Modeling the estuarine circulation and fine sediment transport associated with subglacial buoyant jets in glacial fjords

It has been suggested that high latitude systems are one of the regions where the consequences of global warming are becoming more evident. From an oceanographic point of view, glacial fjords are particularly sensitive to climate change because of the seasonal dynamics of sea-ice formation and melting and the important amount of sediment delivered by tidewater glaciers. Our understanding of glacial fjords dynamics in the context of global warming, however, has been the subject of study only during the last two decades. Glacial fjords are estuaries whose complexity arise from a combination of submarine freshwater discharges, as buoyant jets, a highly non-hydrostatic process. Although buoyant jets and sediment transport associated with these processes have received attention through experimental, numerical and field studies, an integrated study of these processes and the estuarine circulation in glacial fjord has been missing. This is explained partly by the difficulty in collecting field data to validate and compare with modeled and experimental results. This thesis describes the estuarine circulation and fine sediment transport associated with a sub-glacial freshwater discharge in a glacial fjord through simplified numerical simulations. Results showed that the discharge of freshwater underneath a glacier into an idealized fjord induces an estuarine-like circulation which is dynamically unstable in the near field, with gradient Richardson number at the sheared interface less than < 1/4. The dilution factors and velocities of the vertical and surface plumes are strongly and nonlinearly related to the Froude number. The buoyancy flux primarily controls the resulting circulation with the momentum flux playing a secondary role. Fine sediment transport experiments showed that jet-dominated conditions are more sensitive to the presence of suspended sediment in the discharge than buoyancy-dominated conditions. At high concentrations, sediment settles in the far field, driven by convective sedimentation, and is transported back to the near field by the landward estuarine current. Convective sedimentation is triggered when density is increased by the higher sediment concentration at the interface between the upper and lower layer