Accumulations of fine sediments in deep-ocean contourites form a sedimentary record that has been hypothesized to be directly related to bottom-current behavior. This is known as the 'sortable silt' hypothesis and states that the non-cohesive, coarse silt in the 10 to 63 µm size range within a deposit can be used as a proxy for paleocurrent velocity. Slow deposition rates on contourites (2−10 cm/kyr) make it difficult to test this hypothesis in the field and few laboratory studies have been conducted. To test the 'sortable silt' hypothesis in the laboratory, a non-recirculating flume was constructed in which silt and clay could be deposited under a variety of velocities, sediment concentrations, and silt to clay ratios. Samples of the deposited material from each experiment were analyzed to determine the grain-size distribution using a Micromeritics Sedigraph 5120 particle size analyzer. The results of these experiments were used to evaluate the following two hypotheses: 1. The proportion of sortable silt (SS%) compared to the proportion of clay is a better indicator of current velocity than the mean size of the sortable silt (SS). 2. The presence of clay will impact the movement and sorting of silt in the bed. Results show that increased velocity correlates with increased (SS), and that (SS) generally decreases downstream of the sediment source. (SS) was found to be more representative of velocity than (SS%) and, counter to the original hypothesis, clay did not have a significant effect on silt deposition. / Master of Science / The ’sortable silt’ hypothesis states that there is a relationship between the velocity of an ocean current and the size of the sediment that deposits on the bottom of the ocean. These deep-ocean deposits consist of material smaller than sand such as clay and silt. Smaller particles require less force than larger particles to remain suspended, and higher current velocities produce larger forces. For this reason larger current velocities are thought to be associated with the deposition of coarser sediments. It is challenging to test this hypothesis in the field because of the cost and the slow rates at which change occurs. Laboratory studies can help to overcome these challenged by test scenarios otherwise impossible in the field. For this research, a flume was constructed and used to examine how different sediment types sort under flowing water. Most laboratory flumes recirculate water using pumps, but this flume does not. A mixture of dry material and water flows through the flume, depositing a bed over time. This deposited material can then be tested for its size parameters. These size parameters are compared to the material type and the velocity of the current in the flume to help answer two main questions: 1. Is the amount of silt in a sample a better indication of the current velocity than the average size of the material deposited? 2. Will the addition of clay will change the way silt deposits in the system?. Results show that silt does sort with increasing velocity and that the mean sortable silt size is good indicator of current velocity.

La composition isotopique de néodyme (C.I. de Nd) est un traceur de circulation océanique et d'échanges de matière océan/continent. Nous avons mesuré cette grandeur sur près de 200 échantillons d'eau de mer des mers Nordiques (Groenland, Islande, Norvège) et de l'Atlantique Subarctique (au nord de 50°N). L'interprétation de ces données en relation avec l'hydrologie et la géologie de la zone d'étude a permis d'améliorer notre connaissance de la circulation et du traceur CI de Nd.<br /><br />L'étude des signatures isotopiques de l'Eau Subarctique Intermédiaire (SAIW), de l'Eau Profonde de la Mer de Norvège et de l'Eau Modale Subpolaire (SPMW) nous a permis de préciser leur histoire (trajectoires, mélanges). En particulier, nous confirmons que l'origine de la SAIW se trouve dans le courant du Labrador et nous suggérons que la SPMW résulte d'un mélange à deux pôles : l'Eau Centrale Nord Atlantique et des eaux provenant du courant du Labrador.<br /><br />Les C.I. de Nd sont en accord avec les schémas admis pour la formation des couches supérieure et inférieure de l'Eau Profonde Nord Atlantique (NADW). En revanche, elles suggèrent une composition de l'Eau Profonde Nord Est Atlantique significativement différente de celle de la couche centrale de la NADW. Ce point nécessitera des études complémentaires.<br /><br />Nous confirmons robustement la conservativité de la CI de Nd à l'abri d'influence terrigène. Nous mettons en évidence l'influence de sédiments d'origine cristalline sur la C.I. de Nd des masses d'eau et confirmons celle de sédiments d'origine basaltique. Nous suggérons que la CI de Nd perd partiellement la mémoire de l'histoire des masses d'eau lors d'interactions sédiment/océan, dans des zones de forte énergie hydraulique.<br /><br />Enfin nous suggérons que des variations de taux d'érosion dans le passé modifieraient la signature de la NADW, au même titre que des variations de circulation, si ce n'est d'avantage.