Internal tides and currents interacting with sub-surface topography such as continental slopes, islands and seamounts give rise to turbulent processes. The subsequent mixing of waters of different densities is important for maintaining the global overturning circulation. This thesis investigates the turbulent processes occurring at two different topographic features; a steep headland in the eastern Pacific and a continental slope canyon in the north-west Atlantic.

Tidal currents and mean-flows interacting with headlands and islands give rice to turbulent wakes. In Chapter 1, surveys in the wake of a steep headland in both tidal and mean flow regimes reveal turbulent wakes driven by shear and vorticity in the flow. Recent theoretical literature has suggested that turbulence at steep topographic features may drive upwelling necessary to close the abyssal overturning circulation. In Chapter 2, a novel near-bottom dye release provides the first direct evidence of upwelling within a steep canyon and suggests that current 1-d models of near-bottom processes are insufficient to understand the importance of bottom boundary upwelling processes. In Chapter 3, this work is extended using a suite of moorings which observe convergence and divergence in the along-canyon direction indicative of exchange between the boundary and interior, a process that is not included in 1-d models.