux observés dans les océans actuels, semblent insuffisants pour avoir eu une influence significative sur le cycle global du carbone du Jurassique Moyen. / Coccolithophorids are photosynthetic and planktonic marine algae that produce micrometric calcium carbonate (CaCO3) platelets called coccoliths. These algae appeared about 210 Ma ago and produce today most of the CaCO3 in the modern oceans, hence playing a major role in the carbon cycle. Nevertheless, the onset of oceanic CaCO3 production by these organisms during the Jurassic and its impact on carbon cycling remain poorly understood. This study therefore focused on the Middle Jurassic interval (Early Bajocian, -170 Ma) which records the diversification of Watznaueria, an evolutionary important coccolith genus that subsequently dominated oceanic CaCO3 production for more than 80 Myr. The analysis of coccolith assemblages from the Middle Jurassic of southern France and Portugal, based on an automaticcoccolith recognition device used for the first time on Jurassic coccoliths, allowed quantifying the impact of this diversification on CaCO3 production. In addition, the duration of this key interval has been revaluated by the cyclostratigraphic analysis of sedimentary strata from southern France. The reconstructed changes in CaCO3 production were compared to carbon cycle perturbations recorded by carbon isotope ratios and indicate a probable link with a marked increase of ocean fertility. Besides, paleontological analyses show that this diversification episode correspond to the successive appearance of different, probably opportunistic Watznaueria species. The obtained fluxes of pelagic CaCO3 production, by far lower than those recorded in modern oceans, seems too low to have significantly impacted theMiddle Jurassic carbon cycle.