Hamburg, University, Diss., 2003.

Kiel, Christian-Albrechts-Universität, Diss., 2007.

University, Diss., 2005--Bremen.

Les eaux du Golfe du Mexique (GOM) jouent un rôle important dans le systéme climatique global car elles Intluencent les propriétés hydrologiques du Gulf Stream (GS), courant océanique chaud de surface faisant partie Intégrante de la circulation thermohaline (THC). Au cours du dernier cycle climatique, d'énormes écoulements d'eau douce, provenant de la fonte de la calotte Laurentide sur le continent-nord américain, se sont déversées au sein du GOM. moditiant ses caractéristiques hvdrologlques et donc celles du GS. Ces perturbations auraient pu, en altérant la THC, affecter le systéme climatique. La compréhension des transferts entre le continent nord-américain et le GOM au cours du dernier cycle climatique s'avére donc primordiale. En connaissant les principales sources continentales, les facteurs influençant le transport (réalisation de cartes de répartition des minéraux argileux sur le continent nord-américain et dans les sédiments du GOM) et la sédimentation (par modélisation analogique) du matériel terrigéne fin, l'étude des enregistrements sédimentaires (minéralogie des argiles, granulométrie ) et isotopiques ([delta]18O) de deux bassins du nord du GOM (Bassins d'Orca et d'Humphrey) a permis d'appréhender les transferts entre le continent nord-américain et le GOM au cours du dcrnier cycle climatique. La variabilité des apports détritiques du Mississippi et des fleuves du sud-ouest des États-Unis a pu être reliée aux variations paléo-environnementales (fonte de la calotte Laurentide et des glaciers des Montagnes Rocheuses) et paléoclimatiques (modifications des transferts d'humidité depuis le GOM vers le continent) qui affectent le continent nord-américain / The Gulf of Mexico (GOM) is a key area for the global thermohaline circulation (THC) and for the global-climatic system, since its hydrological characteristics (hlgh salinity and temperature) partly control Gulf Stream physical properties. Dunng the last climatic cycle, GOM hydrology was impacted by episodic freshwater inputs via the Mississippi River resulting from intermittent meltmg of the Laurentide Ice Sheet (LIS). The resulting salinity changes affected the THiC. global heat exchange and worldwide climatie conditions. Direct effeets of these freshwater supplies on the GOM paleoceanography have been documented studying the planktonic foraminifera [delta]18O evolution By contras!. terrigenous inputs associated with these meltwater pulses are poorly understood. These detrital fractions are. however. IIkeiv to provide information on the link between continental and marine records during the last climatic cycle. An overview of the main continental detrtital source areas, of the dominant factors controlling clav minerai transport patterns (by drawing clay minerai distribution maps in the US and northem GOM) and of thin terrigenous particle sedimentation in the GOM (by analogical modeIing), lays the groundwork for the use of clay-minerai assembiages for understanding the connection between North America and the GOM. The downcore investigations of sedimentary (clay mineralogy, grain-slze . .) and isotopic ([delta]18O) records ln two minibasins of the GOM (Orca Basin and Basin 4) allow us to explain the fluvial inputs variations, during the last climatic cycle, by paleoenvironmental (ice meltback) and paleocllmatic (atmospheric circulation) fluctuations that affected North America

Ocean circulation is a fundamental component of the Earth's climate system. The Atlantic thermohaline circulation, driven by deep convection at high latitudes, has a central role in regulating European climate through its transport and redistribution of heat. Either directly or indirectly, Mediterranean Water (MW) provides the high salinities found in the Nordic Seas which are required to precondition for deep convection. The precise mechanisms and pathways remain undetermined and yet are fundamental to understanding the effect that any change in the Mediterranean Outflow may have on circulation and ultimately on climate. This thesis investigates the transport of MW in the North Atlantic Ocean using hydrographic and model data. The primary objective is to quantify how much MW flows northwards and how much flows westwards from its source in the Gulf of Cadiz. Two boxes (Med Boxes) were constructed using hydrographic sections in the eastern North Atlantic enclosing the Strait of Gibraltar and Mediterranean Outflow. Inverse methods were used to determine the velocity field from which volume transports and salt fluxes were calculated. The main northward flow of MW across 41°N occurs east of 12°W, at depths of 500 to 1500 m, and transports 50 to 75% of the MW. An advective westward pathway across 20°W transports MW at similar depths into the ocean interior between 35°N and 40°N. Insignificant salt fluxes across the southern section (24°N) at MW depths confirm that no MW crosses the southern Med Box boundary. The net overturning circulation of the Med Box, with inflowing surface waters and outflowing intermediate waters, is attributed both to the exchange at the Strait of Gibraltar and also to water mass transformation associated with entrainment of North Atlantic Water into the Mediterranean Outflow. The magnitude of the circulation provides an estimate of this entrainment of 1.6 ± 0.6 Sv, within the Med Box boundaries. For comparison with these observational estimates, the model used is OCCAM, a level model from the Ocean Circulation and Climate Advance Modelling Project. The primary reason for choosing this model is that experiments have been undertaken with the Strait of Gibraltar both open and closed, enabling a new approach to the investigation of MW transport. MW is identified using the salinity difference between the two model experiments. Although the model circulation (in the open-Strait run) has a similar net overturning to the hydrography, different MW transport pathways are observed. A weak and variable northward pathway along the Iberian Peninsula and a strong southwestward flow from the Gulf of Cadiz result in a higher proportion of MW flowing westwards (61%) than northwards (39%). Seasonal variability is observed, with maximum westward flow in Autumn (70%) and minimum in Spring (50%). There is no evidence in the model that the northward boundary current provides a direct route for Mediterranean salt to reach the Nordic Seas.

No description available.

Zugl.: Kiel, Univ., Diss., 2007

Universiẗat, Diss., 1999--Bremen.

Universiẗat, Diss., 2000--Bremen.

Universiẗat, Diss., 2002--Bremen.